Heat transfer in fish: are short excursions between habitats a thermoregulatory behaviour to exploit resources in an unfavourable thermal environment?

Abstract

Temperature is the primary environmental factor affecting physiological processes in ectotherms. Heat-transfer models describe how the fish's internal temperature responds to a fluctuating thermal environment. Specifically, the rate coefficient (k), defined as the instantaneous rate of change in body temperature in relation to the difference between ambient and body temperature, summarizes the combined effects of direct thermal conduction through body mass, passive convection (intracellular and intercellular fluids) and forced convective heat transfer (cardiovascular system). The k-coefficient is widely used in fish ecology to understand how body temperature responds to changes in water temperature. The main objective of this study was to estimate the k-coefficient of brook charr equipped with internal temperaturesensitive transmitters in controlled laboratory experiments. Fish were first transferred from acclimation tanks (10°C) to tanks at 14, 19 or 23°C (warming experiments) and were then returned to the acclimation tanks (10°C; cooling experiments), thus producing six step changes in ambient temperature. We used non-linear mixed models to estimate the k-coefficient. Model comparisons indicated that the model incorporating the k-coefficient as a function of absolute temperature difference (dT: 4, 9 and 13°C) best described body temperature change. By simulating body temperature in a heterogeneous thermal environment, we provide theoretical predictions of maximum excursion duration between feeding and resting areas. Our simulations suggest that short (i.e. <60 min) excursions could be a common thermoregulatory behaviour adopted by cold freshwater fish species to sustain body temperature below a critical temperature threshold, enabling them to exploit resources in an unfavourable thermal environment.

Ecological and Evolutionary Consequences of Environmental Change and Management Actions for Migrating Fish

“…Migrating between water bodies also offers a means to buffer against changing external physicochemical conditions, maintain internal homeostasis and regulate body temperature to conserve energy expenditure or to maximize aspects of performance (Reynolds and Casterlin, 1980;Nakamura et al, 2015;Pépino et al, 2015;Nordahl et al, 2018Nordahl et al, , 2019. Observations of diel horizontal migrations in juvenile coho salmon (Oncorhynchus kisutch) indicate that individuals that moved to warmer habitats after feeding processed their food more quickly and grew faster compared with individuals that adopted other behaviors (Armstrong et al, 2013).…”

Thermal stratification drives movement of a coastal apex predator

“…As with many other mobile animals, marine fishes can readily exploit thermal gradients to regulate their body temperature and increase their metabolic efficiency 15, 16 . Movement is thus a good behavioural response with which to infer the thermal ecology of a fish species.…”

“…Movement is thus a good behavioural response with which to infer the thermal ecology of a fish species. Controlled laboratory experiments have shown that fish move across thermal gradients to attain a preferred temperature 17, 18 , and have allowed the researchers to investigate the response of an individual’s internal temperature to a fluctuating environment 16 . However, laboratory experiments are not feasible for large marine predators, and hence studies in the wild using acoustic telemetry and bio-logging technologies are a much more practical approach to study the thermal preference of these animals 10, 17, 19 .…”

Waning habitats due to climate change: the effects of changes in streamflow and temperature at the rear edge of the distribution of a cold-water fish

“…In the Cega, Pirón and Lozoya rivers, important losses of thermal habitat will occur that could jeopardize the viability of the trout population. Behavioural thermoregulatory tactics are common in fish (Reynolds and Casterlin, 1979;Goyer et al, 2014); for instance, some species perform short excursions (< 60 min in experiments with brook char, S. fontinalis) that could be a common thermoregulatory behaviour adopted by cold freshwater fish species to sustain their body temperature below a critical temperature threshold, enabling them to exploit resources in an unfavourable thermal environment (Pépino et al, 2015). Brown trout can use pool bottoms during daylight hours to avoid the warmer and less oxygenated surface waters in thermal refugia (Elliott, 2000).…”