The bioactive potential of hydrolysates in modulating myogenic and protein accretion processes has attracted increased interest in the aquaculture industry. This is due to their capacity to promote fish growth and improve feed efficiency, when included in aquafeeds. This study aims to elucidate the impact of replacing high-quality fishmeal (FM) with novel hydrolysates from local agri-food by-products in the diet of European seabass (Dicentrarchus labrax). The study evaluated fish growth performance and nutrient utilization, while also assessing muscle nutritional value, cellularity, and metabolome.
Experimental protein hydrolysates were obtained through the hydrolysis of blue shark skin, fisheries by-products, and swine meat and bones, respectively. A control (CTRL) plant-based diet (with 70% plant proteins) containing 12.5% FM (LT70) was formulated and compared with three experimental diets where 3% of the FM was replaced by one of the previously referred hydrolysates, resulting in three isoproteic diets: SHARK, FISH, and SWINE. Seabass juveniles (initial body weight of 12g) were evenly distributed among twelve tanks and fed the experimental diets three times daily until satiety, with triplicates for each diet. After 86 days of feeding, all fish were weighted and measured. Dorsal muscle samples were collected for determination of nutritional value, morphometric analysis, and primary metabolite profiling by GC-TOF-MS. After the growth trial, nutrient digestibility was evaluated for all diets.
The diets equally promoted specific fish growth rate (1.6), feed conversion ratio (1.1) and nutrient and energy retention efficiencies (% digestible intake). The final condition factor and somatic indexes were statistically increased in fish fed the SWINE diet. Whole-body and muscle composition were similar across groups, and all fillets provided 500 mg of EPA + DHA per 100 g. Regarding the muscle metabolome, the SHARK group exhibited significantly higher levels of glycolytic intermediates and lower levels of glucogenic amino acids (AAs). Muscle cellularity remained unaffected by the dietary treatments, although the number of small-sized fast-twitch fibers (<30 µm) was highest in the FISH group.
The highest somatic indexes in the SWINE group suggest metabolic adaptations in seabass, whilst the muscle metabolome of fish fed the SHARK diet seems to induce protein catabolism to obtain glucogenic AAs. However, these changes were not reflected in fish growth performance and muscle flesh quality, which remained similar among treatments. Results suggest that hydrolysates from agri-food by-products could replace FM in plant-based diets.
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. Luciano E. Santos acknowledges FCT for PhD grant (2023.00947.BDANA).