Insect meal (IM) has demonstrated an enormous potential as an alternative protein source to fishmeal (FM) in diets for European sea bass (Dicentrarchus labrax) (Basto et al., 2021 and 2022), one of the most important marine fish species in Mediterranean aquaculture. However, when IM is included at high levels to totally replace FM, alterations in the intermediary metabolism of sea bass are observed, which may compromise the health status of fish (Basto et al., 2023). In this connection, the impact of total FM replacement by an IM on the innate immune parameters and oxidative stress of European sea bass was assessed.
Material and methods
A FM-based diet with 47% of protein and 20% of fat was formulated and used as a control (CTRL). Two other isoproteic and isolipidic diets were formulated to replace 50 and 100% of FM by defatted Tenebrio molitor larvae meal (TM50 and TM100, respectively). Each diet was assigned to quadruplicate homogeneous groups of 15 fish (69 ± 5 g) that were fed until apparent satiation for 16 weeks. Fish were subjected to a 12-hour light/12-hour dark photoperiod regime and kept in a recirculating saltwater system (35‰, 22 ± 1 °C). By the end of the trial, 3 fish per tank (12 per dietary treatment) were sampled for analysis of health status-related parameters, and other 3 fish per tank were exposed to an acute stress episode consisting of 1 min air exposure followed by 1 h of recovery before sampling. Hematologic profile analysis (i.e., hemoglobin, hematocrit, and red and white blood cells), plasma metabolites (i.e., cortisol, lactate, and glucose) and immune parameters (i.e., total peroxidase, lysozyme, and alternative complement pathway activities), and hepatic oxidative stress (i.e., catalase, superoxide dismutase, and glutathione reductase, S-transferase and peroxidase) were evaluated in all fish sampled.
A clear response to acute stress was observed, regardless of dietary treatment, by a significant decrease in hemoglobin, hematocrit and red blood cells, and a significant increase in almost all evaluated humoral parameters. On the other hand, the activity of total peroxidase and superoxide dismutase was significantly affected by the dietary treatments, being highest in fish fed TM100, but not affected by stress condition. Considering the canonical discriminant analysis, a clear separation between non-stressed and stressed fish was evidenced (Fig.1A). Based on the significant Mahalanobis distance of each group multivariate mean (centroid), it was possible to observe that both non-stressed and stressed fish fed TM100 were significantly different from those fed CTRL and TM50 (Fig. 1A). Non-stressed fish fed TM100 were positively loaded by hematocrit and red blood cells (Fig. 1B), whereas stressed fish fed the same dietary treatment were positively loaded by glucose and lactate levels, as well as by mean corpuscular volume (Fig. 1B).
Discussion and conclusions
The results of the present study demonstrated that the partial substitution of FM by IM did not affect innate immune parameters and oxidative stress of sea bass. Contrarily, total FM replacement by IM seems to compromise fish health status. The increased total peroxidase activity and superoxide dismutase, associated with a trend to higher glucose and lactate levels in fish fed TM100, indicate a counteraction to the excess of superoxide radicals and mobilization of fish energy reserves to overcome the stress condition. To better understand the impact of FM replacement by IM on fish immune response and oxidative stress it would be of high interest to deepen knowledge on their underlying mechanisms upon other challenging rearing conditions (e.g., pathogen exposure, chronic stress).
Work supported by the structured program of R&D&I ATLANTIDA - Platform for the monitoring of the North Atlantic Ocean and tools for the sustainable exploitation of the marine resources (NORTE-01-0145-FEDER-000040).
Basto, A., J. Calduch, B. Oliveira, L. Petit, T. Sá, M. R. G. Maia, S. Cabral-Fonseca, E. Matos, J. Pérez-Sánchez, and L. M. P. Valente. 2021. The use of defatted Tenebrio molitor larvae meal as a main protein source is supported in European sea bass (Dicentrarchus labrax) by data on growth performance, lipid metabolism and flesh quality. Front. Physiol. 12.
Basto, A., A. Marques, A. S. Silva, T. Sá, V. Sousa, M. B. P. P. Oliveira, T. Aires, and L. M. P. Valente. 2022. Nutritional, organoleptic and sensory quality of market-sized European sea bass (Dicentrarchus labrax) fed defatted Tenebrio molitor larvae meal as main protein source. Aquaculture 566.
Basto, A., L. M. P. Valente, V. Sousa, M. Conde-Sieira, and J. L. Soengas. 2023. Total fishmeal replacement by defatted Tenebrio molitor larvae meal induces alterations in intermediary metabolism of European sea bass (Dicentrarchus labrax). J. Anim. Sci. 101.