ABSTRACT
Between January 2009 and December 2010, research on the biology of the silver catfish Chrysichthys nigrodigitatus (Lacèpède, 1803) in Jebba Lake, Nigeria, was conducted. For the study, samples were taken utilizing fleets of experimental gillnets. The mean electrical conductivity (66.4113.89s/cm) and mean phosphate (0.200.15mg/l), which were substantially different (p0.05) at the zones, fluctuated together with the other physico-chemical parameters that were assessed. The growth patterns of the men and females were allometric (2.49) and isometric (3.18), with a good correlation and direct proportionality between length-length for males (0.93) and females (0.93), respectively (0.83). Because it was greater than 1, the condition factor for males (K=1.74) and females (K=1.83) indicated that the lake was favorable for the fish’s survival. The morphometric parameters’ favorable correlations and the meristic
larger men than females. The population’s size distribution ranged from tiny to adult, with few adults present. According on the growth performance index, Chrysichthys nigrodigitatus has a propensity to enlarge. The nine (9) main substances that C. nigrodigitatus ingested varied in abundance throughout months and seasons, ranging from plant elements (21.75%) to animal components (55.65%). Adults consumed more fry (27.86%) than juveniles (36.72% and 28.69%) or subadults (36.72% and 28.69%) did. The amount of food ingested by fish was directly correlated with its size.
Insects were the most significant prey items consumed by juveniles, sub-adults, and adults, respectively, according to the prey importance index, followed by insects (57.61%), insects (53.70%), and fry (39.65%). Fewer fish stomachs without food caused a high feeding intensity. The omnivore Chrysichthys nigrodigitatus has a medium-sized gut. 1.77:1 more men than women made up the population. In August and September, which are spawning months, more gravid females were noted. Males reached first maturity before females, according to the phases I to VI of gonad maturation. Particularly during the rainy season, female C. nigrodigitatus showed a higher gonado-somatic index (9.73) than males (1.32). The mean fertility varied.
Egg production ranges from 1,670 to 3,375, and increases with fish size. Chrysichthys nigrodigitatus, which predominates in zones I and II during the rainy season and is frequently found at the bottom of lakes, was the most prevalent species both within the family Claroteidae (13.06%) and in the overall catch (8.95%) during wet than dry seasons. It is advised that morphometric and meristic factors be utilized to identify the fish, that population structure studies be conducted to reveal more information on class sizes, that culture trials be conducted, and that feed ingredients made of both plant and animal sources be employed.
CHAPITER 1
History of the Study
Fish is a resource that is mostly used by humans and is fundamentally connected to the trophic chain in the entire ecosystem where they are frequently found (Craig et al., 2004). Water bodies in Nigeria’s inland waters are home to a variety of aquatic creatures, including fish, crocodiles, and aquatic animals as well as phytoplankton, zooplanktons, and crustaceans (Atobatele and Ugwumba, 2008).
Due to variations in elements including food composition and availability, spawning rate, and other environmental conditions, fish located in the tropics and tropical water bodies face alterations in their biological parameters and behaviors. According to Welcomme (2001), a variety of changes in fish size, species composition, and abundance in the aquatic environment may result from variables including fishing, pollution, and eutrophication, among others. According to Bisht et al. (2009) and Soyinka et al. (2010), variations in environmental elements such water quality, depth, water current, the availability of food, and substratum have an impact on the existence, quantity, and dispersion of fish.
Millions of Africans continue to live in poverty despite major global development initiatives, including numerous commendable programs and methods to reduce poverty and enhance lives in the fishing industry and other areas of the economy. Seven million people work in the fishing, aquaculture, and related industries in West Africa alone because it provides a significant portion of the income for many coastal towns both inland and along the Atlantic coast. Fisheries are crucial to regional and national economies because they generate cash and jobs (Komolafe and Arawomo, 2011).
With 1.2 million tonnes of fish required annually to meet demand due to an ever-increasing population, Nigeria is the largest consumer of fish in Africa. Based on predicted population growth, the FAO (2000) estimated Nigeria’s annual fish consumption from 1997 to 2025 to be 1.11 million tonnes (2000 – 2010). The nation is extremely fortunate and endowed with large interior freshwater and brackish habitats that are home to numerous fish species with potential for culture. Also, these bodies of water are crucial for Nigerians’ access to protein, particularly since that imported seafood is getting more and more expensive for the average person (Komolafe and Arawomo, 2011).
For all living things to survive, freshwater is an essential natural resource. According to UNESCO’s 2003 study, water is the most important resource for all forms of life on earth and is necessary for the continued viability of the ecosystem in the planet’s crust. Life quality is influenced by water quality. When determining the components of water and the quantity of pollutants or contaminants, physical-chemical parameters are crucial.
These elements are interconnected and dependent on biological elements (plants and animals). Similar to this, these factors had a significant impact on the distribution, richness, and uses of the biota (Unanam and Akpan, 2006). Water movement, depth, turbidity, clarity, temperature, and suspended particles are some of the physical characteristics of water bodies. pH, dissolved oxygen, carbonates, bicarbonates, nitrate, phosphate, carbon dioxide, cations, anions, and dissolved organic matter are among the chemical parameters. (Mustapha and Omotosho 2005). Growth is simply described as a change over time in size (length, weight, and bulk), and in the case of populations, a change over time in numbers as well .
