The process of farm diversification through the integration of aquaculture and agriculture (IAA) is a growing innovation in the developing world. By-products generated such as rice bran and fish offal from this intervention (especially in integrated rice and fish farming (IRF)), may be a major environmental concern if not properly disposed of or utilized. Given the important role sustainable feed development plays in aquaculture development, exploring the opportunities of converting these by-products from IAA for the production of good quality and cost-effective feed for aquaculture development is highly imperative. Knowledge-based on the utilization of these IRF by-products in aquaculture nutrition, therefore, needs to be developed. This study, therefore, investigated the nutrient composition and apparent digestibility coefficient (ADC) of nutrients in rice bran and fish offal in diets fed to Clarias gariepinus and Oreochromis niloticus.
An 8 weeks feeding trial was conducted in the University of Ibadan, Aquaculture Nutrition Laboratory to determine the apparent digestibility of the test ingredients (TI) - rice bran feed (RBF) and fish offal meal feed (FOM) (procured from USAID/MSU IAA intervention project in Nigeria). These TI were analyzed for their Amino Acid Profile and the amino acid contents in each of the samples were further evaluated using Provisional Amino Acid of Egg Scoring Pattern (PAAESP) to determine their Amino Acid Score (AAS) ingredients. In addition, the TIs were included in the diets of Clarias gariepinus and Oreochromis niloticus to formulate 40 % and 30% crude protein (CP) reference diets (RF), respectively. Test diets contained 70 % of reference diets and 30 % of test ingredients, with chromic oxide as the inert marker. Replicated groups of C. gariepinus and O. niloticus (10±0.01; 15±0.01 g. respectively) were fed these diets for 8 weeks. Apparent digestibility coefficients for protein, ash and energy were determined following standard methods. Data were analysed using descriptive statistics, and ANOVA at α0.05.
In this study, the crude protein (%) of 65.83±0.21 and 10.59±0.11 were recorded for fish offal meal and rice bran, respectively (Table 1). These values compared favourably to fish meal (75.4%) and maize (9.4%). Ash contents were 9.61±0.01 (%) in fish offal meal and 9.13±0.02 (%) in rice bran. The essential amino acid profile (Table 2) revealed that FOM has arginine, lysine, methionine and Tryptophan with RB having methionine and Tryptophan at the concentration required for growth in C. gariepinus. The FOM contained histidine, isoleucine, methionine, Phenylalanine, Threonine, and Tryptophan with RB having (Histidine, methionine, Phenylalanine, and Tryptophan) for growth in O. niloticus. The limiting amino acid (LAA) for both the fish offal and rice bran was Met+Cys (TSAA). The ADC of nutrients (Tables 3 and 4) varied significantly across treatments (p<0.05) in C. gariepinus and O. niloticus. ADC of Protein was significantly highest in FOM (77.77 ± 0.49 %) and least in RBF (64.17 ± 0.83 %) in C. gariepinus and FOM (78.61 ± 0.51 %) and least in RBF (63.11 ± 0.19 %) for O. niloticus.
The result of this study revealed that nutrient digestibility by C. gariepinus and O. niloticus was good for both TI while FOM gave better results for the test fishes.