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PROJECT TOPIC AND MATERIAL ON STUDIES ON THE BIOLOGY OF SILVER CATFISH (CHRYSICHTHYS NIGRODIGITATUS LACÈPÈDE 1803) IN JEBBA LAKE, NIGERIA
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ABSTRACT
Studies on the biology of silver catfish Chrysichthys nigrodigitatus (Lacèpède, 1803) in
Jebba Lake, Nigeria was carried out between January 2009 and December 2010. Samples
collected using fleets of experimental gillnets were used for the study. There was
fluctuations in the physico-chemical parameters measured; mean electrical conductivity
(66.41±13.89µs/cm), and mean phosphate (0.20±0.15mg/l), which was significantly
different (p<0.05) at the zones. The males and females showed allometric (2.49) and
isometric (3.18) growth pattern respectively, with strong relationship and direct
proportionality between length-length for males (0.93) and females (0.83). The condition
factor for males (K=1.74) and females (K=1.83) showed that the lake was conducive for
the survival of the fish because it was greater than 1. The positive correlations in the
morphometric parameters, and the meristic counts confirmed the presence of the species in
the lake. The age structure was between 0+ and 3+ with bulk of the samples within ranges
of 2 and 2+, males being bigger than females. Size distribution ranged from small to adult,
with few adults in the population. Chrysichthys nigrodigitatus has the tendency to grow
bigger based on the growth performance index. Nine (9) major items ingested by C.
nigrodigitatus ranged from plant materials (21.75%) to animal components (55.65%),
which vary in abundance across months and seasons. Juveniles and sub-adult fed
predominantly on insects (36.72% and 28.69), while adults on fry (27.86%). There was a
direct relationship between the size of fish and ingested food items. Prey importance index
showed insects (57.61%), insects (53.70%) and fry (39.65%) as the most important items
ingested by juveniles, sub-adults and adults, respectively. There was high feeding intensity
due to few number of fish stomachs without food. Chrysichthys nigrodigitatus is an
omnivore with moderate gut length. There were more males than females (1.77:1) in the
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population. More gravid females were recorded in August and September, which coincide
with the period of spawning. Gonad maturity showed stages I-VI, males attained first
maturity than females. Female C. nigrodigitatus had higher gonado-somatic index (9.73)
than males (1.32) especially during the wet season. Mean fecundity ranged between 1,670
3,375 eggs, which increase with increased in fish size. Chrysichthys nigrodigitatus was the
most abundant species both within the family Claroteidae (13.06%) and in the overall
catch (8.95%) during wet than dry seasons, dominant in zones I and II during the wet
season, and commonly found at the bottom of the lake. It is recommended that
morphometric and meristic parameters be used to identify the fish, study on population
structure to reveal more class sizes be done, culture trials should also be done, and the feed
components to be plant and animals materials.
TABLE OF CONTENTS
Content Page
Title page ……………………………………………………………….. i
Declaration ……………………………………………………………….. ii
Certification ……………………………………………………………….. iii
Acknowledgements ……………………………………………………………….. iv
Abstract ………………………………………………………………… v
Table of contents ……………………………………………………………….. vii
List of tables ……………………………………………………………….. xiii
List of plates ………………………………………………………………. xvi
List of figures ………………………………………………………………. xvii
List of Appendices ………………………………………………………………. xviii
Abbreviations, Definitions and Symbols …………………………………………… xx
CHAPTER ONE ……………………………………………………………….. 1
1.0 INTRODUCTION …………………………………………………………. 1
1.1 Background Information ……………………………………………….. 1
1.2 Research Problems ………………………………………………………… 9
1.3 Justification of the Study ……………………………………………….. 10
1.4 Aim and Objectives of the Study ……………………………………….. 11
1.5 Hypotheses ………………………………………………………………… 12
CHAPTER TWO ……………………………………………………………….. 13
2.0 LITERATURE REVIEW …………………………………………………. 13
2.1 Physico-chemical Characteristics of Water Bodies ……………………… 13
2.1.1 Water temperature ……………………………………………………….. 14
2.1.2 Dissolved Oxygen (DO) …………………………………………………….. 15
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2.1.3 Hydrogen Ion concentration (pH) …………………………………………….. 17
2.1.4 Transparency …………………………………………………………………. 18
2.1.5 Total Alkalinity and Hardness …………………………………………………. 19
2.1.6 Electrical Conductivity (EC) and Total Dissolved Solids (TDS) ………………. 20
2.1.7 Turbidity and Total Suspended Solids (TSS) ………………………………….. 21
2.1.8 Phosphate …………………………………………………………………… 23
2.1.9 Nitrate …….……………………………………………………………………. 24
2.2 Growth and Age Parameters of Chrysichthys nigrodigitatus ………………. 25
2.21 Length-weight relationship and other morphometric parameters of Chrysichthys nigrodigitatus …………………………………………………. 25
2.2.2 Age composition and structure of Chrysichthys nigrodigitatus …………………… 33
2.2.2.1 Operculum ……………………………………………………………………. 34
2.2.2.2 Otoliths ………………………………………………………………………. 35
2.2.2.3 Scale …………………………………………………………………………. 35
2.2.2.4 Others Parts …………………………………………………………………… 36
2.3 Food and Feeding of Chrysichthys nigrodigitatus …………………………… 38
2.3.1 Seasonal changes of the food of Chrysichthys nigrodigitatus items …………………………………………………………………………… 38
2.3.2 Feeding intensity of Chrysichthys nigrodigitatus ….………………………….. 41
2.3.3 Classification of Chrysichthys nigrodigitatus based on feeding habits ………………………………………………………………………………………………… 41
2.3.4 Classification of Chrysichthys nigrodigitatus based on gut length ………………………………………………………………………………………….. 42
2.4 Reproductive Indices of Chrysichthys nigrodigitatus ……………………… 44
2.4.1 Sex ratio of Chrysichthys nigrodigitatus ……………………………………… 44
2.4.2 Maturity stages and Gonadosomatic Index (GSI) of Chrysichthys nigrodigitatus ………………………………………………………………… 45
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2.4.3 Fecundity and lengths/egg size/weight of Chrysichthys nigrodigitatus ………………………………………………………………… 48
2.4.3.1 Gravimetric Method …………………………………………………………. 49
2.4.3.2 Volumetric Method …………………………………………………………. 49
2.4.3.3 Numerical/total counts ………………………………………………………. 49
2.5 Abundance and Distribution of Chrysichthys nigrodigitatus …………….. 52
2.6 Plant and Animal Communities of Jebba Lake ………………………….. 54
CHAPTER THREE ………………………………………….………….…………….. 56
3.0 MATERIALS AND METHODS …………………………………………… 56
3.1 Study Area …………………………………………………………………… 56
3.1.1 Sampling Zones ………………………………………………………………. 56
3.1.2 Description of Sampling Zones …………………………………………………. 58
3.1.2.1 (Zone I) Kpatachi ….……………………………………………………………. 58
3.1.2.2 (Zone II) New Awuru ……………………………………………………………… 58
3.1.2.3 (Zone III) Old Awuru …………………………………………………………….. 58
3.2 Physico-chemical Parameters ……………………………………………… 59
3.3 Sampling of Fish ………………………………………………………………….. 61
3.4 Collection and Identification of Fish Samples ……………………………. 61
3.5 Fish Measurement ………………………………………………………………….. 62
3.5.1 Morphometric Parameters ………………………………………………………. 62
3.5.2 Meristic Parameters …………………………………………………………………. 63
3.5.3 Definition of Terminologies …………………………………………………. 65
3.6 Length-Weight Relationship (LWR) ……………………………………… 66
3.7 Length-Length Relationship (LLR) ……………………………………….. 66
3.8 Condition Factor (K) ……………………………………………………….. 67
x
3.9 Age Composition/Structure Determination ………………………………… 67
3.10 Stomach Fullness Classification ……………………………………………….. 70
3.11 Stomach Contents Analysis …………………………………………………. 72
3.11.1 Frequency of Occurrence ……………………………………………………… 72
3.11.2 Numerical Method ……………………………………………………………. 72
3.12 Index of Relative Importance (IRI) ………………………………………… 72
3.13 Sex Ratio Determination …………………………………………………… 73
3.14 Maturity Stages ……….……………………………………………………… 73
3.15 Length at First Maturity …………………………………………………… 75
3.16 Gonadosomatic Index (GSI) ………………………………………………… 75
3.17 Fecundity Estimation and Oocyte/Egg Diameter…………………………… 75
3.17.1 Volumetric Method .………………………………………………………… 76
3.17.2 Gravimetric Method …………………………………………………………. 76
3.18 Fish Abundance and Distribution ………………………………………… 76
3.19 Statistical Analyses .………………………………………………………… 77
CHAPTER FOUR ………………………………………………………………… …… 78
4.0 RESULTS ………………………………………………………………………. 78
4.1 Mean physico-chemical parameters of Jebba Lake, Nigeria ……..……………….. 78
4.2 Correlation and physico-chemical parameters of Jebba Lake, Nigeria …………………………………………………………………………… 81
4.3 Length-weight relationship (LWR) and length-length relationship (LLR) of C. nigrodigitatus in Jebba Lake ………………………………………….. 85
4.4 Mean condition factor (K) and Morphometric measurements of C. nigrodigitatus in Jebba Lake, Nigeria …………………………………………… 92
4.5 Measurements (%) and correlation of Morphometric parameters of C. nigrodigitatus in Jebba Lake ……………………………….……………… 95
xi
4.6 Meristic parameters and Size distribution of C. nigrodigitatus in Jebba Lake, Nigeria …………………………………………………………….. 98
4.7 Age composition and Growth parameters of C. nigrodigitatus in Jebba Lake .….…..………………………………………………………………………………. 102
4.8 Food composition of C. nigrodigitatus using frequency of occurrence and numerical methods …..…….………………………………………………. 105
4.9 Frequency of occurrence of items ingested by C. nigrodigitatus …….………… 107
4.10 Food composition of C. nigrodigitatus at stages of life in Jebba Lake ……..…………………………………………………………………….. 110
4.11 Index of relative importance and stomach fullness of C. nigrodigitatus in Jebba Lake, Nigeria …………………………………………………………. 113
4.12 Gut length to total length ratio and Sex ratio of C. nigrodigitatus in Jebba Lake ………………………………………………………………………………………. 117
4.13 Stages of gonad maturity, mean gonado-somatic index, fecundity and diameter of eggs of C. nigrodigitatus in Jebba Lake ……….…………….. 120
4.14 Fish species abundance (%) in gillnets in Jebba Lake, Nigeria …..….………. 124
4.15 Monthly and seasonal fish abundance (%) in Jebba Lake, Nigeria ….……….. 126
4.16 Fish abundance (%) in gillnets at the sampling zones in Jebba Lake, Nigeria ………………………………………………………………………………………130
4.17 Fish distribution (%) at various water columns in Jebba Lake, Nigeria ……………………………………………………………………………………………….. 134
4.18 Seasonal fish distribution (%) at the water columns in Jebba Lake …………. 136
4.19 Fish distribution (%) in water columns at sampling zones in Jebba Lake, Nigeria ………………..………………………………………………… 139
CHAPTER FIVE ………………………………………………………………… 142
5.0 DISCUSSION ..…..………………………………………………………… 142
5.1 Physico-chemical Parameters of Jebba Lake ……………………………..142
5.2 Length-weight Relationship and Morphometric Parameters ………… 146
5.3 Age Composition/Structure of Chrysichthys nigrodigitatus …………… 151
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5.4 Food and Feeding Habit of Chrysichthys nigrodigitatus …………………. 152
5.5 Sex Ratio and Fecundity of Chrysichthys nigrodigitatus …………………. 160
5.6 Abundance and Distribution of Chrysichthys nigrodigitatus in relation to other fish species …………………………………………….. 163
CHAPTER SIX …………………………………………………………………… 169
6.0 SUMMARY, CONCLUSIONS AND RECOMMENDATIOS ………… 169
6.1 Summary ……..……………………………………………………………….. 169
6.2 Conclusions ….…………………………………………………………… 170
6.3 Recommendations ………………………………………………………… 171
REFERENCES …………………………………………………………………… 172
APPENDICES ………………………………………………………………..….. 189
CHAPTER ONE
INTRODUCTION
1.1 Background Information
Fish is a resource mostly exploited by man and is basically linked to the trophic chain
in the entire environment where they are commonly found (Craig et al., 2004). Inland
waters of Nigeria consist of water bodies that support a wide array of aquatic
organisms, which includes phytoplankton, zooplanktons, crustaceans, and vertebrates
such as fish, crocodile, and aquatic mammals (Atobatele and Ugwumba, 2008).
Fishes found in the tropics and tropical water bodies experience changes in their
biological parameters and activities due to fluctuations in factors such as food
composition and availability, spawning rate, and other environmental factors.
Welcomme (2001) reported that factors such as fishing, pollution and eutrophication
among others could bring about series of changes in fish size, species composition and
abundance in the aquatic environment. Similarly, Bisht et al. (2009) and Soyinka et al.
(2010) reported that changes in environmental factors such as water quality, depth,
water current, availability of food and substratum influence the occurrence of fish
fauna, abundance and distribution.
Despite massive world-wide development efforts, in terms of many laudable
programmes and ways to reduce poverty and improve livelihoods in fisheries and other
sectors of the economy, poverty remains a nightmare for millions of Africans. In West
Africa alone, seven million people are involved in fishing, aquaculture and related
activities, such as processing and trading because it is a major source of livelihoods in
many coastal communities, both inland and on the Atlantic coast. In addition to
providing employmentand income, fisheries play a very important role in local and
2
national economies (Komolafe and Arawomo, 2011). Nigeria is the largest consumer of
fish in Africa with an approximately 1.2 million tonnes of fish needed annually to
satisfy the demand of the ever increasing population. FAO (2000) estimated fish
demand for Nigeria from 1997 – 2025, based on projected population and gave an
average of 1.11 million tonnes for a decade (2000 – 2010). The country is highly
blessed and endowed with vast expanse of inland freshwater and brackish ecosystems
with abundant fish species, which have potentials for culture. These water bodies also
play an important role in the provision of protein to Nigerians, especially now that
imported fish is becoming expensive to the common man (Komolafe and Arawomo,
2011).
Freshwater is a very important natural resource crucial for the survival of all living
beings. UNESCO (2003)reported that water is the most vital resource for all kinds of
life on earth and essential for sustainability of the earth’s crust ecosystem. The quality
of life depends on the quality of water. Physico – chemical factors are important in
estimating the constituents of water and concentration of pollutants or contaminants.
These factors are interrelated and interdependent with biological factors (plants and
animals). Similarly, these factors immensely influenced the uses as well as the
distribution and richness of biota (Unanam and Akpan, 2006). Physical parameters of
water bodes include water movement, depth, turbidity, transparency, temperature and
suspended solids. Chemical parameters include pH, dissolved oxygen, carbonates,
bicarbonates, nitrate, phosphate, carbon dioxide, cations and anions and dissolved
organic matters (Mustapha and Omotosho, 2005).
Growth is simply defined as change in size (length, weight and bulk) with time and can
also be change in numbers with time in the case of population (Abowei and Ezekiel,
3
2013). Factors that influence growth of fish, according to Welcomme (2001), can either
be endogenous or exogenous. Endogenous factors include genetic components of fish,
which limits the maximum size of a given species, while exogenous factors include
food availability, feeding rate and the nature of food ingested. Length and weight are
two key components in the study of fish growth be it at individual or population level.
The length of a fish is often measured easily than the weight; it is therefore, possible to
determine weight where only length is known. The relationship between length and
weight is important in this regard because it can be used to assess the effect of factors
such as growth and condition factor in fishes. There are basically two patterns of
growth in fish, which relates the length, be it standard or total, to the weight. Isometric
growth pattern shows that the body weight and length of fish grows at a constant
proportion that is, if the coefficient of the relationship (often denoted as b) is equal to 3.
Allometric growth pattern shows that the body weight and length of fish do not grow at
a constant proportion, that is when the value of b is less than or greater than 3. It is
negative allometric growth if the value of b is less than 3, when the fish becomes
slender as it grows, and positive allometric growth if b value is greater than 3, when the
fish becomes robust as it grows. Growth fluctuations are more frequent in fishes of
tropical and subtropical water bodies due to several factors such as environmental
variations, multiple spawning, physiological changes and dynamics of food
composition (Adeyemi et al., 2009).
Condition Factor (K) is another key parameter that describes the well – being or
survival of fish in the aquatic environment. It has been used along with age and growth
studies to indicate the suitability of an environment for fish species (Adeyemi et al.,
2009). If this value is either equal to one or above one, the environment is good or
better for fish survival and not suitable if the value is less than one. Factors such as
4
non-availability of food, predation, competition, fishing intensity, change in water
physico-chemical parameters, spawning and pollution can influence the well-being of
fish in the aquatic environment (Abowei, 2009).
Morphological characters such as morphometric and meristic have been commonly
used to identify stocks of fish (Turan et al., 2005) and the differences between fish
populations (Buj et al., 2008; Torres et al., 2010). These parameters or characters
include standard length, snout length, body depth, head length, pre dorsal distance, pre
pelvic distance, and pelvic length, and anal base length, depth of the caudal peduncle,
eye diameter and suborbital width. Meristic (counts) parameters include numbers of
rays (spines or soft rays), gill rakers, scales and total number of vertebrae. The use of
chromosome numbers and genetic parameters such as DNA sequences (requiring
sophisticated measuring techniques) are the newest methods for identification of fish
stocks (Akin-Oriola et al.,2005).
Age determination in fish is important for the assessment of life history, maturity,
spawning times, growth rate, growth at different age groups and mortality rates of a
given population (Gocer and Ekingen, 2005). Similarly, it is an essential component in
understanding the dynamic changes of fishery in any water body. Accurate age
determination is essential to both fisheries biology and management as it provides
information pertaining to stock age structure, age-at-first maturity, spawning frequency,
individual and stock responses to changes in the habitat, recruitment success and
determination of population changes due to exploitation. Information on age also
enables determination of growth and mortality, which form the basic input parameters
for population dynamics models used in fishery analysis (Welcomme, 2001).
5
Many methods have been used to determine the age of fish, of which three methods
predominates. The first is the mark and recapture method, second is Petersen method,
which involves the comparisons of length – frequency distribution of fish population
samples. Lengths of a large number of fish in a population need to be measured. The
third method is to count growth marks that develop periodically in various hard parts of
fishes (Adeyemi et al., 2009). Those that are considered to be formed on annual basis
are called year marks, annual marks, annual rings or annuli. Methods for estimation of
fish age are reliable especially if these structures possess patterns related to the annual
growth. These structures include vertebrae, otoliths, scales, fin rays, opercular bones
and some other body parts. The suitability and usage of any of these methods differ
from species to species (Gocer and Ekingen, 2005).
Food is a fundamental element in the life of all living organisms including fish, being
the source of energy and nutrients for growth, reproduction, movement that are vital
activities for survival in the aquatic environment. Qualitative and quantitative
compositions of fish diets are important to the growth, maturity and fecundity changes
in fish. Food study reveals the status of foraging, growth rate and seasonal life history
changes in fish, which are useful for rational exploitation of the species (Ugwumba and
Ugwumba, 2007). In addition, the study of food and feeding habits of fish based on
stomach content analysis is commonly used in fishery ecology to show the position of
fish within a food web and to provide information on the contribution of different prey
items to the diets. Information about food habits of fish is also useful in defining
predator-prey relationships, estimating trophic level and in the creation of trophic
models as a tool to understanding complex ecosystem.
6
Different kinds of items, ranging from plant to animal materials, be it micro or macro in
nature, are eaten as food by fish. These items are of great diversity in the aquatic
environment and differ in size and kind (Olojo et al., 2003). Most of this food base
either change or fluctuates in terms of biomass, relative species and other population
responses. Examples of food items eaten by fish include phytoplankton, zooplankton,
zoobenthos, bacterioplankton and fish amongst others. Those that feed on a single type
of item are termed ‘Monophagic’; those that combined plant and animal materials as
food are termed ‘Euryphagic’, while those that eat plant or animal materials are termed
‘Stenophagic’(Welcomme, 2001). Fish may be classified on the basis of food habits as
carnivores, herbivores and omnivores. The carnivores are flesh eaters, and are divided
into two based on specialization. Those that rely solely on insects as their food are
called insectivores and those that dwell entirely on fish are called piscivores. The
herbivores exploits a wide range of plant materials that include plankton, diatoms, algae
and large plants especially rooted aquatic plants. The third category, omnivore, are
those that feed on wide variety of food items that range from animal to plant materials.
Most of fish species in this category eat almost anything they come across.
(Welcomme, 2001).
The diet of fishes, just like in many other vertebrates, also relates to the length of the
gut or intestine. The structure, length and conformation of the intestine are closely
related to the diet of the fish (Miller and Harley, 2002). Therefore, understanding this
relationship is important to predict the diet of fishes, how fishes feed and the
mechanism of feeding (Malami et al., 2007). Herbivores have longer and coiled
digestive tract, carnivores have short digestive tract and omnivores have intermediate
length of digestive tract. According to German and Horn (2006), all vertebrates on the
7
category of herbivores have longer digestive tracts than do carnivores and that the
pattern is consistent among mammals.
Reproduction in fishes is one of the fundamental biological processes that enable
survival and continuity of species in the aquatic environment. Reproductive patterns of
fish, according to Paugy (2002), differ when factors such as habitats, geographical zone
and species are considered, which are influenced by environmental and biotic factors.
These reproductive parameters include sex ratio, stage of maturity, gonad index (GI),
gonadosomatic index (GSI),and fecundity. Knowledge on the reproductive patterns of
fishes as well as growth and mortality characteristics will define the regenerative
capacity of a population. Gonad maturation stages have become increasingly important
in fish production, especially in induced spawning and hybridization in addition to
determine the stock that is, mature, and the size or age at first maturity. Similarly, it can
be used to determine the reproductive potential of fish populations and monitoring of
changes in biological characteristics of exploited fish stock (Williams, 2007). It is also
used to establish reproduction period and length of time it takes the gonads to mature
(Goncalves et al. 2006). It has been shown that fecundity is influenced by a number of
factors such as size of fish, the kind of species, season and reproductive behavior.
Marked differences in fecundity among fish often reflected different reproductive
strategies (Murua and Saborido-Rey, 2003). The eggs of most species of fish vary in
size and chemical composition, which determine the quality of the offspring. There is
also relationship between the fat content of female parent and the egg size and quality
of yolk. There may also be differences in the amount of eggs deposited in individual
species and in population from different water bodies or different parts of the same
body of water (Murua and Saborido-Rey, 2003).
8
Fish abundance refers to the total catch in number or biomass of the species in that
particular water body, while fish distribution is an indication of where fish species
occur, located or are commonly found in the aquatic environment. This consists of the
vertical aspect, that is, surface, mid water and bottom and the horizontal component
such as convex, central and the concave sections across the water body. Species
distribution thus, provides information on whether the fish species is pelagic or
demersal. Such information are vital for fisheries development and management. Fish
abundance and distribution also have influence on the abundance and distribution of
other aquatic organisms in the water (Olopade, 2001). There are several factors that
affect fish distribution and abundance in any water body. These includes availability of
food, spawning rates, breeding grounds plus shelter, vegetation, water depth, breeding
habits, presence of current, migration and vegetation. At a large – scale, abiotic factors
influenced fish assemblages in temperate and tropical regions (Tejerina-Garro et al.,
2005).
Catfishes generally are important fish species in inland water bodies of Africa because
of their high commercial value. Chrysichthys species are among other species that have
been reclassified to the family Claroteidae (Paugy et al., 2003; Olaosebikan and Raji,
2004). Chrysichthys nigrodigitatus, commonly known as ″silver catfish″, grows up to
3kg and even above, which can be found both in fresh and brackish waters. It is known
as Warushe in Hausa, Obokun in Yoruba and Okpo Ocha in Igbo. It is very tasty with
tough flesh and good keeping quality.
Chrysichthys nigrodigitatus commonly known as silver catfish is an important
commercial fish species found in both fresh and brackish waters. It has been thought
not to spawn in captivity and experimental fish or broodstock had been difficult to
9
obtain except from the wild, which is unreliable. There was breakthrough in spawning
of the fish in captivity when more than one hundred spawns were obtained under
controlled condition at Layo in Cote’Ivoire (Ekanem, 2003). Since then, there has been
growing interest in the culture of C. nigrodigitatus and in the past two decades
scientists have worked to provide the necessary information on the biology and ecology
of this valuable fish species, so as to enhance its successful culture. The species is
important, highly valued and common in inland waters of Nigeria and sought for due to
its flavour and chemical composition (Akinsanya et al., 2007; Saliu, 2008; Olarinmoye
et al., 2009).
1.2 Research Problems
Physico-chemical parameters influence the biological productivity of water bodies.
These include species abundance, composition, productivity and physiological
conditions of aquatic organisms (Idowu et al., 2004). There is no current information
on the state of physico-chemical parameters of Jebba Lake, and changes in these
parameters adversely affects aquatic life.
Nigeria is a country blessed with abundant of inland water bodies with diverse fish
species most of which their biology is yet to be fully studied. Catfishes are the
commonly cultivated species of fish in Nigeria. Chrysichthys, a genus of the family
Claroteidae, which is among the important commercial fish species has not been given
due attention since the creation of Jebba Lake. It has been reported as a dominant fish
species in the lake (Abiodun and Odunze, 2011). The silver catfish Chrysichthys
nigrodigitatus with promising aquaculture potential has not been successfully
domesticated, which could be due to improper understanding of the biology. Offem et
10
al. (2008) reported that there is still dearth of information on the biology of C.
nigrodigitatus in some water bodies of Nigeria.
Preliminary report on the abundance and distribution of fish species (including
Chrysichthys species) in Jebba Lake, has been documented for over two decades now
but, no information on other aspects of the biology of the species, such as,
morphometric and meristic, reproductive, age and growth, food and feeding habit
parameters, which makes the management and sustainable utilization of this
economically important fish unrealistic. There has also been reduction in the abundance
of C. nigrodigitatus in Nigerian water bodies, because of over-exploitation and
destruction of habitat (Offem et al., 2008). This has affected the sizes been caught.
Over the years, it has been observed that majority of the sizes caught from Jebba Lake
range from small to medium, even though the fish grows up to 3 kg and even above.
Dearth of scientifically sound management of fish resources based on basic knowledge
of the biology of the species, including information on the population structure,
influence the development of strategies for conserving C. nigrodigitatus in the lake.
1.3 Justification of the Study
Catfishes are economically important groups of fresh and brackish water fishes
worldwide because they form a significant part of the inland fisheries in many
countries; Several specieshave been cultured while others are of great interest to the
aquarium industry (Ekamen, 2003). Fishes in this family, which include Chrysichthys
nigrodigitatus, Chrysichthys auratus longifilis (now Chrysichthys auratus(Paugy et al.,
2003) and Chrysichthys walker, are valued food fish with high demand in the whole of
West Africa especially Chrysichthys nigrodigitatus (Ekanem, 2003). Chrysichthys
11
species have commercial value, which if carefully studied could add to the existing
culturable fish species in the country.
The rearing or culturing of any living organism including fish in a controlled
environment begins with the understanding of aspects of the biology such as age and
growth, reproduction, food and feeding, and abundance. Considering C. nigrodigitatus
for culture and conservation, have resulted in several biological studies on growth and
fecundity (Akinsanya et al., 2007). Studies on C. nigrodigitatus in Nigerian water bodies
include the works of Inyang and Ezenwaji (2004) on size, length-weight relationship,
reproduction and trophic biology in Anambra River, Nigeria; Yem et al. (2005) on
length-weight relationship and condition factor of C. nigrodigitatus in Kainji Lake,
Nigeria; Offem et al. (2008) on reproductive aspects of C. nigrodigitatus in Cross
River, Nigeria; Yem et al. (2009) on food composition and feeding pattern of C.
nigrodigitatus in Kainji Lake, Nigeria; Lawal et al. (2010) on morphometry and diets
of C. nigrodigitatus in Epe Lagoon, Nigeria and Atobatele and Ugwumba (2011) on
condition factor and diet of Chrysichthys nigrodigitatus and Chrysichthys auratus from
Aiba Reservior, Iwo, Nigeria. This study is quite auspicious, so that proper
management plans or strategies to sustain this valuable fish in the lake will be
established.
1.4 Aim and Objectives of the Study
The aim of the study is to investigate the biology of Chrysichthys nigrodigitatus in Jebba Lake with the following specific objectives: a. Determine the physico-chemical parameters of Jebba Lake
b. Determine the morphometric and meristic parameters of Chrysichthys
nigrodigitatus in JebbaLake
c. Determine age and growth parameters of Chrysichthys nigrodigitatus in Jebba
12
Lake
d. Determine food and feeding habit of Chrysichthys nigrodigitatus in Jebba Lake
e. Determine reproductive parameters of Chrysichthys nigrodigitatus in Jebba
Lake
f. Determine the abundance and distribution of Chrysichthys nigrodigitatus in
Jebba Lake
1.5 Hypotheses
a. There is no significant difference in physico-chemical parameters at the various
sampling zones and between seasons in Jebba Lake
b. Morphometric and meristic parameters cannot be used to identify
Chrysichthysnigrodigitatus in Jebba Lake
c. Age and growth between sexes of Chrysichthys nigrodigitatus did not show
any difference
d. Chrysichthys nigrodigitatusdoes not consume a variety of food items in
Jebba Lake
e. There is no difference in reproductive parameters between sexes of
Chrysichthys nigrodigitatus
f. There is no difference in abundance and distribution of Chrysichthys
nigrodigitatus in relation to other fish species in Jebba Lake
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