Use of Endogenous Energy Sources by Larval Turbot Scophthalmus maximus

Abstract

Yolk-sac larvae of turbot from the Baltic Sea were raised at 15, 18, and 21°C in brackish water (17‰ salinity) and larvae from the North Sea were raised at 15°C in seawater (32‰). Rate of yolk utilization and growth of larvae in length and weight were monitored. Decrease of yolk weight was correlated with time and temperature, whereas the increment of larval tissue reached a peak after 2/3 of the yolk-sac phase. During the last 24 h before the larvae acquired the ability to feed, they suffered from energy deficiencies. North Sea larvae, which floated passively at the surface of full-strength seawater, consumed yolk less rapidly than Baltic Sea larvae, which sank in water of 17‰ salinity and had to swim. Yolk-utilization efficiencies (percentage of yolk energy transformed into tissue energy) were highest in seawater at 15°C (72%) and lowest in brackish waters at 21°C (51%). Efficiencies decreased with time during development under all experimental conditions.