A variety of potential stressful stimuli are present in aquaculture production, particularly if we consider the intensification of production to meet the needs resulting from the continuous growth of human population, compromising growth and health of farmed fish. Thus, optimizing the stress resilience of the fish is of utmost importance to improve aquaculture sustainability. Dietary protein hydrolysates have been found to increase somatic growth, promote stress resistance, and have a positive effect on oxidative stress. This trial aimed at evaluating the biological efficacy of different dietary protein hydrolysates in seabass (Dicentrarchus labrax) growth performance and health status following a stress factor.
The trial was performed at the EPPO/IPMA (Olhão, Portugal) and was divided in two phases: 1) 21 days after hatching (DAH) pos-larvae were distributed at a density of 10 larvae L-1 and fed four dietary treatments, Winfast (control diet), and Low, Med, and High concentrations of curcumin. At 72 DAH larvae from all tanks were fed, for one week, a diet with a functional additive with bioactive properties (BP). After this period, larvae were submitted to a stress test (air-exposure).
2) juveniles were stocked at a density of 1.2 kg m-3, with a mean weight of 2.39 ± 0.12- g. Four dietary treatments were tested in triplicate, diets containing protein hydrolysates from fish (Control), shrimp (HP1), poultry feather meal (Pepsol), and BP. After 21 days, fish were submitted to a stress test (confinement). Samples were collected pre- and post-stress in both trials for gene expression analysis and oxidative stress enzymes’ activity.
At the end of trial 1, the larvae fed with MED followed by BP had a better growth performance, including higher length and weight, and the different diets didn’t affect larvae mortality after the stress test. Stress-related genes were up-regulated after the stress and, GR, CAT, and GPX, had a higher relative expression on larvae fed the Control and Low diet.
On trial 2, significant differences in growth performance were obtained between diets Pepsol and HP1. The hepatic expression of the tested genes (GR, HSP90, HSP70, MT, CAT, and GPX) was higher after the stress, particularly in the BP group followed by Pepsol, except for CAT - which was higher in the Pepsol group. Antioxidant enzymes (CAT and GPX) showed no statistical differences between the different treatments, but on average, post-stress juveniles had higher values of expression in the Control diet.
These results suggest that in the early stages, the performance of larvae can be improved with the addition of a functional additive. In juveniles, the substitution of fish protein by Pepsol (an ingredient less expensive than BP), could be used as an alternative to enhance stress response capacity of fish. Nevertheless, in order to validate these results further studies are needed and the identification of the mechanisms involved in this response, as well as the long-term effects of these substitutions, are of paramount importance.
This study was funded by NoStress project – Novos alimentos funcionais para a redução de efeitos do stress em aquacultura (ALG-01-0247-FEDER-047122), and DIVERSIAQUA II (MAR-02.01.01-FEAMP-0175). The technical assistance of EPPO and S2AQUA staff was highly appreciated throughout the study.