THERAPEUTIC POTENTIAL OF BIOACTIVE COMPOUNDS FOR TREATING FISH DISEASE AND THEIR CYTOTOXIC AND GENOTOXIC EFFECTS

Aquaculture is the main source of high quality protein. Due to the growing demand for seafood and high density fish cultures, there are more disease outbreaks. Bacterial diseases like columnaris caused by Flavobacterium columnare, result in huge economic loss to aquaculture farmers. Although there are commercially available vaccines and antibiotics to control bacterial diseases, they are proven to be inefficient. Moreover, antibiotics lead to acquired resistance in bacteria, and the drug residual in fish, resulting in tight regulations for their usage. This calls for new alternative solutions that can be safe and cost-effective to prevent and treat fish diseases.

Plant extracts are well known for their anti-microbial properties and they could be potential alternative candidates. Usage of plant extracts as therapeutics is largely used for human pathologies but there is limited knowledge for the same to treat piscine disease. The anti-microbial effects of plant extracts is due to the presence of bioactive compounds like alkaloids, flavonoids, steroids, and phenols in them. They render the plant extracts, bactericidal and bacteriostatic effects against pathogenic bacteria and also induce host immunity. We have evaluated the anti-microbial properties of extracts from various herbs and spices: Cinnamomum verum, Syzygium aromaticum, Thymus vulgaris, Salvia officinalis, Curcuma longa, Zingiber officinale, Allium sativum, Allium cepa, Coriandrum sativum, Anethum graveolens against Flavobacterium columnare using disc diffusion method. Commercially available antibiotic Oxytetracycline (Terramycin^® 200), that is used to treat columnaris served as positive control. The bactericidal effects of our extracts were compared to it. We find that all the extracts (30mg/ml) we have tested, had bactericidal effects against Flavobacterium columnare (3x10⁸ CFU/ml). Interestingly, Syzygium aromaticum and Cinnamomum verum showed highest antimicrobial activity against Flavobacterium columnare with an average inhibition of 16mm and Cuminum cyminum showed 14mm, which is similar to Oxytetracycline. We have also determined the minimum inhibitory concentrations of all the plant extracts along with Oxytetracycline. We are currently testing the cytotoxic and genotoxic effects of these extracts using various molecular assays. We speculate that Syzygium aromaticum and Cinnamomum verum are potential alternative therapeutics to treat columnaris in fish that would not have regulations and be cost-effective.