Behavioural modifications in the early life stages of Siberian sturgeon (Acipenser baerii, Brandt)

Behavioural modifications of Acipenser baeri were studied during early onto geny at 18 degrees C by means of specific tests and general observations. D uring A. baeri ontogeny, several different periods could be clearly disting uished by behavioural patterns. From hatching to 3 days post hatch (p.h.), specimens exhibited swimming-up and drift behaviour. A transition from a pe lagic to benthic behaviour occurred between 4-5 days p.h. and specimens wer e positively rheotactic. At 7-8 days p.h., prelarvae aggregated into school s of different shapes. During prelarval development, specimens were positiv ely phototactic, preferred white bottoms and did not show any preference fo r bottom concealment. Between 9-10 days p.h. coinciding with the onset of t he exogenous feeding, larvae were active bottom swimmers, schooling behavio ur disappeared and larvae dispersed. During early ontogeny, changes in body coloration were observed among those specimens who swam over bottoms of di fferent brightness and during the day/night cycle. From 9 to 12 days p.h., larvae were positively phototactic, denied bottom cover and showed preferen ce for white substrates. At 13 days p.h., the percentage of fish exhibiting positive phototactism, preferring open to concealed bottom habitats and wh ite bottoms started to decrease, while at 20 days p.h. specimens showed a c lear preference for bottom concealment and black and greyish bottoms. The s ignificance, use and evolution of the former behavioural patterns is deeply discussed.