Chemical and nutritional quality of stored fermented fish (tilapia) silage

Abstract

Abstract Fermented fish silage was produced from minced tilapia ( Oreochromis niloticus ), 15% molasses and 5% Lactobacillus plantarum culture. Initially, batches of the fish silages were fermented at 5, 20, 30 or 35°C for 30 days. The pH declined rapidly at 20, 30 and 35°C but at 5°C, pH decline was slower. Protein solubilization (autolysis) in the fish silages was temperature-dependent as the non-protein nitrogen content (NPN) increased rapidly at higher temperatures. In a second experiment, fish silage was fermented at 30°C for 7 days after which autolysis was halted, then stored at 30°C for 180 days and analysed at intervals. The NPN attained a maximum of 51·4% of total nitrogen content after 180 days. Proximate composition of tilapia silages varied slightly during storage and there was a slight loss of tryptophan during fermentation and storage. The stored wet tilapia silages were blended with soybean meal (1:1, w/w) and dried. The nutritional value of co-dried tilapia silage as a dietary protein supplement for catfish ( Clarias gariepinus ) was studied in digestibility experiments. Although the protein quality of wet tilapia silage was reduced during storage, there were no differences ( P > 0·05) in the apparent protein digestibility coefficients of diets containing co-dried tilapia silages. It is suggested that autolysis in the stored tilapia silages had little effect on proten digestibility in the catfish.