THE INFLUENCE OF EGG SIZE AND INCUBATION-TEMPERATURE ON THE CONDITIONOF SOLEA-SOLEA (L) LARVAE AT HATCHING AND FIRST FEEDING

Sole (Solea solea (L.)) eggs of different sizes, spawned by a captive broodstock were held at 9, 12 and 15 degrees C. Development of the hat ched larvae was monitored until the yolk reserves were exhausted. Yolk utilization and morphometric changes were monitored during the pre-fe eding stages. Whole larva concentrations of nucleic acids (RNA and DNA ) were measured to assess their value as indicators of growth and nutr itional condition. Larvae hatching from the larger eggs had more yolk and were both longer and had deeper myotomes than those hatching from the smaller eggs. Further, more yolk remained at the time a functional jaw had developed, in larvae from the larger eggs compared with those from the smaller eggs. The temperatures investigated affected growth rate after hatching but not the relative timing of changes in growth i n length and myotome height of the Larvae. These were similar when com pared on a timescale based on the duration of embryo development at ea ch temperature. At 9 degrees C, however, the relative time of formatio n of an articulated jaw appeared to be delayed compared with larvae de veloping from the same size eggs held at 12 or 15 degrees C. There was no evidence of incipient starvation before the jaw was functional for larvae from either egg size at these temperatures, although there was shortly afterwards, particularly in larvae from the small eggs. DNA c oncentration proved to be a more useful indicator of larval nutritiona l condition than other nucleic acid ratios.