Variation in parasite communities in Oreochromis niloticus linked with precipitation

Abstract

The aquatic environment can be studied either directly by a regular monitoring of water quality parameters or indirectly by using bioindicators, such as fish parasites. The most common groups of parasites examined to date in response to environmental stress are ectoparasites including trichodinids and monogeneans. To assess the effects of drought on the prevalence of ectoparasites and the number of species of parasites in fish, we collected fish specimens in the summer and early autumn (January to April) in the years 2014 and 2015. The first collection took place after a year with regular precipitation; however the second collects occurred after reduction of about 70% in rain rates. We collect 85 samples of fish. The parasites were surveyed by the fresh smears of gills and feces, or by histopathological examination with Hematoxylin-Eosin and Giemsa stain. Before the drought (in the first collection in 2014), the prevalence of parasites in fish collected was 28.5% (18/63,), but after the drought in 2015, the prevalence was 73.5% (64/87). We counted at random, the number Trichodina sp. of the histopathology of the gills of fish and we observed that the parasites average before the drought was 08.04 ± 2.05e after the drought was 3.33 ± 1:35, with no statistically significant difference between the observation periods. Before the drought, Trichodina sp. (18/23) Myxobolus sp. (3/23), Henneguya sp. (9/23) and Ichthyophthirius multifiliis (2/23) were found. After dry the found parasites were: Trichodina sp. (27/27, 100%), Henneguya sp. (4/27, 14.8%) and Monogenea (2/27, 7.4%). We conclude that the reduction in precipitation and the water crisis generated by it significantly increased the prevalence of ectoparasites in gills, which reinforces the parasites indication of fish as a biological indicator of changes in environmental quality. The study suggested that the species composition of fish parasites is influenced by environmental parameters.