ZPC Salad

“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

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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).

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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

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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

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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

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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

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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).

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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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