Larval behaviour and effect of the timing of initial feeding on growth and survival of Siberian sturgeon ( Acipenser baeri) larvae under small scale hatchery production

Abstract

Behaviour of larval Siberian sturgeon and the effect of the timing of first feeding (5, 7, 9, 11, 13, 15 and 17 d post hatch) of a dry commercial diet were examined at 18 °C. Hatchlings (< 1 -day old larvae) and 1–3-day old larvae were strongly photopositive and exhibited a vertical swim-up and drift behaviour. Older 4–8-day post hatch larvae aggregated and were positively rheotactic and benthic. 9 and 10-day post hatch larvae were active swimmers and dispersed across the bottom of the tank. At this age, yolk sac is depleted and exogenous feeding occurs. Feeding was positively correlated with melanin plug ejection. Availability of feed significantly affected survival, body size and specific growth rate of fish larvae ( P < 0.05), but no abnormal behaviour was observed as a consequence of food deprivation. Fry with the highest survival rates (76–83%), growth in weight and length (288–308 mg and 35.9–37.2 mm respectively) and specific growth rates (13.4–13.1% day −1) were those fed at days 5, 7 and 9 after hatching. Condition factor decreased dramatically from 1.39 to 0.44–0.49 during the endogenous feeding phase. However, from the beginning of the exogenous feeding to 22 days after hatching, condition factor slightly increased and achieved adult shape values (0.60–0.63). These results confirm the importance of the initial feeding time and suggest that food should be offered to sturgeon larvae at 9 d after hatching, coinciding with the disappearing of schooling behaviour, the scattering of larvae across the bottom of the tank and the apparent full resorption of yolk-sac reserves. Feeding Siberian sturgeon larvae during the phase of transition between yolk-sac nutrition to exogenous feeding (5–7 days post hatch), did not provide any advantage. Expulsion of melanin plug can not really be used to determine the time of transition to active feeding, as it appears to be a consequence of first feeding.