Fermented rice bran: A high-protein feed ingredient for black tiger shrimp
Solid-state fermentation technology
Many Asian countries still rely on imported feed ingredients for black tiger shrimp, of which soybean meal (SBM) is the most critical protein source. However, the aquaculture industry is competing for SBM supplies with the livestock sector. Therefore, domestic feed ingredients like rice bran have attracted attention due to their low cost and abundant supply.
Rice products are generally not used in shrimp feed because they are priced similarly to wheat products but lack binding properties.
Numerous studies have been conducted to improve the quality of rice bran to enhance its usability as an animal feed ingredient. Biomass transformation through solid-state fermentation (SSF) is one such technique. This process enhances nutrient availability through changes driven by microbial metabolic activity, increasing protein and soluble sugars while reducing complex carbohydrates.
To date, no reports have been published on the use of fermented rice bran (FRB) in shrimp feed. Recently, the hatchery of the Institute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas in Miagao, Philippines conducted a trial using fermented rice bran with high-quality, disease-free black tiger shrimp postlarvae (PL15).
The shrimp larvae were acclimated and reared in a lined pond for 30 days. At the end of the nursery phase, the shrimp were transferred to the experimental system. The juvenile shrimp were randomly distributed among 20 plastic tanks of 60 liters each, equipped with a recirculating seawater system, at a density of 15 shrimp/tank, and acclimated for 7 days.
Trial using fermented rice bran (FRB) as a protein alternative to soybean meal (SBM) in the basal diet of black tiger shrimp. Specifically, FRB replaced SBM at rates of 0% (T0), 12.5% (T12.5), 25% (T25), 37.5% (T37.5), and 50% (T50). All five treatments contained 44% crude protein, with each treatment replicated 4 times over a 50-day period.
Improving the nutritional value of rice bran
The study's results showed that the fermentation process reduced the fiber content of rice bran by about sevenfold compared to unfermented rice bran. Total dietary fiber (TDF) in rice bran ranges between 20-30%, and nearly 90% of that is insoluble dietary fiber (IDF). High insoluble fiber content is the reason for the low nutritional value of rice bran and its limited use in animal feed.
Solid-state fermentation technology increased the protein content in rice bran by about three times compared to the raw material. The quantity of amino acids in FRB also increased compared to unfermented rice bran, indicating an improvement in protein quality. Other studies have also noted similar improvements in protein content and amino acid quality. This protein enhancement is linked to microorganisms, which represent a natural protein essence containing easily digestible proteins with a full profile of essential amino acids.
The essential amino acid index of FRB reaches 84%, which is evaluated as a good quality protein source and comparable to soybean meal. The chemical score of FRB shows that tryptophan is the limiting amino acid. The amino acid profile of fermented rice bran depends on the microbial species and raw materials used in the fermentation process.
Replacing soybean meal
The results of this study confirm the feasibility of FRB in replacing soybean meal in the diet of black tiger shrimp postlarvae. Replacing 25% of soybean meal with FRB resulted in significant improvements in weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio. However, there was no significant effect on growth performance when replacing soybean meal at higher levels. This indicates that fermentation can enhance the nutritional value of rice bran, allowing it to partially replace soybean meal in diets for black tiger shrimp.
In a previous study on striped catfish (tra fish), FRB replaced 20% of SBM. Other studies also reported positive effects on shrimp growth when replacing SBM with agricultural waste. For example, whiteleg shrimp showed improved growth when fed fermented sweet potato flour.
FRB did not negatively affect the nutritional composition of black tiger shrimp. Furthermore, protein retention in shrimp was improved when SBM was replaced up to 25%. However, at higher SBM replacement levels, protein retention was similar to the control group due to the increase in essential amino acids in diets containing FRB, leading to more efficient protein retention. This finding contrasts with other studies where partial replacement of SBM with fermented agricultural waste had no significant effect on shrimp protein retention.
Amino acid analysis of black tiger shrimp after the feeding trial showed that lysine levels in shrimp fed 50% FRB replacing soybean meal were significantly higher than in the control group. Lysine, along with many other amino acids, plays an important role in shrimp flavor. Furthermore, glutamic acid—a key determinant of palatability—was higher in the group of black tiger shrimp fed 50% FRB. These results indicate that FRB can improve the sensory characteristics of black tiger shrimp.
The current study indicates that solid-state fermentation can improve the nutritional value of rice bran into a high-protein feed ingredient for black tiger shrimp by increasing protein content, reducing fiber content, improving amino acid profiles, and enhancing the digestibility coefficient of the ingredient. The results show that FRB can partially replace SBM in diets without affecting growth performance and the nutritional value of the shrimp.
Replacing 25% of SBM with FRB promotes shrimp growth, and replacing 50% with FRB can completely substitute SBM without adversely affecting shrimp development. Therefore, further research is needed to evaluate the complete replacement of SBM with FRB.