An integrated assessment of gross marine protein sources used in formulated microbound diets for barramundi (Lates calcarifer) larvae

A series of three feeding trials was conducted to determine the influence of different marine protein sources on growth, survival and thyroid hormone (T3 and T4) levels in barramundi larvae. Experimental diets including various proportions of fish meal, squid powder, mussel meal and krill meal were assessed in 14-day feeding trials. The suitability and appropriate inclusion levels of these protein sources for microbound diet formulations were assessed in an integrated manner, relating protein quality indices (amino acid profile and digestibility) to larval performance indices (growth, survival and thyroid hormone level) to elucidate mechanisms underlying the nutritional regulation of growth promotion in Lates calcarifer. Larvae fed diets containing a combination of fish meal and squid powder showed greater growth than larvae fed diets containing either mussel meal or krill meal. Larvae fed diets containing a 9:1 ratio of fish meal to squid powder, on a gross protein basis, had a higher final mean dry weight than those fed all other diets except the diet containing an 80:20 ratio of fish meal to squid powder, which had an intermediate value. Fish meal and squid powder were found to have a high nutritional value as protein sources for L. calcarifer larvae, by virtue of a synergistically favourable amino acid profile, moderate to high digestibility and low water solubility. The digestibility of squid powder was found to be significantly higher than that of fish meal, indicating that further development of this diet may benefit from processing techniques to increase fish meal digestibility. Thyroxine (T4) levels were found to relate strongly to growth, but did not relate specifically to any particular dietary composition, indicating that T4 is an appropriate indicator of growth performance in L. calcarifer larvae, though may not directly and quantitatively mediate nutritional growth promotion