Tilapia culture has emerged as a convenient and highly profitable fish farming in over 120 countries . It has shown an 11% annual growth during 1987–2017 . In 2017, FAO (2019) ranked tilapia as the 4th most popular culture fish and included in the top 10 aquaculture producing fish species group. This trend is guiding researchers to explore various growth improvement techniques in tilapia to bridge the demand and supply gap. Fish growth is linked to multiple factors, including plausible environmental conditions, availability of feed ingredients, growth-promoting system, and management.
The recent studies have shown the importance of micronutrients that promote fish growth by improving the activity of endogenous digestive enzymes (DE) during the digestion process of fish feed. Selenium is a micronutrient indispensable for the steady growth of fish. However, it is an exceptional example of a nutritional paradox; being essential at lower quantity but toxic if slightly higher. It is an antioxidant in stress defenses and an integral for DNA and proteins. For instance, it has been observed to perform an essential functions in maintaining enzyme and the immune system. It is an essential constituent of the glutathione peroxidase (GPX) enzyme, which acts as an active antioxidant against reactive oxygen species. The optimal level of selenium in fish ranges between 0.21 and 1.18 mg/kg of feed. It is an essential ingredient of selenoproteins, which are vital to living organisms. Therefore, provision of dietary selenium at optimal levels promotes fish tolerance to environmental stresses. That is why, in aquaculture, selenium acts as a balancing micronutrient that improves the nutritive profile of fish feed .
The level of enzymatic secretions could be used as indicators of digestion, nutritional status, and regulation of feed and feeding strategies in fish. Therefore, estimation of the DE activity is of particular concern due to their crucial role in fish growth and uptake of nutrients . The DE activity ultimately guides the fish nutritionists to determine the appropriate inclusion levels of carbohydrates, lipids and proteins in fish diets. The aim of this study to evaluate the growth performance of juvenile tilapia and intestinal enzyme activity under the impact of supplemental selenium.
In conclusion, the results have confirmed hypothesis that selenium in fish feed acts as a growth enhancer in juvenile tilapia. The fish displayed weight and length gains, better FCR and SGR under 2 mg Se/kg. The growth results were further supported by the gut enzymes activity at the lower level selenium and vice versa. The fish exhibited arrested growth in selenium-deficient treatment with the lowest enzyme activity. This study provides interesting findings on the inclusion of selenium in fish feed to boost growth and DE activity. Therefore, we recommend tilapia farmers adopt 2 mg/kg of selenium in fish feed to boost their production and revenue generation.