Feeding and development of Senegal sole (Solea senegalensis) larvae reared in different photoperiods

The effects of 14L:0D and 24L:0D photoperiods on feeding activity and the development of cultured Senegal sole larvae were studied. Pre-metamorphic larvae up to an age of 8 days after hatching (DAH) depended on light to capture rotifers. Nearly 0% and less than 30% of the population had no stomach content after 10 h and 7 h in darkness, respectively. Under the permanent light regime, maximum larval feeding incidence varied with age from 67% +/- 4 (3-4 DAH) to 93% +/- 4 (7-8 DAH). However, a reduced feeding activity, with less than 24 +/- 5% of the larvae between 3 and 8 DAH capturing preys, occurred at morning hours, in spite of lights had been on overnight. Ceasing of feeding during the light phase did not occur in larvae subject to 14L 1 OD or I OR 14L photoperiods that corresponded to opposite times of the day when the dark phase was artificially applied. These results suggest the existence of a circadian feeding rhythm that can also be modified by manipulating light conditions. From 10 DAH onwards, all Solea senegalensis stages, including those metamorphosing from 12 to 20 DAH, were feeding both during light and dark phases. Food ingestion was not affected by photoperiod (P > 0.05) at any age. It increased from first feeding till the commencement of metamorphosis, reaching a stable average ingestion rate of 176 +/- 18 mu g dry food larva(-1) d(-1) for 11 to 16 DAH larvae. By the end of metamorphosis, ingestion increased to 271 +/- 21 mu g dry food larvae(-1) d(-1). The daily radon was also unaffected by photoperiod (P > 0.05). It was highest between 5 and 12 DAH, when 715 +/- 58 mu g per mg larval dry biomass was ingested by Senegal sole larvae every day. Daily rations were lower both for 3-4 DAH larvae (515 +/- 174 mu g mg(-1)) and at the initial stages of metamorphosis on days 13-14 (459 +/- 31 mu g mg(-1)), and decreased thereafter to 215 +/- 16 mu g mg(-1) throughout metamorphosis. Food conversion was similar under all photoperiods (P > 0.05), with average ratios of 3.2 for 3 to 10 DAH larvae, and 1.66 for 11 to 20 DAH individuals, respectively. Growth did not change (P > 0.05) as a consequence of photoperiod, and an average specific growth rate of 0.118 was found for pelagic stages, whereas it decreased to 0.081 for metamorphic stages. Survival was high in all instances, achieving 74.5% +/- 2.9, 81.1% +/- 7.8 and 80.0% +/- 5.2 for 14L:10D, 10D:14L and 24L:0D photoperiods, respectively. No abnormalities of development were detected in fish exposed to 14L:10D photoperiods. However, 1.8% of the total population reared in permanent illumination exhibited an incomplete eye migration after metamorphosis. (c) 2006 Elsevier B.V. All rights reserved.