Introduction: Advanced aquaculture technology has led to the selection of resistant shrimp against diseases and environmental conditions, which not only reduces the risk of mortality but also significantly increases the yield per hectare. The increasing demand for consumption, short cultivation periods, and profitability of the product are considered as factors driving the progress of this industry. Despite many ups and downs, shrimp farming in our country holds a good position. Research by the Iranian Fisheries Organization has even included the propagation, cultivation, and domestication of Western Whiteleg Shrimp (Litopenaeus vannamei), which has an economic justification compared to other native Iranian species, in its program. This study aimed to investigate the effects of different levels of rosemary extract on cholesterol, triglycerides, hemolymph immune parameters, and the stress tolerance of whiteleg shrimp post-larvae under salinity stress.
Material and Methods: In this laboratory experiment, 2,100 post-larvae were obtained from Kouhestak hatchery and fed diets enriched with prepared rosemary extract. The experimental treatments included three levels: control (no extract), 0.2 g/L, and 0.4 g/L of rosemary extract, each with three replicates. After the feeding period, the post-larvae were exposed to salinity shock to assess stress tolerance and physiological quality. For data analysis and to examine the presence or absence of statistically significant differences among treatments regarding the studied parameters, a one-way ANOVA was used, and for comparing the means of the examined factors across different treatments, Duncan’s multiple range test was applied at a 95% confidence level.
Results and Discussion: The results showed that rosemary extract significantly reduced cholesterol and triglyceride levels and modulated certain hemolymph biochemical parameters in the 0.2 and 0.4 g/L treatments (p<0.05). Analysis of biochemical indices showed that urea, uric acid, glucose, triglycerides, calcium, and phosphorus levels were higher in the control treatment than in the other treatments. These elevated values are generally associated with increased stress, impaired liver and kidney function, and disturbances in energy metabolism. In treatments containing rosemary extract, the reduction of these metabolites can be attributed to the plant’s anti-inflammatory, antioxidant, and protective effects. Several studies, including Diwan et al. (2022), have demonstrated that rosemary extract improves metabolic and osmotic balance in aquatic organisms by reducing oxidative damage to liver and kidney tissues. The reduction in glucose and triglycerides may also result from modulation of metabolic pathways and more efficient energy utilization. Additionally, immune parameters, including total hemocyte count and granular cell count, were significantly enhanced. Immune parameters, including total hemocyte count and granular cells, also increased in treatments containing rosemary extract, particularly at the level of 0.4 g. Hemocytes play a central role in phagocytosis, tissue repair, coagulation, and antimicrobial responses, and their increase is an indicator of immune stimulation. The phenolic and antioxidant compounds of rosemary are capable of activating immune-related signaling pathways such as NF-κB, which leads to increased production of cytokines, antimicrobial proteins, and enhanced phagocytic activity (Wade et al., 2015; Karataş et al., 2020). In addition, antioxidant protection of hemocytes prevents cellular damage caused by stress, which in turn increases the number and efficiency of immune cells. Domestic studies also confirm that natural immunostimulants, including mangrove leaf extract, can improve immune quality and post-larval survival (Hajiian et al., 2017). Furthermore, rosemary extract improved survival under salinity stress, with the 0.4 g/L treatment showing a statistically significant increase compared to the control.
Conclusion: Overall, the findings indicate that rosemary extract, particularly at 0.4 g/L, can improve biochemical indices, reduce blood lipids, enhance immunity, and increase the resilience of whiteleg shrimp post-larvae to salinity stress. Therefore, it has potential as a natural dietary supplement to reduce stress and improve post-larval quality. These findings align with the global trend in aquaculture towards using plant-based compounds and reducing antibiotic use. Future studies are recommended to focus on determining optimal administration periods, evaluating long-term cumulative effects, and assessing the combination of rosemary extract with other bioactive additives. Developing new formulations based on plant extracts could also be a significant step toward sustainable and safe shrimp farming.
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