Occurrence of ectoparasites and seasonality of young st.peter’s fish from the nile (Oreochromis niloticus) after sexual reversion in the Northwestern region of Paraná state

Abstract

The study of fish parasites has become important due to intensification of pisciculture activity in the last few years. The most serious diseases found in St. Peter’s fish are caused by ectoparasites such as the protozoan Trichodina, Ichthuophthirius Multifiliis, Chilodonella, and the monogenetic helminthes Dactylogyrus and Gyrodactylus (ROBERT; SOMERVILLE, 1996; VARGAS et al., 1997; LEONARDO et al., 1998). Vargas et al. (1997), and Leonard et al. (1998) registered ectoparasitism in 89% and 95% of the samples respectively, from which 87% and 85% were Trichodina, 31.5% and 2.5% were Monogenea and 29% and 7.5% simultaneously with both parasites, with a higher occurrence in the Spring (100%) than during the Summer (75.6%). This work aimed at assessing the monthly occurrence and seasonality of ectoparasites in young St. Peter’s fish from the Nile (Oreochromis niloticus) after sexual reversion in fishponds in Maringá’s region. The pathological examinations showed the occurrence of 100% of ectoparasitism in all batches of fish assessed monthly. Out of a total of 110 fish, 73.6% presented Trichodina, 19.1% Dactylogyrus, 11.8% I. Multifiliis, and 0.09% Chilodonella. The higher occurrences took place during the colder months, apart from November when parasitism was also high, probably due to the higher incidence of rain, responsible for the sharp changes in water temperatures.