The susceptibility of fishes to haemoflagellates at different ambient temperatures

Abstract

SummaryTrout acclimated to 20 °C could not be infected with Cryptobia salmositica. Those acclimated to 5 °C had longer pre-patent periods and considerably lower parasitaemias than those at 10 °C. Forty days after infection, the parasitaemias in fish at 10 °C fluctuated, while this was not observed in those at 5 °C. In vitro incubation of Cryptobia in plasma from 20 °C fish did not affect the motility nor the infectivity of the parasite. Fish infected at 15 °C (low parasitaemias and 2 weeks after inoculation) lost their infections when the ambient temperature was raised to 20 °C. However, in fish with more acute infections (4 weeks after inoculation), the parasitaemias were only substantially reduced when the ambient temperature was raised to 20 °C. Trypanosoma danilewskyi were detected in goldfish acclimated to 10, 20 and 30 °C. However, the parasitaemias in goldfish at 10 and 30 °C were consistently much lower than those at 20 °C.