L-carnitine and its attributed functions in fish culture and nutrition - a review

This review summarizes the different studies on L-carnitine supplementation and its various attributes in fish culture and nutrition. Based on its role in vertebrates, the use of L-carnitine supplementation in fish diets in aquaculture has been advocated for multi functional purposes: as a growth promoter, specifically aiding in the utilization of high fat levels in the diet and thus providing a protein sparing effect; providing protection against toxic levels of ammonia and xenobiotics; alleviating stress related to water temperature extremes and facilitating better acclimation to water temperature changes. Levels of dietary L-carnitine supplementation examined ranged from a few hundred to over 4000 mg/kg of diet. The studies on fish exhibit conflicting results: in a number of cases L-carnitine supplementation led to better growth and changes in lipid utilization while in others no effect could be detected. Contradicting results have been reported even with the same fish species. Explanations are provided in an attempt to clarify the discrepancies. Cost effectiveness is an important issue to be considered, and even in cases where L-carnitine has shown positive effects, the levels of this rather expensive substance required might not be economically justifiable. (c) 2005 Elsevier B.V. All rights reserved.