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Activities of the digestive enzymes and concentrations of thyroid hormones and cortisol in developing embryos and yolk-sac larvae of turbot ( Scophthalmus maximus L.) were measured in this study. Results showed that the embryonic mass presented “decrease-increase-decrease-increase-decrease” trend, appearing the minimal value of 0.34 mg at 7.5 h after fertilization (HAF) before the onset of blastula stage. As for egg diameter, it increased on the whole from 1.027 mm at 0.5 HAF to 1.079 mm at 95.67 HAF. In general, digestive enzymes presented four patterns in the present work. The patterns of alkaline phosphatase (AKP), pepsin (PG), chymotrypsin (CP), trypsin (TRY), leucine aminopeptidase N (LAP), lactate dehydrogenase (LDH) and glutamic oxalo acetic transaminase (GOT) were similar, showing low level before segmentation stage followed by increases until hatching day. Besides AKP, the other enzymes reached the peaks at 2 days after hatching (DAH). Enzyme activities of acid phosphatase (ACP), lipase (LIP) and pyruvate kinase (PK) presented similar “decrease-increase” changes on the whole. Leucine-alanine peptidase (LAPP) was detected from fertilized eggs onwards, increased till 86 HAF at segmentation stage and then decreased thereafter. Amylase (AMY) activity was undetectable before gastrula stage and presented upward tendency thereafter. T 3 concentration declined to the lowest value of 61.82 ng/g sample at 3.17 HAF and exhibited “increase-decrease-increase” patterns during cleavage stage, then it elevated markedly until 29.5 HAF, and then maintained high stable levels before the onset of yolk-sac larval days, reaching the highest value of 220.62 ng/g sample at 72.5 HAF, followed by obvious decline until the end. T 4 concentration showed opposite tendencies to that of T 3 before segmentation stage with the maximal value of 160.95 ng/g sample at 39.17 HAF and the minimal value of 85.94 ng/g sample at 24 HAF, and remained high levels before 0 DAH, followed by a slight decrease thereafter. Cortisol concentration presented three obvious declines during 2.67–4.67 HAF, 5.67–9.67 HAF and 10.67–24 HAF. The maximal value was 147.86 ng/g sample at 5.67 HAF and the minimal value was 73.60 ng/g sample at 24 HAF, respectively. The above results are very valuable to illuminate the evolvement of enzymes and hormones to better understand their functions during endogenous nutritional periods and serve as a basis for future related studies in this fish. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]