The Way to Accessible Fish is through its Gastrointestinal Tract

Fish is a source of low-calorie, highly proteinaceous food rich in essential vitamins and polyunsaturated fatty acids (PUFAs), making it an essential component of a healthy diet. In recent years, the output from capture fishery has stagnated, making aquaculture the primary source of fish we eat. However, the fish from aquaculture comes at a higher cost than capture fishery, mainly due to expenses associated with fish feed, which contributes 50 – 60 % of the operational cost of an aquaculture farm. My lab integrates the concepts of animal physiology with nutritional biology to develop cost-effective feed for better growth and other functions such as colour enhancement, disease and stress mitigation. To this end, we are currently working on three major areas; i) development of functional feed, ii) replacement of costly feed ingredients with locally available cheaper ingredients, and iii) development of a vitamin-mineral mixture to increase the nutritional value and efficiency of farm-made fish diets. We have identified that Hibiscus flower extract through diet can modulate fish energy metabolism and reproductive performance. The Hibiscus extract, equivalent to 1000 µg polyphenols/ Kg of diet, improved fish growth performance, translating into better feed efficiency and dietary protein utilization. Improved dietary efficiency was also associated with reduced fat deposition in the fish muscles, suggesting improved utilization of dietary energy by the fish. The dietary treatment also increased fecundity, although with reduced ova diameter compared to the control. Improved dietary efficiency and protein utilization can reduce the operational costs of an aquaculture venture. Also, the flowers were procured from the temple waste, and thus their use in feed offers an effective strategy to convert waste into dietary protein. Regarding finding the alternatives for costlier feed ingredients, we are using Azolla pinnata as a potential candidate. Due to its symbiotic association with cyanobacteria, Azolla can fix atmospheric nitrogen and accrete 20–22 % of protein (w/w; dry weight basis). However, Azolla is deficient in essential amino acids – especially methionine. Our results have demonstrated that Azolla, with suitable methionine supplementation, can substitute 20 % of oil cakes in fish feed. Since oil cakes are costlier, available only in a particular season of the year, and in high demand from the cattle industry, their replacement can also substantially reduce feed cost. Our lab is in the process of registering a vitamin-mineral supplement formulated especially for carps. The formulation is based on extensive set of information made available by toxicologists and biologists on uptake mechanism and physiological interactions of micro and macronutrients in fish.