EMBRYOGENESIS AND LARVAL DEVELOPMENT OF THE OMANI ABALONE

(HALIOTIS MARIAE WOOD, 1828)

MOHAMMED BALKHAIR,* ALI AL-MUSHIKHI AND RODRIGO RIVERA

Fisheries Research Center-Salalah, Ministry of Agriculture and Fisheries Wealth, PO Box 33, Salalah217, Sultanate of Oman

ABSTRACT Recognizing the physiological changes of invertebrates during early life is essential to understand the species

biology. Studies describing the development of early stages of Omani abalone (Haliotis mariae) are scarce. Therefore, this article

presents the first detailed description of embryonic and larval development of the Omani abalone (H. mariae). The eggs obtained

by a successful artificial spawning using a combination of hydrogen peroxide and ultraviolet irradiated- seawater, were observed

carefully under compound microscope. The chronicle order of the embryonic and larval development of 26 distinct stages, from

fertilization until reaching the presettlement stage when the larvae are competent and distinguished by formation of the third

tubule tentacle, were illustrated. The changes during several stages were documented and photographed. The eggs were spherical,

green, and negatively buoyant at the beginning then became planktonic; average fertilized egg diameter was 185 ± 7 mm.Hatching

occurred at 9 h 16 min after fertilization, whereas larvae were competent at 46 h 48 min post fertilization. The average seawater

temperature during the embryonic and larval observation was 24.7�C ± 1.0�C. The survival rate prior to settlement was 24.2%.

This study provide a first detailed informative illustration of embryonic and larval development of Omani abalone (H. mariae),

assisting in understanding the biology and ecology and supporting steps toward sustainable development of the aquaculture and

management of this species.

KEY WORDS: aquaculture, Haliotis mariae, larval development, Omani abalone

INTRODUCTION

Larval development is a critical stage in different marine

species, such as molluscs. Generally, the larval development ofmolluscs started with a basic stage of trochophore and thenprogressively develop into lecithotrophic or planktotrophic

veliger larvae, which are characterized by the formation of thevelum. After a brief planktonic stage, the metamorphosis stageallows the larvae to initiate the crawling stage and settle into

benthic habitat. The early juvenile will pass a series of de-velopmental phases to reach the adult stage. There are severalstudies of abalone larval development around the world(Leighton 1974, Hahn 1989, Courtois de Vicose et al. 2007,

Visser-Roux 2011); however, the most frequently cited guidefor abalone larval development was conducted on the Japaneseabalone (Haliotis discus hannai) by Ino (1952). The study works

as a primer for the larval development of all other abalonespecies around the world. In general, there are four major stageswhich are larval, post larval, juvenile, and adult (Hahn 1989).

The transition from one stage to another is determined by anexplicit development process. For instance, the post larvae stageis determined by the settlement and metamorphosis of thelarvae, whereas the formation of the first respiratory pore

indicates the juvenile stage and finally the adult stage is definedwhen the first sexual maturity is observed (Hahn 1989).

The Omani abalone (Haliotis mariae) is a prevalent species

distributed along the southern coast of Oman. They areconsidered as one of the premium seafood delicacies in Omanand have the highest commercial value among all Omani

fisheries products (Balkhair et al. 2013). Historically, the Omaniabalone was traded to other regions including Yemen andIndia, andmore recently China. During the last few decades, the

Omani abalone stock has been seriously overexploited because

of concentrated fishing; illegal harvest by fishing out of thepermitted season; the harvest of small, immature specimens,

and a fishery practice of overturning boulders and thus destroy-

ing the abalone habitat (Al-Hafidh 2006). Recently, it was

apparent that the Omani abalone populations could not be

maintained under the sustained fishing pressures. Therefore,

research on biological and technological methods for the seed

production ofH. mariae has been undertaken with emphasis on

spawning induction and larval rearing development and latterly

restocking of hatchery-bred seeds of Omani abalone to the

natural habitat has been implemented. Although the mass

production of Omani abalone is currently successful, there are

still many issues associated with the percentage of survival rates

that need to be resolved.The embryonic and larval development stages of Haliotis

mariae have scarcely been studied. Only three to six phases have

previously been identified from larval to postlarval stages (Stirn

& Al-Hashmi 1996, Iwao 2000, Benny et al. 2003, Al Rashdi &

Iwao 2008). The first attempt of identifying the embryonic

development of Omani abalone was conducted by Stirn and Al

Hashmi (1996) which identified six stages; nonfertilized egg,

cleavage (4-cell stage), advanced embryo (morula), unhatched

trochophore larvae, initial veliger, and finally advanced veliger.

Benny et al. (2003) have mentioned only three stages; hatching,

early veliger, and settled larvae. Whereas, Al Rashdi and Iwao

(2008) have described only four stages from fertilization to

presettlement as follows; fertilized egg, hatch-out trocophore,

presettlement veliger, and metamorphosed larvae. Therefore,

this study is believed to provide a first detailed illustration of

embryonic and larval development of Omani abalone (H.

mariae) along with the time required for each stage. As it is

predicted that Omani abalone has an auspicious future espe-

cially when it is coincided with the linear increase in demand for

abalone in the international market, this study is anticipated to

enhance the knowledge of the specific life history of H. mariae*Corresponding author. E-mail: darbat2001@yahoo.com

DOI: 10.2983/035.035.0308

Journal of Shellfish Research, Vol. 35, No. 3, 625–631, 2016.

625

and developing the abalone aquaculture and seed productionin Oman.

MATERIALS AND METHODS

A spawning trial was performed specifically to carry outinvestigation of the larval development of the Omani abalone in

January 2014. The broodstock used in the spawning trial wasobtained from the wild and kept in captivity in fiberglass tanksuntil they became ripe. The gonad ripeness of the broodstocks

was measured following Uki (1989).The animals with gonadal stages 2 and 3 were collected for

the spawning trial. The selected animals were cleaned with soft

brush and held in air for 1 h prior to the commencing of thespawning inducement trial. Afterward, the animals placed in the20-l transparent plastic aquariums with ultraviolet-irradiatedseawater were filtered by using a 5-mm cartridge filter. A total of

26 female and 9 male abalones were used in this study and keptat 4–6 animals per aquarium. The seawater temperature in theaquariums was 25�C. In this trial, spawning inducement of the

Omani abalone broodstock was applied by using the hydrogenperoxide method (Morse et al. 1977). The Tris solution(HOCH2)3CNH2 was added to the aquariums that contained

the animals to raise the pH of the seawater and 15 min later, the6% hydrogen peroxide was added to the same tanks. Next, thewater inside the aquariums were exchanged 95 min after

addition of hydrogen peroxide and refilled with fresh irradiated,filtered seawater. The response of the animals to the spawninginducement was recorded and the eggs were collected forfertilization. The observations of the larval development were

recorded from fertilization until the third tubule tentacleformed, identifying competent larvae ready for settlement. Allsampled larvae were collected from the same aquarium during

the investigation by taking three aliquot 1-ml samples. Theduration and temperatures of every observed developmentalstage were recorded. The embryonic and larval development

was carried out using a compound microscope (Carl ZeissMicroImaging GmbH, Germany). Photographs showing theembryonic and larval development of the Omani abalone(Haliotis mariae) were taken using a digital camera (Sony,

HDR-CX405) and described following the stages identified byHahn (1989) for comparison.

RESULTS

Spawning Response

Males spawned before females, as is usually the case for the

Omani abalone (Haliotis mariae). The males and females com-menced spawning 3 and 5hafter the additionof hydrogenperoxide,respectively. The overall mean fertilization rate was found to be87.5% ± 3.1% and more than eight million eggs were obtained.

Embryonic and Larval Development

The survival rate from the onset of fertilization until the

presettlement stage was 24.2%. The egg color was greenish andthe average diameter of the spherical unfertilized eggs was 185 ±7 mm. The mean temperature recorded throughout larval stage

developments was 24.7�C ± 1.0�C.The developmental stages during this study were divided into

three intervals. The first interval is cleavage, which commenced

with fertilization ending at blastula, the second interval beginswith gastrula stage until hatching stage, and finally, the third

interval starts with trochophore and ends with the appearance ofthe third tubule on cephalic tentacles.

Although there were additional stages identified during theobservations, 26 distinctive stages were highlighted. The chron-

icle of the embryonic and larval developmental stages of Omaniabalone (Haliotis mariae) compared with other tropical andtemperate Haliotis spp. is illustrated in Table 1.

Shortly after fertilization (stage 1), the discharge of the firstpolar body (stage 2) has been detected within 11 min (Fig. 1A,B). After that, the second polar body (stage 3) is discharged

(Fig. 1C). The first cleavage development (stage 4) observed36 min post fertilization; the second cleavage (stage 5) was reachedin 1 h 1 min, and the third cleavage (stage 6) in 1 h 26 min (Fig.1D–F). The morula (stage 7) was attained 20 min later (Fig.

1G). Next, the egg development passes through blastula andgastrula (stages 8 and 9) followed by the formation of cilia andprototrocal girdle (stage 10) (Fig. 1H–J). The complete forma-

tion of prototrocal girdle is clearly outlined by now (stage 11)(Fig. 1K). The embryo became apparent and resembled theshape of a trochophore larva. Gradually, the egg membrane

became fragile and was accompanied by active internal rotationof the trochophore (stage 12), which developed in puncturingthe membrane and allowing hatching (Fig. 1L). The trocho-

phore larvae hatched in nearly 9 h, the newly hatched larvaewere positively phototactic, clustering close to the watersurface. The larval shell secretion began soon after hatching(stage 13) (Fig. 1M). The veliger larvae were characterized by

their flat apical region and completely developed velum withcilia (stage 14) (Fig. 1N). The incipient cap-shaped shell velum isconsidered as the locomotion apparatus. The formation of

organs progressed, with the appearance of the larval retractormuscle (stage 15), proceeded by the formation of the integ-umental attachment to the larval shell (stage 16) (Fig. 1O). At

stage 17, the foot mass protrudes to the top of the shell and thelarval shell is completely developed. Torsion was initiated byrotating the cephalopedal mass by 90� (stage 18) (Fig. 1P), untilfinally reaching a 180� rotation from its original position (stage

19) (Fig. 1Q). Soon after torsion was completed, spines at theend of metapodium and the operculum were formed (stage 20).Veligers tended to withdrew into their shells at the slightest

provocation. At this stage, cilia developed on the foot sole(stage 21) followed by formation of propodium (stage 22).Subsequently, a cephalic tentacle was identified on the velum

(stage 23) and apophyses formed from twisting of the propo-dium (stage 24) (Fig. 1R–T). The pediveliger larvae appeared totest substrata before they settled by using their foot. They swam

down and up again exploring the substrates. The otolith becamevisible and short spines were formed on the cephalic tentacles(stage 25) (Fig. 1U). Finally, the third tubule became obvious oncephalic tentacles (stage 26). By then, the metamorphosed

larvae were deemed competent and attached to the bottomand the sides of the aquariums, appearing ready to be trans-ferred to the settlement tanks (Fig. 1V).

DISCUSSION

In this study, the Omani abalone (Haliotis mariae)responded positively to the induction of spawning. The fertil-ization rate inH.mariaewas found to be 87.5% ± 3.5%which is

BALKHAIR ET AL.626

satisfactory. Both sexes were kept separately and fertilizationwas achieved by mixing the eggs and sperm immediately afterspawning, as described by Kikuchi and Uki (1974).

Egg Diameter

In general, the embryonic and larval development observed

for Haliotis mariae was faster than other abalone species, suchas Haliotis rufescens (Ebert & Houk 1984), Haliotis midae(Genade et al. 1988), and Haliotis varia (Najmudeen & Victor

2004), but less rapid than Haliotis asinina (Jarayabhand &Paphavasit 1996, Sawatpeera et al. 2001).

Table 2 shows the size of fertilized eggs ofHaliotis mariae incomparison with other Haliotis spp. The average size of

fertilized eggs of H. mariae was 185 ± 7 mm which was smallercompared with the temperate species. The reported size of thefertilized egg for other Haliotis species was 230 mm in Haliotis

discus, 280 mm in Haliotis sieboldii, 270 mm in Haliotis gigantea(Ino 1952), 230 mm in Haliotis iris (Harrison & Grant 1971),200 mm in Haliotis sorensini (Leighton 1972), and 205 mmHaliotis tuberculata (Courtois de Vicose et al. 2007). On theother hand,H.mariae egg size was more or less similar to that ofrelative tropical species, such as 190 mm in Haliotis diversicolor

supertexta (Chen, 1989), 190 mm inHaliotis asinina and 180 mminHaliotis ovina (Jarayabhand & Paphavasit 1996), and 180 mmin Haliotis varia (Najmudeen & Victor 2004). The difference of

the egg size was species dependent (Hahn 1989) and might bedue to broodstock dissimilarities in broodstock size, age, andorigin (Courtois de Vicose et al. 2007).

Pigmentation

The divergence in pigmentation among abalone species has

been recorded by several researchers. The eggs were found to beolive in Haliotis corrugata, brown in Haliotis fulgens, beige inHaliotis sorenseni, and violet in Haliotis coccinea canarensis(Harrison &Grant 1971, Hahn 1989). The egg color of (Haliotis

mariae) was dark green, which was in agreement with thoseobserved by other temperate Haliotis species like Haliotisrufescens, Haliotis cracherodii, Haliotis walallensis, Haliotis

assimilis, andHaliotis kamtschatkana (Leighton 1972) and witha tropical species like Haliotis asinina (Sawatpeera et al. 2001).Furthermore, the dark green color ofH. mariaewas noted to be

retained by trochophore and veliger larvae. Leighton (1972)argues that egg color is attributable to retention of pigmentsderived from the parental yolk.

TABLE 1.

The chronicle of the embryonic and larval stages of Omani abalone (Haliotis mariae) compared with other Haliotis spp.

Stage Description

Time (h.min)

H. mariae

(24.7�C % 1.0�C)*Haliotis

ovina (na)†

Haliotis

asinina

(25�C)‡

Haliotis

tuberculata

(23�C % 0.5�C)§

Haliotis

midae

(18�C){

Haliotis

coccoradiata

(20�C)k1 Fertilization 0.00 0.00 0.00 0.00

2 1 polar body 0.11 0.10 0.25 0.25 0.40

3 2 polar body 0.20 0.15 0.33 0.39 1.00

4 First cleavage (2 cells) 0.36 0.20 0.50 0.49 1.30 0.51

5 Second cleavage (4 cells) 1.01 0.40 1.00 1.26 2.00 1.15

6 Third cleavage (8 cells) 1.26 2.00–4.00 1.33 1.32 3.30 1.45

7 Morula 1.46 2.38 2.30 5.00

8 Blastula 3.31 3.83 3.13 6.00

9 Gastrula 4.36 5.50 4.30 7.00 7.00

10 Cilia formation, PG 6.18 6.00 6.21 8.00 8.30

11 Complete formation of PG 7.25 8.00 8.20 11.00

12 Trochophore 9.16 5.00–6.00 9.11 12.00 11.00

13 LS secretion 9.52 10.50 9.35 16.00 19.30

14 Completion of velum veliger 13.01 10.00–12.00 12.00 11.45 18.00 20.00

15 Appearance of larval retractor muscle 15.06 13.50 15.20

16 Formation of integumental attachment to LS 17.46 14.50 15.20 20.00

17 Completion of LS 19.01 16.50 18.17

18 90� Torsion of cephalopedal mass 19.26 18.00 18.38 22.00

19 180� Torsion of foot mass 20.36 21.00 21.29 26.00

20 Appearance of long spines at the end of

metapodium and formation of operculum

22.46 25.00–29.00 22.38 28.00

21 Appearance of cilia on foot sole 24.46 30.50 26.29

22 Appearance of propodium 30.31 41.00 36.10

23 Appearance of CT 31.21 43.50 40.20 72.00

24 Appearance of apophysis on propodium 35.46 51.00 47.50

25 Appearance of otolith and short spine in CT 42.48 55.00–57.00 53.20

26 Third tubule appearance on CT 46.48 60.00 61.42

CT, cephalic tentacles; LS, larval shell; PG, prototrocal girdle; na, data not available.

* The present study, † Jarayabhand and Paphavasit (1996), ‡ Sawatpeera et al. (2001), § Courtois de Vicose et al. (2007), { Visser-Roux (2011),

and k Wong et al. (2010).

EMBRYOGENESIS AND LARVAL DEVELOPMENT OF THE OMANI ABALONE 627

Larval Stages

Overall, observations inHaliotis mariaewere consistent withother studies which have shown that there are no differences

in larval development among most of abalone species fromfertilization to trochophore. Instead, this study has been unableto demonstrate the formation of short cilia in the prototrocal

stage, as observed in the tropical abalone Haliotis asinina. Allprevious studies on Haliotis species have shown similarity inembryonic and larval development, except that of H. asinina,where Sawatpeera et al. (2001) discussed three differences

compared with other species. Not only was the number of cellsin the fourth cleavage of H. asinina found to be 12, which wasless than that of normal 16-cell development, but also the

number of cells in the fifth cleavage was 16 instead of the usualnumber of 32 cells. Moreover, the cilia that appeared on theprototrochal cells were long and short in H. asinina, whereas

only long ones were typically observed on other species. Theshort cilia might be incompletely developed, ultimately growingto full length. Turning to the third difference, which was the

appearance of the apical tuft, has been the source of somedisagreement. Boutan (1899) reported the absence of an apical

tuft at all stages; however, Crofts (1937) noted apical cilia were

observed only during the veliger stage. Conversely, the apical

tuft was observed on trochophores just before hatching into the

veliger stage, before the velum division (Koike 1978).

The larval development of Haliotis mariae, from trocho-phore stage to torsion, was similar to that of Haliotis discus

hannai, Haliotis discus, Haliotis sieboldii, Haliotis asinina, and

Haliotis diversicolor supertexta. The formation of the larval

retractor muscle was followed by formation of integumental

attachment. Moreover, the development of the operculum

occurred in H. mariae after these stages.

Ino (1952) suggested larval shell formation after torsion forHaliotis sieboldii. Furthermore, spines at the end of the

metapodium were observed after the formation of operculum.

In contrast, in this study, the shell ofHaliotis mariaewas formed

before torsion occurrence which was similar to many other

abalone species like Haliotis discus hannai and Haliotis asinina,

Figure 1. (A) Stage 1, Fertilization occurred. (B) Stage 2, discharge of first polar body. (C) Stage 3, discharge of second polar body. (D) Stage 4, 2-cell

stage. (E) Stage 5, 4-cell stage. (F) Stage 6, 8-cell stage. (G) Stage 7,Morula. (H) Stage 8, Blastula. (I) Stage 9, Gastrula. (J) Stage 10, cilia formation,

PG. (K) Stage 11, complete formation of PG. (L) Stage 12, unhatched trochophore larvae. (M) Stage 13, Larval shell secretion. (N) Stage 14, veliger

larvae with completion of velum. (O) Stage 15, appearance of larval retractor muscle. Stage 16, Formation of integumental attachment to larval shell.

(P) Stage 17, shell is completely formed. Stage 18, 908 torsion of the cephalopedal mass. (Q) Stage 19, 1808 torsion of foot mass. (R) Stage 20, appearance of

long spines at the end of metapodium and formation of operculum. Stage 21, appearance of cilia on foot sole. (S) Stage 22, appearance of propodium.

Stage 23, appearance of cephalic tentacles. (T) Stage 24, appearance of apophysis on propodium. (U) Stage 25, Appearance of otolith and short spine in

cephalic tentacle. (V) Stage 26, third tubule appearance on cephalic tentacles.

BALKHAIR ET AL.628

and spines at the end of the metapodium were observed beforethe formation of operculum. These results are broadly consis-

tent with earlier findings of Seki and Kan-no (1977) inH. discushannai. As with the findings of Koike (1978) in Haliotis tuber-culata, cephalic tentacles, foot, and operculum appearance were

noticed in posttorsional veligers in H. mariae.The current study observations were consistent with those

of Haliotis discus hannai (Seki & Kan-no 1977) and Haliotisasinina (Sawatpeera et al. 2001), in terms of the same presence of

cephalic tentacles, apophysis on propodium, otolith, and shortspines on cephalic tentacles prior to metamorphosis. The firstepipodial tentacle was observed later after the onset of meta-

morphosis in Haliotis gigantea which was different fromfindings of this study for Haliotis mariae.

The otolith appearance in Haliotis mariae was in line with

those of previous observations ofHaliotis discus hannai (Seki &Kan-no 1977) andHaliotis asinina (Sawatpeera et al. 2001). Theearly creeping behavior observed 46 h 48 min after fertilization

at which time the otolith, cilia on propodium, and third tubulein the cephalic tentacle were formed. At that stage, the larvaecan attach to the surfaces, but they are not yet able to creep

(Koike 1978). The cessation of the planktonic stage is the mostcritical stage in the life cycle of invertebrate larvae (Najmudeen &

Victor 2004).In fact, the larvae of Haliotis mariae were observed to be

lecithotrophic, as with other abalone larvae. The lecithotrophiclarval stage of abalone, fuelled primarily by lipid, demands that

the egg contains enough energy reserves to last for several days(Moran & Manahan 2003).

Because tropical abalone species, for example, Haliotis

asinina and Haliotis diversicolor supertexta, have shorter larvaldevelopment period compared with temperate species, there-fore, the cost of rearing period will effectively be reduced. As

absence of supplementary feeding requirement during the earlylarval rearing period is thought an advantage forHaliotis sp. ingeneral and certainly for Haliotis mariae production, a shortlarval development period for H. mariae makes it an excellent

candidate for aquaculture as potential threats accompanyingextended larval rearing periods are diminished.

Phototactic behavior in Haliotis mariae larvae was noticed

from hatching to veliger. Trochophores and veligers were mostabundant near the surface of the water (Ault 1985). The H.mariae veligers swam in spiral movement. In addition, larvae

were retracted into their shells following external stimulation.In comparison of previous studies of embryonic and larval

development of Omani abalone from fertilization to settlement

stage with the current study, many issues have been clarified.Benny et al. (2003) have mentioned only few stages with timerequired for each stage. Also, Al Rashdi and Iwao (2008) havedescribed only four stages without allocating the time required

for each stage except the hatching stage which occurred 8 h25 min and 6 h 30 min post fertilization at 23.6�C and 24.7�C,respectively. Moreover, Stirn and Al Hashmi (1996) have

identified six stages with the time required, but the veliger andsubsequent pediveliger larvae were elongated and showedabnormal development based on the figures illustrated at their

study. Table 3 shows a summary of different embryonic andlarval development on Haliotis mariae published in earlierstudies. Most of the stages in this study had not been describedbefore in H. mariae.

The rate of larval development varied among species. Thisvariation is thought to be temperature reliant, the higher thetemperature the more rapid the development (Ebert & Houk

1984, Pe�na 1986, Hahn 1989). In particular, the variation inlarval development between different Haliotis species resulted

TABLE 2.

The size of fertilized eggs of Haliotis mariae in comparisonwith other Haliotis spp.

Species

Egg diameter

(mm) Reference

Haliotis rubra 200 Harrison and Grant (1971)

Haliotis tuberculata 205 Courtois de Vicose et al. (2007)

Haliotis midae 220 Visser-Roux (2011)

Haliotis discus 230 Ino (1952)

Haliotis iris 230 Harrison and Grant (1971)

Haliotis sorensini 200 Leighton (1972)

Haliotis ovina 180 Jarayabhand and

Paphavasit (1996)

Haliotis varia 180 Najmudeen and Victor (2004)

Haliotis Diversicolor

supertexta

190 Chen (1989)

Haliotis asinina 148 Sawatpeera et al. (2001)

Haliotis coccinea

canarensis

103 Pe�na (1986)

Haliotis coccoradiata 175 Wong et al. (2010)

Haliotis mariae 185 The present study

TABLE 3.

Summary of embryonic and larval development on Haliotis mariae published in earlier studies.

Description

Time required (h:min)

Stirn and Al hashmi 1996 Benny et al. 2003 Al rashdi and Iwao 2008

Fertilized egg na na na

Cleavage (4-cell stage) 1–2 h na na

Advanced embryo (8-cell stage) 6 h na na

Prehatched out larvae 12–14 h na na

Hatched trocophore larvae na 10 h 8 h 25 min at 23.6�C6 h 30 min at 24.7�C

Early veliger 32–36 h 18 h na

Late veliger 48 h na na

na, data not available.

EMBRYOGENESIS AND LARVAL DEVELOPMENT OF THE OMANI ABALONE 629

from different larval rearing temperatures. Also, the compari-son of the duration of larval development between the Omaniabalone and other abalone species emphasizes the rapid larval

development of this species (Table 4). Furthermore, based onthe results of this study, Haliotis mariae seemed to have thesecond fastest larval development among all Haliotis species

studied, including Haliotis asinina. In addition, the studyconducted by Sawatpeera et al. (2001) has investigated thelarval development of H. asinina at different ranges of temper-ature, which resulted in confirming the negative relationship

between temperature and larval development period. The timerequired to reach the presettlement stage when the third tubulewas formed was 46 h 48 min for H. mariae at 23.5�C compared

with 60 h for H. asinina at 25�C. Thus, the Omani abaloneH. mariae exhibit rapid embryonic developmental stages com-pared with many otherHaliotis species. Because, theH. asinina

larval development was faster than that of H. mariae at highertemperatures of 28–34�C. Therefore, research is needed todetermine the most rapid growth and optimum survival of

H. mariae at different water temperatures.This study has found that, generally, hatching occurs at 9 h

16 min postfertilization at 24.6�C, the transition from trocho-phore to veliger with velum takes place at 13 h and torsion at

19 h 26 min after fertilization. The literature on larval develop-ment shows a variety of 32–42 stages in different abalone speciesaround the world. In comparison, this study highlights the

embryonic and larval development beginning from the onset of

fertilization to the formation of the third tubule in cephalictentacles only, which may reduce the total number of stagesobserved in this study compared with other studies which

addressed the development until the juvenile stage.This study generated valuable information on the early life

history and developmental stages of theOmani abaloneHaliotis

mariae. To our best knowledge, this is the first study to providea detailed description of embryonic and larval development ofOmani abalone accompanied by the time required for eachstage. This work is a contribution to the biology and ecology of

H. mariae, which might be of great use to take appropriate stepstoward sustainable development of the culture and managementof this species. Because no similar complete and informative

descriptions of larval development for H. mariae have beenavailable so far, this study will assist to better understand thedetails of larval physiology, morphogenesis, and biology of

this species and its behavior besides its potential for broaderapplication under captive conditions.

ACKNOWLEDGMENTS

We would like to thank the Agriculture and Fisheries Devel-opment Fund (AFDF) for funding this study. We would also

like to thank the staff of theMirbat Aquaculture Station (MAS)and Fisheries Research Center in Salalah for their help in manyways, and Virgie Sol Titular and Basheer Kunhimon for their

effort and help.

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TABLE 4.

Comparison of time required of developmental stages between Omani abalone (Haliotis mariae) and other selected Haliotis spp.

Species

Temperature

(�C)

Time (h.min)

ReferenceTrochophore

Larval retractor

muscle

Torsion

(90�)

Appearance

of cephalic

tentacles

Third tubule appearance

on cephalic tentacles

Haliotis tuberculata 23 9.11 15.20 18.38 40.20 61.42 Courtois de Vicose et al. (2007)

Haliotis coccoradiata 20 11.00 na 22.00 72.00 na Wong et al. (2010)

Haliotis asinina 25 na 13.50 18.00 43.50 60.00 Sawatpeera et al. (2001)

Haliotis mariae 24.7 9.16 15.06 19.26 31.21 46.48 The present study

na, data not available.

BALKHAIR ET AL.630

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