Suitability of selected raw materials and by-products in formulated feeds for Nile tilapia Oreochromis niloticus and African catfish Clarias gariepinus

Suitability of selected raw materials and by-products in formulated feeds for Nile tilapia Oreochromis niloticuc and African catfish Clarias gariepinus. Abdel-Wahab A. Abdel-Warith The current status of global aquaculture production was reviewed with a special emphasis on Africa and in particular Egypt. The main species of interest in this study were tilapia Oreochromis niloticus and African catfish Clarias gariepinus which are gaining popularity and are of considerable importance in the market of farmed fish in this continent and of economic relevance to Egypt and other Middle Eastern countries. Research was principally directed to establishing the suitability of specific feed ingredients and materials that could be included in balanced diets for both species. Various animal and plant by-products were selected to evaluate their nutritional value for either species. The experimental protocols, materials and methods and techniques employed are described for nutritional investigations with tropical freshwater fish. These included the various parameters assessed in the growth and digestibility studies relevant to the species in question. These include Specific Growth Rates (SGR), Feed Conversion Ratios (FCR), Protein Efficiency Ratio (PER) and Apparent Net Protein Utilisation (ANPU). An initial investigation to determine the coefficients of digestibility of protein, amino acids and energy was first undertaken using tilapia as the model warmwater fish species. This investigation was able to provide useful data and information as a prelude for successive growth trials with both tilapia and catfish. Fishmeal, soyabean meal, corn gluten meal, poultry by-products including feathermeal and blood meal were all tested at a variety of inclusion levels in successive trials. Apparent digestibility coefficients (ADC %) for tilapia fed diets containing 60% LT 94 fishmeal and 40% of each ingredient are reported. ADC of dry matter (DM) and protein (CP) and energy (E) for the reference fishmeal diet were 83.99 DM; 92.60 CP; and 93.31E respectively. For each test ingredient, these values were as follows; 1PBM (56.99 DM; 69.30 CP & 73.47 E), 2Feathermeal (54.09 DM, 45.53 CP & 49.11 E), 3Blood meal (76.13 DM; 85.79 CP and 75.96 E), 4Solvent extracted soyabean meal (85.83 DM; 93.46 CP & 82.16 E), 4Full fat soyabean meal (75.86 DM; 86.99 CP & 74.84 E). The amino acid availability coefficients reflected the same trends as protein digestibility, and these varied from >87% on average for the essential amino acids in fishmeal, 83% for maize gluten and 85% for solvent extracted soyabean meal with an average of 63% for feathermeal and only 61% for poultry meat meal. The importance of plant protein sources and especially soyabean meal was the focus of a complete nutritional study with juvenile tilapia, The influence of full fat soyabean meal (FFSB) inclusion on growth performance, feed utilisation and the gastrointestinal digestive enzymes was also measured in this experiment. It was found that soyabean meal levels above 50% could reduce growth performance and adversely affect gut enzyme activities. Tilapia fed a series of diets with FFSB (58,63 and 63% + DLmethionine did not perform as well as the control group. SGR values ranged between 2.42 to 2.12, and ANPU between 39.41-34.46. Supplementation of the diet with