Survival value of fever in fish

Abstract

THE phenomenon of behavioural fever, manifested as an increase in preferred temperature following injection of live or killed bacteria, or other pyrogenic substances, has been demonstrated in bony fishes^1–3, amphibians^4,5, reptiles^5–10, and mammals^11,12. Ectothermic vertebrates, including some newborn mammals¹¹, are unable to increase their body temperatures much above ambient by physiological means, and so are largely limited to behavioural thermoregulation by selecting favourable temperatures in their environment. The behavioural febrile response of a lizard, Dipsosaurus dorsalis, has been shown to have adaptive value^5,8–10 in conferring increased survival during infection by the Gram-negative bacterium Aeromonas hydrophila. A. hydrophila is pathogenic to bony fishes, amphibians and reptiles, causing haemorrhagic septicaemia. All three classes show similar (1–5 °C) elevations in preferred temperature in response to injection of this bacterium^1–10. The absolute preferred temperatures, however, both normal and febrile, differ considerably among these vertebrates. The preferred temperatures of lizards such as D. dorsalis (about 40 °C) are quickly lethal to most fishes and amphibians. We report here that fever significantly enhances survival of goldfish, Carassius auratus, at febrile temperatures about 10 °C lower than those of D. dorsails, after injection with live A. hydrophila.