Biomonitoring potential of a Caryophyllaeid tapeworm: Evaluation of Adenoscolex oreini infection level and health status in three fish species of the genus Schizothorax across eutrophication and pollution gradients

Endoparasitic infections vary significantly across altered aquatic ecosystems, making these organisms ideal for the biomonitoring of degraded environments. To assess the biomonitoring potential of the Caryophyllaeid tapeworm Adenoscolex oreini and the possible impact of water quality on fish species, a study was carried out in three lakes with marked eutrophication and pollution gradients. The A. oreini infection level in three host fish species of the genus Schizothorax and corresponding fish health status were determined. The pattern of cestode infection varied significantly in the three fish species across the pollution gradient. The prevalence of infection in two fish species (Schizothorax esocinus and S. curvifrons) was significantly greater (P < 0.05) in the eutrophic lake than in the reference lake, whereas in S. niger, the maximum was reached in the hypereutrophic lake. The estimated marginal mean intensity and other infection indices varied significantly (P < 0.05) across the inter- and intra-pollution gradients of lakes. Multivariate statistical analysis results revealed maximum cestode infection in the eutrophic lake. An altered seasonal pattern was observed in the highly stressed lake. The gonadosomatic index (GSI) and condition factor values were significantly greater in fish collected from the reference lake than in those collected from the other lakes. A significant negative relationship between GSI and cestode prevalence was observed in the hypereutrophic lake as compared to least eutrophic lake. These findings indicate that infection indices of the Caryophyllaeid tapeworm and health attributes of fish can act as surrogates for the environmental quality of deteriorated lentic water bodies of the north-western Himalayan region, which is currently undergoing environmental degradation.