Community structure of fish parasites and their intermediate hosts in relation to Trophic conditions of lakes.

Abstract

The present study was undertaken to evaluate the helminth communities in populations of three fish species along the trophic gradient of lakes. Data were collected from three lakes of differing trophic status in the Kashmir Himalayas, namely Anchar (severely eutrophic), Dal (highly eutrophic) and Manasbal (moderately eutrophic) during June 2006 to May 2008. The main objectives of the study were: (1) to examine the physico-chemical characteristics of lakes and (2) to assess the helminth assemblage patterns in fish populations of lakes. In addition, a follow-up study was undertaken to study the density profiles of intermediate hosts during the second year (June 2007 – May 2008). Fish species studied included one native species Schizothorax niger Heckel and three non-native species – Cyprinus carpio communis Linnaeus, C. c. specularis Linnaeus and Carassius carassius (Linnaeus). A comparison of physico-chemical parameters and depth revealed that the study lakes presented a mosaic of different trophic gradients; Anchar was most affected by eutrophication, followed by Dal, whereas Manasbal was the least eutrophic among the three lakes. A total of seven helminth parasite species were recorded during the investigation period. These included three trematodes: Diplozoon kashmirensis Kaw, Clinostomum schizothoraxi Kaw, and Posthodiplostomum cuticola Dubios (Neascus cuticola Nordmann); two cestodes: Bothriocephalus acheilognathi Yamaguti and Adenoscolex oreini Fotedar and two acanthocephalans: Pomphorhynchus kashmirensis Kaw and Neoechinorhynchus manasbalensis Kaw from Acanthocephala. The populations of different intermediate host guilds such as cyclopoid copepods, gastropods, oligochaetes, ostracods, and amphipods showed interlake variations. The densities of intermediate hosts especially cyclopoid copepods, gastropods and oligochaetes were higher at Anchar, suggesting a positive response of the invertebrate host community to cultural eutrophication. However, the pattern exhibited by ostracods and amphipods were not so distinct which agreed well with the rare status of their parasites in lakes. The analysis of data showed a clear habitat effect on the abundance pattern of helminth species. Helminth infracommunity richness was highest in host populations of S. niger and C. carassius from the Anchar lake compared to two other lakes. On the otherhand, there was no observed pattern of community structure in the case of C. carpio in the three lakes.Digital copy of Ph.D thesis.University of Kashmir