Brackishwater Brackishwater Fish CultureFish Culture

Dr. Sameer G ChebbiDr. Sameer G ChebbiIndustrial fish and fisheriesIndustrial fish and fisheries

Dept. of ZoologyDept. of ZoologyKarnatak Science College, Karnatak Science College,

DharwadDharwad

Gray Mullet Fish Culture Gray Mullet Fish Culture That the mullets have high rates of growth, That the mullets have high rates of growth,

together with that they tolerate wide ranges of together with that they tolerate wide ranges of environmental parameters, makes them highly environmental parameters, makes them highly attractive attractive for culture purposes. for culture purposes.

Various forms of mullet farming are being Various forms of mullet farming are being practised. practised.

Grey mullet has been farmed for centuries in Grey mullet has been farmed for centuries in extensive and semi-intensive ponds in many extensive and semi-intensive ponds in many countries. countries.

Subsistence farming in ponds and enclosures Subsistence farming in ponds and enclosures has been traditional in the Mediterranean has been traditional in the Mediterranean region, South East Asia, Taiwan Province of region, South East Asia, Taiwan Province of China, Japan and Hawaii. China, Japan and Hawaii.

Traditional valli culture methods Traditional valli culture methods employed for raising mullet are now employed for raising mullet are now advanced, especially in Italy. advanced, especially in Italy.

Flathead grey mullet is a very Flathead grey mullet is a very important aquaculture species in important aquaculture species in Egypt, where its farming has been Egypt, where its farming has been traditional in the hosha system in the traditional in the hosha system in the delta region for centuries.delta region for centuries.

In the Russian Federation mullet In the Russian Federation mullet aquaculture has been practised in the aquaculture has been practised in the Black Sea and Caspian Sea regions Black Sea and Caspian Sea regions since 1930.since 1930.

Flathead grey mullet is also cultured in Flathead grey mullet is also cultured in Korea and is considered as an important Korea and is considered as an important foodfish in the southwest region. foodfish in the southwest region.

In Taiwan Province of China, nearly 40 In Taiwan Province of China, nearly 40 percent of the total commercial percent of the total commercial production (fisheries and aquaculture) production (fisheries and aquaculture) of of Mugil cephalusMugil cephalus has been pond reared  has been pond reared since the 1960s, being cultured with since the 1960s, being cultured with carp in ponds. carp in ponds.

In the United States of America, mullet In the United States of America, mullet has been cultured as bait fish since the has been cultured as bait fish since the 1940s. Small-scale trials of mullet 1940s. Small-scale trials of mullet vulture have been carried out in Saudi vulture have been carried out in Saudi Arabia and other Gulf States.Arabia and other Gulf States.

This species was first introduced to be This species was first introduced to be cultured with carp in Israel in 1957. In cultured with carp in Israel in 1957. In the Philippines, mullet has been raised the Philippines, mullet has been raised with milkfish since 1953. with milkfish since 1953.

The intensive culture of mullet in Hong The intensive culture of mullet in Hong Kong was successful in fertilized ponds Kong was successful in fertilized ponds with the traditional practice of carp with the traditional practice of carp polyculture since 1940. polyculture since 1940.

It has been reported that mullet have It has been reported that mullet have been farmed in India since ancient been farmed in India since ancient times; for example, it has been times; for example, it has been extensively cultured in Bengal, Madras extensively cultured in Bengal, Madras and Kerala since 1947. and Kerala since 1947.

In India, culture of mullets with other fin fishes In India, culture of mullets with other fin fishes and prawns is being carried out traditionally in and prawns is being carried out traditionally in the states of Tamil Nadu, Kerala and West the states of Tamil Nadu, Kerala and West Bengal.Bengal.

Research in intensive culture began when Research in intensive culture began when rearing experiments with young mullet were rearing experiments with young mullet were conducted in Madras at the Fisheries conducted in Madras at the Fisheries Department farm at Ippur and at Chingleput Department farm at Ippur and at Chingleput Fort moat fish farm in 1942. Fort moat fish farm in 1942.

Improvements for the brackishwater farming of Improvements for the brackishwater farming of mullet in the Gangetic delta were in 1944. mullet in the Gangetic delta were in 1944.

the adoption of Chinese and Philippine methods the adoption of Chinese and Philippine methods of culture in Bengal farms were started.of culture in Bengal farms were started.

its culture in West Bengal, Madras and Kerala its culture in West Bengal, Madras and Kerala with the possibility of introducing polyculture of with the possibility of introducing polyculture of Indian major carps together with mullet and Indian major carps together with mullet and other commercially important euryhaline other commercially important euryhaline species, viz., milkfish and prawns, in low-saline species, viz., milkfish and prawns, in low-saline waters.waters.

Habitat and biologyHabitat and biology Mugil cephalusMugil cephalus is cosmopolitan in the  is cosmopolitan in the

coastal waters of most tropical and coastal waters of most tropical and subtropical zones. In the western Atlantic subtropical zones. In the western Atlantic Ocean, it is found from Nova Scotia, Ocean, it is found from Nova Scotia, Canada south to Brazil, including the Gulf Canada south to Brazil, including the Gulf of Mexico. of Mexico.

It is absent in the Bahamas and the It is absent in the Bahamas and the Caribbean Sea. In the eastern Atlantic Caribbean Sea. In the eastern Atlantic Ocean, the striped mullet occurs from the Ocean, the striped mullet occurs from the Bay of Biscay (France) to South Africa, Bay of Biscay (France) to South Africa, including the Mediterranean Sea and the including the Mediterranean Sea and the Black Sea. Black Sea.

The eastern Pacific Ocean range includes The eastern Pacific Ocean range includes southern California south to Chile.  southern California south to Chile. 

The flathead grey mullet is catadromous, frequently The flathead grey mullet is catadromous, frequently found coastally in estuaries and freshwater found coastally in estuaries and freshwater environments. environments.

Adult mullet have been found in waters ranging Adult mullet have been found in waters ranging from zero salinity to 75‰, while juveniles can only from zero salinity to 75‰, while juveniles can only tolerate such wide salinity ranges after they reach tolerate such wide salinity ranges after they reach lengths of 4–7 cm. lengths of 4–7 cm.

Adults form huge schools near the surface over Adults form huge schools near the surface over sandy or muddy bottoms and dense vegetation and sandy or muddy bottoms and dense vegetation and migrate offshore to spawn in large aggregations.migrate offshore to spawn in large aggregations.

The larvae move inshore to extremely shallow The larvae move inshore to extremely shallow water, which provides cover from predators as well water, which provides cover from predators as well as a rich feeding ground. as a rich feeding ground.

After reaching 5 cm in length, these young mullet After reaching 5 cm in length, these young mullet move into slightly deeper waters. move into slightly deeper waters. 

Flathead grey mullet is a diurnal feeder, Flathead grey mullet is a diurnal feeder, consuming mainly zooplankton, dead consuming mainly zooplankton, dead plant matter, and detritus. plant matter, and detritus.

Mullet have thick-walled gizzard-like Mullet have thick-walled gizzard-like segments in their stomach along with a segments in their stomach along with a long gastrointestinal tract that enables long gastrointestinal tract that enables them to feed on detritus. them to feed on detritus.

They are an ecologically important link They are an ecologically important link in the energy flow within estuarine in the energy flow within estuarine communities. communities.

Feeding by sucking up the top layer of Feeding by sucking up the top layer of sediments, flathead grey mullet remove sediments, flathead grey mullet remove detritus and microalgae.detritus and microalgae.

They also pick up some sediment which They also pick up some sediment which functions to grind food in the gizzard-like functions to grind food in the gizzard-like portion of the stomach. portion of the stomach.

Mullet also graze on epiphytes and epifauna Mullet also graze on epiphytes and epifauna from sea grasses as well as ingest surface from sea grasses as well as ingest surface scum containing microalgae at the air-water scum containing microalgae at the air-water interface. interface.

Larval flathead grey mullet feed primarily on Larval flathead grey mullet feed primarily on microcrustaceans. microcrustaceans.

Copepods, mosquito larvae, and plant debris Copepods, mosquito larvae, and plant debris have been found in the stomach contents of have been found in the stomach contents of larvae under 35 mm in length. larvae under 35 mm in length.

The amount of sand and detritus in the The amount of sand and detritus in the stomach contents increases with length, stomach contents increases with length, indicating that more food is ingested from indicating that more food is ingested from the bottom substrate as the fish matures.the bottom substrate as the fish matures.

Biological featuresBiological features Body cilindrical, robust. Head broad, its width more than Body cilindrical, robust. Head broad, its width more than

width of mouth cleft; adipose eyelid well developed, width of mouth cleft; adipose eyelid well developed, covering most of pupil; upper lip thin, without papillae,  covering most of pupil; upper lip thin, without papillae,  labial teeth of upper jaw small, straight, dense, usually in labial teeth of upper jaw small, straight, dense, usually in several rows;  mouth cleft ending below posterior nostril.  several rows;  mouth cleft ending below posterior nostril. 

Two dorsal fins; the first with 4 spines; the second with 8-9 Two dorsal fins; the first with 4 spines; the second with 8-9 soft rays; origin of first dorsal fin nearer to snout tip than to soft rays; origin of first dorsal fin nearer to snout tip than to caudal fin base; origin of second dorsal fin at vertical caudal fin base; origin of second dorsal fin at vertical between a quarter and a half along anal fin base. between a quarter and a half along anal fin base.

Anal fin with 8 soft fin rays. Anal fin with 8 soft fin rays. Pectoral fins with 16-19 rays; pectoral axillary about one-Pectoral fins with 16-19 rays; pectoral axillary about one-

third length of fin.  Pyloric caeca 2.  Scales in leteral series third length of fin.  Pyloric caeca 2.  Scales in leteral series 36-45.  36-45. 

Colour back blue/green, flanks and belly pale or silvery; Colour back blue/green, flanks and belly pale or silvery; scales on back and flanks usually streaked to form scales on back and flanks usually streaked to form longitudinal stripes; dark pectoral axillary blotch.longitudinal stripes; dark pectoral axillary blotch.

  the fecundity of the golden grey mullet was 70,0881 to the fecundity of the golden grey mullet was 70,0881 to 4,29,987 eggs. 4,29,987 eggs.

Mullet fish has high reproductive capacity. The absolute Mullet fish has high reproductive capacity. The absolute fecundity of 25-30cm long mullet is an average 500-600 fecundity of 25-30cm long mullet is an average 500-600 thousands eggs which increased to 2-3 million eggs among thousands eggs which increased to 2-3 million eggs among those of 45-50 cm long fish.those of 45-50 cm long fish.

Gray Mullet (Mugil cephallus)

Production cycleProduction cycle

Most of the flathead grey mullet fry used in Most of the flathead grey mullet fry used in commercial aquaculture are collected from the commercial aquaculture are collected from the wild, especially in the Eastern and Southern wild, especially in the Eastern and Southern Mediterranean, Saudi Arabia and Gulf States Mediterranean, Saudi Arabia and Gulf States and South East Asia. and South East Asia.

Seed produced through artificial propagation Seed produced through artificial propagation is used on a limited scale in Italy and Hawa.is used on a limited scale in Italy and Hawa.

During the autumn and winter months adults During the autumn and winter months adults migrate to the sea in large aggregations to migrate to the sea in large aggregations to spawn. Fecundity is estimated as 0.5–2.0 spawn. Fecundity is estimated as 0.5–2.0 million eggs per female, depending upon the million eggs per female, depending upon the adult size. adult size.

Hatching occurs about 48 hours after Hatching occurs about 48 hours after fertilization, releasing larvae approximately fertilization, releasing larvae approximately 2.4 mm long. When the larvae are 16–20 mm, 2.4 mm long. When the larvae are 16–20 mm, they migrate to inshore waters and estuaries, they migrate to inshore waters and estuaries, where they can be collected for aquacultural where they can be collected for aquacultural purposes during late August to early purposes during late August to early December. December.

Shoals of fry are collected by fine seine nets, Shoals of fry are collected by fine seine nets, transported in seawater to hapas or shore transported in seawater to hapas or shore aggregation tanks for a few hours. They are aggregation tanks for a few hours. They are then transported by trucks to separate then transported by trucks to separate nursery units, or nursery facilities in grow-nursery units, or nursery facilities in grow-out farms. out farms.

On arrival, they need to be acclimatized, On arrival, they need to be acclimatized, especially in terms of salinity; this takes especially in terms of salinity; this takes place over several hours, during which water place over several hours, during which water from the nursery pond is gradually added from the nursery pond is gradually added and mixed with the transport water. and mixed with the transport water.

Mortality rates of up to 100 percent can Mortality rates of up to 100 percent can occur during the following two weeks if this occur during the following two weeks if this process is neglected or not properly carried process is neglected or not properly carried out before stocking fry into the nursery.out before stocking fry into the nursery.

Hatchery production Hatchery production  Full-scale commercial production Full-scale commercial production

of of Mugil cephalusMugil cephalus is not yet common.  is not yet common. Induced spawning and production of fry Induced spawning and production of fry has been achieved on an experimental has been achieved on an experimental and semi-commercial basis in the United and semi-commercial basis in the United States of America and Taiwan Province States of America and Taiwan Province of China, and the production of mullet of China, and the production of mullet fry on a limited scale for aquaculture fry on a limited scale for aquaculture has been reported in Italy, Israel, Egypt has been reported in Italy, Israel, Egypt and now in India. and now in India. 

In these systems large numbers of sexually In these systems large numbers of sexually mature individuals (over two years of age, 32–mature individuals (over two years of age, 32–50 cm long and 1.0–2.1 kg each) are kept 50 cm long and 1.0–2.1 kg each) are kept under optimum environmental conditions with under optimum environmental conditions with limited physical disturbance. limited physical disturbance.

Prior to spawning, fish are kept at 32–35‰ Prior to spawning, fish are kept at 32–35‰ and 12–15 °C. Ripe fish are selected and and 12–15 °C. Ripe fish are selected and placed in plastic or fibreglass tanks filled with placed in plastic or fibreglass tanks filled with seawater saturated with oxygen at a 2–3:1 seawater saturated with oxygen at a 2–3:1 male:female ratio shortly before spawning. male:female ratio shortly before spawning.

Females are injected with regulated and Females are injected with regulated and successive doses (2–3 injections) of pituitary successive doses (2–3 injections) of pituitary gonadotropin. gonadotropin.

Females spawn 12 hours after the last Females spawn 12 hours after the last injection. injection.

Spawning is heralded by a violent quivering of the Spawning is heralded by a violent quivering of the male, which liberates sperm as a response of the male, which liberates sperm as a response of the release of eggs. release of eggs.

Eggs are produced at a rate of 650–850/g female Eggs are produced at a rate of 650–850/g female body weight. Mullet eggs are spherical (880–980 µm) body weight. Mullet eggs are spherical (880–980 µm) and transparent, with a smooth surface and a single and transparent, with a smooth surface and a single large oil globule making the egg extremely buoyant. large oil globule making the egg extremely buoyant.

Eggs are carried with the overflow of water, sieved Eggs are carried with the overflow of water, sieved and transferred to incubation jars. Eggs are and transferred to incubation jars. Eggs are incubated at a temperature of 22–24 °C in seawater incubated at a temperature of 22–24 °C in seawater (30–32‰) saturated with oxygen. (30–32‰) saturated with oxygen.

Hatching takes place after 50–64 hours. After Hatching takes place after 50–64 hours. After hatching, the larvae are transferred to fibreglass hatching, the larvae are transferred to fibreglass indoor tanks and fed with live food (rotifers, and indoor tanks and fed with live food (rotifers, and later withlater withArtemiaArtemia nauplii).  nauplii).

Larvae are kept in indoor tanks for 14 days, and then Larvae are kept in indoor tanks for 14 days, and then transferred to larger tanks until they reach 10–2 mm transferred to larger tanks until they reach 10–2 mm before transport to outdoor nursery ponds.before transport to outdoor nursery ponds.

Nursery RearingNursery Rearing After acclimatization, fry are stocked in After acclimatization, fry are stocked in

earthen nurseries at high densities (up to earthen nurseries at high densities (up to 125/m²), where they depend mainly on 125/m²), where they depend mainly on natural food.natural food.

From 2.5 to 5.0 tonnes/ha of animal manure From 2.5 to 5.0 tonnes/ha of animal manure are added to the soil before filling with are added to the soil before filling with water; then chicken manure and chemical water; then chicken manure and chemical fertilizers (usually phosphate and nitrates) fertilizers (usually phosphate and nitrates) are added in suitable amounts on a weekly are added in suitable amounts on a weekly basis to keep secchi disc readings of 20–30 basis to keep secchi disc readings of 20–30 cm. Rice or wheat bran is sometimes used cm. Rice or wheat bran is sometimes used as an additional source of food.as an additional source of food.

Fry are kept in the nursery ponds for 4–6 Fry are kept in the nursery ponds for 4–6 months (from August or November till months (from August or November till April) until they are about 10 g BW. April) until they are about 10 g BW.

Optimum temperatures are 20–26 °C, both Optimum temperatures are 20–26 °C, both in the nursery and grow-out stages. The in the nursery and grow-out stages. The fingerlings are then caught, either by fingerlings are then caught, either by draining the nursery ponds into catch draining the nursery ponds into catch ponds or by netting. ponds or by netting.

Over-wintered mullet fingerlings are sold Over-wintered mullet fingerlings are sold for ongrowing in various culture systems for ongrowing in various culture systems but especially for semi-intensive but especially for semi-intensive aquaculture. aquaculture.

In the rare cases that fry supply exceeds In the rare cases that fry supply exceeds demand, they are retained and grown-on to demand, they are retained and grown-on to market size in the nurseries.market size in the nurseries.

Rearing techniques Rearing techniques  In many countries mullet fry and fingerlings are In many countries mullet fry and fingerlings are

stocked in inland lakes and reservoirs as a form stocked in inland lakes and reservoirs as a form of fisheries enhancement (culture-based of fisheries enhancement (culture-based fisheries). fisheries).

They have been transferred into inland water They have been transferred into inland water lakes of the El Fayyum area of Egypt since the lakes of the El Fayyum area of Egypt since the 1920s, and into the Black Sea and Caspian Sea 1920s, and into the Black Sea and Caspian Sea regions of Russia since 1930. regions of Russia since 1930. 

Cultured flathead grey mullet are usually grown Cultured flathead grey mullet are usually grown in polyculture in semi-intensive ponds and netted in polyculture in semi-intensive ponds and netted enclosures in shallow coastal waters. enclosures in shallow coastal waters.

Mullet can be polycultured successfully with Mullet can be polycultured successfully with many other fish, including common carp, grass many other fish, including common carp, grass carp, silver carp, Nile tilapia and milkfish, and carp, silver carp, Nile tilapia and milkfish, and can be reared in freshwater, brackishwater and can be reared in freshwater, brackishwater and marine water.marine water.

Prior to stocking, aquaculture ponds are Prior to stocking, aquaculture ponds are prepared by drying, ploughing and prepared by drying, ploughing and manuring with 2.5–5.0 tonnes/ha of cow manuring with 2.5–5.0 tonnes/ha of cow dung. dung.

Ponds are then filled to a depth of 25–30 Ponds are then filled to a depth of 25–30 cm and kept at that level for 7–10 days cm and kept at that level for 7–10 days to build up a suitable level of natural to build up a suitable level of natural feed. feed.

The water level is then increased to 1.5–The water level is then increased to 1.5–1.75 m and fingerlings are stocked. 1.75 m and fingerlings are stocked.

Productivity (measured by secchi disc – Productivity (measured by secchi disc – see nursery section) is kept at the see nursery section) is kept at the required level by adding chicken required level by adding chicken manure and/or chemical fertilizers. manure and/or chemical fertilizers.

Optimal dissolved oxygen is maintained by the Optimal dissolved oxygen is maintained by the use of various types of aerators, especially after use of various types of aerators, especially after sunset. sunset.

Extruded feed is supplied to semi-intensive Extruded feed is supplied to semi-intensive ponds to cover the feeding requirements of ponds to cover the feeding requirements of both carps and tilapia grown in the same ponds.both carps and tilapia grown in the same ponds.

The growing season is normally about 7–8 The growing season is normally about 7–8 months. If mullet are monocultured, manuring months. If mullet are monocultured, manuring may be sufficient to reach the required feed may be sufficient to reach the required feed level. In many cases, mullet has been found to level. In many cases, mullet has been found to feed directly on chicken manure and good feed directly on chicken manure and good levels of production have been recorded. levels of production have been recorded.

Growth is checked by sampling, and if growth Growth is checked by sampling, and if growth rates are not as expected, rice and/or wheat rates are not as expected, rice and/or wheat bran is added daily in amounts of 0.5–1 percent bran is added daily in amounts of 0.5–1 percent of biomass to supplement the natural feed in of biomass to supplement the natural feed in ponds. ponds.

When mullet are reared in polyculture, they When mullet are reared in polyculture, they are usually stocked with tilapia, common carp are usually stocked with tilapia, common carp and silver carp. In this case, feeding and and silver carp. In this case, feeding and fertilization programmes are usually targeting fertilization programmes are usually targeting the other cultured species and the mullet feed the other cultured species and the mullet feed on the natural feed, detritus and feed on the natural feed, detritus and feed leftovers.leftovers.

Acclimatized to the appropriate salinity, and Acclimatized to the appropriate salinity, and stocked as 10–15 g individuals at 6 175–7 stocked as 10–15 g individuals at 6 175–7 410/ha, a harvest of 4.3–5.6/tonnes/ha/crop 410/ha, a harvest of 4.3–5.6/tonnes/ha/crop can be obtained. can be obtained.

In semi-intensive polyculture with tilapia and In semi-intensive polyculture with tilapia and carp, mullet fingerlings are stocked at 2 470–carp, mullet fingerlings are stocked at 2 470–3 705/ha together with 1 850–2 470/ha of 100 3 705/ha together with 1 850–2 470/ha of 100 g common carp juveniles and 61 750–74 g common carp juveniles and 61 750–74 100/ha 10–15 g Nile tilapia fingerlings. Total 100/ha 10–15 g Nile tilapia fingerlings. Total harvests are typically 20–30 tonnes/ha/crop, harvests are typically 20–30 tonnes/ha/crop, of which 2–3 tonnes are mullet.  of which 2–3 tonnes are mullet. 

After an rearing season of 7–8 months in After an rearing season of 7–8 months in either culture systems in the subtropical either culture systems in the subtropical region, flathead grey mullet reach 0.75–1 region, flathead grey mullet reach 0.75–1 kg; if kept for two rearing seasons, they kg; if kept for two rearing seasons, they reach 1.5–1.75 kg each. reach 1.5–1.75 kg each.

Rearing for a second year depends on the Rearing for a second year depends on the market requirements; in some countries market requirements; in some countries mullets are marketed at a size of 1.5 kg and mullets are marketed at a size of 1.5 kg and larger. larger.

The two seasons are continuous, as fish are The two seasons are continuous, as fish are kept in ponds for over wintering, fish then kept in ponds for over wintering, fish then grow in the same ponds through the next grow in the same ponds through the next spring and summer until they reach that spring and summer until they reach that size. As usual, the choice of rearing size. As usual, the choice of rearing technique depends on market demand and technique depends on market demand and economics.economics.

Feed supply  Feed supply  In monoculture, mullet feeds on In monoculture, mullet feeds on

natural food and on the by-products of natural food and on the by-products of grain mills and rice polishing plants. grain mills and rice polishing plants.

In polyculture, manufactured extruded In polyculture, manufactured extruded pellets are produced either in feed pellets are produced either in feed mills specialized in the production of mills specialized in the production of fish feed or, in many cases, in chicken fish feed or, in many cases, in chicken feed mills that have a line for fish feed feed mills that have a line for fish feed production. production.

Feed is formulated according to the Feed is formulated according to the dietary requirements of the major dietary requirements of the major cultured species (i.e. tilapia and cultured species (i.e. tilapia and common carp).common carp).

Harvesting techniques Harvesting techniques  Harvesting can be partial in ponds or net Harvesting can be partial in ponds or net

enclosures. enclosures. Daily harvesting, according to market demand, Daily harvesting, according to market demand,

can be carried out using gillnets of suitable can be carried out using gillnets of suitable mesh size. mesh size.

Nets are stretched in a zigzag line across ponds Nets are stretched in a zigzag line across ponds at sunset and collected at the early morning.at sunset and collected at the early morning.

In semi-intensive culture, total drain-harvesting In semi-intensive culture, total drain-harvesting is used in late autumn or early winter. is used in late autumn or early winter.

Fish usually move with the flow of water to a Fish usually move with the flow of water to a concrete catch pond at the pond outlet. concrete catch pond at the pond outlet.

A seine net can be used to collect those that do A seine net can be used to collect those that do not reach the catch pond.not reach the catch pond.

Pearl Spot Fish Culture (Pearl Spot Fish Culture (Etroplus Etroplus suratensissuratensis))

The Pearl spot, The Pearl spot, Etroplus suratensisEtroplus suratensis commonly  commonly known as “Karimeen” in Kerala is an indigenous known as “Karimeen” in Kerala is an indigenous fish extensively found along the east and south-fish extensively found along the east and south-west coasts of Peninsular India. west coasts of Peninsular India.

It is an important candidate species for It is an important candidate species for aquaculture in ponds in both brackishwater and aquaculture in ponds in both brackishwater and freshwater environments. freshwater environments.

It is cultured in traditional ponds in Kerala It is cultured in traditional ponds in Kerala where it is considered a delicacy fetching a high where it is considered a delicacy fetching a high price up to Rs. 150/ kg. price up to Rs. 150/ kg.

Though growth is slow, at a high stocking Though growth is slow, at a high stocking density table-size fish can be harvested in 9-12 density table-size fish can be harvested in 9-12 months culture period.months culture period.

Pearlspot Fish Culture (Pearlspot Fish Culture (Etroplus Etroplus suratensissuratensis))

Seed productionSeed production Seed of pearlspot is available throughout Seed of pearlspot is available throughout

the year along the east and south-west the year along the east and south-west coasts of India. coasts of India.

The peak season of abundance is during the The peak season of abundance is during the months of May-July and November-months of May-July and November-February. February.

It can be easily collected from both the It can be easily collected from both the brackishwater and freshwater tanks and brackishwater and freshwater tanks and ponds. ponds.

A simple method of seed collection is A simple method of seed collection is adopted taking advantage of the tendency of adopted taking advantage of the tendency of the fish to congregate in large numbers for the fish to congregate in large numbers for feeding on epiphytic growth. feeding on epiphytic growth.

In this method twigs or branches are kept In this method twigs or branches are kept submerged in the water a week ahead of day submerged in the water a week ahead of day of collection. of collection.

The juveniles congregating for feeding The juveniles congregating for feeding purpose are trapped using an encircling net purpose are trapped using an encircling net or trap. or trap.

Fecundity of pearl spot is low and has been Fecundity of pearl spot is low and has been estimated to be around 3000-6000; hence a estimated to be around 3000-6000; hence a successful hatchery production of seeds is successful hatchery production of seeds is difficult. difficult.

However, Central Institute of Brackishwater However, Central Institute of Brackishwater Aquaculture (CIBA), Chennai using the Aquaculture (CIBA), Chennai using the technique of environmental manipulation, has technique of environmental manipulation, has successfully demonstrated the hatchery seed successfully demonstrated the hatchery seed production of pearl spot.production of pearl spot.

Pond PreparationPond Preparation Before letting in water, the ponds are drained Before letting in water, the ponds are drained

and lime is applied at the rate of 300 kg/ha. and lime is applied at the rate of 300 kg/ha. In undrainable ponds, piscicide (Mohua oil In undrainable ponds, piscicide (Mohua oil

cake @ 200-250 ppm) may be used to cake @ 200-250 ppm) may be used to eliminate the weed fishes etc. eliminate the weed fishes etc.

After a time gap of 10-15 days for the After a time gap of 10-15 days for the neutralization of the residual effect of the neutralization of the residual effect of the piscicide, water is let in through screens to piscicide, water is let in through screens to avoid the entry of undesirable fishes. avoid the entry of undesirable fishes.

The pond is filled up to the appropriate level The pond is filled up to the appropriate level (1.2 m) and cow dung applied at the rate of (1.2 m) and cow dung applied at the rate of 1500-2000 kg/ha for promoting plankton 1500-2000 kg/ha for promoting plankton production.production.

Acclimatization and stocking of breedersAcclimatization and stocking of breeders Adult Adult Etroplus Etroplus in the weight range of 50-125 g in the weight range of 50-125 g

procured from the wild or culture ponds are procured from the wild or culture ponds are stocked @ 5000/ha after one week of stocked @ 5000/ha after one week of fertilization of the pond. fertilization of the pond.

Breeders collected from the wild are to be Breeders collected from the wild are to be disinfected by dipping in 1% commercial disinfected by dipping in 1% commercial formalin and acclimatised before introducing formalin and acclimatised before introducing into the pond. into the pond.

Since the fish is monomorphic, sex Since the fish is monomorphic, sex differentiation is difficult and it has to be differentiation is difficult and it has to be assumed that the sex ratio of the stocked assumed that the sex ratio of the stocked breeders is approximately 1:1. breeders is approximately 1:1.

Additional breeders have to be added to the Additional breeders have to be added to the existing stock from the second year onwards to existing stock from the second year onwards to compensate the natural mortality of breeders. compensate the natural mortality of breeders.

Breeders once stocked will be normally viable Breeders once stocked will be normally viable for three years.for three years.

Provision of spawning surfacesProvision of spawning surfaces In the natural environment the fish In the natural environment the fish

attaches its eggs to submerged attaches its eggs to submerged substrata like stones, aquatic plants substrata like stones, aquatic plants etc. etc.

As a prepared pond may not have As a prepared pond may not have such natural spawning surfaces, such natural spawning surfaces, materials like palmyrah leaves tied in materials like palmyrah leaves tied in bunches to fixed poles, coconut leaf bunches to fixed poles, coconut leaf petioles, coconut husks, bricks, petioles, coconut husks, bricks, pieces of asbestos sheets etc., have pieces of asbestos sheets etc., have to be provided in the ponds.to be provided in the ponds.

Water quality monitoring and managementWater quality monitoring and management Maintenance of optimum water quality is Maintenance of optimum water quality is

important for the successful breeding important for the successful breeding of of Etroplus. Etroplus. 

Water quality parameters like salinity (15-30 Water quality parameters like salinity (15-30 ppt), dissolved oxygen (>3.5 ppm), pH (7-8), ppt), dissolved oxygen (>3.5 ppm), pH (7-8), temperature (24-32°C), transparency (>50 cm) temperature (24-32°C), transparency (>50 cm) and ammonia (<1 ppm) have to be maintained. and ammonia (<1 ppm) have to be maintained.

Optimum water level in the pond is 1.2 m. The Optimum water level in the pond is 1.2 m. The loss of water due to seepage and evaporation is loss of water due to seepage and evaporation is to be compensated by pumping in water. to be compensated by pumping in water.

Exchange of pond water through sluice or any Exchange of pond water through sluice or any other means is not desirable, as it will lead to other means is not desirable, as it will lead to escape of hatchlings and fry. escape of hatchlings and fry.

Salinity should not be allowed to go beyond 30 Salinity should not be allowed to go beyond 30 ppt. The fishes should not be disturbed ppt. The fishes should not be disturbed frequently.frequently.

FeedingFeeding Feeding of the breeders has to be Feeding of the breeders has to be

initiated within 3-4 days after stocking. initiated within 3-4 days after stocking. Artificial feed prepared with groundnut Artificial feed prepared with groundnut

oil cake 40%, rice bran 45% and fish oil cake 40%, rice bran 45% and fish meal 15%, fortified with vitamin and meal 15%, fortified with vitamin and mineral mix @ 2.5 kg per 100 kg feed, mineral mix @ 2.5 kg per 100 kg feed, is to be supplied daily @ 3-5% of the is to be supplied daily @ 3-5% of the fish biomass, either in pelleted form. fish biomass, either in pelleted form.

Feed can be supplied in feeding trays Feed can be supplied in feeding trays kept at the bottom of the pond. kept at the bottom of the pond.

The feeding trays should be examined The feeding trays should be examined daily and cleaned outside the pond. daily and cleaned outside the pond.

The quantity of the feed can be reduced The quantity of the feed can be reduced whenever left-over feed is present in the whenever left-over feed is present in the trays, to avoid wastage and water trays, to avoid wastage and water pollution. pollution.

The presence of hatchlings indicates The presence of hatchlings indicates that the pond is to be manured with cow that the pond is to be manured with cow dung @ 500 kg/ha for the production of dung @ 500 kg/ha for the production of plankton, which forms the food for the plankton, which forms the food for the hatchlings. hatchlings.

Small quantities of the artificial feed Small quantities of the artificial feed (250-300 g/pond of 1000 m2) also can (250-300 g/pond of 1000 m2) also can be broadcast in powder form during be broadcast in powder form during early morning.early morning.

Fry production and harvestingFry production and harvesting The experiment conducted in a pond of 100 m2 The experiment conducted in a pond of 100 m2

area gave an actual production of 3500 fry area gave an actual production of 3500 fry from five sets of spawnings in a year from five sets of spawnings in a year (projected production rate is 3.5 lakhs/ha/yr) (projected production rate is 3.5 lakhs/ha/yr) when the breeders were stocked at the rate of when the breeders were stocked at the rate of 6800/ha. 6800/ha.

Fry production from a pond of 300 m2 area Fry production from a pond of 300 m2 area from 3 sets of spawnings over a period of 5 from 3 sets of spawnings over a period of 5 months was 9600 and this works out to more months was 9600 and this works out to more than 5 lakhs/ha/year from five sets of than 5 lakhs/ha/year from five sets of spawnings, when the breeders were stocked at spawnings, when the breeders were stocked at the rate of 5400/ha. the rate of 5400/ha.

This probably indicates that the rate of fry This probably indicates that the rate of fry production may be enhanced from a bigger production may be enhanced from a bigger pond even at a low stocking density of pond even at a low stocking density of breeders.breeders.

Larval rearingLarval rearing The eggs are oblong in shape, about 1 to 2 The eggs are oblong in shape, about 1 to 2

mm in diameter, attached at one end by mm in diameter, attached at one end by means of a short stalk to the nesting means of a short stalk to the nesting object. object.

The newly laid eggs are yellowish in colour The newly laid eggs are yellowish in colour and as the embryo develops, the colour and as the embryo develops, the colour becomes brownish and the yolk sac becomes brownish and the yolk sac becomes pigmented. becomes pigmented.

The incubation period lasts from 82 to 100 The incubation period lasts from 82 to 100 hours. hours.

During hatching, the egg membrane bursts During hatching, the egg membrane bursts first over the head of the larvae, which is first over the head of the larvae, which is at the free end, and this continues along at the free end, and this continues along the upper side by the waving of the tail. the upper side by the waving of the tail.

The early larval stage lasts for 7 days The early larval stage lasts for 7 days during when the larvae develops into a during when the larvae develops into a free-swimming individual. free-swimming individual.

During late larval stagethe larvae, though During late larval stagethe larvae, though free swimming, are quite different from the free swimming, are quite different from the adult. adult.

The tail remains long and the caudal fin is The tail remains long and the caudal fin is continuous with dorsal and anal. continuous with dorsal and anal.

After a fortnight, the primary After a fortnight, the primary chromatophores on the back disappear and chromatophores on the back disappear and permanent colour bands begin to appear. permanent colour bands begin to appear.

The larvae assume adult form within a The larvae assume adult form within a month after hatching and measure about month after hatching and measure about 18mm.18mm.

The young ones feed almost The young ones feed almost exclusively on zooplankton, the exclusively on zooplankton, the advanced fry on aquatic insect advanced fry on aquatic insect larvae, filamentous algae and other larvae, filamentous algae and other vegetable matter, while the adult fish vegetable matter, while the adult fish subsists mainly on filamentous algae, subsists mainly on filamentous algae, aquatic macrovegetation and aquatic macrovegetation and planktonic organisms. planktonic organisms.

Worms, shrimps and insect larvae Worms, shrimps and insect larvae also form part of its food. Adult pearl also form part of its food. Adult pearl spot can be fed with pelleted fish spot can be fed with pelleted fish feeds.feeds.

Grow-out CultureGrow-out Culture The pearlspot is suitable for culture in confined, The pearlspot is suitable for culture in confined,

fresh and brackishwaters. fresh and brackishwaters. It is cultured in the traditional manner, in the It is cultured in the traditional manner, in the

'Pokkali' fields (paddy fields). 'Pokkali' fields (paddy fields). An annual yield of 3 to 5 tonnes is obtained from An annual yield of 3 to 5 tonnes is obtained from

these fields, of which, prawns constitute 80%, these fields, of which, prawns constitute 80%, while the mullets and pearlspot form 20%. while the mullets and pearlspot form 20%.

In mixed-culture operations along with prawns In mixed-culture operations along with prawns and other fishes ranged from 768.2 kg/ha/3 and other fishes ranged from 768.2 kg/ha/3 months at a stocking density of 25,200/ha (24000 months at a stocking density of 25,200/ha (24000 prawns + 1200 fish) to 845.4 kg/ha/110 days at a prawns + 1200 fish) to 845.4 kg/ha/110 days at a stocking density of 20,300/ha (20,000 prawns + stocking density of 20,300/ha (20,000 prawns + 300 fish) have been reported. 300 fish) have been reported.

The culture of pearlspot is more economical under The culture of pearlspot is more economical under polyculture system especially with milkfish and polyculture system especially with milkfish and mullets than under monoculture.mullets than under monoculture.

The fish can attain a marketable size of 120-150 The fish can attain a marketable size of 120-150 g over a period of 8-10 months. Though growth g over a period of 8-10 months. Though growth rate is relatively slow, high stocking density rate is relatively slow, high stocking density with low input management can yield optimum with low input management can yield optimum production. production.

Under monoculture at stocking densities Under monoculture at stocking densities ranging from 20,000 to 30,000 / ha, an average ranging from 20,000 to 30,000 / ha, an average production of 1,000 kg/ha/year can be obtained production of 1,000 kg/ha/year can be obtained in brackishwater ponds. The fish can also be in brackishwater ponds. The fish can also be reared in the backyard ponds and tanks in the reared in the backyard ponds and tanks in the rural areas. rural areas.

Being a herbivorous fish it is suitable for Being a herbivorous fish it is suitable for polyculture. Pearlspot farming could be adopted polyculture. Pearlspot farming could be adopted to any scale integrating with other occupations to any scale integrating with other occupations like poultry farming. like poultry farming.

The poultry droppings form good manure for The poultry droppings form good manure for natural food production in the culture ponds.natural food production in the culture ponds.

Adult fish in the weight range of 50-125 g are Adult fish in the weight range of 50-125 g are stocked in ponds @ 5,000 nos./ha. The fish are fed stocked in ponds @ 5,000 nos./ha. The fish are fed with supplementary feed @ 3.5% of the body weight with supplementary feed @ 3.5% of the body weight (prepared with groundnut oil cake 40%, rice bran (prepared with groundnut oil cake 40%, rice bran 45% and fish meal 15% fortified with vitamin and 45% and fish meal 15% fortified with vitamin and mineral mix @ 2.5 kg per 100 kg of feed). mineral mix @ 2.5 kg per 100 kg of feed).

The feed is supplied in pellet or dough form. The The feed is supplied in pellet or dough form. The hydrographical parameters desirable for the hydrographical parameters desirable for the breeding and seed production of pearl spot are: breeding and seed production of pearl spot are: water temperature 24-32°C, salinity 15-30 ppt, water temperature 24-32°C, salinity 15-30 ppt, dissolved oxygen > 3.5 ppm, pH 7.0 to 8.0 and dissolved oxygen > 3.5 ppm, pH 7.0 to 8.0 and transparency > 50 cm. transparency > 50 cm.

To facilitate egg attachment, the pond is provided To facilitate egg attachment, the pond is provided with substrate materials such as palmyrah leaves, with substrate materials such as palmyrah leaves, coconut leaf petioles, coconut husks, wooden twigs, coconut leaf petioles, coconut husks, wooden twigs, bricks etc. bricks etc.

Breeding occurs within 30-40 days of introduction of Breeding occurs within 30-40 days of introduction of the brooders. A production of upto 6 lakhs the brooders. A production of upto 6 lakhs fry/ha/year can be achieved. fry/ha/year can be achieved.

Harvesting is usually undertaken by Harvesting is usually undertaken by draining the water from the ponds draining the water from the ponds and operating a seine net, cast net or and operating a seine net, cast net or a drag net for capturing the fish.a drag net for capturing the fish.

Chanos chanos Chanos chanos (Forsskal, 1775 ) Milkfish Culture(Forsskal, 1775 ) Milkfish Culture Biological features Biological features Body fusiform, elongated, moderately compressed, smooth Body fusiform, elongated, moderately compressed, smooth

and streamlined. Body colour silvery on belly and sides and streamlined. Body colour silvery on belly and sides grading to olive-green or blue on back. grading to olive-green or blue on back.

Dorsal, anal and caudal fins pale or yellowish with dark Dorsal, anal and caudal fins pale or yellowish with dark margins. Single dorsal fin with 2 spines and 13-17 soft rays. margins. Single dorsal fin with 2 spines and 13-17 soft rays. Short anal fin with 2 spines and 8-10 soft rays, close to Short anal fin with 2 spines and 8-10 soft rays, close to caudal fin.caudal fin.

Caudal fin large and deeply forked with large scale flaps at Caudal fin large and deeply forked with large scale flaps at base in adults. base in adults.

Pectoral fins low on body with axillary (inner basal) scales. Pectoral fins low on body with axillary (inner basal) scales. Pelvic fins abdominal with axillary scales and 11 or 12 rays. Pelvic fins abdominal with axillary scales and 11 or 12 rays.

Scales cycloid, small and smooth, 75-91 on lateral line. No Scales cycloid, small and smooth, 75-91 on lateral line. No scutes (modified pointed scales) along belly. Transparent scutes (modified pointed scales) along belly. Transparent 'adipose' tissue covers eye. 'adipose' tissue covers eye.

Mouth small and terminal without teeth. Mouth small and terminal without teeth. Lower jaw with small tubercle at tip, fitting into notch in Lower jaw with small tubercle at tip, fitting into notch in

upper jaw. No bony gular plate between arms of lower jaw. upper jaw. No bony gular plate between arms of lower jaw. Four branchiostegal rays supporting underside of gill Four branchiostegal rays supporting underside of gill covers. Gill rakers fine and numerous. covers. Gill rakers fine and numerous.

Attains typical length of 1 m but may reach maximum Attains typical length of 1 m but may reach maximum length of 1.8 m (male).length of 1.8 m (male).

Chanos chanos Chanos chanos (Milkfish (Milkfish Culture)Culture)

Milkfish farming in Indonesia, Taiwan Province of China Milkfish farming in Indonesia, Taiwan Province of China and the Philippines started about 4-6 centuries ago. and the Philippines started about 4-6 centuries ago.

Culture methods in a variety of enclosures are constantly Culture methods in a variety of enclosures are constantly being improved upon. Since the 1970s, large investments being improved upon. Since the 1970s, large investments have been made in the Philippines as well as in Taiwan have been made in the Philippines as well as in Taiwan Province of China, Indonesia and Hawaii. Province of China, Indonesia and Hawaii.

For example, the Southeast Asian Fisheries Development For example, the Southeast Asian Fisheries Development Center (SEAFDEC) Aquaculture Department (AQD) was Center (SEAFDEC) Aquaculture Department (AQD) was established in Iloilo, Philippines in 1973 with a special established in Iloilo, Philippines in 1973 with a special remit to find solutions for milkfish aquaculture problems. remit to find solutions for milkfish aquaculture problems.

In this work, research and development on farming In this work, research and development on farming systems, breeding and fry production technologies was systems, breeding and fry production technologies was carried out. carried out.

There was no attempt at genetic improvement but fry There was no attempt at genetic improvement but fry translocation and trade occurred between Indonesia, translocation and trade occurred between Indonesia, Taiwan Province of China and the Philippines and Taiwan Province of China and the Philippines and geographic variations and heterogeneity were geographic variations and heterogeneity were documented. documented.

More recently, unconfirmed reports indicate that milkfish More recently, unconfirmed reports indicate that milkfish are now being cultured to fingerling or juvenile size in the are now being cultured to fingerling or juvenile size in the South Pacific Islands and in Singapore as tuna bait. South Pacific Islands and in Singapore as tuna bait. 

Milkfish farming was previously a Milkfish farming was previously a traditional industry, with little emphasis on traditional industry, with little emphasis on producing sexually mature, reproductively producing sexually mature, reproductively active fish in captivity. active fish in captivity.

The traditional milkfish industry depended The traditional milkfish industry depended totally on an annual restocking of farm totally on an annual restocking of farm ponds with fingerlings reared from wild-ponds with fingerlings reared from wild-caught fry. caught fry.

As a result, the industry suffered from As a result, the industry suffered from regional, seasonal and annual variations in regional, seasonal and annual variations in fry availability. fry availability.

These variations are generally These variations are generally unpredictable, and may be quite large over unpredictable, and may be quite large over short periods of time.  short periods of time. 

Thus, the central problem faced by the Thus, the central problem faced by the international milkfish industry was to find a way international milkfish industry was to find a way to produce a reliable, adequate, high quality to produce a reliable, adequate, high quality supply of milkfish fry that was not subject to supply of milkfish fry that was not subject to large unpredictable variations in time and space. large unpredictable variations in time and space.

During the past decade, much progress has been During the past decade, much progress has been made, particularly in regard to milkfish made, particularly in regard to milkfish propagation and the mass production of fry by propagation and the mass production of fry by private hatcheries, research institutions and private hatcheries, research institutions and government agencies. government agencies.

Instead of relying on wild-caught fry, milkfish Instead of relying on wild-caught fry, milkfish farms in the Philippines, Taiwan Province of farms in the Philippines, Taiwan Province of China and Indonesia now obtain the majority of China and Indonesia now obtain the majority of their fry from hatcheries, mainly due to the their fry from hatcheries, mainly due to the significant shortage of wild-caught fry.significant shortage of wild-caught fry.

Habitat and biologyHabitat and biology Milkfish (Milkfish (Chanos chanosChanos chanos) is the only ) is the only

species in the Family Chanidae. species in the Family Chanidae. Its distribution is restricted to either low Its distribution is restricted to either low

latitude tropics or the subtropical latitude tropics or the subtropical northern hemisphere along continental northern hemisphere along continental shelves and around islands, where shelves and around islands, where temperatures are greater than 20 °C temperatures are greater than 20 °C (Red Sea and South Africa to Hawaii and (Red Sea and South Africa to Hawaii and the Marquesas, north to Japan and south the Marquesas, north to Japan and south to Victoria, Australia; and in the Eastern to Victoria, Australia; and in the Eastern Pacific from San Pedro, California to the Pacific from San Pedro, California to the Galapagos). Galapagos). 

Adults occur in small to large schools near the Adults occur in small to large schools near the coasts or around islands. coasts or around islands.

They are well developed, migratory, large (up to They are well developed, migratory, large (up to 1.5 m and 20 kg), and mature sexually in 5 1.5 m and 20 kg), and mature sexually in 5 years. Milkfish only spawn in fully saline waters. years. Milkfish only spawn in fully saline waters.

The activity is most often correlated with the The activity is most often correlated with the new or full moon phases, takes place mostly in new or full moon phases, takes place mostly in the night and, in most regions, has one or two the night and, in most regions, has one or two seasonal peaks. seasonal peaks.

In the natural environment, spawning takes In the natural environment, spawning takes place near coral reefs during the warm months place near coral reefs during the warm months of the year, and populations near the equator of the year, and populations near the equator spawn year-round. Juveniles and adults eat a spawn year-round. Juveniles and adults eat a wide variety of relatively soft and small food wide variety of relatively soft and small food items, from microbial mats to detritus, items, from microbial mats to detritus, epiphytes and zooplankton. epiphytes and zooplankton. 

Milkfish is a heterosexual fish; Milkfish is a heterosexual fish; hermaphrodism has not been reported. hermaphrodism has not been reported.

In natural spawning stocks the sex In natural spawning stocks the sex ratio is almost equal, with a slightly ratio is almost equal, with a slightly higher amount of females. The higher amount of females. The determination of sex is very difficult, determination of sex is very difficult, because there are no easily because there are no easily identifiable morphological differences identifiable morphological differences between males and females; however, between males and females; however, the pheromone (prostaglandin) has the pheromone (prostaglandin) has been found to be an effective way to been found to be an effective way to identify mature male milkfish. identify mature male milkfish. 

Milkfish eggs (1.1-1.2 mm in diameter) and larvae (3.5 Milkfish eggs (1.1-1.2 mm in diameter) and larvae (3.5 mm at hatching) are pelagic and stay in the plankton mm at hatching) are pelagic and stay in the plankton for up to 2-3 weeks. Egg division begins an hour after for up to 2-3 weeks. Egg division begins an hour after and hatching occurs 35-36 hours after spawning. In the and hatching occurs 35-36 hours after spawning. In the wild, eggs are probably released in deeper oceanic wild, eggs are probably released in deeper oceanic waters and in the outer reef region. waters and in the outer reef region.

Older larvae migrate onshore and settle in coastal Older larvae migrate onshore and settle in coastal wetlands (mangroves, estuaries) during the juvenile wetlands (mangroves, estuaries) during the juvenile stage, or occasionally enter freshwater lakes. stage, or occasionally enter freshwater lakes.

The larvae eat zooplankton and can thrive and grow in The larvae eat zooplankton and can thrive and grow in water as warm as 32 °C. water as warm as 32 °C.

They then migrate onshore and where they can be They then migrate onshore and where they can be caught by fine-mesh nets operated along sandy caught by fine-mesh nets operated along sandy beaches and mangrove areas; these 'fry' are 10-17 mm beaches and mangrove areas; these 'fry' are 10-17 mm long and are used as seedstock in grow-out ponds, pens long and are used as seedstock in grow-out ponds, pens and cages.and cages.

In the wild, juveniles are found in mangrove areas and In the wild, juveniles are found in mangrove areas and coastal lagoons, and even travel upriver into lakes; coastal lagoons, and even travel upriver into lakes; they go back to sea when they get too large for the they go back to sea when they get too large for the nursery habitat, or when they are about to mature nursery habitat, or when they are about to mature sexually. sexually. 

Milkfish can reach a maximum size of Milkfish can reach a maximum size of 180 cm (male/unsexed) and 124 cm 180 cm (male/unsexed) and 124 cm (female). (female).

The maximum recorded weight and The maximum recorded weight and age is 14.0 kg and 15 years age is 14.0 kg and 15 years respectively. respectively.

Its fisheries importance is highly Its fisheries importance is highly commercial, especially in commercial, especially in aquaculture, and it is also used in aquaculture, and it is also used in game fish as bait. game fish as bait.

It is especially valued as a food fish in It is especially valued as a food fish in Southeast Asia.Southeast Asia.

Production cycleProduction cycle

Spawning of Milkfish; Maturation is reached Spawning of Milkfish; Maturation is reached rather week season, April- July and rather week season, April- July and September -November. September -November.

Late in life at least age 4 years in males and 5 Late in life at least age 4 years in males and 5 or older in females.or older in females.

Fertilization in external, the eggs reign Fertilization in external, the eggs reign released in the open sea near the shore do released in the open sea near the shore do float to the surface.float to the surface.

As many as 7million eggs have been As many as 7million eggs have been estimated to produce by a single large female.estimated to produce by a single large female.

All attempts to obtain from females either by All attempts to obtain from females either by natural spawning or by stripping in ponds natural spawning or by stripping in ponds have failed.have failed.

In others milkfish spawn only during summer.In others milkfish spawn only during summer.

Production systemsProduction systems Seed supply  Seed supply  Milkfish fry can either be obtained Milkfish fry can either be obtained

through collection from coastal areas through collection from coastal areas or littoral waters or can be produced or littoral waters or can be produced in captivity. in captivity.

The supply of wild fry is often The supply of wild fry is often unpredictable; catches in recent unpredictable; catches in recent years have diminished and cannot years have diminished and cannot satisfy the demand from culture satisfy the demand from culture farms.  farms. 

Fry from captive broodstock and spawnersFry from captive broodstock and spawners To develop broodstock under captive To develop broodstock under captive

conditions, large juvenile milkfish may be conditions, large juvenile milkfish may be stocked, fed and maintained in floating sea stocked, fed and maintained in floating sea cages in protected coves or in large, deep, fully cages in protected coves or in large, deep, fully saline ponds (as practiced in the Philippines), saline ponds (as practiced in the Philippines), or in large deep concrete tanks on land (as or in large deep concrete tanks on land (as practiced in Indonesia and Taiwan Province of practiced in Indonesia and Taiwan Province of China), until they reach sexual maturity with China), until they reach sexual maturity with an average body weight of at least 1.5 kg. an average body weight of at least 1.5 kg.

Land-based broodstock facilities are entirely Land-based broodstock facilities are entirely dependent on fresh pumped seawater supplies dependent on fresh pumped seawater supplies and are often integrated with a hatchery.and are often integrated with a hatchery.

Broodstocks reach maturity in five years Broodstocks reach maturity in five years in large floating cages, but may take 8-10 in large floating cages, but may take 8-10 years in ponds and concrete tanks. years in ponds and concrete tanks.

On average, first-spawning broodstocks On average, first-spawning broodstocks tend to be smaller than adults caught from tend to be smaller than adults caught from the wild. As a result, first-time spawners the wild. As a result, first-time spawners produce fewer eggs than wild adults, but produce fewer eggs than wild adults, but larger and older broodstocks produce as larger and older broodstocks produce as many eggs as wild adults of similar size. many eggs as wild adults of similar size.

Broodstocks of about 8 years old and Broodstocks of about 8 years old and averaging 6 kg produce 3-4 million eggs.averaging 6 kg produce 3-4 million eggs.

Breeding milkfish in captive conditions and Breeding milkfish in captive conditions and the mass production of fry, as practised in the mass production of fry, as practised in Taiwan Province of China, Indonesia and the Taiwan Province of China, Indonesia and the Philippines, is mostly dependent on natural Philippines, is mostly dependent on natural spawning, which assures high survival rates. spawning, which assures high survival rates.

Artificial induction is not normally used. Artificial induction is not normally used. On days when natural spawning occurs, the On days when natural spawning occurs, the

fish may feed less than usual but show fish may feed less than usual but show increased swimming activity and exhibit increased swimming activity and exhibit chasing, occasional leaping, and water-chasing, occasional leaping, and water-slapping activities from late noon to early slapping activities from late noon to early evening. evening.

Spawning usually takes place around midnight Spawning usually takes place around midnight but daytime spawning sometimes occurs. but daytime spawning sometimes occurs. 

Wild-caught fryWild-caught fry

Wild-caught fry are collected with Wild-caught fry are collected with fine-mesh seines and bag nets of fine-mesh seines and bag nets of various indigenous designs in the various indigenous designs in the Philippines, Taiwan Province of China Philippines, Taiwan Province of China and Indonesia. and Indonesia.

The most commonly used gear are The most commonly used gear are push net 'sweepers' and dragged push net 'sweepers' and dragged seines. seines.

Hatchery production Hatchery production  Milkfish hatcheries consist of larval Milkfish hatcheries consist of larval

rearing tanks, culture tanks for rearing tanks, culture tanks for rotifers (rotifers (BrachionusBrachionus) and green ) and green algae (e.g. algae (e.g. ChlorellaChlorella) and hatching ) and hatching tanks for brine shrimp (tanks for brine shrimp (ArtemiaArtemia). ).

Larval rearing may be either Larval rearing may be either operated in outdoor or indoor operated in outdoor or indoor systems, depending on the specific systems, depending on the specific conditions in the countries where conditions in the countries where fry are being produced.fry are being produced.

Hatchery operations utilize either intensive (high Hatchery operations utilize either intensive (high stocking density, high volume tanks, daily stocking density, high volume tanks, daily feeding and water exchange) or semi-intensive feeding and water exchange) or semi-intensive (low stocking density, high volume tanks, (low stocking density, high volume tanks, minimal water exchange, feeding with mixed minimal water exchange, feeding with mixed diet) systems, with an average survival rate of 30 diet) systems, with an average survival rate of 30 percent (from stocked newly-hatched larvae). percent (from stocked newly-hatched larvae).

After hatching, the larvae are ideally kept at After hatching, the larvae are ideally kept at 50/litre in hatchery tanks (either concrete, 50/litre in hatchery tanks (either concrete, fibreglass, canvas or polypropylene-covered fibreglass, canvas or polypropylene-covered earthen tanks) maintained with earthen tanks) maintained with ChlorellaChlorella and fed  and fed with rotifers during the early stages and later with rotifers during the early stages and later with copepods or brine shrimp for a total of 3-4 with copepods or brine shrimp for a total of 3-4 weeks. weeks.

Following this, their size ranges between 2-3 cm Following this, their size ranges between 2-3 cm and they are ready for transport to nurseries. and they are ready for transport to nurseries.

The fry may change hands two or more The fry may change hands two or more times before being used for grow-out; times before being used for grow-out; each time this happens, they are each time this happens, they are sorted and counted, transported, and sorted and counted, transported, and stored for different periods of time. stored for different periods of time.

Fry are a highly perishable commodity Fry are a highly perishable commodity and some of them die during and some of them die during gathering, storage, transport, nursery gathering, storage, transport, nursery rearing and grow-out. rearing and grow-out.

The technologies for fry storage and The technologies for fry storage and transport are generally effective, transport are generally effective, although perhaps not yet optimized. although perhaps not yet optimized.

Fry are stored in a cool place in plastic Fry are stored in a cool place in plastic basins or clay pots at 100-500/litre, in basins or clay pots at 100-500/litre, in water of 10-25‰, which is renewed water of 10-25‰, which is renewed daily. daily.

Dealers may store fry for 1-7 days, Dealers may store fry for 1-7 days, depending on the demand. Fry can be depending on the demand. Fry can be maintained on wheat flour or cooked maintained on wheat flour or cooked chicken egg yolk for 1-2 weeks but soon chicken egg yolk for 1-2 weeks but soon begin to die, despite continued feeding. begin to die, despite continued feeding.

Recently, micro-encapsulated feeds have Recently, micro-encapsulated feeds have become commercially available for become commercially available for finfish but the cost compared to finfish but the cost compared to conventional live feeds is higher.conventional live feeds is higher.