Fermented soybean as a substitute for fishmeal in shrimp diets

Shrimp: Fasting growing species

On the menu tables, shrimp, which is one of the favourite seafood dishes, is reported to be one of the fastest-growing species in the crustacean aquaculture industry. In a 2020 report, FAO ranked the whiteleg shrimp (Litopenaeus vannamei) as the top-produced aquaculture species with approximately 5.81 Mmt.

Reliance on fishmeal impedes long-time development

Due to its high digestibility and rich amino acid profile, fishmeal has long been used in aquafeed formulations as a source of high-quality protein. However, reliance on fishmeal is a significant impediment to the aquaculture industry’s long-term development because of its consistent price increase due to limited supply and increased incorporation in livestock and aquaculture feed.

Research: Cheaper & more sustainable options

Current research is pursuing the use of less expensive and more sustainable alternative protein sources of both animal and plant origin to reduce fishmeal levels in aquafeed without impairing growth performance.

Soybeans: Nutritional drawbacks

On the other hand, soybean as an alternative has some nutritional drawbacks, including the presence of anti-nutritional factors (ANFs) that reduce feed utilisation and absorption. Among the processing methods available, fermentation of soybean meal has been reported to be cost-effective for improving its nutritional quality through increased protein content, biodegradation of ANFs and prebiotic effects that help improve nutrient digestibility and enhance immune function.

Fishmeal vs Fermented soybean meal

In the current study, researchers assessed the effects of long-term feeding fermented soybean meal at different inclusion levels of replacement compared with fish meal on juvenile whiteleg shrimp (Litopenaeus vannamei). For 12 weeks, shrimp juveniles were fed 4 test diets that differed in the inclusion levels of fermented soybean meal (FSBM) as a replacement for fishmeal, as follows:

• Fishmeal diet: (no inclusion of FSBM)
• FSBM diets: three diets where 20%, 30%, and 40% of fishmeal was replaced with fermented soybean meal.

The benefits of substituting for fishmeal with fermented soybean were evaluated through the measurements of growth performance, feed utilisation, immunological parameters and antioxidant status.

Growth performance and feed utilisation

The inclusion of 20% FBSM led to enhanced growth performance (Table 1) and feed utilisation compared to the higher inclusion levels. The improvement in growth was attributed to the improved lipid digestibility of FSBM and the reduction of anti-nutritional components during fermentation. According to the researchers, the observed increase in lipid retention is associated with dietary plant protein, which is associated with an increase in hepatic lipogenic enzyme activity, as observed in previous sea bass and salmonids studies.

On the other hand, it was highlighted that haemolymph metabolites serve as physiological, nutritional, and immunological stress indicators in crustaceans; in the current study, the inclusion of FSBM in the diet had a significant effect on the haemolymph total protein (TP) content, with the maximum TP concentration observed in groups fed 20% FSBM, and lowest in groups fed the higher level of 40% FSBM. On the contrary, the decreased TP concentration in 40% FSBM was associated with the possible detrimental effect of high soya bean levels on the digestibility, absorption, and utilisation of dietary protein. In addition, the 20% FSBM group had higher levels of hepatopancreas and intestinal protease and lipase digestive enzymes, supporting improved digestion with the 20% inclusion level.

20% replacement of fishmeal with fermented soybean meal improves growth performance

Improving immunity and antioxidant status

The findings of this study indicate that 20% of FM can be substituted with FSBM without harming shrimp health. Studies show that, with its antibacterial effectiveness against bacterial infection, lysozyme activity is one of the most important indicators of shrimp immunity; in the current study, the addition of Saccharomyces cerevisiae to ferment soybean meal was beneficial in regulating lysozyme activity as the results showed an increase in the lysozyme activity of 20% FSBM-fed groups. Studies also show that the process involved in boosting the immune system of shrimp hinges on the protein recognition pattern of the circulating sugars which evoke the immune cells; in the current study, it was assumed that the yeast harbouring β-glucan effectively stimulated lysozyme synthesis.

Antioxidants’ function in cells is to maintain balance and scavenge excess reactive oxygen species (ROS) to mitigate their corrosive effect. In this study, hepatopancreas antioxidant enzymes catalase, superoxide dismutase, and glutathione peroxidase activities increased significantly in the group fed 20% FSBM, indicating that the 20% substituted FSBM meal had a greater anti-oxidative effect than that found in fish fed fishmeal and the other 2 concentrations. In addition, the hepatopancreatic malondialdehyde (MDA) level of shrimp given 20% FSBM was much lower than that of shrimp fed the FM and other diets, demonstrating that the dietary replacement of FM with FSBM did not stimulate oxidative stress but rather decreased it.

“This could be attributable to the FSBM’s high iso-flavonoid content, which can neutralise free radicals and prevent lipid peroxidation. In addition to the enhanced flavonoid content created during soybean fermentation, tiny peptides, and organic acids are also produced. On the other hand, Saccharomyces cerevisiae produces vitamins and other metabolites that serve as exogenous antioxidant sources,” the researchers said.

Concluding remarks

In conclusion, this study demonstrates that 20% replacement of fishmeal with fermented soybean meal improves growth performance, feed utilisation, immunological parameters, and the antioxidant status of juvenile whiteleg shrimp. This improvement is mainly attributed to the increased nutritional content and lipid digestibility of fermented soybean meal and the reduction in anti-nutritional components during fermentation.

Based on an original article by Asmaa S. Abd El‑Naby, A. E Eid, Alkhateib Y. Gaafar, Zaki Sharawy, A. A Khattaby, Mohamed S. El‑sharawy, and Amel M. El Asely. 2023. Overall evaluation of the replacement of fermented soybean to fish meal in juvenile white shrimp, Litopenaeus vannamei diet: growth, health status, and hepatopancreas histomorphology. Aquaculture International, 1-19.