Differences in growth rates of juvenile Solea solea and Solea senegalensis in the Tagus estuary, Portugal

The growth patterns of juveniles of Solea solea and Solea senegalensis were compared, within the nursery areas of the Tagus estuary. Growth was estimated by modal progression analysis of length-frequency data, using the Bhattacharya method based on 1327 and 3255 individuals of S. solea and S. senegalensis, respectively. For the two species several cohorts of the same age-group were identified, being the number relative to S. senegalensis higher compared to S. solea. 0-group individuals of S. solea begin to occur within the nursery in May, while for S. senegalensis the recruitment is longer (from June to October). The number of individuals of the first cohort was higher relative to those belonging to the subsequent cohorts. The growth rate of S. solea juveniles varied from 0.01 mm d(-1) to 1.51 mm d(-1) and that of S. senegalensis was between 0.22 mm d(-1) and 0.89 mm d(-1). Although no significant differences were found when comparing growth rate values determined for the different cohorts, age-groups and species, it was noticed that the estimates determined for cohort I were generally higher at the beginning of the nursery colonization period. The differences in the seasonal variation of growth rate of S. solea and S. senegalensis reflected their spawning behaviour and time spent in the plankton and also their differential habitat use pattern.