Modulation of nutrient digestibility and digestive enzyme activities in aquatic animals: The functional feed additives scenario

Considering the costs of feed costs (nearly 60% of production cost), nutrition, feeding and feed utilization are among the most important factors in commercial aquaculture. During the last decade, administration of functional feed additives has been practiced for enhancing nutrient digestibility and digestive enzyme activities of cultured fish and shellfish. Traditionally, antibiotics were used for boosting growth performance and nutrient digestibility in commercial aquaculture. However, emergence of resistance pathogens and possible risk to human health resulted in limitation or prohibition of prophylactic administration of antibiotics. Recently, there was increasing attentions towards dietary administration of functional feed additives that include probiotics, prebiotics and synbiotics for elevation of digestive enzyme activity and nutrient digestibility. The results of those studies revealed contradictory effects of different pro-, pre- or synbiotics on various fish species. It seems that the effects are species specific and related to modulation of the intestinal microbiota. In view of this issue, the present review provides a comprehensive sight on the effects of different pro-, pre- and synbiotics on digestive enzyme activity and nutrient digestibility in different species with special focus on the mode of action. In addition, the present review highlighted the gaps of existing knowledge as well as suggesting the subjects which needs additional studies.