Introduction: Siberian sturgeon (Acipenser baerii) is widely cultured due to its rapid growth, high stress tolerance, and strong adaptability to farming conditions (Falahatkar et al., 2022; Yang et al., 2022, 2023). Successful sturgeon aquaculture largely depends on effective juvenile rearing, reduction of mortality, and early adaptation to formulated feeds. Moreover, adequate nutrient supply through properly formulated diets is a key factor influencing the quality and survival of larvae and juveniles (Lazo et al., 2007). Dietary supplements have been recognized for their ability to enhance immune function and stimulate non-specific humoral and cellular immune responses (Bricknell and Dalmo, 2005; Taheri et al., 2023). The natural diet of sturgeons is rich in insects (Saldau, 1948), making insect meal a suitable dietary ingredient for these species (Rawski et al., 2021). Insects provide high-quality protein as well as antimicrobial peptides (AMPs) and chitin, which are bioactive compounds with immunostimulatory properties. These components can enhance immune function and modulate the composition of the gut microbiota (Oliva-Teles, 2012). In addition, insects contain secondary metabolites, such as phenolic compounds, which exhibit antioxidant, anti-inflammatory, and antimicrobial activities and may become more bioavailable following hydrolysis (Yoon et al., 2023). The yellow mealworm (Tenebrio molitor) is among the seven insect species approved for use by the European Union (Tan et al., 2018). Previous studies investigating hydrolyzed fish by-product protein in aquatic species, including rainbow trout (Oncorhynchus mykiss), Siberian sturgeon (A. baerii), and Asian seabass (Lates calcarifer), have demonstrated improvements in hematological parameters, antioxidant enzyme activity, and immune responses (Javaherdoust et al., 2020; Yeganeh and Adel, 2021; Siddik et al., 2018; Poonnual et al., 2025). However, the nutritional and physiological effects of hydrolyzed mealworm protein in Siberian sturgeon have not been specifically evaluated. Therefore, in this study, the effects of dietary hydrolyzed mealworm protein on hematological indices, immune responses, antioxidant enzymes, and hepatic enzymes in Siberian sturgeon were assessed.
Materials and Method: A total of 300 Siberian sturgeon (A. baerii) with a mean body weight of 23.26 ± 1.96 g were included in the experiment. Fish were randomly allocated to five groups, including one control and four experimental groups, each with three replicates. Enzymatic hydrolysis of mealworm was carried out using Alcalase, following the method described by Ovissipour et al. (2010). The chemical composition of hydrolyzed mealworm was determined using standard methods (AOAC, 2000). Diets were formulated using WUFFDA software. Five experimental diets were prepared containing 0% (control), 0.5%, 1%, 1.5%, and 2% hydrolyzed mealworm protein (Javaherdoust et al., 2020). Hydrolyzed mealworm protein replaced fish meal in the diets. Fish were fed the experimental diets at 3% of body weight, four times daily (08:00, 12:00, 16:00, and 20:00), for 56 days in fiberglass tanks. At the end of the experimental period, blood samples were collected from the caudal vein using 2.5 mL syringes. After clotting, blood samples were centrifuged at 4500 rpm for 10 min. Serum was separated and stored at −20 °C until analysis. The remaining blood samples were transferred to heparinized microtubes for measurement of selected hematological indices (Akrami et al., 2015).
Results and Discussion: significant changes in hematological, biochemical, and immune parameters. WBC, RBC, and HCT were significantly higher in all hydrolyzed protein groups compared with the control (p < 0.05). MCV was not affected (p > 0.05). The highest Hb levels were observed in the 0.5% and 2% groups. Both MCH and MCHC showed significant changes (p < 0.05). These results are consistent with the findings of Andrews et al. (2019), who reported increased hematological indices in Indian carp (Labeo rohita). These observations suggest that hydrolysates enhance immune function and WBC counts across species. Cholesterol and triglyceride levels were reduced in supplemented groups (p < 0.05). This effect may result from bioactive peptides derived from hydrolysis, which exhibit emulsifying, antioxidant, immunomodulatory, and antibacterial activities (Venkatesan and Nazeer, 2014). Similar reductions have been reported with hydrolyzed soybean protein (Song et al., 2014), hydrolyzed fish protein (Hevroy et al., 2005; Xu et al., 2016; Javaherdoust et al., 2019), and hydrolyzed cottonseed protein (Gui et al., 2010). Total protein and albumin were higher in hydrolyzed protein groups, with the highest values in the 1%, 1.5%, and 2% groups. Increased albumin may be due to enhanced hepatic production associated with dietary hydrolyzed protein (Abdel-Tawwab et al., 2007; Acar et al., 2015). Similarly, Javaherdoust et al. (2019) reported elevated serum total protein and albumin in rainbow trout (O. mykiss), indicating higher peptide bioavailability. All hydrolyzed protein groups showed lower AST and ALT compared with the control, with the lowest values in the 1.5% group. The lowest ALP activity was observed in the 1% group. No significant difference between the 2% group and control suggests that hydrolyzed protein at the tested levels did not induce hepatic damage (Fan et al., 2022). Similarly, Dai et al. (2020) reported that marine hydrolyzed proteins reduced AST and ALT in largemouth bass (Micropterus salmoides), indicating a favorable physiological response. SOD, GPX, and CAT activities were higher in some hydrolyzed protein groups compared with control. The highest SOD and GPX activities were observed in the 1.5% group, whereas CAT activity peaked in the 1% and 1.5% groups. Bui et al. (2014) reported increased SOD activity in red seabream (Pagrus major) fed hydrolyzed aquatic proteins. Antioxidant properties of hydrolyzed proteins vary depending on hydrolysis degree, composition, and amino acid sequence (Wu et al., 2003). Immunoglobulin levels were higher in the 1%, 1.5%, and 2% hydrolyzed protein groups. Complement activity was elevated in all hydrolyzed protein groups. Tang et al. (2008) reported that hydrolyzed fish proteins enhanced lysozyme, complement, and immunoglobulin activity in large yellow croaker (Pseudosciaena crocea). Complement defends against foreign organisms and lyses external cells (Gasque et al., 2004). In this study, serum lysozyme activity was significantly increased in fish fed 1% and 1.5% hydrolyzed protein. Similarly, Liang et al. (2006) reported that inclusion of 15% hydrolyzed protein in Japanese seabass (Lateolabrax japonicus) diets enhanced lysozyme and complement. Previous studies also showed elevated lysozyme levels in various fish species following low-level hydrolyzed fish protein (Siddaiah et al., 2022; Zheng et al., 2013; Sanguino-Ortiz et al., 2025; Javaherdoust et al., 2019).
Conclusion: The results of this study demonstrated that dietary hydrolyzed mealworm protein can effectively enhance health and physiological performance in Siberian sturgeon (A. baerii). Among the tested inclusion levels, the diet containing 1.5% hydrolyzed protein produced the most pronounced positive effects, suggesting it as an optimal dosage for improving fish health. This supplementation improved hematological indices. RBC and HCT were increased, reflecting enhanced oxygen-carrying capacity and overall physiological condition. Blood lipid profiles were favorably modulated, with significant reductions in cholesterol and triglycerides, indicating improved lipid metabolism and reduced risk of metabolic stress. Protein metabolism was also positively affected, as serum total protein and albumin levels were elevated, suggesting enhanced hepatic protein synthesis and greater availability of dietary peptides. Liver function was maintained and even improved, as demonstrated by reductions in AST and ALT activities, highlighting the hepatoprotective effects of hydrolyzed mealworm protein. Antioxidant defense mechanisms were strengthened in fish receiving hydrolyzed protein. SOD, GPX, and CAT activities increased, indicating an improved capacity to neutralize reactive oxygen species, reduce oxidative stress, and enhance cellular and overall fish health. Immune responses were also significantly enhanced. Serum immunoglobulin levels, complement activity, and lysozyme activity were elevated, suggesting that hydrolyzed mealworm protein strengthens innate immunity and enhances overall disease resistance. Overall, these findings indicate that dietary inclusion of 1.5% hydrolyzed mealworm protein represents an effective and practical approach to improving growth performance, health status, and immune competence in Siberian sturgeon. From an applied perspective, incorporating hydrolyzed mealworm protein into commercial diets can optimize fish health, increase survival rates, reduce metabolic and oxidative stress, and strengthen immune defenses. These benefits not only improve productivity but also support sustainable practices in Siberian sturgeon aquaculture, achieving both economic and environmental objectives. |
