Assessment of the relative bioavailability between betaine and l-carnitine for Nile tilapia

This study evaluated tilapia fed diets supplemented with levels of betaine and l-carnitine, simultaneously. Diets supplemented with levels of l-carnitine (500 and 1000 mg kg⁻¹ of feed) and betaine (500 and 1000 mg kg⁻¹ of feed) were used, in addition to the control diet. Weight gain, daily weight gain, and specific growth rate in fish fed diets containing 1000–500 and 1000–1000 mg kg⁻¹ betaine and l-carnitine performed worse than the other inclusion levels, including the control diet. The lipid content of fish fillets was higher in those fed with levels of 1000–1000 mg kg⁻¹ of betaine and l-carnitine in the diet. There was a reduction in total plasma protein levels in fish fed with 1000–500 mg kg⁻¹ of betaine and l-carnitine in the diets, and glucose was higher when fish were fed with levels of 1000–1000 mg kg⁻¹ of betaine and l-carnitine in feed. Catalase activity was higher at levels of 1000–500 mg kg⁻¹ of betaine and l-carnitine in the diet. The height and width of the villi had greater development in fish fed with 1000–500 mg kg⁻¹ of betaine and l-carnitine in the diet. Assessment of muscle histology indicated the interaction of betaine and l-carnitine at levels of 1000–500 mg kg⁻¹ of inclusion in the diet, triggering greater muscle growth. The inclusion of 500–500 mg kg⁻¹ of betaine and l-carnitine in diets improves the development of fish, providing a reduction in carcass lipids and greater muscle development, and reducing oxidative stress in the liver.