Introduction
Temperature is a key environmental factor regulating fish physiology and performance, and sudden decreases in water temperature represent a major challenge for warm-water species such as gilthead seabream (Sparus aurata) (Ibarz et al., 2010). Dietary protein hydrolysates (PH), as sources of highly digestible peptides and antioxidant amino acids (AAs), may enhance the capacity of fish to cope with the energetic and oxidative demands imposed by cold stress (Siddik et al., 2021; Wei et al., 2017). However, little is known about how PH from different sources modulate hepatic metabolic adaptations to cold stress. Therefore, this study characterised the metabolic and oxidative responses of juvenile gilthead seabream to low-temperature exposure and evaluated the modulatory effects of dietary PH from different sources.
Methodology
Fish were fed four experimental diets for 88 days at 20 °C: a control diet (CTRL) containing 3% commercial PH (CPSP90), and three other diets in which CPSP90 was replaced with PH derived from insect meal (INSECT), fish by-products (FISH), or swine by-products (SWINE). At the end of the feeding trial, fish were either sampled immediately (non-stressed) or exposed to 15 °C for 5 days before sampling (stressed). Plasma and hepatic metabolites, biomarkers of oxidative status, and antioxidant enzyme activities were assessed.
Results & Discussion
As previously demonstrated, replacing a commercial PH with an alternative PH maintained growth performance and feed efficiency in gilthead seabream (Alves-de-Oliveira et al., 2026). Cold exposure induced marked metabolic changes, characterised by decreased plasma cortisol, lactate, cholesterol, and triglyceride levels, together with increased glucose and non-esterified fatty acid levels, consistent with the mobilisation of endogenous energy substrates to maintain energy homeostasis. Metabolomic analyses further revealed significant shifts in carbohydrate and AA metabolism, with distinct metabolic signatures among dietary treatments. Lower hepatic threonine concentrations were observed in FISH- and SWINE-fed fish, whereas INSECT-fed fish showed higher hepatic cholesterol and triglyceride concentrations.
Cold exposure also remodelled the antioxidant defence system by increasing superoxide dismutase and catalase activities while reducing glutathione peroxidase activity, without increasing hepatic lipid peroxidation (LPO). Dietary PH also modulated these responses, with FISH- and SWINE-fed fish showing lower hepatic LPO than CTRL- and INSECT-fed fish despite the stress challenge.
Overall, the results suggest that selected PH can contribute to enhanced resilience to low-temperature stress through the modulation of energy metabolism and redox homeostasis.
Acknowledgments
This work was supported by the Blue Bioeconomy Pact (Pep4Fish project; C644915664-00000026), co-funded by the European Union, and by the Foundation for Science and Technology (FCT; UIDB/04423/2020 and UIDP/04423/2020). A. Alves-de-Oliveira and L. Rodrigues-dos-Santos acknowledge FCT for their PhD grants (2023.02611.BD and 2023.00947.BDANA).
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