Fish productivity in aquaculture is affected by disease-causing microorganisms. To treat the diseases, antibiotics are used. But indiscriminate use leads to antibiotic resistance in the microorganisms.
Instead of using antibiotics, we could improve the resistance of aquaculture fish to infections using immune-stimulants to activate immune responses to the infections.
Recently, researchers at the Karnataka Veterinary, Animal and Fisheries Sciences University, Mangalore used bay laurel leaves for the purpose. The leaves are rich in secondary metabolites with antimicrobial, wound-healing, and neuroprotective properties.
Bay leaves from Laurus nobilis tree. Image: Benjamint444 via Wikimedia Commons
The team grew Nile tilapia, a popular fish in the aquaculture industries, to test the idea of adding bay leaf powder to fish food. To get baseline information about the nutrient content of the fish food, they measured the food’s protein, carbohydrate and lipid levels. Adding bay laurel leaves, they found, made no significant difference to the nutrient quality of the diet.
Tilapia, Oreochromis-niloticus Image: Bjørn Christian Tørrissen via Wikimedia Commons
They added different amounts of powdered bay laurel leaf to the fish diet and fed it to different groups of young tilapia fingerlings. Throughout the experiment , the researchers monitored the quality of the water in which the fish were kept by measuring the water’s physicochemical parameters.
Tilapia fingerlings fed on the diet with bay laurel leaf powder at 15 grams per kilogram of body weight showed a significant increase in antioxidant levels, improved blood serum parameters and an activated immune system. This led to an increase in body weight.
To test the immuno-stimulant property of the bay leaf supplement, the team infected the fish with Aeromonas hydrophila, a bacterium that causes disease in freshwater fish, a major threat in aquaculture. Bay laurel leaf powder at 15 grams per kilogram of body weight in the diet protected the fish from the pathogen and promoted 100 per cent survival.
Aquaculture farmers can now start experimenting with bay leaf powder in fish feed to improve profits.
DOI: 10.1007/s10695-023-01210-8;
Fish. Physiol. Biochem. Online ahead of print, July 2023
Reported by M. S. Shivakumar,
Periyar University, Salem
*This report was written during the fourth online workshop on science writing organised by Current Science.
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