Ontogenetic changes in the optimal temperature for growth of juvenile marbled flounder Pseudopleuronectes yokohamae

We conducted a laboratory experiment and field collections of juvenile marbled flounder (Pseudopleuronectes yokohamae) to assess growth rates of juveniles. In the laboratory, cultured juveniles of approximately 31 and 46 mm standard length grew fastest at 20 °C, while juveniles of approximately 21 mm grew faster at 12–14 °C than at 20 °C. This result confirmed that optimal temperature for growth of juveniles changes ontogenetically. Juveniles were also collected from shallow estuaries during April to May, during which the water temperature increased from 13 to 22 °C. The increase in optimal temperature is advantageous for juveniles, because both juvenile size and ambient temperature increase as the season progresses. Growth rates of juveniles were nearly maximum under given temperatures in the field when assessed from otolith microstructure. Thus, juveniles grow at high rates in the field, although ambient temperatures are not necessarily optimal for growth.