Carob seed germ meal as a partial substitute in gilthead sea bream (Sparus aurata) diets: Amino acid retention, digestibility, gut and liver histology

The use of carob seed germ meal (CG) as a substitute for fish meal was evaluated in fingerlings (average weight 10 g) of gilthead sea bream fed isonitrogenous (46% Crude Protein, CP) and isolipidic (19.5% Crude Lipid, CL) diets containing four CG levels (0, 17, 34 and 52%). The duration of the trial was 83 days. The diets were tested in triplicate, and the fish were fed to satiation twice daily. The apparent protein and energy digestibility coefficients decreased in response to the dietary inclusion of CG. The decreases in the values of the ADC ranged from 93% for the 0 diet to 80% for the 52 diet. The amount of digestible Arg in the diets increased with the inclusion of CG, from 3.2 g Arg 100 g(-1) in the 0 diet to 4.81 g Arg 100 g(-1) in the 52 diet. The digestible Arg content increased in the diets because the amounts of the remaining digestible amino acids decreased. The fish reached weights of 72, 72, 69 and 53 g on the 0, 17,34 and 52 diets, respectively. The 52 diet gave the lowest specific growth rate (SGR, 1.95% day(-1)) relative to those found for the other three diets (2.32% day(-1)). The 52 diet produced the least satisfactory results for feed intake (FI) and the food conversion ratio (FCR) (2.23 g 100 g fish(-1) day(-1) and 1.38, respectively). The efficiency of retention of His, Phe and Leu in the fish fed the 52 diet showed the lowest values (17.3, 25.5 and 28.5%, respectively), but the efficiency of retention of Met in the fish fed the 52 diet showed the highest value (48.2%). In the distal intestine and liver, histological alterations were found in the fish fed the 34 and the 52 diets. In fish fed the 52 diet, the mucosal fold was significantly shorter and thinner and exhibited a smaller number of goblet cells. These changes could affect nutrient uptake by modifying the digestibility of the diet. The histology of the liver did not show severe degradation in any treatment. The results of the present experiment demonstrated that CG can be included at levels up to 34% in diets for short term feeding of gilthead sea bream without any adverse effects on fish growth and nutritive parameters. (c) 2012 Elsevier B.V. All rights reserved.