Although one does not usually think of fish as being able to control their body temperature much, research by researchers from Australia and the UK published in the most recent issue of the Journal of Fish Biology suggests that some fishes have limited control over their body temperature by adopting different behaviours.
Ashley Ward and coauthors studied the behaviour of threespine stickleback (Gasterosteus aculeatus) and common minnows (Phoxinus phoxinus) in the presence of a thermal gradient in the water.
The authors hypothesised that the fishes would occupy a different position in the water column if a temperature gradient were present compared to the condition where the column was of a uniform temperature.
They predicted that juvenile fishes would occupy the warmer water near the top of the column more often than adults in order to maximise their growth rate, and that recently fed fishes would do the same (compared to starved individuals) in order to maximize metabolic efficiency.
The authors observed groups of six fish (either sticklebacks or minnows) that were placed in six aquaria subjected to one of two different water temperature treatments: either a constant water temperature of 14°C throughout each aquarium or a vertical temperature gradient ranging from 11°C at a depth of 85cm to 17°C at a depth of 5cm.
The positions of the fishes were noted every two hours for 24 hours during the experimental period. The experiments were carried out with adult and juvenile fishes of both species.
The results of the experiments showed that juvenile fishes positioned themselves higher in the water column than adult conspecifics in the presence of a thermal gradient.
At the same time, they also indicated that both juvenile and adult fishes of both species migrated to warmer waters following feeding (as compared to being starved), although the effect displayed by juvenile fishes was less marked (probably because there was less leeway, since the juveniles were already preferentially occupying the upper portions of the water olumn).
These results validated the authors’ hypotheses.
For more information, see the paper: Ward, AJW, EMA Hensor, MM Webster and PJB Hart (2010) Behavioural thermoregulation in two freshwater fish species. Journal of Fish Biology 76, pp. 2287–2298.