Introduction
Advancing sustainable aquaculture practices requires the replacement of finite marine-derived proteins in fish diets with alternative, eco-friendly sources to reduce environmental impact and reliance on limited resources. While plant-based proteins and land-animal by-products are already commonly used, their deficiency in taurine, a conditionally essential amino acid for marine fish, raises important nutritional and physiological concerns. Taurine plays a crucial role in several biological processes in fish, including growth and development during early life stages, osmoregulation, bile acid metabolism, and antioxidant defense (Aragão et al., 2022).
Throughout the production cycle, fish are exposed to various human-induced stressors, particularly during routine procedures such as grading and vaccination. These practices involve crowding, chasing, and air exposure, which can trigger acute stress responses. Such events may lead to significant physiological disruptions, including changes in endocrine function, which can negatively impact stress and antioxidant responses, potentially increasing mortality or disease susceptibility (Ciji & Akhtar, 2021)
Understanding how nutritional strategies can modulate stress responses is essential for improving fish welfare and promoting sustainable aquaculture practices. Thus, the aim of this study was to evaluate the effect of taurine supplementation in low fishmeal diets on oxidative status and stress response of European seabass following a stress challenge.
Materials and Methods
Three isonitrogenous, isolipidic and isoenergetic diets were formulated using practical ingredients: a control diet (MARINE), formulated as a premium diet rich in marine ingredients; a low fishmeal diet (PAP), containing only 5% fishmeal with marine ingredients replaced by animal by-products, namely poultry meal and poultry blood meal: and a diet with a formulation similar to the PAP diet but supplemented with 1% of L-taurine (TAU).
Triplicate groups of 23 juvenile European seabass (34.5 ± 7.4 g) were arbitrarily distributed into 100 L cylindrical tanks in a recirculating aquaculture system. Each diet was randomly assigned to three replicate tanks. Fish were fed by hand until apparent satiation, twice daily for 15 days. Tanks were supplied with filtered seawater at 20.1 ± 0.2 ºC. Dissolved oxygen, nitrogenous compounds and pH were checked and registered daily and maintained at levels within the recommended limits for the species. Fish were exposed to a natural summer photoperiod.
At the end of the feeding period, and before the stress challenge, five fish from each tank were sampled (plasma, liver, and anterior intestine) to assess the basal physiological status (T0). Immediately after this sampling, fish were subjected to an acute stress event (overcrowding, net chasing and one minute of air exposure) and were returned to their respective tanks. The same number of fish and biological samples that were collected at T0 were also taken at 1, 4 and 24 hours post-stress, thereafter referred to as T1, T4 and T24, respectively.
Results and Discussion
At T0, no significant differences were observed in the analyses conducted for either the stress response or antioxidant status, indicating that the replacement of fishmeal with animal by-products and the addition of taurine did not significantly affect the basal levels of these parameters. Regarding the stress response results, no significant differences were observed in glucose, cholesterol, lactate, or triglyceride levels at any time point. However, for cortisol, significant differences were detected at T1 and T24, with fish fed the TAU diet showing lower levels compared to those on the other two diets. These findings suggest that taurine supplementation at this level may exert beneficial effects by modulating cortisol release in response to stress.
As for the antioxidant status, in the liver, significant differences in catalase activity were observed at T1, with fish fed the TAU diet exhibiting significantly lower catalase activity compared to those on the other two diets. At the same time point, total glutathione levels were significantly higher in fish fed the MARINE diet than in those fed the PAP and TAU diets. Additionally, at T24, fish fed the MARINE diet showed significantly lower levels of lipid peroxidation compared to the other two groups. Regarding the anterior intestine, significant differences in catalase activity were observed only at T24, with fish fed the MARINE diet showing a significant increase in activity.
These initial findings suggest that diets rich in marine ingredients provide more effective protection against oxidative stress by reducing lipid damage and supporting both enzymatic (catalase) and non-enzymatic (total glutathione) antioxidant defenses. In contrast, the PAP and TAU diets exhibit more limited effects on antioxidant responses. However, taurine supplementation appeared to confer beneficial effects on the stress response. Therefore, while taurine supplementation may have the potential to enhance the resilience of fish fed low-fishmeal diets, further refinement of these formulations is needed to improve their ability to mitigate oxidative stress effectively.
References
Aragão, C., Gonçalves, A. T., Costas, B., Azeredo, R., Xavier, M. J., & Engrola, S. (2022). Alternative Proteins for Fish Diets: Implications beyond Growth. In Animals (Vol. 12, Issue 9). MDPI. https://doi.org/10.3390/ani12091211
Ciji, A., & Akhtar, M. S. (2021). Stress management in aquaculture: a review of dietary interventions. In Reviews in Aquaculture (Vol. 13, Issue 4, pp. 2190–2247). John Wiley and Sons Inc. https://doi.org/10.1111/raq.12565
Acknowledgements
This study has received funding through the Fundação para a Ciência e Tecnologia (FCT), Portugal to CCMAR (UIDB/04326/2020, UIDP/04326/2020 and LA/P/0101/2020), MC (2021.06497.BD).