Importance of food availability for growth of juvenile southern flounder (Paralichthys lethostigma) in the Pamlico River Estuary, North Carolina, USA

Results presented in an earlier paper showed that differences in temperature and salinity could explain approximately 30% of the variability in growth rates of juvenile southern flounder (Paralichthys lethostigma) in different creeks of the Pamlico River estuary. In addition, the maximal growth rate was lower than expected from published laboratory results, suggesting food limitation. In the present paper, the obtained mean and maximal growth rates are related to simultaneously collected data on the amount of food available in the creeks. Thirteen different groups of food items were observed in the stomachs of the flounder. Most of the stomachs of flounder collected outside the cages contained only mysids (65 to 75%). Inside the cages, 25 to 45% of the flounder stomachs contained only mysids, while 85 to 100% of the stomachs contained both mysids and other food categories. Individual growth rates of the founder were only significantly related to the number of mysids in the stomachs, and not to any of the other food categories. Stomachs of other fish species mostly showed food categories other than mysids. This indicates that interspecific competition for food did not occur. The four creeks of the cage experiment showed significant differences in abundance of mysids. However, in only one of the two trials the abundance of mysids was significantly related to the observed growth rates. It can be concluded that mysid abundance does not unequivocally explain the variability in growth rates of juvenile southern flounder in low salinity nursery areas of Pamlico Sound, and that the hypothesis of food limiting maximal growth is not supported by the results of this study.