NUTRITION

The protein component of the aquaculture diet is the single most expensive portion and important dietary nutrient. Fishmeal remains the major dietary protein source ranging between 20-60% of fish feed (Kaushik, 1989; Tacon and Jackson, 1985) but escalating cost, uncertainty in availability and lesser quantity has necessitated the use of other animal and plant protein sources to reduce the feed cost without compromising growth. Therefore, efforts are now being directed in different parts of the world to find altyernate protein sources which ideally are less expensive and readily available as substitutes for the expensive fishmeal component in practical diets.

The need for a cheaper relatively abundant source of fish feed necessitates the search for an alternative source of fish meal production, such that the potency will meet or be close to the standards of the present stock of imported fish meal available in the market, with crude protein levels ranging from 65%-72%.(Tacon and Jackson, 1985)

Lack of readily available nutritive fish feed ingredients have continued to be a major constraint to the survival of aquaculture in the competitive global food production system (F.A.O., 2006; Ogunji et al.2005). Consequently, fish nutrition experts world over have considered the recruitment of alternative protein feed ingredients necessary for inclusion in fish diet Proteins are organic compounds composed of amino acids that comprise about 70% of the dry weight of fish muscle. Since protein is in a dynamic state, continually being synthesized and degraded, a dietary supply is needed throughout life to provide amino acids and nonspecific nitrogen for maintenance and growth .There is no single level of dietary protein that is optimum for meeting the nitrogen needs of catfish. This is because several factors affect the dietary protein requirement, including fish size, water temperature feed allowance, amount of non protein energy in the diet, protein quality, natural food available, and management practices. Even so, catfish are typically fed the same diet throughout the grow-out phase. This is largely because of logistical issues associated with manufacturing and supplying a number of different diets. Further, there is a general perception that protein quantity equates to feed quality. That is, the more protein the better the feed; thus, the producer may feed a high-protein feed throughout grow out even though it may not be needed. In reality, the actual percentage of dietary protein is not as critical as the concentrations and proportions of amino acids provided in the protein. To ensure that catfish feeds are of high quality, the nutritionist must consider the amino acid composition of various feedstuffs, their digestibility, and the proper balance of protein and energy. The most economical method to achieve the proper balance between protein quantity and quality is to use a mixture of complementary protein feedstuffs and (if needed) supplemental amino acids. Feeds used for grow out of catfish have traditionally contained 32–35% dietary protein. Commercial catfish feeds contain a liberal amount of relatively expensive, high-quality protein, and feed cost is the major variable operating cost associated with production of catfish; therefore, considerable effort has been expended to determine the quantity and quality of dietary protein necessary to achieve optimum performance of catfish. (Edwin and menge, 2007)

Nigeria aquaculture produced over 20,000 tonnes of various fish species in the year 2000 which involved the input of supplementary and complete feeds that accounted for between 40-60% of production costs. Since diets generally represent the largest single cost item of most fish farm operation, it holds that the selection of feed ingredients for use within diets will play a major role in dictating the nutritional and economic success of farmed fish.

Fishmeal which serves as the main protein sources for fish feed because of the high quality protein content, which is not only very expensive but also usually unavailable (Tacon and Barg, 1998) particularly in developing countries. Efforts to replace fishmeal with vegetable protein from more sustainable sources have been embarked upon by(Fagbenro,1999;Fagbenro and Davies,2001; Oguji and Wirth, 2001;Osuigwe et. al., 2002; Fagbenro and Davies,2003; Oguji et. al., 2003).

The need to substitute fishmeal in animal feed has necessitated the use of plant derived feedstuffs.

Legume seeds have been highly favourable because of their rich protein composition, energy and, mineral content and widespread distribution in the tropics. However, only few of these plant

proteins have been utilized and investigated (Tacon and Jackson 1985; Webster et al., 1992; Ogunji and Wirth 2001). The presence of anti nutritional factors in these legumes have limited their widespread usage and direct incorporation into animal feeds.

However, in the compounding of fish ration with plant protein sources, cautions need to be exercised as to their inclusion levels in fish diets as well as ensuring their proper processing for effective utilization (Francis et al., 2001; Pillay, 1990). The need for such recommendations have been due to the presence of certain limiting factors in those ingredients such as high crude fiber content (Nwanna et al., 2008), anti nutritional factors such as in Vigna subtarreana (Alegbeleye et al.2001). Studies have shown that, excessive consumption of plant protein sources by fish could cause slower growth rates and poor performance which may result in mortalities if condition persists (Cho et al., 1974; Francis et al., 2001). Leucaena leucocephala (Lamde Wit) demonstrated good potential to serve as a useful plant protein source in fish ration and in the livestock industry generally (D’Mello & Acamovic., 1989,Jones, 1979,, Ter Muelen, 1981). However, it has been established that leucaena contain mimosine-a  non-protein amino acid capable of inhibiting protein biosynthesis in animal causing growth retardation if consumed intensively (D’Mello & Acamovic., 1989, Ter Muelen, 1981).