A recent study explored the potential of phytobiotics to enhance the health and resilience of Nile tilapia (Oreochromis niloticus). Researchers examined the effects of dietary supplementation with three herbal extracts: lemon balm (Melissa officinalis), marjoram (Origanum majorana), and chamomile (Matricaria chamomilla). Phytobiotic supplements of these herbal extracts were shown to improve fish stress tolerance and immune activation for a certain period under stressful conditions or unchanged water, based on the stocking density, dosages of herbs used, and the extent of deterioration of the water quality.
- Introduction
Recently, water scarcity, harsh climate, rapid population growth, and per capita consumption of animal protein have weighed on the modern aquaculture sector. The aquaculture sector is the largest contributor to the fish supply as production from sea-caught fisheries has almost stagnated in recent years (FAO, 2022; El-Sayed et al., 2022; Eyayu et al., 2024). However, the rapid evolution of intensification practices is exaggerating stressors on fish, increasing the risk of low water quality and disease outbreaks (Ndashe et al., 2023). Other challenges include wastewater-based agriculture, a major source of nitrogenous components, organic carbon, suspended matter, and phosphates, which pose a major threat to aquatic ecosystems (Kim et al., 2020; Li et al., 2023). These sources of pollution can lead to a rapid deterioration of water quality, which negatively affects fish health and the proliferation of pathogenic microbes; this can eventually lead to fish death and economic losses in farmed fish species (Mehrim and Refaey, 2023). Another important factor, fish stocking density, affects water quality as oxygen requirements vary with fish species, age, fish size, and water temperature (Dunham, 2023).
Faced with the water scarcity crisis, several alternative systems have been proposed including water exchange, biofilters for recirculating aquaculture systems, Biofloc technology, and aquaponics to maintain aquaculture water quality and quantity (Abdel-Aziz et al., 2024; Salin and Vinh, 2023). These aquaculture maintenance technologies have tended to provide sustainable models based on minimal and zero water use. However, some of these water-saving technologies can be laborious and expensive, incur high electricity generation costs, and introduce pathogens (Zimmermann et al., 2023). In addition, chemotherapeutic options have limitations such as negative effects caused by the excessive use of chemicals, disinfectants, and antimicrobials, which also pose risks to humans, the aquatic environment, and the development of microbial resistance (Bondad-Reantaso et al., 2023).
Nonetheless, these alternative technologies have shown differential efficacy responses in growth performance, immune response, and nutritional value. In Zero Exchange Biofloc (BFT) technology, adult Nile cichlids were stored in high densities and experienced poor growth performance, disturbances in clinical biochemistry, and a reduction in crude protein in their carcasses. Furthermore, high levels of settleable solids (74 ml L-1) and nitrate (1.09 g L-1) and degenerative effects on the gill structure of all stocking densities were found (Manduca et al., 2020).
Therefore, environmentally friendly and sustainable alternative approaches to aquaculture disease and ecosystem control have recently received attention (Hossein et al., 2023). For example, functional nutrition, optimized feeds, and feeding regimes help promote fish health and resistance to infection. Also, enhanced immunity is largely regulated by immune stimulants such as algae and plant extracts, probiotics, prebiotics, yeast extracts, and micro-ingredients such as minerals and vitamins (Sharawy et al., 2020; Van Doan et al., 2020). Phytobiotics or herbal extracts are promising alternatives because they minimize chemotherapeutic risks and help maintain ecosystem balance (Dien et al., 2023; Rabelo-Ruiz et al., 2023).
The effectiveness of phytobiotics is related to their bioactive metabolites, which may act as immunostimulants, improve digestive system functionality, increase feed conversion efficiency, improve growth performance, and increase antioxidant activities (Gabriel et al., 2015; Yang et al., 2015; Yilmaz, 2019; and Abdul Kari et al., 2022). In addition, phytobiotics are considered inexpensive alternative immunostimulants that are biofriendly and biodegradable (Hoseinifar et al., 2020; Zakaria et al., 2022). Among the vital dietary herbs, lemon balm, Melissa officinalis L., is a therapeutic herb and an aromatic perennial plant; it commonly grows in the Mediterranean region and Western Asia and is intensively cultivated in Europe. It is a good source of antioxidants, antimicrobials, and rosmarinic acid, all of which have beneficial effects on fish survival rates, growth performance, and immune response (Ghiulai et al., 2020; Bilen et al., 2020; Jafarpour and Fard, 2016). Also, Origanum majorana (marjoram) is a tender perennial undershrub, is naturalized in Mediterranean regions, and is particularly found in the temperate regions of the Himalayas. Its leaves are known to contain antioxidant and antimicrobial compounds and high concentrations of phenolic compounds that improve fish growth, nutrition, and economic efficiency (El-Dakar et al., 2004; El-Kholy, 2012; Roby et al., 2013). Currently, Matricaria chamomilla (chamomile) is widely distributed all around the world. M. chamomilla is an annual herb that grows on all soil types and is resistant to cold. It is native to southern and eastern Europe, and northern and western Asia. Its flower supplements have been found to improve non-specific immune responses and increase fish growth rates (Abdelhadi et al., 2010; Zaki et al., 2012).
Edwardsiellosis is a dangerous bacterial infection that infects various aquatic habitats and causes economic losses worldwide (Oh et al., 2020; Haenen et al., 2023). The Edwardsiella genus includes E. tarda, E. ictaluri, E. hoshinae, E. piscicida, and E. anguillarum (Shao et al., 2015). Outbreaks of Edwardsiellosis have been ecologically correlated with highly stressful conditions in poor water quality (Davies et al., 2018).
Although phytobiotics are a new frontier in aquaculture, there is a fundamental need to achieve a clear and direct dose-dependent stimulatory effect on fish growth, immune status, and physiology. Furthermore, there is limited knowledge on the effectiveness of herbal-based phytobiotics for maintaining fish health under stressors such as reduced and/or absent water exchange and intensive aquaculture conditions. Therefore, the efficacy of Matricaria chamomilla flower extract (MCE), Melissa officinalis leaf extract (MOE), and Origanum majorana leaf extract (OME) as feed additives in tilapia feeds was assessed in stressful conditions with unchanged water. We also measured immunological response, growth performance, and histological indications. Additionally, using the same severe culture conditions, an experimental study was conducted to determine the antibacterial efficacy of herbal feed additives against the pathogenic bacteria E. tarda.
2. The Experiment test
The trial involved three herbal extracts: lemon balm (Melissa officinalis), marjoram (Origanum majorana), and chamomile (Matricaria chamomilla). Treated groups were compared with control groups, including a positive control (0% water exchange) and a negative control (20% daily water exchange).
Fish were cultured at a stocking density of 20 fish per cubic meter, with a biomass of 1.8 kilograms per cubic meter. Water quality was monitored, and clinical responses, growth, and immune parameters were assessed. Additionally, herb-supplemented fish were challenged with a pathogenic strain of Edwardsiella tarda, and mortality rates were recorded.
3. Results and Discussion of study
The study revealed several significant findings:
Improved Growth Performance: Fish supplemented with herbal extracts exhibited better growth performance, including increased weight gain and improved feed conversion rates, compared to the positive control group.
Enhanced Immune Response: Herb-treated fish demonstrated strong immune responses, as indicated by elevated immune parameters. This suggests that phytobiotics can stimulate the immune system, making fish more resistant to diseases.
Greater Disease Resistance: When exposed to the pathogenic bacteria Edwardsiella tarda, herb-treated fish showed significantly higher survival rates than control groups, indicating enhanced infection-fighting capacity.
Stress Tolerance: The study found that phytobiotic supplementation helped fish cope with stressful conditions such as poor water quality and high stocking densities. Herbal extracts appeared to mitigate the negative impacts of these stressors on fish health and performance.
4. Conclusion
After culturing O. niloticus with different water quality and stocking density risk variables, it can be inferred that herbal dietary supplements have immunostimulatory, growth-promoting, and antipathogenic properties. The supplements increased the capacity of O. niloticus to tolerate well-exceeded deteriorated water limits that cause clinical toxicities of ammonia, nitrate, and nitrite. In addition, the herbal supplements yielded improvements in growth performance, feed conversion rate, and antibacterial effectiveness compared to the positive control group. Despite the benefits of the dietary herbal extracts, prolonged stress caused a significant decrease in growth rate and mortality rates. The current study confirmed the possibility of rearing fish without changing the water for 30 days using the tested doses of dietary supplementation with all the herbal extracts and for 45 days using the tested dose of leaf marjoram extract.
Source : Fadel, A., Metwally, M. M., Hassan, H. U., Abdelmageed, A. A., Arai, T., Ahmed, M. Z., & A., M. F. (2024). Growth, immunomodulatory, histopathological, and antibacterial effects of phytobiotic-incorporated diets on Oreochromis niloticus in unchanged water. Frontiers in Marine Science, 11, 1473053. https://doi.org/10.3389/fmars.2024.1473053
