Fishmeal (FM) is considered to be the ideal protein source for fish production. However, due to its limited availability worldwide and its negative environmental impact, there is a need to focus on sustainable alternatives to reduce the reliance on fishmeal. Recently, fermented soybean meal (FSBM) has attracted considerable interest due to its improved nutritional profile, reduced anti-nutritional factors (ANFs), improved digestibility and associated health benefits. The aim of this study was to evaluate the potential of FSBM as an alternative protein source in the diet of European seabass (Dicentrarchus labrax) and to investigate its effects on feed efficiency, growth performance, immune response and intestinal health.
For this purpose, a 13-week trial was performed to investigate the effects of different inclusion levels of FSBM (INOLASA, COSTA RICA) replacing FM. Six isonitrogenous (46.5% crude protein) and isolipidic (16% crude lipid) diets were formulated, a control diet containing 30% FM and five experimental diets replacing FM by 15, 30, 50, 70, and 80%. All diets (3.5 mm pellets) were produced by cooking extrusion. Juvenile European seabass were obtained from a commercial fish farm and transferred to the HCMR research facilities where they were randomly distributed into 18 cylindroconical experimental tanks of 1,000 L, 35 fish per tank, with 3 replicates for each diet.
The average initial weight of the seabass was 30.48 ± 0.14g (SD). Fish were hand-fed to apparent satiation twice daily, and uneaten feed was collected in the waste collector of each tank to calculate daily feed consumption. Similarly, feces were collected and stored at -20 oC pending digestibility analysis. The average seawater temperature was 20.2 ± 5.6 oC. At the end of the study, three fish per tank were randomly sampled and tissues from the intestine (anterior and mid) and liver were collected and immediately fixed in 10% buffered formalin for histological analysis. In addition, blood was collected from the caudal vein of the fish, and serum was used for immunological assessments.
This study showed that the tested FSBM could replace at least up to 50% of the FM in the diets of European seabass without affecting growth performance and feed utilization. Digestibility of protein and lipids was found to be lower in the 70% and 80% diets compared to the control. Overall, the FSBM diets didn’t induce severe immune responses that would indicate adverse effects on fish physiology. However, the high inclusion rates of FSBM in the 70% and 80% groups significantly reduced fish serum lysozyme levels compared to the control group.
Finally, the histological evaluation of fish tissues from the anterior, midgut, and liver showed no statistically significant differences between the diets, and no enteritis or signs of inflammation or cellular damage were observed.