Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino : II. Amino acid composition of abalone and six species of macroalgae with an assessment of their nutritional value

This study was conducted to evaluate the nutritional value of protein in natural feeds for the two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. The amino acid compositions of 6 species of macroalgae ( Ulva lactuca, Chondrus crispus, Palmaria palmata, Alaria esculenta, Laminaria digitata and Laminaria saccharina) and of the whole soft body of these abalone were determined and compared. The effects of these algal diets on the free amino acid (FAA) profiles in the viscera and muscle of animals were investigated. To find a suitable index to evaluate the protein quality of natural diets for algivores, several indices were computed and correlated to the growth performance of abalone using correlation analysis. These two species of abalone have a very similar amino acid composition, indicating that they may have similar amino acid requirements. In all the selected algae, arginine may be the limiting amino acid, and in some instances methionine, threonine or histidine may be also limiting. Judging from the results of feeding test and amino acid analysis, P. palmata and A. esculenta seem to have the better amino acid pattern and availability among the selected algae. On the other hand, U. lactuca and C. crispus appear to be poor in their amino acid availability and/or pattern. Dietary treatments significantly affected the FAA profiles in animal tissues. The essential amino acid index (EAAI) and the degree of similarity (DS) of EAA patterns may not be applicable to evaluating the nutritional value of protein in natural feeds for the algivorous molluscs. Among the indices examined, the newly proposed index—balance and adequacy of free EAA in viscera (BAEAAv)—seems to be suitable for estimation of protein quality of natural feeds for abalone, because it takes into account the balance, adequacy and availability of EAA in natural diets.