Rearing of the Nile tilapia (Oreochromis niloticus) on diets containing cotton seed meal enriched with vitamin E

Abstract

The present experiment was conducted to evaluate the effect of α-tocopherol as an antioxidant for avoiding the side effects of incorporation of cottonseed meal (CSM) in the diet of the Nile tilapia as a replacer of fish meal (FM). Twodiets were prepared; the first one contained fish meal and was considered as a control, in the second diet, FM was completely replaced by CSM. The second diet was divided into ten parts, the first one is a control and the other 9 diets were enriched with increased levels of vitamin E (1, 5, 10, 15, 20, 25, 30, 35 and 40 times of gossypol in CSM). Each diet was offered in three aquaria (3 replicates for each diet) and each aquarium was stocked with 25 fish (2.0-2.1g). Results are summarized in the following:- The highest average body weight (9.91 g) was recorded for the control group fed on thebasal diet (contained FM) and the lowest BW (5.66 g) was obtained for fish fed the dietD2 in which FM was completely replaced by CSM without vitamin E. Incorporation ofvitamin E in the experimental diet significantly improved the BW. Similar trend wasobserved for the other growth performance parameters body length (BL), weight gain(WG) and specific growth rate (SGR).- The best feed conversion ratio (FCR) was recorded for fish group fed on the diets D1and D3 which significantly differed from values recorded for the other treatments. Theworst FCR was recorded in fish group fed on the diet D2 in which FM was completelyreplaced by CSM without addition of vitamin E. Incorporation of vitamin E in theexperimental diets improved FCR specially fish group fed on the diet D3.- Protein content of the whole fish body ranged between 41.33 to 50.97% and thedifferences were significant. Fat content of fish fed the diet D2 significantly higherthan those obtained for fish fed the other groups. Compared to the two control dietsD1 and D2 all vitamin levels in the experimental diets increased ash content of thefish whole body and the graded levels of vitamin E in the diets significantly alteredthe ash content of tilapia fish.- The highest values for hematocrite (Ht) and haemoglobin (Hb) were obtained forfish fed on the control diet (D1). Incorporation of vitamin E in the experimentaldiets at increasing levels significantly affected Hb and Ht. Compared to thecontrol group (Diet1) aspartate transaminase (AST) and alanine transaminase(ALT) levels significantly increased fish groups fed on the other experimentaldiets.