Dietary strategies to improve the growth and feed utilization of barramundi, Lates calcarifer under high water temperature conditions

Several dietary strategies to ameliorate poorer growth observed to occur at temperatures above the upper thermal optima were examined with juvenile barramundi (Lates calcarifer). A reference (REF) and three experimental diets, one with an increased protein to energy ratio (PRO), another with an increased level of the amino acid histidine (HIS) and a third with supplementation of dietary nucleotides (NUC), were each fed to fish at either 30 degrees C or 37 degrees C for a 28-day period. Growth was affected by both temperature and diet. Fish fed the PRO diet at 30 degrees C grew fastest, but not faster than those fed the NUC diet at the same temperature. The addition of the amino acid histidine to the diet did not improve growth rates at either temperature. At water temperatures of 37 degrees C, only the fish fed the PRO diet had growth rates equivalent to those of fish at the 30 degrees C temperatures. Other key factors including feed intake, feed conversion rate, nutrient and energy retention and plasma enzymology were also all affected by temperature and diet. This study shows that the use of a diet with an increased protein to energy ratio provides significant benefits in terms of reducing the impact of growth retardation at higher temperatures.