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 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.
1.1 Background
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 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,2013).