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).