The effects of egg incubation temperature and parental cross on the swimming activity of juvenile brown trout Salmo trutta

Abstract

Personality varies among individuals and is influenced by the environment. Here, we tested the hypothesis that egg incubation temperature had carry-over effects on swimming activity of juvenile brown trout, Salmo trutta. Eggs from different crosses involving anadromous and lacustrine-adfluvial parents were incubated under two temperature regimes, unheated (cold) or heated c. 2.5 °C above ambient temperature (warm), until first exogenous feeding. In the laboratory, we used open-field tests to quantify swimming activity in a new environment, and mirror-image tests to measure time spent swimming and resting motionless near a mirror, measures often used as proxies for aggression. These tests were conducted for two cohorts, with one tested in June 2018 and the other in June and August 2019, enabling us to test for repeatability and if differences persisted over the summer. In June, when adjusting for differences in body size between cold- and warm-incubated trout, we found that juvenile trout incubated as embryos at cold temperatures showed more swimming activity and took less time to initiate swimming for their size than those incubated in warm water. There were also body size and year effects but no effects of parental cross. For August, none of the incubation temperature effects observed in June persisted, but cold-incubated trout spent a larger proportion of their time motionless near the mirror than warm-incubated trout and there was a general body size effect on time to initiate swimming. The lack of any persistent effects of incubation temperature between June and August suggests that the effect is ephemeral. Notwithstanding, these results support the hypothesis that incubation temperature has short-term effects on activity of juvenile of brown trout during their first summer.Significance StatementWe studied the effect of embryonic temperature on juvenile fish behavior, focusing on swimming activity under different conditions. Brown trout eggs were incubated under two temperature regimes, cold and warm. We show that juvenile trout originating from cold conditions as embryos spent a greater proportion of time swimming and less time to initiate swimming than trout originating from warm conditions. These effects were present in June but not August, which suggests that the effect is short-lived, and occurs during the first summer when mortality of juveniles is high. The duration of the effects needs further study as our previous studies have shown persistent embryonic temperature effects on metabolism, body shape, reproductive potential and emigration of subsequent life stages of salmonids. These results also have bearing on ongoing climate change as even small differences in embryonic temperature may have ecological consequences for subsequent life stages.