Introduction
The rapid expansion of global aquaculture has intensified the need for sustainable, safe, and effective alternatives to antibiotic growth promoters and chemotherapeutics. Increasing concerns over antimicrobial resistance, environmental impact, and residue accumulation in aquatic products have driven research toward natural bioactive compounds with multifunctional benefits.
Plant-derived polyphenolic phytochemicals, particularly hydrolysable tannins (HT), have emerged as promising candidates due to their well-documented antimicrobial, antioxidant, immunoregulating and gut-modulating properties. Natural chestnut extracts, rich in ellagitannins, a specific type of HT, have demonstrated significant potential in terrestrial animal nutrition; however, its application in aquaculture remains relatively underexplored.
In fish and shrimp farming systems, maintaining an optimal growth performance while ensuring disease resistance is critical. Hydrolysable tannins from chestnut extract may enhance feed efficiency, modulate gut microbiota, improve intestinal integrity, support the immune system, and exert antimicrobial activity against pathogenic bacteria commonly affecting aquaculture species.
Materials and Methods
Pathogen-free Pacific white shrimp (Penaeus vannamei) were fed four experimental diets during 90 days, after the corresponding acclimation period and placement in the corresponding tanks. The dietary treatments were as follows: Control (commercial feed), T1 (including 1 kg HT/ton of feed), T2 (including 2kg HT/ton of feed), and T3 (including 3 kg HT/ton of feed). After these 90 days, shrimp were collected and sampled for assessment of the growth performance, hepatopancreatic histology and immune-related gene expression.
Results and Discussion
The dietary inclusion of HT resulted in a significantly lower (p<0.05) FCR of shrimp compared to the Control group. In addition, shrimp fed diets T1 and T2 had significantly higher (p<0.05) final body weight (FBW) and specific growth rate (SGR). Shrimp fed diet T1 also had a significantly higher (p<0.05) weight gain (WG) than those fed diet Control. The improvement in the growth performance obtained with the inclusion of HT in the diets was in agreement with the results reported by Novriadi et al. (2023), who also observed a better growth performance in Pacific white shrimp when using similar dietary levels of inclusion of HT.
Regarding the histology of the hepatopancreas, and compared to the Control group, shrimp fed diet T1 had a higher number of vacuoles in the B cells, a lower amount of hemocytes in the intertubular regions, thicker epithelial tissue, presence of R cells, more lipidic reserves and no tissue atrophy. These results were in line with those reported in Pacific white shrimp by Novriadi et al. (2023) with the inclusion of 2 and 3 kg of HT per ton of feed. The hepatopancreas is the main digestive gland of shrimp, and a key indicator of their metabolism (Novriadi et al., 2023). Thus, the observed beneficial effect of the inclusion of 1kg HT per ton of feed on the hepatopancreas, could be indicative of an improved digestive function, when compared to the Control group.
In relation to the immune response, genes related to the immunity, stress tolerance, and antioxidant capacity, were evaluated to assess the effect of the dietary inclusion of HT on the defense system of shrimp. The results indicated a higher (p<0.05) transcriptional response of two out of a total of five genes analysed, these two belonging to the immune and antioxidant responses, in shrimp fed diet T1 compared to those fed diet Control. These results were in agreement with previous studies reporting antioxidant and antimicrobial activity of HT in shrimp, such as that by Huang et al. (2024). Results on the gene expression, as well on the abovementioned parameters, will be further presented and discussed.
To conclude, results from the present study indicated an overall beneficial effect of the dietary inclusion of HT on cultured Pacific white shrimp, suggesting 1kg of HT per ton of feed as the optimal level of inclusion in shrimp diets.
References
Huang, H.T., Hu, Y-F., Liao, Z-H., Lin, Y-R., Chen, Y-Y., Wang, Y-C., Chang, J-J., and Nan, F-H., (2024). Dietary supplementation with hydrolyzable tannins improves nonspecific immune responses, intestinal morphology, and disease resistance against Vibrio alginolyticus in whiteleg shrimp. Aquaculture Research, 2024, 3486022, p. 1-13. https://doi.org/10.1155/2024/3486022
Novriadi, R., Fadhilah, R., Wahyudi, A.E., and Trull��s, C. (2021) Effects of hydrolysable tannins on the growth performance, total haemocyte counts and lysozyme activity of Pacific white leg shrimp Litopenaeus vannamei. Aquaculture Reports 21(33): 100796. https://doi.org/10.1016/j.aqrep.2021.100796
Novriadi, R., Soebhakti Hasan, O.D., Nguyen, K., Davies, S., Panjaitan, Z.G., Sektiana, S.P., Gaddipati, G.R., and Trull��s, C. (2023). Functional effects of hydrolyzable tannins on the growth, health status, and hepatopancreas histology of Pacific white shrimp penaeus vannamei reared under commercial pond conditions. Aquaculture Research, 2023, 6644113, p.1-13. https://doi.org/10.1155/2023/6644113