14 SEPTEMBER 2012 Aquaculture in Asia has grown substantially in recent years. As aquaculture production has intensified, the incidence of disease, including various infectious diseases, has increased, resulting in dramatic economic losses. Hormones, antibiotics and vitamins are common medicines listed in farmers’ handbooks for fish and shrimp disease treatments. Farmers are often unaware of or deliberately ignore the important factors and precautions for use of these substances, such as proper application method, dosage and side-effects. Consequent misuse of these chemicals has led to the appearance of drugresistant bacteria and environmental degradation, which is harmful for humans and aquatic animals. Although chemicals have been tested as growth promoters, antibacterials and other purposes (Jayaprakas and Sambhu 1996), they cannot be recommended in commercial mariculture because of residual accumulation in the edible tissues of fishes and prawns. The use of antibiotics in shrimp hatcheries has resulted in tissue biomagnification that in turn leads to rejection of the total consignment during export. The Marine Product Export Development Authority of India has instructed hatchery operators and farmers not to use antibiotics such as chloramphenicol, nitrofurans (including furazolidone, nitrofurazone, furaltadone, nitrofurantoin, furylfuramide, nifuratel, nifursoxime, nifurprazine and all their derivatives), neomycin, nalidixic acid, sulphamethoxazole and related formulations, chlorpromazine, colchicine, dapsone, dimetridazole, metronidazole, ronidazole, ipronidazole and other nitroimidazoles, clenbuterol, diethylstilbestrol, sulfonamide (except approved sulfadimethoxine, sulfabromomethazine and sulfaethoxyrpyiadine), floroquinolones and glycopeptides. Many of these are currently used in hatcheries and farms (Sanandakumar 2002). Globally people understand the adverse effects of antibiotics and are now shifting to natural products (Fauci 1993). Plants are storehouses and sources of safer and cheaper chemicals. The practice of herbal medicine dates back to the very earliest period of known human history. There is evidence of herbs having been used in the treatment of human diseases and for revitalizing body systems in almost all ancient civilizations (Aftab and Sial 1999). The majority of herbal plants are safe and economical. Generally use of plant extracts does not lead to drug resistance. Herbal preparations are known to play an important role in disease control because they contain active ingredients with antioxidant, antimicrobial, antistress, growth promotion, appetite stimulation, tonic and immunostimulation, and aphrodisiac properties. These properties are related to plant compounds such as alkaloids, flavonoids, pigments, phenolics, terpenoids, steroids and essential oils. The application of herbal medicine has been used in laboratories and reported in papers with little field practice. Some farmers have experience with this treatment method but have far to go to apply it on a large scale. This article summarizes the major applications of herbal biomedicine in aquaculture production systems. Antioxidant Properties Antioxidants help organisms deal with oxidative stress caused by free radical damage. Free radicals are chemical species that contain one or more unpaired electrons, causing them to be highly unstable and damage other molecules by extracting electrons from them to attain stability. Reactive oxygen species (ROS) formed in vivo, such as superoxide anion, hydroxyl radical and hydrogen peroxide, are highly reactive and potentially damaging transient chemical species. These are continuously produced in the human body, inasmuch as they are essential for energy supply, detoxification, chemical signaling and immune function. The ROS are regulated by endogenous superoxide dismutase, glutathione peroxidase and catalase. Induced by exposure to external oxidizing substances or a failure of defense mechanisms, an over-production of ROS causes damage to cell structures, DNA, lipids and proteins (Valko et al.2006) that increases the risk of more than 30 diseases (Aruoma 1998). Flavonoids and phenolic acids, widely present in higher plants, are effective against the deleterious effect of ROS. Some compounds in basil (Ocimum) possess strong antioxidant activity (Middleton and Kandaswami 1993). Cinnamon has antioxidant activity comparable to that of the synthetic antioxidant butylated hydroxytoluene (BHT) (Middleton and Kandaswami 1993). Antimicrobial Activity Many phenolics, polysaccharides, proteoglycans and flavonoids can play a major role in preventing or controlling infectious microbes. Guava (Psidium guajava) has antibacterial activity against Vibrio and Aeromonas hydrophila at minimum levels of 1.25 and 0.625 mg/mL, respectively. Guava eliminates Herbal Biomedicine – an Alternative to Synthetic Chemicals in Aquaculture Feed in Asia Thongam Ibemcha Chanu 1, Arun Sharma 2, S. Dam Roy 1, Ajit Keshav Chaudhuri 1 and Pradyut Biswas 3 Herbs play an important role in disease control because they contain active ingredients with antioxidant, antimicrobial, antistress, growth promotion, appetite stimulation, tonic and immunostimulation, and aphrodisiac properties.
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