Study of Caligus minimus (Otto, 1821), (Caligidae Copepoda) infections of the sea Bass Dicentrarchus labrax (L.) in Bardawil lagoon.

Abstract

Caligus minimus (Otto, 1821) is a common parasite of Dicentrarchus labrax in Bardawil Lagoon and it also occurs sporadically on D. punctatus in this lagoon. It has also been found on D. labrax which were recently established in the Gulf of Suez. The incidence as well as the intensity of infection showed a distinct pattern of seasonal variation with maximum levels during winter and early spring and lowest levels of infection during summer and early autumn. Overall infection levels also showed distinct annual variation. Occurrence of larval stages on the fish followed the seasonal pattern observed in infections by adults copepods. The highest occurrence was observed every year in May. However, at any month of the year ovigerous females, and at least a few copeptides or chalimi may be found. Spatial distribution of infection among the fish was significantly contagious and with some exceptions followed the Poisson log normal distribution. However, the magnitude of overdispersion showed distinct seasonal fluctuations, with more extreme overdispersion in summer and autumn. These fluctuations apparently resulted from the diversity of temperature and salinity conditions in the lagoon which were most extreme during the summer and autumn. Positive correlation between host size and infection was evident only in the winter and spring months with highest levels of infection in the largest fish. Female copepods usually out number male copepods. The dominance of female over males was also evident in the preadult stages.