In a groundbreaking study published in the Proceedings of the National Academy of Sciences on December 24, researchers have discovered that Nile tilapia (Oreochromis niloticus) exhibit a fascinating behavior known as "behavioral fever" when faced with infection. After exposure to the pathogen Edwardsiella piscicida, these fish actively sought out warmer water, around 34° Celsius, for five days—approximately 5 degrees above their normal temperature. This intentional increase in body temperature has shown significant benefits in enhancing their immune response.
Behavioral fever in Nile tilapia appears to trigger the adaptive immune system, a sophisticated defense mechanism characterized by its acquired memory of specific pathogens. Notably, Nile tilapia are among the oldest living animals with T cells, which are crucial components of adaptive immunity. The study revealed that fish which swam in warmer water had fewer bacteria in their livers just four to six days post-infection and demonstrated a higher survival rate compared to those maintained at their usual temperature.
Further examination of the fish's spleens five days after infection underscored the positive impact of fever on T cell survival and their ability to eliminate infected cells. However, this advantageous effect dissipated by the eighth day as disease-fighting T cells began to die off, a process necessary to preserve immune homeostasis.
Daniel Barreda of the University of Alberta in Edmonton, Canada, commented on the findings:
"It was really exciting to see a concrete link between fever and adaptive immunity [in fish]. That’s something that hadn’t been solidified before."
The research highlights the role of elevated temperatures in bolstering the immune response, providing a natural mechanism for fighting infection. The study's implications extend beyond understanding fish immunity, offering potential insights into the evolutionary roots of fever as a defense strategy across species.
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