Anchovy and giant squid hydrolysates can enhance growth and the immune response of European seabass (Dicentrarchus labrax) fed plant-protein-based diets

The aim of the present study was to evaluate: 1) the in vitro bactericidal and bacteriostatic activities of four selected marine hydrolysates, from anchovy or giant squid, against several fish pathogens, and 2) if the inclusion of 3% of those hydrolysates in a plant-protein-based diet could result in similar growth, feed efficiency, humoral immune status and haematological parameters of juvenile European seabass (Dicentrarchus labrax), compared to a fish meal-based diet, during an in vivo trial. Four marine hydrolysates from anchovy (ANC) or giant squid (GS) were obtained by hydrolysis using either a single protease (P1, endopeptidase activity; or P2, endo - and exopeptidase activities) or a mixture of P1 and P2 (MIX). Bactericidal and bacteriostatic activities of each hydrolysates were evaluated in vitro against several fish pathogens. Afterwards, four experimental diets with ANC (ANC-P1 and ANC-P2) or GS (GS-MIX and GS-P2) hydrolysates, a positive control (PC) diet with a higher content of a fishmeal (25%), and a negative control (NC) diet, where 50% of fishmeal of PC diet was replaced by plant sources, were formulated for an in vivo trial. Diets were fed to triplicate groups of juvenile European seabass (7.0 +/- 2.0 g) distributed into tanks of 250 L each, at a density of 3.7 kg m(-3), for 60 days. At the end of the in vivo trial, growth performance, nutrient utilization, whole body composition and humoral immune status of fish were evaluated. The in vitro trial showed that all marine hydrolysates conferred resistance against fish pathogens, as they had bactericidal and bacteriostatic activities against a great number of bacteria belonging to the Vibrionaceae family. However, GS hydrolysed by a single peptidase (P2) resulted in a lower bactericidal activity (P < .050) against Vibrio harveyi than the others hydrolysates. During the in vivo trial, fish fed ANC-P1, ANC-P2 and GS-MIX diets had similar (P > .050) growth compared to fish fed PC diet, whereas fish fed GS-P2 had lower (P <= .001) final body weight and specific growth rate than fish fed PC. However, the experimental diets barely affected innate immunity. These results showed that the 3% inclusion of ANC and GS hydrolysates, mainly ANC hydrolysed by a single protease with both endo - and exopeptidase activities (P2) or GS hydrolysed by a protease mix (MIX), in plant-protein-based diets for juvenile European seabass could be good options to hamper the negative effects caused by plant ingredients.