THE EFFECT OF ALTERNATIVE FEED INGREDIENTS ON GROWTH AND STRESS RESPONSE OF EUROPEAN SEABASS Dicentrarchus labrax KEPT IN RECIRCULATING AQUACULTURE SYSTEMS

Introduction

Aquaculture feeds are urgently needing alternative sources of protein for the declining fish meal supplies as well as their mostly unsustainable origin (Ceccotti et al., 2019). Most of these current alternatives consist of plant-based ingredients, whereby these alternative protein sources often lead to a decreased digestion rate, health as well as welfare of the fish across species (Booman et al., 2018; Pelletier et al., 2018).

In our study, we investigated the effect of alternative feed formulation on growth characteristics, feed utilization and stress response of European seabass (Dicentrarchus labrax).

Material and Methods

From June to September 2020 experiments were conducted with European seabass in a recirculating aquaculture system (RAS) at the Alfred Wegener Institute (Bremerhaven, Germany). Fish were kept at standardized conditions (20 ± 0.9  °C, 95.21 ± 6.71% oxygen saturation, salinity 49.95 ± 0.87 mS cm-1, pH 7.7 ± 0.04) in 700 L tanks (1 m² bottom area) throughout the entire trial.

A total of 375 fish were individually pit-tagged and randomly distributed to 15 tanks (25 fish/tank). The mean fish weight was about 320 g ± 72.4 g as well as the mean fish length about 30.5 ± 2.1 cm. Fish were fed twice a day (at 9:00 a.m. and 2:00 p.m.). Feeding at 9:00 a.m. was based on approximately 50 g pellets/tank and the feeding at 2:00 p.m. was ad libitum.

Five experimental diets (Sparos Ltd, Olhão, Portugal) were tested in four replicate tanks: (i) control (CTRL) consisting of 18 % fish meal and 10 % poultry meal; (ii) no processed animal protein (NOPAP) consisting of approx. 3 % fish meal from hydrolysates and 35 % insect meal, fermented biomass and algae; (iii) processed animal protein (PAP) consisting of 3 % fish meal from Hydrolysates and 31 % animal and insect meal; (iv) PLUS consisting of 23 % fish meal and was used as a positive control for the best growth performance; and (v) MINUS consisting of 3 % fishmeal and 34 % animal protein and was used as a negative control for growth performance (see Table 1).

Every four weeks all fish were weighted and measured in length to identify the growth performance. Additionally, blood and organs were sampled of five fish per tank at the end of the trial to identify the health and welfare parameters. Further, another five fish per tank were sampled at the end of the trial to identify the sensory quality of the fish filet.

Results and Discussion

The parameters for the growth performance showed no difference between the alternatively fed diets, neither for final weight (lowest MINUS group 459 ± 104 g; highest NOPAP group 475 ± 102 g), nor for voluntary feed intake or condition factor (lowest MINUS group 1.18 ± 0.006; highest PLUS group 1.21 ± 0.02). Significant differences were found in the relative growth rate between the control group and the fish fed NOPAP, MINUS and PLUS diets. This indicates that the fish fed the control group still had the best growth performance. However, this trend was not observed for the FCR, as the control group was not significantly different from the fish fed the alternative diets.The results showed slightly decreased health parameters for the PAP and MINUS groups with a significant increase in the viscerosomatic index between the fish fed the control/PLUS diet and the fish from the MINUS group.

The biochemical analyses of the fish plasma was conducted for a better interpretation of the growth parameter results as well as the fish stress response (Papaharisis et al., 2019). Lactate dehydrogenase showed no significant differences, ruling out diet-dependent effects on the inflammatory response of the fish. Blood parameters glucose and lysozymes did not show significant differences between fish fed the alternative diets, but interestingly, total protein content showed significant differences. Further analysis of the data is needed to better interpret the alternative diets in regard to welfare parameters.

Sensory analysis of the fillet showed no significant differences in taste, odor, juice deposition, protein deposition, and fat deposition. Post-cooking consistency was affected by the alternative diets, with fish fed the control being significantly firmer to the bite than fish fed the MINUS and PLUS diets.

Overall, these preliminary results seem to support the hypothesis that the NOPAP and PLUS diets are viable options for feeding European seabass compared to the commercial diet (CNTRL). However, results showed slightly decreased health parameters for the PAP and MINUS groups, while sensory function was not significantly affected by any of the diets tested (except for consistency after cooking). Interestingly, fish fed the PLUS diet had significantly lower total plasma proteins and significantly firmer-to-bite filets after cooking.

References

Booman, M., Forster, I., Vederas, J. C., Groman, D. B., & Jones, S. R. (2018). Soybean meal-induced enteritis in Atlantic salmon (Salmo salar) and Chinook salmon (Oncorhynchus tshawytscha) but not in pink salmon (O. gorbuscha). Aquaculture, 483, 238-243

Ceccotti, C., B. S. A. Al-Sulaivany, O. A. M. Al-Habbib, M. Saroglia, S. Rimoldi and G. Terova (2019). "Protective Effect of Dietary Taurine from ROS Production in European Seabass under Conditions of Forced Swimming." Animals (Basel) 9(9).

Papaharisis, L., T. Tsironi, A. Dimitroglou, P. Taoukis and M. Pavlidis (2019). "Stress assessment, quality indicators and shelf life of three aquaculture important marine fish, in relation to harvest practices, water temperature and slaughter method." Aquaculture Research 50(9): 2608-2620.

 Pelletier, N., Klinger, D. H., Sims, N. A., Yoshioka, J. R., & Kittinger, J. N. (2018). Nutritional attributes, substitutability, scalability, and environmental intensity of an illustrative subset of current and future protein sources for aquaculture feeds: Joint consideration of potential synergies and trade-offs. Environmental science & technology, 52(10), 5532-5544