Population structure of the monogenean, Paramazocraes thrissocles (Mazocraeidae) on the gills of clupeoid fish, Thryssa mystax of Visakhapatnam coast, Bay of Bengal.

An investigation was undertaken on the population biology of the mazocraeid monogenean Paramazocreas thrissocles occurring on the gills of the engraulid fish Thryssa mystax at Visakhapatnam coast , Bay of Bengal. The influence of season and host size on the parasite population density and the dispersion pattern of the parasite in the host population were analysed. A distinct seasonal pattern in the prevalence and intensity to infection is noted with higher parasite loads prevailing during warmer summer months and very low or no infection during winter months. The heavy infections are found to be promoted by high temperatures prevailing during summer months coupled with high host density and the larger size of fish examined during this period. A positive correlation between host size and prevalence and mean intensity to infection with the monogenean was noted, larger fish often carrying heavy infections. Further the monogenean showed an aggregated distribution on the host population as evidenced by the low value of negative binomial parameter 'K'.