THE EFFECTS OF DIETARY SYNTHETIC AMINO ACID (LYSINE) LEVELS ON GROWTH AND FEED UTILIZATION OF Clarias gariepinus FINGERLINGS
In Nigeria, fish alone contributes on the average 20 – 25% per caput animal intake and could be as high as 80% in coastal and reverine communities (Food and Agriculture Organisation, 2000). Tobor (1992) and Ajana (2002) reported that the average annual demand for fish in Nigeria between 1995 and 2000 was estimated at 1.22 million metric tonnes and that this might increase to about 1.425MMT by the year 2005. FAO (2000) estimated the projected population and fish demand/supply from 1997 to 2025, with domestic fish production by the year 2007 as 0.77 million tonnes. Adamu (2007) however, gave the actual total domestic fish production in 2005 as 579,500 tonnes, while production from aquaculture was 56,300 tonnes in the same year. Fasasi (2003) put the demand – supply gap of fish in Nigeria as 1.0 million metric tonnes.
Aquaculture, the rearing of aquatic organisms, has high prospects in Nigeria. With a projected population of 139.1 million people in 2007, the fish demand is estimated at 1.06 metric tonnes, while supply stands at 0.81 metric tonnes leaving a deficit of 0.25 metric tonnes (FAO, 2000). Faturoti (1999) noted that recent trends all over the world point to a decline in landing from capture fisheries which is an indicator that fish stocks have approached or even exceeded the point of Maximum Sustainable Yield (MSY). Aquaculture therefore remains the only viable alternative for increasing fish production in order to meet the protein need of our people.
Aquafeed production on global scale has been rising steadily from 14.2MMT in 1997 to 16.70mmt in 2001 (Olele, 2011) with fish meal being used as the conventional source of animal protein because of its balanced amino acids, vitamins content, palatability and growth factors (Tacon, 1993). Because of the increasing cost of high quality fishmeal required for aquafeed and due to competition for feed in animal husbandry, there is now need for alternative sources of animal protein for fish feeds especially in developing countries like Nigeria (Sales and Janssens, 2003).
The alternative sources of animal protein selected must be able to satisfy the dietary requirements of the fish at the cheapest cost (Least Cost Formulation) because animal protein is the most expensive dietary macro-nutrient that directly affects fish weight gain (Abdelghany, 2000). Although there has been a lot of research work on production of fish feed to meet the nutrient requirements of culturable fish in Nigeria at low cost (Omitoyin 1995; Olukunle and Falaye, 1998); good quality fish feed pellets are still sparingly used by fish farmers. This is due to high cost of most fish feed ingredients particularly fishmeal and its competitive use by livestock farmers. There are also few commercial fish feed producers in Nigeria, a lot of farmers depend on imported quality fish feeds which are expensive and not affordable. This increases their cost of production and reduces their profit margin.
It has been determined that fin-fish have an essential requirement of 10 amino acids (Silva and Anderson, 1995). Deficiencies in these amino acids cause anorexia, poor growth and low food conversion in general (Halver and Wilson, 1986). Lysine is one of the 10 essential amino acids that must be provided by the diet. It is also the least abundant amino acid in many feedstuffs; as a result, extra care must be taken to provide enough lysine synthetically when formulating catfish diets containing a large percentage of protein from plant sources. In commercial diet, both the lysine and the methionine appear to be the most limiting amino acid. Although data from Robinson (1994) demonstrated that fingerlings of channel catfish utilize synthesized lysine supplemented into a lysine- deficient feed when the fish were fed multiple feedings. Lysine is one of the ten indispensable amino acids required in the dietary protein for several fish species because lysine is generally the most limiting amino acids in fish feed. In addition to meeting the basic metabolic requirement for maximum growth, dietary lysine supplementation has been shown to have other positive effects on various animals including fish (Cheng and Hardy, 2003).
Plant proteins generally have unbalanced proportion of essential amino acids. The primary plant protein sources used in catfish feed are oil seed meal, such as soybean meal, cotton seed and groundnut cake. Generally, most plant proteins are deficient in lysine and methionine. Groundnut cake for example with crude protein content of 40 – 45% is a good supplement to fish meal. It promotes growth and is palatable to fish but deficient in lysine and methionine and also has a limited amount of tryptophan and threonine but amino acid quality improves in artificial diet reinforced with lysine, methionine and tryptophan supplements (Eyo and Olatunde, 1998).
Nutritionally, lysine is an essential amino acid because it cannot be produced by the fish and hence must be provided by the diet. Dietary lysine supplementation is related to advantages on weight gain, feed conversion, nitrogen retention and reduction in body lipid content (Marcouli, et al; 2006). The quality of amino acid content is the most important factor on optimizing the utilization of dietary protein in catfish feeds. According to Palavesam et al; (2008), protein must be supplied to the fish with sufficient amount of essential amino acids, the lower the protein content in the diet; the higher must be the concentration of these amino acids in the protein.
According to Food and Agriculture Organization (2010), Aquaculture is one of the fastest growing sectors of the global livestock production. It provides food fish which complement the ones obtained from the wild which in recent times is in dwindling states due to over-fishing and pollution of various forms of the water bodies. Aquaculture remains the only means through which the gap between fish and fish products demand and supply can be bridged. This objective has not been met due to high cost of animal protein source such as fish meal to supply the essential amino acids such as lysine in fish feed formulation. In view of this, synthetic amino acid (lysine), one of the essential amino acids is supplemented in the fish diet to determine the level of its utilization by catfish because it is believed that most fish do not respond well to synthetic amino acids as against natural amino acids, so this study is aimed at investigating this fact with African Catfish (clarias gariepinus) fingerlings.
The objectives of the study include the following:
1. To compare the synthetic amino acid (lysine) levels for clarias gariepinus fingerlings.
2. To check the effects of the various treatments on the growth rate of clarias gariepinus fingerlings,
3. To compare the utilization of synthetic lysine by clarias gariepinus fingerlings.