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“FISH, MAN AND ENVIRONMENT:
STRATEGY OF SURVIVAL”
An Inaugural Lecture Delivered at Oduduwa Hall,
Obafemi Awolowo University, Ile-Ife, Nigeria
On Tuesday 20th
August, 2019
By
OLANIYI OLUSOLA KOMOLAFE
Professor of Zoology
Inaugural Lecture Series 342
© OBAFEMI AWOLOWO UNIVERSITY PRESS, 2019
ISSN 0189-7848
Printed by
Obafemi Awolowo University Press Limited,
Ile-Ife, Nigeria
1
PREAMBLE
Mr. Vice-Chancellor Sir, Academic and Administrative
Colleagues, Students of this great University, Distinguished
Guests, Ladies and Gentlemen. With deep sense of humility and
gratitude to the Almighty God I am here before you to deliver the
342nd
Inaugural Lecture entitled “Fish, Man and Environment:
Strategy of Survival” which is the 12th from the Department of
Zoology and the 3rd in Fish Biology.
Some years ago, a friend of mine, late Mr. Mudasiru Ayoade rode
from Abeokuta to Lagos on his Yamaha motor bike to show me the
names of candidates admitted into the University of Ife in the
“Daily Times”. On that same day, climbing behind him, we rode to
Abeokuta and back to Ile-Ife the following day. The result?, I was
given seven injections to cure pneumonia at the University Health
Center after my registration as a student. At Zoology department, I
was curious to know why University staff queued to buy fresh fish
caught in Opa Reservoir at Prof. G.A.O. Arawomo‟s Office, hence
my interest to know more about fish compared to other aspects of
Zoology. After my Master‟s degree in Zoology, I veered into the
unknown which made me to take Israelites journey of circling a
mountain for some years at Adeyemi College of Education, Ondo,
an appendage of Obafemi Awolowo University. I came back into
the mainstream at Ile-Ife four years after my Ph.D. degree in
Zoology. Since then my research activities have been critically
focused on ecology of fish as well as the impact of man and
environment on a commodity found all over the world supplying
protein to billions of world inhabitants, to both the rich and the
poor.
INTRODUCTION
Fish Biology
Fishes are aquatic a nimals. They are a part of the numerous cold-
blooded craniate vertebrates such as the bony fish like Tilapia,
catfish, sturgeons, eels, mackerels and cartilaginous fish (shark,
ray, chimaera) whose skeleton is largely composed of cartilage.
Other groups of fish include jawless fish, (Agnatha) such as
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Cyclostomes and other extinct related forms which are primitive
vertebrates. Fish species can be identified through external
morphological features. These include: body shape, scale size,
pattern of colours, scale count, relative position of fins and the
number of fin rays. Other defining physical features include the
standard length, total length, head length and width. Fish species
are found in rivulets, streams, rivers, ponds, lakes, lagoons, seas
and oceans. In some odd places all over the world, different fish
species have adapted to various environments such as high
mountain lakes in high temperature tropical waters and in regions
where the temperature is below zero. Nearly all fishes hide. Some
fishes hide to escape from their enemies while some hide to prey
on food or for both purposes. Some of the fishes also camouflage
while others hide by similar colouring (food fish) transparency or
countershading (mud catfish) and by changing their colours.
In every other parts of the world, fish species are used as food,
thereby contributing to a high percentage of protein supply to
individuals. They are also used as recreational animals whereby
anglers derive joy in angling. Some people use them for sports and
festivals as in the case of Argungu Festival in Kebbi State of
Nigeria while others derived joy watching them in tanks, concrete
aquaria glass etc. Some fishes are used to control pests and weeds
as observed in Tilapia species. Fishes are used as scientific
specimens in different fields such as in Animal behaviour,
Histology, Anatomy, Morphology, Embryology and even as
indicators of polluted environment. Other uses include fish oil for
making soap, fish skin for leather works, fish scales for beads and
ear-rings. The eyes and head of fish contain polysaccharide which
helps to keep the blood vessels and skin flexible. The bone
contains calcium while the skin contains vitamins A and B2. Fish
tissues also contain high grade of protein and vitamins.
Inland Water Bodies and Surface Area in Nigeria
The Nigerian Inland water bodies or fresh water bodies can be
grouped into three. These are Rivers Niger and Benue, with
tributaries flowing southwards; River Yobe and its tributaries
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empting their waters into Lake Chad; and the South Coastal Rivers
such as Rivers Ogun, Osun, Benin, Cross River, Imo and Akwa-
Ibom (Arawomo, 2004). The feature of these drainage system
(Fig.1) is the lateral flooding in the high-water season as a result of
local rains and floods arising from higher areas in the catchment.
The Nigerian inland water surface area is estimated to be
approximately 19,958,000 (ha). Thus, the major rivers constitute
the majority of inland surface water in the country (Table 1).
Figure 1: Map of Nigeria showing rivers and other water
bodies
Table 1: Inland Water Resource and their Area
Inland Water Resource Area (ha)
Fresh Water Bodies e.g. Basins and Flood
plains
3,221,500
Major Rivers 10,812,400
Major Lakes and Reservoirs 853,600
Deltas and Estuaries 858,000
Minor Reservoirs 98,900
Miscellaneous Wetlands 4,108,100
Fish Ponds 5,500
Source: Arawomo (2004)
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Water Quality Assessments Water is essential to life. Its quality determines the nature of
aquatic animals living within it. Fishes are able to survive in water
where they perform all their activities be it, behavioral patterns,
feeding, reproduction and growth activities. Aquatic environment
performs many functions such as purification, recycle of nutrients,
supply of food materials and adequate habitat for all its inhabitants.
The good benefit of having aquatic habitat for fish comes to an end
when its natural quality is disturbed. At this point the ability of fish
to absorb stress is exceeded. Water, therefore, is an extremely
inert body in relation to other chemical substances because of its
unique physical properties such as specific heat, latent heat,
thermal conductivity, expansion before freezing, viscosity, surface
tension, solvency and buoyancy.
In-depth knowledge of water quality assessment in relation to
animals and human activities can be fully explored by
limnologists. However, water quality in relation to the
sustainability of fish involves the knowledge of its physical and
chemical properties. The physico-chemical properties of water
involve its air and water temperature, water PH, depth,
transparency, electrical conductivity, total dissolved solids,
dissolved oxygen, biological oxygen demand, alkalinity, calcium,
magnesium, water hardness, organic matter, nitrate, phosphate,
sulphate, urea, ammonia etc. Fresh water bodies such as lakes,
rivers, and streams are open to anthropogenic activities. This is
why water quality is not constant in nature but varies with the time
of the day, season, weather conditions, water source, soil type,
temperature, stocking density, feeding rate and culture system
(Davenport, 1993). The presence of impurities reduces the quality
and the uses to which water may be deplored as well as serves as a
major factor controlling the state of health of fishes both cultured
and the wild.
The interactions of physical and chemical properties of water play
a significant role in the composition, distribution and abundance of
aquatic organism including fish species. (UNEP, 2006) gives an
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insight into the relationships between fishes and their environment
which can be used to determine water quality and productivity of
the water body. Hence, the presence or absence of a particular
chemical element in a water body might be a limiting factor in the
productivity of such water body (Mustapha and Omotosho, 2005).
Changes in environmental quality can be associated with changes
in water quality using parameters such as sediment load, nutrient
concentration, temperature, PH and dissolved oxygen level (UNEP,
2006). The balance of physical, chemical and biological properties
of water in lakes, ponds, reservoirs and rivers is an essential
requirement for the successful production of fish species.
Fresh Water Reservoir Studies
In Nigeria, there are about 268 species of fresh water food fishes.
Research studies have shown that fish species in fresh water
reservoirs are widely distributed in all the vast expanse of our
inland waters. The reservoirs and ponds built for various purposes
have also increased. Majority of the reservoirs are not adequately
monitored and studied for their fisheries. This is why the pressure
on the water resource for recreation, domestic and agricultural
purposes as well as urbanization, civilization and industrialization
have contributed immensely to the pollution of the aquatic system
and environmental degradation. A typical example is the Erinle
Reservoir which is badly damaged through such human actitivites
as farming, dredging, deforestation and unapproved use of fishing
gears. (Komolafe and Badejo, 2016); (Plates 1a and b).
6
Plate 1(a): Evidence of Erosion around Erinle Reservoir
(b) Wood logs covered with sand ready for baking to
charcoal close to shoreline
a
b
b
7
In Nigeria, reports on the decline of fish population and diversity
through its unsustainable exploitation are things of concern (Dada
and Gnanadoss, 1983). However, it has been suggested that there
are substantial opportunities to increase productivity of reservoirs
through better harvesting strategies and adapted stock
enhancement which also involves holistic approach of biological
principles. In a bid to improve on fish production in the Country
the Nigerian Government set up an Aquaculture and Inland
Fisheries Project (AIFP) in the 36 states of the Federation. The
report of AIFP shows that a substantial number of Nigeria Fish
ponds and reservoirs have little or no recorded information or data.
Nigerians are large fish consumers, consuming over 2.7 million
metric tons annually. The unmanaged inland water bodies
accounted for only 30% of this demand. Poor management
practices and over exploitation of inland waters have attributed to
downward trend of fish intake (Komolafe and Arawomo, 2008b).
MY CONTRIBUTION TO FRESH WATER FISHES
Fish Composition, Abundance and Distribution Mr. Vice-
Chancellor Sir, in line with the Yoruba adage “Ile la ti n ko eso
rode” („charity begins at home‟), I started my research into fresh
water fishes here at Obafemi Awolowo University precisely at
Aho-Stream, a tributary of Opa Reservoir. This is the stream
between Conference Centre and Road 2 Bridge. Through electro-
fishing gadgets, I observed three families of fish comprising four
species viz: Barbus ablabis, B.callipterus, Epiplatys infrafasciatus
and Clarias gariepinus. These species of fish are flushed into Opa
reservoir annually at the peak of the rainy season. The diversity of
fish species at Aho-Stream was low. In the main Opa Reservoir, a
total of 4,789 fish samples caught showed six families comprising
eleven species (Komolafe, 2008a); (Table, 2).
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Table 2: Relative abundance of fish species caught in Opa
Reservoir
The family Cichlidae constitute 99% of the total catch at Opa
Reservoir. The diversity of fish, as observed in Erinle Lake at Ede,
was high with 19 species made up of 10 families. There were
seven species of cichlids in the lake and these species constitute
98.7% of the total catch (Komolafe and Arawomo, 2011a). At the
recently impounded Osinmo Reservoir near Ejigbo, the diversity of
fish species showed four families comprising 7 species in the
habitat and the Cichlidae family comprised 59.6% of the total
catch. When Osinmo Reservior was revisited three years later,
there were eight families of fish made up of 14 species (Komolafe
and Arawomo, 2008b, 2011b); (Komolafe, et al, 2012).
The abundance and distribution of fish species at the incomplete
Osu Mini waterworks was very low. Three families consisting of
four species were observed. However, the cichlids dominated
other species with 92.8% of the total catch. The family Cichlidae,
with six species of fish, also dominated the abandoned gold mine
reservoirs at Igun with 86.2% of the total catch. At Igun
reservoirs, there were seven families of fish with twelve species
(Komolafe et al. 2016). In all the reservoirs studied, the
distribution, composition and abundance of fish species differed
form one habitat to another. However, the family Cichlidae was
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available in all the seasons irrespective of what man and
environment had dictated.
Varieties of fishing gears such as hooks and line, gill-net, cast-net
and traps were used at various times in my research. The
selectivity of gill-net as a fishing gear varies with mesh size and
this was observed on Coptodon zillii, Oreochromis niloticus and
Clarias gariepinus in Opa Resevoir at various times. Gill-net with
stretched mesh size of 5.1cm caught 48.65% of all C. zillii as
compared to 2.5cm stretch mesh size (19.92%) and 7.6cm
stretched mesh size (32.43%). Similarly, I also discovered that a
gill-net stretched mesh size of 10.2cm was the most efficient in
catching 93.34% of O. niloticus and 51.9% C. gariepinus in Opa
Reservoir (Komolafe, 2005a ; Abayomi et al, 2005).
At Opa Reservoir, the spatial and vertical distribution of O.
niloticus was examined by using a graded set of five gill-nets each
measuring 32m long and a depth of 3.78m. The mesh sizes of the
nets were 2.5cm, 5.1cm, 7.6cm, 10.2cm and 12.7cm. The reservoir
was also divided into three segments A, B and C (Fig. 2). Forty-
four samplings were made on each segment of the reservoir. Fish
specimens representing 30.5% of the total catch were caught in
segment A, while 41.78% and 27.65% were caught in segments B
and C. The spatial distribution when tested statistically (X2 cal
27.39 < X2 tab 67.51; df: 820) showed that the species was not
spatially distributed. The majority of the specimens, constituting
90.5% of the total catch, were caught at the lower part of the gill-
nets indicating that the species did not concentrate at the surface of
water (X2 cal 557.9 > X
2 tab 76.15; df: 820); (Komolafe, 2005a).
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Figure 2: Opa Reservoir showing fish sampling site
In another study, 78.7% of C. gariepinus specimens was caught
within the in-shore area of Opa Reservoir while 21.3% was caught
off-shore. This species as shown statistically concentrated more
along the shore line of the reservoir (X2 cal 127 > X
2 tab 67.51; df:
1,252). The species was mostly found at the lower part of the gill-
net (96.6%) while 3.4% was caught at the upper part of the gill-net
(X2 cal 277.6 > X
2 tab 67.51; df: 1,252). The percentage catch of the
specimens in long line, gill-net, cast net and traps were 69.8%,
25.5%, 2.9% and 1.8% indicating the preference of longline in the
exploitation of C. gariepinus at Opa Reservoir (Abayomi and
Komolafe, 2005).
Food Items, Feeding Habits and Diurnal Feeding Rhythm
The adaptive nature of fish species has resulted in intra and inter
specific differences in feeding expedient of fishes leading to many
11
species feeding on variety of food items which is an indication of
food selectivity. Food has been observed to determine population,
growth rate and the condition of fish. Food items eaten by fish
species change with seasons and as the fish grows in age. Fish
species can be herbivorous or detritophagic, they may be
carnivorous or predators. However, some have parasitic mode of
life such as intraspecific parasitism. There are several methods of
studying food eaten by fishes. These methods include the
numerical and frequency of occurrence methods. At Opa
Reservoir, I discovered that Oreochromis niloticus fed on detritus,
unicellular green algae such as Closterium sp, Euglena sp and
Synedra sp, Diatoms included Navicula sp, Stauroneis sp. Other
food items observed in the stomach of the fish include higher plant
fragments and insect remains. The feeding rhythm of the species
showed that 35.3% of all fish specimens had full stomachs
between 6.00 am and 3.00 pm. During the same period, 25.6% had
three-quarter stomach fullness and 21% with half stomach fullness.
Specifically, 37.7% of 624 fish specimens had full stomach
between 9.00am and 12.00 noon. The number of fishes with full
stomach increased to 51.4% between 12.00 noon and 3.00 pm. In
Opa Reservoir, 89.4% of all fish specimen caught fed between
6.00 am and 3.00 pm indicating that the species peak feeding
period was between 12.00 pm and 3.00 pm (Komolafe and
Arawomo, 2003).
Coptodon zillii which is 27.38% of 4,789 fishes caught in Opa
Reservoir fed on blue-green algae, green algae either unicellular,
filamentous or colony, diatoms, dinoflageletes, rotifers,
zooplanktons, higher plant fragments and insect remains. The
analyses of stomach content by numerical and frequency of
occurrence methods showed twenty-two food items. The juveniles
of the species fed on twelve of these food items in the reservoir. C.
zillii was observed to feed during the day with a peak feeding
period at 12.00 mid-day (Fig. 3). About 49% of the fish was caught
in the middle segment of the reservoir indicating that C. zillii was
not spatially distributed in the habitat where it ranked third in
12
abundance. A lot of food materials fed upon also supported its
population in the environment (Komolafe, 2008a).
Figure 3: Feeding rhythm of Tilapia zillii (Number of replicates
= 8)
The food items in C. gariepinus contain elements from diverse
plants and animals. These include earthworms, plant seeds,
detritus, palm fruit shaft, seven different species of insects, fish
and fish parts, two species of crustaceans, two species of
protozoans; two species of molluscs, four species of rotifers, eight
species of diatoms and six species of algae. The fish is an
omnivore. None of the 400 specimens studied had an empty
stomach and the feeding rhythm started at 6.00 am reaching a peak
at 12.00 noon. The feeding rhythm declined thereafter and rose
again after 6.00 pm reaching another peak at 12.00 mid-night. The
species feeding rhythm declined until 6.00 am. Two peak feeding
periods were observed during which full stomach contents were
established (Abayomi and Komolafe, 2005).
The food and diet of two economically important fish species-
Parachanna obscura and C. gariepinus-were examined in Osinmo
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Reservoir using Schoener‟s overlap Index Cxy, between species x
and y (Schoener, 1970)
Cxy = 1-0.5 ∑ |Pxi-Pyi|
Where Pxi and Pyi are the frequencies or proportions by number of
prey type i in the diet of species x and y in the seasons
respectively. In the reservoir, the three main diets of P. obscura
that constituted 73% of all food intake included fish, algae and
insects. However the five main diets constituting 79% of all food
taken by C. gariepinus were fish, detritus, algae, insect and
diatoms. In the reservoir, C. gariepinus is a bottom grazer with
high proportion of diatoms in the food. P. obscura was an obligate
piscivore. Even though, they fed on related food items, the value
of Schoener‟s Index of proportional overlap for the two species
was 0.02 indicating no feeding overlap. In rainy and dry seasons,
Schoener‟s overlap Index values for the two species were 0.05 and
0.02, showing that the food items of the species did not overlap in
the habitat (Komolafe and Arawomo, 2011b).
In the abandoned gold mine reservoirs of Igun, the red belly
Tilapia, C. zillii exploited more food items (23 of 27) compared to
mouth brooder Chromidotilapia guntheri which is 17 of 27. The
study showed that C. zillii and C. guntheri exhibited benthopelagic
exploitation and are mainly herbivorous and omnivorous
respectively based on the food items observed in their stomachs.
The fish species fed on related food items as confirmed by
Schoener‟s overlap Index of 0.65, suggesting that there was an
overlap in dietary requirements of C. zillii and C. guntheri in the
habitat (Komolafe et al, 2018b).
Determination of Age and Growth in Fishes
Estimates of age and growth in fishes are fundamental to an
understanding of the biology of fishes. This can be done by
identifying patterns of growth in some structures of fish which is
expected to be formed throughout the life of an individual fish.
Such parts of fish that can be used for ageing include, Otoliths,
Spines, and Scales. At Opa Reservoir, the scales of 1,310
specimens of C.zillii were examined. Annuli formation on the
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scales were recognized by characteristic crossing-over of circuli
between December and February of each year (Plate, 2). I also
observed that circuli were not laid down regularly on the scales in
other months of the year. In the same habitat, annular rings were
formed on the scales of 1,430 specimens of O. niloticus between
January and April (Komolafe and Arawomo, 1998), (Komolafe,
2004a).
Plate 2: The scale of C. zillii Figure 4: Graph of Log.
showing annulus standard length against
formation Log. scale length in O.
niloticus
15
The age of each fish was determined by direct proportionality
formula (Bagenal, 1978) viz:
Ln – C = Sn/S (L – C)
In O. niloticus and C. zillii, annular ring formation on the scales at
Opa Reservoir coincided with the peak of dry season in the
catchment area. The relatively low temperature caused by
harmattan during the period affected the hydrological
conditions of the reservoir and physiological state of the fishes
in such a way as to cause annulus formation on the scales. The
peak annulus formation on the scales of O. niloticus was in the
month of March.
O. niloticus gave a significant correlation (r = 0.835; p< 0.001)
between log. fish standard length and log. fish scale length (Fig.,
4). Similarly, the peak annulus formation on the scales of C. zillii
was the month of January. A significant correlation (r = 0.681;
p<0.001) between log. fish standard length and log. fish scale
length was observed for C. zillii. The results showed a steady
increase in the size of fish with age. I also noticed a reduction in
the rate of growth of fish with ageing process in both the male and
female O. niloticus and C. zillii. Male fish specimens grew bigger
than the females in all age groups. The age of fish determined by
back-calculation with scales revealed that O. niloticus and C. zillii
caught in Opa reservoir could be grouped into six and five year
classes. The length-weight relationship of O.niloticus showed a
statistically significant correlation (r = 0.969; p<0.001) between
logarithms of weights and standard lengths (X2 cal 137.00 > X
2 tab
2.617; df: 1,398). The calculated regression line gave the
relationship. W = 325 + 0.81L (Fig 5).
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Figure 5: Graph of Log. Fish weight against Log. Standard
Length in O. niloticus
Allometric growth was observed for O. niloticus at Opa Reservoir
with a value of 2.62. Similarly, the length-weight relationship of
C. zillii in the same habitat showed a statistically significant
correlation (r = 0.960; p<0.001) with allometric growth value of
2.43. At Aiba reservoir Iwo, annulus formation on 507 specimens
of Labeo coubie was between November and January. The peak
annulus formation on the scales of the fish was the month of
December.
Fish Reproduction
Information on fish reproduction helps to establish reproductive
potential and consequently for its exploitation and management
practices. Breeding behavior of fishes differs but fish care for eggs
and larvae in a similar way. Research work on 1,486 specimens of
C. zillii collected by gill-net at Opa Reservoir was examined. The
length at maturity of the male fish was 15.1 cm and 13.2 cm for the
female fish. This is less than three-year-old by age and growth
calculation.
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The sex ratios of the 1991, 1992, and 1993 populations 1:0.8, 1:0.7
and 1:0.9 (male: female) are similar and they follow the same
pattern. The deviation of each of the values from the expected 1:1
ratio was not statistically significant (p>0.05; df: 1,484). C. zillii is
a substratum brooder. Male and female pairs guard dug-up nests
along Opa Reservoir shoreline. Some males were caught with a
brilliantly reddish-brown ventral surface, which was a
characteristic of „breeding dress’ exhibited by the species. The fry
of this species become more numerous during the month of July
even though C. zillii was observed to breed throughout the year.
Highest fecundity of 6,473 eggs was observed in a fish weighing
224 g, with total length of 23.7 cm and standard length of 18.4 cm.
The mean fecundity of C. zillii was 4,329 ± 1,159.9 eggs, n = 685
with an egg diameter of 1.06 mm ± 0.69 mm; n = 619. The mean
relative fecundity was 29.6 egg per body weight (g) (Komolafe,
2004b). In this habitat, the reproductive strategy of another fish
viz: O. niloticus was investigated. The species was a maternal
mouth brooder. Working on 1,430 specimens caught by cast-
netting and gill-netting, the egg diameter of 639 female fish varied
between 2.12 mm and 2.69 mm with a mean value of 2.47 ± 0.02.
Mature eggs were yellowish and pear shaped. The gonadosomatic
index was used to follow the seasonal development of the gonads.
In the testis of male fish, gonadosomatic indices varied between
0.03 g and 1.67 g with a mean value of 0.39 ± 0.02. The index was
1.34 ± 0.01 with values between 0.12 g and 4.06 g in the female
fish.
During my investigation, eleven female fish specimens were
caught with eggs in their mouths. The total number of eggs found
in the mouth of each fish varied from 39 eggs to 241 eggs. Some
eggs were lost from the mouth as the fish struggled to escape.
Similarly, the arrangement of the eggs in the mouth was also
altered. Only one fish was caught with 46 alevins in the buccal
cavity. Some of the alevins had been lost during capture (Plates 3a
and b) (Komolafe and Arawomo, 2007).
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Plate 3: Two females of O. niloticus (a) carrying eggs and (b)
alevins in their buccal cavities
The fishing gears used to catch 1,253 specimens of C. gariepinus
in Opa Reservoir included baited long line, gill-netting and traps
baited with palm fruits. The sex ratio of the species in the habitat
was 2:1 (male to female). Egg diameter varies between 0.4 mm to
1.8 mm. Gonadosomatic indices was between 0.09 g to 0.8 g in the
male fish and 0.4 g to 11.58 g in the female fish. C. gariepinus
bred throughout the year in the reservoir. Fecundity was between
1,567 eggs and 650,625 eggs with a mean fecundity of 57,814 eggs
(Abayomi and Komolafe, 2005). At Aiba Reservoir Iwo, the
fecundity of Chrysichthys aureus was between 120 eggs and 1,061
eggs. The mean fecundity of the species was 239 eggs with a
a
b
19
relative fecundity of 4.64 eggs per body weight (g). Similarly, the
fecundity of Hepsetus odoe at Osu Mini waterworks ranged from
3,153 eggs to 9,646 eggs with a mean fecundity of 5,573 eggs.
Mr. Vice-Chancellor Sir, in 2008, my research work in fish
biology shifted to the impact of man and environment on fish
species, most especially fishes of economic importance which are
readily available to man. The tributaries of Opa Reservoir were
expanded within the town up to Road 7 in the campus. The effect
was devastating because it led to the beginning of the „death’ of
Opa Reservoir which was impounded in 1978. All the
alochothonous materials including plastics had been brought into
the reservoir a result of which the reservoir became loaded with silt
in such a way that the water holding capacity of the reservoir
reduced drastically. The result is very simple – less water to the
community. If nothing is done about this deplorable state of the
reservoir, it will become a river just passing through the campus in
some years to come. The fishes in the reservoir were not
unaffected by this event. Poachers on the reservoir have not
allowed Department of Zoology and other interested individuals
such as anglers and recreation fish lovers to benefit from the
Reservoir for a long period of time. Two departmental wooden
boats with outboard engines were sunk by poachers, since then the
Department of Zoology, Opa Dam Authority and University
Management have been silent. We took a bold step to access the
reservoir to check for heavy metal concentration in the organs of
some fish species in 2013. Our efforts was met with a stiff
resistance from the poachers. However, we negotiated with one of
the unions and paid them before they collected fish specimens for
us on their own terms. The results of our investigation on S.
galileaus, Tilapia dageti and Hemichromis fasciatus showed that
the concentration of heavy metals in the fillet, gills and liver of the
fishes was low compared to FEPA and WHO recommended
values. At the same time, Aho stream was revisited and both C.
gariepinus and Parachenoglanis fasciatus, caught in the stream
showed relatively low bioaccumulation of heavy metals in their
organs (Komolafe et al. 2013).
20
There were five reservoirs at Igun village in Atakumosa West Local
government area. These reservoirs were abandoned by the Nigeria
Mining Cooperation in 1941 after the impoundment of three streams –
Oika, Eleripon and Osun. The streams discharging to the reservoirs
were worked upon by illegal miners while the reservoirs have been
overgrown by weeds and ferns (Plates 4a and b)
Plate 4a: Illegal miners at work in Igun village
Plate 4b: Igun Reservoir four covered with aquatic plants
a
b
21
Assessing the concentrations of heavy metals Arsenic, Chromium,
Lead and Zinc in the fillet and gills of three Tilapine species viz;
C. zillii, Hemichromis fasciatus and Sarotherodon galilaeus in the
abandoned reservoirs showed excessive bioaccumulation of heavy
metals in the fishes (Table,3). Irrespective of the time of collection
and the seasons (dry and wet), Chromium was the mostly found
heavy metal in all the fishes. H. fasciatus had more heavy metals
than C. zillii and S. galilaeus (Lawal and Komolafe, 2012).
Table 3: Seasonal variation of heavy metals (µg/g) in the fish
species of Igun reservoir
Heavy metal concentration in the gills and fillet of fishes at Igun
Reservoirs was high compared to WHO and FEPA recommended
values in fish food. Further studies on the survival strategy of fresh
water fishes in polluted habitats led to the pathological study of
some organs of five fishes Parachanna obscura, S. galilaeus, O.
niloticus, Hemichromis fasciatus, and C. zillii in the abandoned
gold mine reservoirs of Igun village and in Opa fresh water
reservoir. In the polluted reservoir of Igun, the gills, fillet and liver
of the fish species were highly affected by necrosis of muscle
bundles, vascular congestion of central and portal vein,
degeneration of liver cells, hypertrophy of the primary lamellae,
22
shortening of secondary lamellae and nucleus, atrophy of muscle
bundles, fusion of secondary lamellae as compared to the rupture
of portal artery and hepatopancreas degeneration in Opa Reservoir.
More severe alterations were found in the organs of Igun fish
species due to accumulation of heavy metals as a result of mining
activities which was the main cause of the pollution (Plates 5
a,b,c,d,e,f,g,h ); (Komolafe et al., 2017, 2018a).
Plate5a: Photomicrograph of gill Plate 5b: Photomicrograph of
section in C. zillii of Opa reservoir gill section in C. zillii of Igun
(Mag. X400) reservoir (Mag.X400)
Keys: hyperplasia of secondary lamellae (HSL), mucous cell
(MC), rupture of chloride cells (RCC), and degeneration of
secondary lamellae (DSL).
Haematoxylin and Eosin stain.
Plate 5c: Photomicrograph of Fillet Plate 5d: Photomicrograph of
Section in S. galilaeus of Opa Fillet Section in S. galilaeus of
Reservoir (Mag. X40) Igun Reservoir (Mag. X40)
RCC
DSL
NMB AMB
RCC
MC
HSL
MC DSL
NMB
AMB
23
Keys: atrophy of muscle bundles (AMB), necrosis of muscle
bundles (NMB)
Haematoxylin and Eosin stain.
Plate 5e: Photomicrograph of Liver Plate 5f: Photomicrograph of
Section in P. obscura of Opa Section Liver in P. obscura of
Reservoir (Mag. X40) Igun Reservoir (Mag. X40)
Keys: Central vein (CV), degeneration of liver cells (DLC),
vascular congestion (VC)
Haematoxylin and Eosin stain
Plate 5g: Photomicrograph of Fillet Plate 5h: Photomicrograph of
Section in H. fasciatus of Opa Fillet Section in H. fasciatus of
Reservoir (Mag. X400) Igun Reservoir (Mag. X400)
Keys: splitting of muscle bundles (SMB) and splitting of muscle
myofibrils (SMM)
Haematoxylin and Eosin stain
Between 2010 and 2011, water samples were also collected in
Osinmo Reservoir. This was done in order to know the effects of
seasonal changes and variations in the physico-chemical properties
of the water on tissue distribution of the metabolism enzymes:
CV
DLC
VC
CV
SMM
SMB SMB
DLC
CV
CV
SMM
24
Arginase and Rhodanese, on two important fish species viz:
Clarias gariepinus and Heterotis niloticus (Okonji et al., 2013;
Adedeji et al., 2015). It was observed that in-flux of water from
adjoining streams into the reservoir affected the quality of water
and enzyme distribution in the tissues of fishes. The presence of
arginase in the reservoir water and its distribution in tissues of C.
gariepinus and H. niloticus is an indication of the acidity and
alkalinity of the reservoir. Arginase, an enzyme which catalyzes
the conversion of arginine to urea becomes more effective in
aquatic organisms, especially fresh water fishes when their
environment becomes polluted and made more alkaline. Similarly,
Rhodanese, also known as thiosulphate-cyanide suphurtransferase,
is widely distributed in the body tissue (Agboola and Okonji,
2004). Rhodanese detoxified cyanide to a less toxic thiocyanate.
The activity of these enzymes was found to be high in rainy season
at Osinmo Reservoir. This could be explained on the premise that
enzyme can be induced in the presence of cyanide. Also, under the
condition of low dissolved oxygen, cyanide is more toxic to fresh
water fishes (EPA, 1980). On the distribution of arginase and
rhodanese enzymes in the intestine, stomach, liver and gills of C.
gariepinus and H. niloticus, the activities were more in the liver.
This is because of the function of liver in metabolism, and in
particular detoxification. The results provide further evidence of
the importance of the two enzymes in the survival of fish species.
With respect to the survival of these fishes, a study was carried out
at Igun polluted reservoirs to determine cyanide level and activity
of cyanide detoxifying enzymes in the water and tissues of eleven
fish species. The mean levels of cyanide in the reservoirs both in
rainy and dry seasons were extremely high (Table, 4).
25
Table 4: Physicochemical parameters of water quality at Igun
reservoir
Table 5: Mean (±SEM) total rhodanese activity in tissue
homogenates of fish species
Varying degrees of enzyme activities were detected in the gills,
gut, liver and fillet of all the fish investigated. The pattern of
distribution of rhodanese in different tissues of fish is species
specific (Table 5). With the high level of cyanide in water, no
cyanide was detected in the tissue of fish samples. The distribution
patterns of rhodanese and 3-mercaptopyruvate sulphur transferase
26
3-MST in the tissues of fish species in Igun Reservoir may be
traced to the function of these enzymes in cyanide-detoxification.
The presence of high rhodanese and 3-MST activity in the gut of
fishes ensures cyanide detoxification before it reaches general
circulation. This could explain the survival of inhabitant fish
species in this unfriendly environment through enzyme-based
mechanism. At Igun abandoned gold mine Reservoirs, the effects
of physico-chemical properties of water and sediments on Arginase
and Rhodanese distribution on the organs of six fish species was
investigated. The reservoir sediment was acidic (4.78 ± 0.37) in
nature. The higher the physico-chemical property of water, the
greater the arginase activity in the fish organs and the more the
urea produced by the fishes. The fish species were able to survive
due to their ability to convert ammonia to urea at higher rate
(Oriyomi et al 2015; Asafa, 2018 and Okunola, 2018).
CONCLUSION AND RECOMMENDATIONS
Mr. Vice-Chancellor Sir, I have tried, in this lecture, to present
most of the issues that have engaged my research time in this great
University. My research efforts have shown that our land is blessed
with abundant water system: rivulets, streams, rivers, ponds,
natural and man made lakes. However, as an index of a country
where laws and orders are violated with impunity, our rich aquatic
environment has been polluted by individuals, corporate bodies
and government agencies in order to satisy their selfish interest. A
pertinent question to ask now is: why is the aquatic environment
at the mercy of man. My research efforts have shown that not all
the fishes that we consume are healthy because many of the waters
from which those fishes grow have been vitiated through all kinds
of water pollution. The government at local, state and federal
levels are not unaware of this problem, but no finger has been
lifted to solve it.
The Nigerian government at all levels need to work hand-in-hand
with the NGOs, multinationals and individuals to start proper
management practices so as to reduce over exploitation of inland
water fisheries. There is a need for the collation of various research
27
works to enhance proper data for the commencement of fresh
water biodiversity conservation.
Concerted and collaborative efforts of government, NGOs, private
sectors and individuals most especially artisan fishermen are
required to enforce compliance with the laws governing the use of
our water-body system. The abuse of land use as a result of
domestic and agricultural practices in farming, dumping of waste
materials by industries into water-bodies, as observed in urban
cities, must stop immediately. Our fresh water bodies must be
arranged and grouped to show their sizes, qualities and wellness
through physico-chemical and biological properties.
Mr. Vice-Chancellor Sir, Opa reservoir was built primarily to
supply potable water to this community. One of the ancillary
benefits of the reservoir is the production of fish. The Internally
Generated Revenue through fish production has been taken over by
the poachers. This is why Opa reservoir must be properly secured
and its tributaries cleared of unwanted materials. The reservoir,
which is heavily loaded with silt, needs to be dredged. The
intervention of the Federal Government is urgently needed,
Mr. Vice-Chancellor Sir, the take away of my lecture today is “let
us watch what we eat”. This is because heavy metals concentration
in fish species may cause severe damate on fish, thus endanger fish
health, and constitute respectable risk for human health via
consumption of heavy metals contaminated fish. Fishes are good
but not all fishes are good for eating. But let me assure you that the
fishes at Opa reservoir are healthy for consumption. So, let us
continue to eat and derive maximum food values from fishes from
the reservoir except at Igun reservoirs.
Mr. Vice-Chancellor Sir, I am eternally grateful to the Almighty
God, who the Apostle Paul also acknowledged in I Corinthians
15:10 “But by the grace of God I am what I am and His grace
which was bestowed upon me was not in vain”. I wish to express
my gratitude to Obafemi Awolowo University through which the
28
Federal Government gave me scholarship during my (M.Sc.)
programme, and the University Research Committee during my
Ph.D. programme. I want to appreciate retired Prof. G.A.O.
Arawomo who guided me in the field of Fish and Fisheries. Also,
appreciated are retired Prof. (Mrs.) E.A. Adesulu, Prof. I.F.
Adeniyi Prof. J.A. Adegoke, Prof. J.I. Awopetu in the fields of
Fish nutrition, Hydrobiology & Limnology and Genetics
respectively. I also thank Professors S.O. Asaolu, J.O. Ojo, A.I.
Akinpelu and Dr. R.E. Okonji, who have been a source of help
over the years. I am grateful to my colleagues and administrative
staff in the department for their love, support and cooperation and
above all, living as a family. My regards to all my past and present
undergraduate and graduate students. It is my pleasure to
acknowledge the tremendous assistance received from the Vice-
Chancellor, Elizade University, Prof. Olukayode Amund, the
Registrar, Mr. Omololu Adegbenro, the Bursar, Mr. Segun
Ajeigbe, Profs. T. O. Fadayomi, Kole Omotoso, Drs. K. K. Agbele,
O.S. Onile, Mr. O.K. Arowolo, Mrs. A.D. Oyelana, Mrs. F.A.
Okeleji and all my colleagues and staff of the Faculty of Basic and
Applied Sciences. I whole heartedly thank academic and
administrative staff of Elizade University.
I am highly indebted to my parents, the late Mr. Benjamin O.
Komolafe, and late Mrs. Felicia Dada Komolafe who first took me
to school. When things were rough and a teacher was sent from
Otapete Methodist School, Ilesha, to ask if I am still coming to
school, my mother promised the teacher that I would come. The
promise she made is the outcome of today‟s lecture. Thank you my
sweet mother. My late brother and late sister – Mr. D.O. Komolafe
and Mrs. B.O. Adegbayibi, I thank you for the parts played in
those difficult days. My sincere appreciation to Dr.‟Segun
Komolafe (formerly at the Faculty of Pharmacy), he took over
from my parents during my undergraduate days. He was highly
committed to my course. May the Lord reward you greatly. I
cannot forget my immediate brother, Mr. Ayoola Komolafe for his
help, advice and prayers always. The children of my late uncle
Mr. S.M. Komolafe and Late Aunty Mrs. S.O.I Fadugba were
29
always with me. I thank you all. Mrs. Bolanle Oke you have been
so wonderful to my family, thank you very much. I also recognize
the parts played in my family by Prof. and Late (Mrs.) Wanwa
Adeniyi, Mr. and Mrs. Isijola, Dr. and Mrs. Abayomi, Late Dr.
O.O. Oke and Mrs. C.J. Obadofin at Adeyemi College of
Education, Ondo. Special thanks to my in-laws Pa. Moses and Mrs.
Adenike Dada who stood by me over the years. I am very grateful
to every member of the family. Finally, I express my profound and
unreserved gratitude to my nuclear family. During my stay in the
wilderness, I constantly heard a voice, I traced the voice and found
her. This is my God sent wife – Dr. Mrs. O. A. Komolafe, you are
really the best for me. To my three Ns, you are all wonderful
children. Thank you for tolerating my actions and reactions in the
course of training you. I am highly indebted to you all. I wish to
express my sincere appreciation to Pastor Olaoluwa Role, of
Rhema Chapel International Churches, Ile-Ife and all the
congregation for their prayers and support always. I return all the
glory and honour to God Almighty.
Mr. Vice-Chancellor Sir, Ladies and gentlemen, I thank you all for
your attention. God bless you, Amen.
30
Coptodon zillii Oreochromis niloticus
Sarotherodon galilaeus Hepsetus odoe
Hemichromis fasciatus Ctenopoma kingslayae
Heterotis niloticus Parachanna obscura
31
Mormyrus rume Barbus ablabes
Clarias gariepinus Barbus callipterus
Epiplatys infrafasciatus Chrysichthys auratus
Labeo cuobie Malapterurus electricus
32
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