Selected herbs as growth promoters in aquaculture

INTRODUCTION

Plants depict a significant part of the chemo-diverse planet. Many plants are desired for a wide variety of uses such as food, pharmaceuticals, and cosmetics. Present studies have shown antiviral, antifungal, and antibacterial activities of a large variety of plants in animal husbandry and aquaculture. Proper nutrition and supplementation of fish diet can affect our health status and can decide the quality of life on a physiological level.^[1]

Fish consist of vast nutrients that are required for our bodies to run efficiently. To sustain and produce aquaculture, we require rigorous planning, which entails new and natural approaches. Numerous studies have previously depicted the promoting effects of medicinal herbs in aquaculture.^[2,3] They are proved to increase the growth and performance of cultured fish.^[4,5] In addition, they can promote fish’s immune system, resulting in milder diseases with less mortality and economic loss.^[4-6] Although they are not a drug, these raw or extracted products have antimicrobial effects that can limit pathogens and improve fishes’ immune systems.^[7,8]

There are several reports on the antimicrobial resistance in aquatic pathogens resulting from the extensive use of antibiotics.^[9-11] These benefits for fish farmers and the consumers justify the use of plant-derived products in aquaculture. Furthermore, the application of such natural methods to prevent infectious diseases in fish farms will result in safer products for consumers.^[3,12] In this paper, we tried to address the benefit of selected plants mostly used in previous research, with a focus on their growth-promoting effects.

ECHINACEA

Echinacea purpurea is an important member of the Asteraceae family. This herb can mainly be found in North America; however, it is also found across the globe. This plant is more commonly used among the native people of North America as a therapeutic for infections, trauma, inflammation, and fever. Most of the plant’s immunostimulatory substances exist in the root and are extracted to be used orally and topically.^[16] Alongside its immunostimulatory effects, WG has been observed in a variety of studies. Aly et al.^[17] conducted a study to assess the efficiency of Echinacea in tilapia fish. Aside from this, they evaluated the SGR and body gain. Their study resulted in significantly higher SGR in treated fish in the summer months. On the contrary, not much difference was noted when the same diet was supplied during the winter period. The SGR and CF also had positive modifications (0.29 SGR and 0.14 CF) in Poecilia reticulata fed with E. pupurea supplementation. In the same study, fish length was observed to increase a total of 0.6 mm.^[17] This mode of action can be attributed to the enhancements in digestive system functions.^[18] SGR was also seen to increase (0.35 SGR) and FCR to decrease (0.9 FCR) in Somayeh et al.’s (2011) study where they fed Oncorhynchus mykiss with dietary E. purupurea. Mesalhy et al. (2007) observed similar results when they conducted studies similar to ones mentioned on O. niloticus fish.

GARLIC

Garlic is considered an immunostimulant. It contains immunomodulatory ingredients such as allicin. Allicin is known to boost the immune system and also is considered an odor stimulant to increase tilapia fish response.^[18,19] The daily growth rate maximized when tilapia fish were fed with 1% garlic in feed and surprisingly dropped when they were treated with 3%, and 5% garlic in feed. Subsequently, the absolute WG had a similar pattern when fish were treated with the abovementioned feeds.^[18] Another study displayed the same pattern when it came to modifying Benni fish diet with garlic. They emphasized that the fish fed with 10 kg^–1 of garlic powder had major augmentation unlike any other.^[19] Nabil et al. (2010) investigated the effects of fresh and dry garlic in Nile tilapia. They administered garlic orally via dietary modification and evaluated specific parameters. Their results signified a maximum total WG of 89.76 g, daily WG of 0.58 g; the SGR of 4.81, and a survival rate of 93.89%. The fish that were administered dried garlic (56/kg) were considered to have the best FCR (ratio). A variety of studies with similar procedures were conducted by Dong-Hoon et al. (2012) in which they all observed augmentation of weight parameters such as SGR, TWG, and decrease in CF whilst remaining above 1.0 to signify healthy fish status. Fish that were used in their study included Acipenser ruthenus, and O. mykiss, respectively.

THYME

Thyme belongs to the Labiate family. This common herb places its roots in the Eurasian and Mediterranean regions. Historically, thyme has been used as a medicinal herb in some regions and a cooking additive in others. This plant not only carries a great taste and fragrance but also contains immunomodulatory effects that can affect the immunohistological response a living organism shows to pathogens.^[11]

To understand the vast effects of thyme on WG, Mohiseni, et al.^[24] administered Shirazi thyme (Zataria multiflora Boiss) in common carp fish. PWG and feed conversion efficiency (FCE) were observed to augment similar to protein, Cholesterol, and Glucose profiles. In an experiment, Al Safah et al.^[25] signified that the maximum growth rate increase was seen in fish (Cyprinus carpio) fed with 1.5% enriched thyme. This group even succeeded the fish that were fed with a greater amount of enriched thyme (2%). This signifies that the herbal enrichment-growth rate is not linear; thus specifying the exact amount of thyme to feed fish as an additive is highly important. In their study, Oana et al. (2015) depicted WG from different parameters and observed and analyzed length increase in the studied fish.^[26] In a recent study, the effect of a combined plant (Mentha longifolia, Thymus carmanicus, and Trachyspermum copticum) on growth performance, immune responses, and key immune gene expression of rainbow trout. This is the first and the only study on the effects of T. carmanicus plant on fish. This plant is grown in the central parts of Iran, with a high carvacrol level that can affect fish maintenance. According to the results, growth parameters including FCR and digestive enzymes were improved. Immunological responses such as lysozyme and ACH50 were significantly improved and stress biomarkers decreased. The key Immune-related genes were significantly up-regulated in the fish that received 3% medicinal plants, compared to other treatments. Furthermore, antioxidant enzyme coding genes were strongly up-regulated in the fish that were supplemented 1 and 3% of the combined plants. Raissy et al. have suggested that 1% inclusion of the mixture of M. longifolia, T. carmanicus, and T. copticum (T2) can be used to improve the growth and immunity of rainbow trout.^[27]

CONCLUSION

Herbal extracts have the potential to be used as key nutritional supplements in aquaculture. Each herb consists of a specific composition and affects living organisms in different methods. Some herbs like E. purpurea and garlic have been observed to have immunostimulatory effects, while herbs such as A. vera tend to be used in the cosmetic industry more commonly. Alongside these benefits, these plants were also identified to have stimulatory effects on growth parameters in various types of fish. These parameters included SGR, WG, PWG, FCR, and FCE. The outcome of these studies depicted that A. vera, Echinacea, Garlic, Peppermint, and Thyme all have positive effects on growth parameters when administered in a specific dosage.