Monogenean community structure of Oreochromis niloticus in relation to heavy metal pollution and host reproductive cycle.

Abstract

The community structure of monogenean parasites of Oreochromis niloticus and its relation to the variations of heavy metal concentrations in water and the host reproductive cycle (gonadosomatic index, GSI) was studied. Fish were collected from Fishermen Lake, Ismailia. Monogenea community consisted of seven species, Cichlidogyrus halli typicus (57.8%), C. thurstonae (35.3%), C. ergensi (13.8 %), C. tiberianus (16.4%), C. arthracanthus (13.8%), Scutogyrus longicornis (22.4%) and Gyrodadtylus cicchlidarum (18.9 %). The overall mean species richness per host was 4.45 +/- 0.34. Responses of monogenea regarding their prevalence, abundance and intensity to the host sex and seasonal variations varied according to the species. Monogenean community showed different responses to the heavy metal concentrations and GSI. Positive correlations were found between species richness and both gonadosomatic index (rs = 0.2, P = 0.03) and Cd concentrations (rs = 0.89, P=0.04). Prevalence of C. halli typicus and C. thurstonae showed significant negative and positive correlations, respectively with the levels of Cu and Pb. G. cicchlidarus showed significant positive correlation with Cd level. The abundance and intensity of those species showed also correlations with the metal concentrations. Other monogenean species did not show any response to the metal levels such as C. tiberianus. Zn did not show any effect on the infection parameters of any species of monogenean community. The possibility of using some monogenean species to act as indicators for environmental pollution was discussed.