Sardine (Sardinella spp.) protein hydrolysate as growth promoter in South American catfish (Rhamdia quelen) feeding: Productive performance, digestive enzymes activity, morphometry and intestinal microbiology

This study evaluated the effects of dietary inclusion of sardine (Sardinella spp.) protein hydrolysate (SPH) on productive performance, digestive enzymatic activity, morphology and intestinal microbiology of South American catfish (Rhamdia quelen) juveniles. SPH was produced from sardine processing wastes using Protamex® protease complex from Novozymes A/S. Four levels of inclusion were evaluated (0, 2, 5 and 10%). A total of 480 South American catfish juveniles (average weight 11.3 ± 2.46 g) were distributed in 24 polyethylene containers, in a completely randomized design with four treatments and six replications. The fish were fed twice daily until apparent satiation with isoproteic (39%) and isoenergetic (4376 kcal.kg−1) diets for 56 days. Regardless of the SPH inclusion levels in the diets, average weight gains (36.28 g), specific growth rate (2.56% day−1), apparent feed intake (40.51 g) and apparent feed conversion rate (1.12) were improved when compared to the control treatment (average of 24.95 g; 2.11% day−1; 31.00 g and 1.28, respectively). Total alkaline protease activity of the gastrointestinal tract of the South American catfish juveniles was higher in the treatment that received 5% SPH (0.61 ± 0.23 U. mg−1 of protein) than in the control (0.26 ± 0.08 U.mg−1 of protein). The amylase activity was higher in the treatments with 2% SPH (1.58 ± 0.19 U. mg−1 of protein) and 5% SPH (1.43 ± 0.44 U. mg−1 of protein) when compared to the control (0.40 ± 0.18 U. mg−1 of protein). In the 5% SPH treatment, higher amounts of lactic acid bacteria and Vibrionaceae were detected than in the other treatments. No difference was found for total heterotrophic bacteria. There was no difference in the intestinal morphometry of the South American catfish for any one of the analyzed parameters. Inclusion levels of up to 10% SPH in the diets of South American catfish showed improvement in the productive performance and nutritional efficiency, acting as a growth promoter. The inclusion level of 5% SPH caused an increase in the digestive enzymatic activity and populations of intestinal lactic acid bacteria. Thus, a prebiotic effect on the fishes was observed and the inclusion level may determine the effects of SPH.