Ecto- parasitic infection in Nile tilapia (Oreochromis niloticus) fry during male reversal in Veracruz, México

The monogenean gyrodactylids and some ciliated protozoa species may cause ectoparasitic epidemics in tilapia hatcheries. An experimental framework was developed with fish reared during male reversal treatment. The infection dynamics were examined: mean intensity, prevalence, condition factor (K), fish growth and mortality. A total number of 3400 infected tilapia fish were transferred from high density (45 fish L-1) to a low-density tank (2 fish L-1). In the fish (0.012 ± 0.003 g) there were identified four ectoparasitic species; a worm, Gyrodactylus cichlidarum and 3 ciliated protozoa (Trichodina sp. Chilodonella sp. and Ambiphrya sp.). The infection dynamic examined during 31 days showed that the parasitic load and parasite richness for the different ecto-parasites demonstrated positive interspecific correlations, in spite of that, non-synergistic or antagonistic interactions were manifested. The condition factor K was strongly affected (p < 0.05) by G. cichlidarum during the course of infections. The growth and survival recovered after 31 days at low density.