Effect of water temperature on the beginning of active feeding of tugun and nelma larvae

Temperature conditions of transition to active feeding of tugun Coregonus tugun (Pallas, 1814) and nelma Stenodus leucichthys nelma (Pallas, 1773) larvae to substantiate elements of artificial reproduction biotechniques were studied experimentally. We added live food (Artemia nauplii) and placed larvae a day after the transition to the first stage of the larval period in aquaria with different constant temperatures. The proportion of larvae that started feeding consistently increased in the temperature range 0.2–10 °C reaching 100% at daily exposure of experiments. The 50% level of transition to active feeding was observed at 6 °C. The ability of larvae with preliminary feeding experience to consume food at a temperature 1–5 °C lower than that of larvae that had not fed before was found. The individual duration of larvae transition to active feeding varied significantly from 1 to 8–9 days in a series of experiments at a stable low temperature (0.2 °C). Delayed initiation of exogenous feeding due to the limiting effect of low temperatures is physiologically equivalent to larval starvation. This may negatively affect the subsequent development of larvae. Species specificity was not significantly revealed in all series of experiments. We recommend keeping the water temperature at least 10°C from the time of embryo transition to larval development when rearing juveniles under intensive technologies to reduce the diversity of planting material in terms of size parameters. In this case, the duration of the time interval necessary for the beginning of active feeding of all larvae will be maximally reduced.