Introduction
Gilthead seabream (Sparus aurata) is a key species in European aquaculture; however, its production is challenged by low-temperature stress, impairing growth, metabolism, and immune function. Increasing thermal variability in Atlantic waters is expected to intensify these challenges by subjecting fish to repeated temperature fluctuations that disrupt homeostasis and limit recovery between stress events. Functional diets enriched with protein hydrolysates from animal by-products are emerging as a strategy to enhance fish resilience under stress by providing bioactive peptides and immunostimulants. However, their effectiveness under fluctuating temperature conditions remains unclear. Therefore, this study aimed to evaluate whether dietary inclusion of poultry or swine protein hydrolysates can mitigate the impacts of fluctuating temperature on growth, nutrient utilisation, and intestinal health in gilthead seabream.
Material and Methods
Juvenile gilthead seabream (~23.8 g) were fed three isoproteic and isoenergetic diets: with 3% of commercial fish hydrolysate (CSPS90; COM), 3% poultry hydrolysate (POULTRY) or 3% swine hydrolysate (SWINE). Fish were fed three times per day to apparent satiety and maintained under constant (CT; 22 °C) or fluctuating temperature (FT; 22-15-22 °C) regimes in a recirculating aquaculture system. Growth and feed intake were monitored every 4 weeks at three time points: before, after prolonged exposure, and post-recovery. At the end of the trial, nutrient utilisation and anterior intestinal morphology were also assessed. Nutrient and energy apparent digestibility coefficients were determined in a parallel trial, at 15 °C and 22 °C.
Results
Thermal regime influenced all measured parameters, with FT reducing body weight, voluntary feed intake, nutrient utilisation, and whole-body composition. Distinct dietary effects were observed despite the influence of temperature. All dietary treatments supported growth, with a trend toward increased performance in the POULTRY group. Differences in voluntary feed intake were observed between diets, with higher values in the POULTRY diet compared to the SWINE diet, alongside differences in whole-body lipid content. Nutrient and energy digestibility was higher at 15 °C than at 22 °C and was not significantly affected by diet. While FT did not affect anterior intestine integrity, it significantly reduced the number of acid and total goblet cells; whereas the POULTRY diet increased goblet cell numbers.
Discussion
The negative effects of fluctuating temperature on performance are consistent with reduced feed intake under thermal stress. The higher feed intake observed with the POULTRY diet may be indicative of differences in palatability, likely related to the presence of low-molecular-weight peptides. This higher feed intake could be linked to the differences in lipid deposition and growth trends. In contrast, the SWINE diet maintained growth despite lower feed intake, indicating differences in nutrient utilisation. The reduction in goblet cell numbers under FT indicates impaired mucosal function, which was partially mitigated by the POULTRY diet. Digestibility was higher at lower temperatures, likely resulting from reduced feed intake at lower temperatures and longer gastrointestinal transit time, which can enhance nutrient absorption efficiency. However, digestibility was not affected by diet, suggesting that absorptive capacity was not directly linked to differences in goblet cell abundance.
Acknowledgment
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. Ana Claro acknowledges Funda����o para a Ci��ncia e a Tecnologia (FCT) for the PhD grant (2024.00449.BDANA). This research was also partially funded by national funds through FCT, I.P., and by the European Commission's Recovery and Resilience Facility, within the scope of UID/04423/2025 (https://doi.org/10.54499/UID/04423/2025), UID/PRR/04423/2025 (https://doi.org/10.54499/UID/PRR/04423/2025), and LA/P/0101/2020 (https://doi.org/10.54499/LA/P/0101/2020).