Total lipids, lipid classes and their associated fatty acids were quantified in developing eggs, yolk-sac larvae and starving larvae (from day 1 to day 5 after hatching) of the Senegal sole,Solea senegalensis Kaup. Larvae during early development and starvation consumed about 0.6% of its dry weight per day, mainly due to lipid catabolism. There was a net consumption of approximately 1.7% total lipid per day, and a net energy utilization of 1.3 kcal g(-1) dry weight biomass day(-1), mostly derived from lipid depletion. The overall decrease of total neutral lipids (mainly triacylglycerols and sterol esters) was 3.4 faster than that of total polar lipids (primarily phosphatidylcholine), with rates of 29.2 and 8.7 μg mg(-1) dry weight biomass day(-1), respectively. There was a concomitant increase in PE, PS and phosphatidic acid during the period under study. Total saturated and total monounsaturated fatty acids were catabolized (primarily 16∶0 and 16∶1 (n-7)) as energy substrates at rates of 7.4 and 10.9 μg mg(-1) total lipid day(-1), whereas total PUFAs were conserved. DHA was specifically retained in PE, whereas EPA and DHA were catabolized in PC and triacylglycerol. Total DMA and AA contents in total lipid increased during early development and starvation. The data denote a pattern of lipid metabolism during early development of Senegal sole similar to that of other marine larval fish, with eggs containing high amounts of total lipids (presence of oil globule/s), from temperate waters and with short developmental periods; the pattern contrasts with fish larvae from eggs of cold water fish species that contain low levels of total lipids (lack of oil globule/s) and have long developmental periods.

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Thyroid hormone-induced metamorphosis seems to represent an ancestral feature of chrordates (urochordates, cephalochordates and vertebrates), but also of nonchordate animals. Although thyroid hormones and thyroid hormone receptor profiles during metamorphosis have been analyzed in different vertebrate taxa, including fish, developmental expression and activity of type 2 (dio2, D2) and type 3 (dio3, D3) iodothyronine deiodinases, two key enzymes in anuran metamorphosis, remain unknown in any fish species. The aim of this work was to investigate the development of thyroid hormone system during the metamorphosis of a flatfish species, the Senegalese sole, focusing on the deiodinases developmental profile. We have cloned sole D2 and D3 and analyzed several parameters of thyroid hormones system in pre-, early-, middle-, and late-metamorphic larvae. Both deiodinases contain in their catalytic centers an UGA triplet encoding for a selenocystein (Sec) residue as expected. Left eye migration and rotation in body position were associated with a significant increase in both thyroid hormones and thyroid hormone receptors at the middle-late metamorphic stages. Although dio2 expression slightly increased during metamorphosis, D2 activity augmentation was much more significant. Sole dio3 expression declined only slightly, whereas the D3 activity clearly decreased at mid-late metamorphic period. This developmental profile of deiodinases sustained the rise of thyroid hormones levels observed during sole metamorphosis. No clear cut daily rhythms were observed in the parameters analyzed although it seemed that thyroid hormone system was more active during daytime, in particular at late metamorphic stages. These developmental changes point out the importance not only of thyroid hormones and their receptors but also of dio2 and dio3 in mediating flatfish metamorphosis, as it has been described in amphibians.

The objectives of this experiment were to (i) determine the efficacy of essential oils of clove (CO) and Lippia alba (EOLA) to induce deep anaesthesia in juvenile specimens (49.0 AE 6.2 g body mass, 16.6 AE 0.8 cm; n = 8 per treatment) of meagre (Argyrosomus regius); and (ii) study the feasibility of these substances, together with 2-phenoxyethanol (2-PHE), as potential sedatives [low concentration: (i) EOLA: 12 mg L À1 ; (ii) CO: 1 mg L À1 ; and (iii) 2-PHE: 33 mgÁL À1 ; n = 8 per treatment] for live fish transport of this species. All test were performed at a constant temperature (18°C). Thus, the main primary stress indicator (plasma cortisol) and secondary factors (plasma metabolites) were evaluated. In addition, growth hormone (GH) mRNA expression was also evaluated in the pituitary gland. The results indicated that EOLA is considered to be effective for deep anaesthesia when the concentration is close to 160 mg L À1 , while CO produces the same effect when lower concentrations are added (40-50 mg L À1 ). Regarding sedative concentrations, a significant~3-fold increase in plasma cortisol levels was detected in the EOLA group when compared to control specimens. In addition, glucose levels were not reduced and significantly increased (~1.6-fold) for 2-PHE in relation to the control fish. None of the anaesthetics promoted a significant difference for GH expression with respect to the control group, but a significant~2-fold increase for 2-PHE treatment with respect to the EOLA exposition was found in this gene expression. Results show that none of the anaesthetics analysed, at least in the ranges of concentrations used in this study (EOLA 12 mg L À1 , CO 1 mg L À1 , 2-PHE 33 mg L À1 ), are recommended for live fish transport, as shown by the absence of inhibition on the stress parameters assessed.