As aquaculture expands, intensified conditions raise animal stress and disease outbreaks, urging innovative prophylactic measures to promote fish robustness and welfare. Protein hydrolysates, rich in bioactive peptides and amino acids, emerge as stress-reducing functional ingredients in aquafeeds. Gilthead seabream (Sparus aurata) is highly susceptible to cold-induced "winter disease", characterized by a decrease in metabolic rate and hindering production. This study evaluates the potential of novel hydrolysates from local agri-food by-products to improve seabream growth and stress resilience in low water temperatures.
Four isoproteic and isoenergetic practical diets were formulated: a commercial-like diet containing 20% fish meal (CTRL) and three experimental diets (INSECT, FISH, SWINE) that replaced 3% of high-quality pre-digested fishmeal (CPSP90) with the corresponding hydrolysate. Each experimental diet was randomly assigned to triplicate homogenous groups of 65 fish (IBW 11 g), fed thrice daily for 88 days at 20ºC. Following the feeding period, fish were subjected to thermal stress by reducing water temperature from 20ºC to 15ºC and kept at 15ºC for 5 days. Plasma and liver samples were collected from stressed and unstressed fish.
At the end of the feeding trial, the SWINE group exhibited significantly higher body weight compared to the INSECT group, which in turn exhibited higher body weight than the CTRL. Feed intake and nutrient utilization remained unaffected by the dietary treatments, but a trend towards increased N and energy gain was observed in fish fed the hydrolysates compared with the CTRL. Intestinal integrity was maintained across all experimental groups. The FISH group exhibited significantly lower values for both VSI and HSI, whilst the SWINE-fed fish showed a decreased HSI compared to the CTRL group. Under thermal stress, plasma metabolites shifted: NEFA levels increased, cholesterol and cortisol dropped across groups. Lactate was significantly reduced in all experimental groups except SWINE group, which maintained lactate levels similar under stress and non-stress conditions. Triglycerides’ levels were significantly affected by diet, with the INSECT group showing the highest values regardless of stress condition. Glucose remained unaffected. Oxidative stress results will be further discussed.
In conclusion, our findings suggest that diets supplemented with SWINE and INSECT hydrolysates hold potential as growth enhancers for seabream. Additionally, the SWINE diet influenced fish metabolism, resulting in a decrease in fish HSI by the end of the trial. Notably, following thermal stress, lactate levels in the SWINE group remained similar to those in the non-stress group, indicating the preservation of anaerobic metabolism and highlighting its potential to alleviate the metabolic disruptions triggered by the low temperatures.
Acknowledgments: This work was supported by the Blue Bioeconomy Pact (C644915664-00000026), for the exercise of activities in the WP6 FEED (Pep4Fish project) through international funds provided by the European Union. A. Oliveira acknowledges FCT for the PhD grant (2023.02611.BD).