Effect of water temperature on the early development and hatchery rearing of a locally threatened species—crucian carp (Carassius carassius)

Abstract Climate change is expected to alter native fish distributions by driving temperatures beyond their physiological capabilities. However, the thermal limits of many species remain insufficiently defined, limiting accurate predictions of viable range shifts. This study investigated the early ontogeny of Carassius carassius , a threatened freshwater fish native to much of Europe, across a range of water temperatures to assess their effects on embryonic and larval development, growth, and survival. In experiment 1, the timing of developmental stages was examined at 13, 19, and 25 °C, revealing faster development at higher temperatures. Experiment 2 evaluated nine temperatures (7–31 °C, at 3 °C intervals) to determine their impact on key ontogenetic events, including incubation duration, hatching, onset of exogenous feeding, yolk-sac resorption, larval growth, and survival. Incubation and hatching durations were inversely related to temperature (13–31 °C), with no hatching observed at 7–10 °C. Hatchlings reached maximum body size at 28 °C and minimum size at both 13 and 31 °C, while yolk-sac volume declined progressively with rising temperature. The onset of exogenous feeding and completion of yolk-sac absorption were accelerated with increasing temperature. The body size and yolk-sac volume of first-fed larvae decreased with rising temperature, and this decreasing trend in body size persisted through to yolk-sac absorption. Survival analysis identified a thermal tolerance zone of 10–31 °C, with optimal range (16–28 °C), sublethal (10–16 °C, 28–31 °C), and lethal (< 10 °C, > 31 °C) thresholds. These findings provide essential insights to improve hatchery management and conservation strategies for this declining species.