Changes of biochemical compositions during development of eggs and yolk-sac larvae of turbot Scophthalmus maximus

Abstract In the present study, biochemical compositions changes and the related digestive enzymes activities were analyzed during development of eggs and yolk-sac larvae of turbot Scophthalmus maximus . Results showed that activities of pepsin and chymotrypsin increased on the whole, although small decreases occurred at gastrula stage. Trypsin activity presented the minimal value of 25.72 U/mg protein at blastula stage followed by obvious increase thereafter. Amylase activity was not detected until gastrula stage and increased later. As for lipase, it kept fluctuant tendency. The changes of digestive enzymes activities revealed the biochemical compositions dynamics. Both essential amino acids (EAA) and non-essential amino acids (NEAA) increased to the peak at blastula stage and decreased thereafter. Furthermore, the main components were leucine, lysine, valine, arginine and phenylalanine in EAA, and glutamic acid, aspartic acid, alanine and proline in NEAA. Free essential amino acids (FEAA) and non-essential amino acids (FNEAA) contents presented similar patterns of “decrease-increase-decrease-increase-decrease” as development went on, showing the maximal value of 271.00, 133.00 μg/g weight respectively at hatching day. Meanwhile, the main components were leucine, valine, threonine and lysine within FEAA, and alanine, tyrosine and serine within FNEAA. Regarding fatty acids contents, the quantitatively predominant fatty acids were C16:0 in saturates fatty acids (SFA), C18:1n-9 in monounsaturates fatty acids (MUFA), and C18:2n-6, C20:4n-6 (ARA) as well as C22:6n-3 (DHA) in polyunsaturates fatty acids (PUFA). Considering the utilization, there existed the preferential consumption of the unsaturated fatty acids (UFA) from cleavage to blastula stages, from segmentation stage to hatching and from 1 days after hatching (DAH) to 2 DAH, and SFA in other periods. Within the UFA, PUFA were consumed at a higher rate than MUFA from cleavage stage to blastula stage as well as yolk-sac periods, while MUFA were used at a more rapid rate during the other days. As for the individual fatty acids, there was a preferential consumption of C16:0, C16:1n-7 and C20:5n-3 during ontogeny. Overall, the changeable biochemical compositions revealed that the predominant energy fuel is carbohydrates before cleavage stage, amino acids until gastrula stage and fatty acids until 2 DAH. The above results are very valuable for clarifying nutritional requirements of turbot embryos and larvae, and deeply understanding the developmental mechanism.