Polyphenols are plant-derived compounds with known biological activities and potential health benefits. Over the past decade, there are an increasing number of studies have investigated the application of polyphenols and polyphenol-rich additives in aquaculture as functional feed additives. There are several types of polyphenolic compounds such as flavonoids, phenolic acids, lignans, and stilbenes of widely known beneficial influences on the overall performances and immunity of fish, and thereby improving the health status and production of fish farms. This review discusses the beneficial applications, optimum recommended dose, and potential side effects of these natural compounds on the growth performance, proximate body composition, immune responses, disease resistance, reproductive performance, and fillet quality of different fish species. Also, it points out that the biological functions and mechanisms associated with the polyphenolic compounds involved in the pathways of antioxidant and pro-oxidant activities, as well as the modulation of gene expression and different immune parameters. The output of this review article provided overwhelming evidence to support the claim that natural polyphenols can be considered as relatively safe and viable alternatives to synthetic chemical compounds that not only to improve the fish health status but also to enhance the fish quality, productivity, and food safety while reducing the use of chemicals and antibiotics in the aquatic eco-systems.

The crucial need for safe and healthy aquatic animals obligates researchers in aquaculture to investigate alternative and beneficial additives. Medicinal herbals and their extracts are compromised with diverse effects on the performances of aquatic animals. These compounds can affect growth performance and stimulate the immune system when used in fish diet. In addition, the use of medicinal herbs and their extracts can reduce oxidative stress induced by several stressors during fish culture. Correspondingly, aquatic animals could gain increased resistance against infectious pathogens and environmental stressors. Nevertheless, the exact mode of action where these additives can affect aquatic animals’ performances is still not well documented. Understanding the mechanistic role of herbal supplements and their derivatives is a vital tool to develop further the strategies and application of these additives for feasible and sustainable aquaculture. Gene-related studies have clarified the detailed information on the herbal supplements’ mode of action when administered orally in aquafeed. Several review articles have presented the potential roles of medicinal herbs on the performances of aquatic animals. However, this review article discusses the outputs of studies conducted on aquatic animals fed dietary, medicinal herbs, focusing on the gene expression related to growth and immune performances. Furthermore, a particular focus is directed to the expected influence of herbal supplements on the reproduction of aquatic animals.

This study evaluated the effects of grape seed extract (GSE) on the growth performance, immune response, and disease resistance of common carp ( Cyprinus carpio ). Fish were distributed in four groups and fed diets with varying levels of GSE at 0, 10, 20, and 30 g/kg for 56 days. The final length in fish fed with 20 and 30 g GSE/kg diet significantly increased in comparison with the control group ( P 0.05). However, fish fed with 30 g GSE/kg diet displayed a significantly higher WBC count than the other group ( P <0.05). The serum total protein and globulin in fish fed with 20 g GSE/kg diet significantly increased compared to the control ( P <0.05). A similar pattern was noticed in results for serum and mucus lysozyme activity with a significant increase in fish fed with 20 and 30 g GSE/kg diet compared to the control ( P <0.05). Total antibody levels in serum and mucus samples were also increased in fish by dietary GSE with maximum levels by 20 and 30 g GSE/kg diet. Besides, mucus protease activity was higher in fish that received 20 and 30 g GSE/kg diet with maximum level shown in fish fed with 30 g GSE/kg diet compared to the control group ( P <0.05). Meanwhile, all groups showed higher mucus antibacterial activity against Aeromonas hydrophila with the highest activity in 30 g GSE/kg diet in comparison with the control group. The cumulative mortality was 36.67% when fish were fed with 30 g GSE/kg diet and challenged with A. hydrophila . However, the mortality rate was 40% and 53.33% in fish fed 20 and 30 g GSE/kg diet, respectively. This study suggests that supplementation of GSE could significantly enhance the growth performance, immune responses, and disease resistance against A. hydrophila in common carp.

The role of dietary lemon peel (LM) and/or Bacillus licheniformis (BL) on the growth, immunity, and resistance against Aeromonas hydrophila in common carp, Cyprinus carpio was investigated in this study. LM and BL were included in diets at 0% (T0), 10⁸ CFU/g BL (T1), 1.5% LM and 10⁸ CFU/g BL (T2), and 3% LM and 10⁸ CFU/g BL (T3). Fish fed with T1, T2, or T3 had higher weight gain, specific growth rate, white blood cells count, and blood total protein with lower feed conversion ratio than T0 group (p < .05). The albumin increased significantly (p < .05) in fish fed both BL and LM (T3). The serum superoxide dismutase (SOD), catalase, lysozyme, and bactericidal activities were significantly increased in fish fed both BL and LM (T2 and T3), while serum glutathione peroxidase increased in fish fed BL (T2) (p < .05). Fish fed T1, T2, and T3 diets displayed higher SOD and lower malondialdehyde than fish fed T0 (p < .05). After the A. hydrophila challenge, the mortality rate was significantly lower in T1, T2, and T3 groups than the T0 group (p < .05). The obtained results revealed that LM and BL could be used to increase resistance against A. hydrophila infection in carp. However, further field studies should be performed to confirm the obtained results.

In this study, the effect of artemisia ( Artemisia annua ) leaves extract (ALE) on the immune system, growth performance and antioxidant capacity of common carp ( Cyprinus carpio ) was investigated. Fish with initial weight (90.32 ± 1.12 g) were fed various levels of ALE (0, 0.5, 1 and 1.5 g/kg) for 8 weeks. The results showed that the growth performance (FW, WG, SGR, PER, and LER) in fish fed 1 g/kg ALE was increased significantly ( P <0.05) and the feed conversion ratio (FCR) was improved in fish fed 1 and 1.5 g/kg ALE in comparison to the control group ( P <0.05). Skin mucus total protein was higher in fish fed diet containing 0.5 g/kg ALE than the other experimental groups ( P <0.05), while the lysozyme, immunoglobulin and protease was increased by increasing of ALE in diets. Respiratory burst activity and serum immune parameters were higher in fish fed 0.5 g/kg ALE than the other treatments ( P <0.05). Increasing of catalase (CAT) and decreasing of malondialdehyde (MDA) were observed in fish fed ALE, while glutathione peroxidase (GPx) increased only in fish fed 0.5 g/kg ALE. Hence, it can be concluded that ALE has considerable potential as a natural immunostimulant and growth promotor supplement for the common carp’s aquaculture.