LARVAL BEHAVIOR AND EFFECT OF THE TIMING OF INITIAL FEEDING ON GROWTHAND SURVIVAL OF SIBERIAN STURGEON (ACIPENSER BAERI) LARVAE UNDER SMALL-SCALE HATCHERY PRODUCTION

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 commer cial diet were examined at 18 degrees C. Hatchlings (< 1-day old larva e) 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 po st hatch larvae were active swimmers and dispersed across the bottom o f the tank. At this age, yolk sac is depleted and exogenous feeding oc curs. Feeding was positively correlated with melanin plug ejection. Av ailability of feed significantly affected survival, body size and spec ific growth rate of fish larvae (P < 0.05), but no abnormal behaviour was observed as a consequence of food deprivation. Fry with the highes t survival rates (76-83%), growth in weight and length (288-308 mg and 35.9-37.2 mm respectively) and specific growth rates (13.3-13.1% day( -1)) were those fed at days 5, 7 and 9 after hatching. Condition facto r 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 achie ved adult shape values (0.60-0.63). These results confirm the importan ce of the initial feeding time and suggest that food should be offered to sturgeon larvae at 9 d after hatching, coinciding with the disappe aring of schooling behaviour, the scattering of larvae across the bott om of the tank and the apparent full resorption of yolk-sac reserves. Feeding Siberian sturgeon larvae during the phase of transition betwee n yolk-sac nutrition to exogenous feeding (5-7 days post hatch), did n ot provide any advantage. Expulsion of melanin plug can not really be used to determine the time of transition to active feeding, as it appe ars to be a consequence of first feeding. (C) 1997 Elsevier Science B. V.