Comparative energetics during early development of two marine fish species, Solea senegalensis (Kaup) and Sparus aurata (L.)

Growth, energy content, ingestion and respiration rates and energetic effic iencies were measured in the larvae of two marine fish (Solea senegalensis and Sparus aurata) whose eggs have a similar diameter (approximately 1 mm) and energy content (approximately 1 J), but whose larvae reach a quite diff erent mass after the first month of life. Experiments were carried out in p opulations reared under the same conditions in the laboratory during the fi rst month after hatching. Solea senegalensis grow from hatching to the star t of metamorphosis (approximately day 14) at twice the rate of Sparus aurat a (specific growth rate for Solea senegalensis 0.25 mug day(-1); specific g rowth rate for Sparus aurata 0.12 mug day(-1)). The tissues in Solea senega lensis larvae accumulated energetic reserves that were used during metamorp hosis, which occurred during the third week after hatching. Ingestion and r espiration rates differed in the two species during the experimental period , Although Solea senegalensis continued eating during metamorphosis, the sp ecific ingestion rates decreased during the process. Nevertheless, no great differences in specific ingestion rates and rates of oxygen consumption we re observed when comparing the same larval mass range. Larvae of both speci es showed an allometric relationship between respiration rate and biomass, The energetic efficiencies calculated in the present study denoted differen t metabolic patterns in each species. In Solea senegalensis, the energy use d for growth increased progressively during the larval (pelagic) period and then, from the first signs of metamorphic transformation, remained almost constant. In this species, the energy allocated to growth was greater than that allocated to metabolic processes. Sparus aurata invested less energy i n growth than in metabolic processes and displayed a constant energy alloca tion throughout the experimental period. During the first month after hatch ing, Solea senegalensis always allocated more energy for growth than did Sp arus aurata.