Shoals in troubled waters: Data

Rising water temperatures across aquatic habitats, in the current global
climate change scenario, in freshwater systems, can increase, directly
affecting metabolism and food intake in fish species. These can
potentially alter their physiological, behavioural and, potentially
altering their shoaling properties. In the current study, we examined the
effects of future temperatures on metabolism, foraging, and shoaling of
tropical fish. Mixed-species shoals, (comprising flying barbs, zebrafish
and gambusia) and as well single-species (flying barbs and zebrafish)
shoals of flying barbs and zebrafish were conditioned for 45 days to one
of the following three kinds of temperature regimes: the Current
Temperature Regime (CTR) in which shoals were at 24°C (i.e., the current
mean temperature of their habitat), The Predicted Temperature Regime (PTR)
which maintained a water temperature of 31°C, (i.e., simulating conditions
projected for their habitat in 2100), and The Dynamic Temperature Regime
(DTR) which experienced daily temperature fluctuations between 24°C and
31°C, (i.e., resembling rapid temperature changes expected in their
natural environments) or the Current Temperature Regime (CTR) in which
shoals were at 24°C, the current mean temperature of their habitat. Our
results revealed species-specific responses to these temperature regimes.
Flying barbs exhibited significantly lower body weight at PTR but
maintained consistent glycogen content across all temperature regimes. In
contrast, zebrafish and gambusia displayed significantly elevated muscle
glycogen content at PTR, with similar body weights across all three
temperature regimes. Bloodworm intake showed there were no significant
temperature-related changes on feeding behaviour. Cohesion within flying
barb shoals and cohesion/polarization in mixed-species shoals decreased
significantly at PTR. Shoals exposed to DTR exhibited intermediate
characteristics between those conditioned to CTR and PTR, suggesting that
shoals may be less impacted by dynamic temperatures as compared to
prolonged high temperatures. This study highlights species-specific
metabolic responses to future temperatures and their potential
implications for larger-scale shoal properties.