Selective growth and mortality of juvenile 0-group plaice Pleuronectes platessa in the Dutch Wadden Sea: a consequence of irreversible non-genetic adaptation during early pelagic life

In this paper, we have addressed the question of whether selective growth a nd mortality of juvenile 0-group plaice Pleuronectes platessa (L.) occurs i n the Dutch Wadden Sea as a consequence of irreversible non-genetic adaptat ion to water temperature conditions during early pelagic life. As tracers, the number of vertebrae, and of dorsal and anal fin rays were used, since t he variability in these characteristics reflects the phenotypic plasticity induced by differences in environmental conditions, and especially water te mperature, during early pelagic life. From the onset of larval immigration in March 1995, the juvenile O-group plaice population was sampled frequentl y and the variability in its meristic characteristics was analysed. The num ber of vertebrae appeared to be established by water temperature conditions during the egg stage, while the number of dorsal and anal fin rays seemed to be determined during the larval stage. As a consequence, the number of v ertebrae was not correlated with either the number of dorsal fin rays or th e number of anal fin rays, but the numbers of anal fin rays and dorsal fin rays were strongly correlated. Strong support was found for Kinne's (1962; Comp Biochem Physiol 5:265-282) 'irreversible non-genetic adaptation' hypot hesis-that the variability induced by environmental conditions during early life still expresses itself later on in juvenile life-as there was a signi ficant positive relationship in our study between growth and the number of vertebrae during the period April to July. Also, instantaneous mortality wa s positively related to the number of vertebrae. It is suggested that the r elationship with mortality results from a correlation between vertebral num ber and some important characteristic involved in avoiding predators, such as locomotory performance. Also, mean growth rate during the growing season and instantaneous mortality rate were positively correlated for each meris tic characteristic. It is argued that the relationship between growth and m ortality will vary over the years and will depend on the combination of env ironmental conditions during egg and larval stage compared to those during the subsequent juvenile stage.