Effects of different levels of aqueous extract from date palm (Phoenix dactylifera) waste on growth performance, immune parameters, and antioxidant activity in juvenile red tilapia (Oreochromis mossambicus × Oreochromis niloticus)

Abstract:
Introduction: Given that the available potential of water and land resources for fish farming and rearing is not unlimited, maximizing resource use efficiency is crucial to achieve higher production per unit area in aquaculture. Nutritional strategies and improving feed composition for important commercial fish species have received considerable attention in research on sustainable aquaculture. These studies focus primarily on increasing the efficiency of nutrient components such as proteins and fats and improving their digestibility. Proper nutrition is recognized as a crucial factor for fish growth and health. It is essential to ensure that an appropriate diet not only meets the physiological needs of the fish but also contributes to their overall well-being. Various studies conducted on human samples suggest that dates have numerous beneficial effects and play an important role in boosting various immune levels, including antioxidant properties, immune stimulation, antimicrobial, anti-inflammatory, and anti-cancer effects. However, despite the positive effects of dates, there is little research on their effects in aquaculture as an immune and growth stimulant in fish.
Materials and methods: A total of 240 red tilapia with an initial average weight of 1.15 ± 0.04 g and initial average length of 3.37 ± 0.10 cm were randomly allocated to 12 aquaria with four treatments, each with three replicates. The fish were subjected to different feeding regimens over 8 weeks, including the control group: feeding with a diet without date extract; treatment 1: feeding with 100 mL date extract per kg feed; treatment 2: feeding with 200 mL date extract per kg feed; and treatment 3: feeding with 300 mL date extract per kg feed. After the experiment, the final weight of the fish was measured, followed by the collection of 15 fish from each treatment for biochemical analysis of body composition. In addition, mucus and serum samples were collected from the nine fish in each treatment to evaluate mucosal immune parameters, serum biochemical markers, and antioxidant defense indices. The data obtained were analyzed using a One-way analysis of variance followed by a Duncan post hoc test with a 95% confidence level. Before analysis, normality of data and homogeneity of variances were checked using SPSS version 26.
Results and Discussion: The findings suggest that dietary supplementation with 200 mL date extract significantly improves the growth performance of red tilapia. Biochemical analyses indicated that this treatment group exhibited higher total protein levels and lower fat content than the control group (P<0.05). Furthermore, glucose, cholesterol, and triglyceride levels were significantly reduced in the group receiving date extract. Notably, protein and albumin levels also increased substantially in this group (P<0.05). Immunological assessments demonstrated significant increases in total protein, immunoglobulin levels, and lysozyme activity in the mucus of red tilapia fed with date extract (P<0.05). Antioxidant defense indices revealed heightened activities of catalase, superoxide dismutase, and glutathione peroxidase, along with reduced malondialdehyde levels in the treatment groups compared to the control (P<0.05). Overall, the enhancements observed in growth and nutritional indices are attributed to the high nutritional value of dates, which are abundant in fiber, vitamins, enzymes, and essential minerals. This improved nutritional status arises from dietary supplementation with date extract.
Conclusion: Since Iran is among the world's largest producers of dates, utilizing this cost-effective immune stimulant derived from waste dates could be recommended as a viable strategy for the aquaculture industry. The findings of this study suggest that incorporating 200 mL date extract into the diet of red tilapia positively influences immune indices and mucosal immune parameters.