Heart function and individual variability play major roles in temperature tolerance of fish

Maanantai 14.11.2022 klo 14.42 - Mikko Nikinmaa

Climate change has major effects on fish, especially fish in lakes, since the whole water body can warm up as a result of long-lasting heat waves. Because of the uniform temperature regardless of the depth, fish cannot seek colder temperatures near the bottom. As a consequence, massive fish mortalities occur in shallow lakes of temperate zone every summer nowadays.

The reasons, why fish die as a result of increased temperature can only be understood by studying the functional changes occurring as a result of temperature elevation. Thus, physiological studies should be in the centre of climate change studies. If the reasons for vulnerability to increased temperature are known, it can also be estimated, which measurable responses predict fish mortalities. This as a background, and recognizing that individual variability of fish determines why some die and others remain living, we studied how fish tolerant and intolerant to high temperatures differed from each other. The results of the extensive studies are reported by Anttila et al in Comparative Biochemistry and Physiology (//doi.org/10.1016/j.cbpa.2022.111340).

Our results show that for a given age group, heart function is decisive in determining temperature tolerance. The efficiency of heart is markedly different in different individuals, whereby marked individual variability in temperature tolerance occurs. Thus, in predicting the effects of climate change on fish populations, we should not restrict our analysis to the mean response but also to the variability observed. In future it must be evaluated to which extent the thermal tolerance and its variability are heritable, as this will have significant impact on the vulnerability of species to global warming.