Fig. 5

Proportion of Acipenser gueldenstaedtii prelarvae engaged in non-rheotactic schools (NRS) and/or rheotactic schools (RS) under light (L), dim light (DL), and dark (D) conditions between day 3 and day 5. Quantitative assessment was carried out with only two tanks (tank 1 and tank 2). Under D conditions, prelarval counts without typical signs of schooling behavior are indicated by dots (day 3/day 4 in tank I and day 3 in tank II). There was no significant difference in the proportions of the prelarvae exhibiting schooling behavior between L and DL conditions in both tanks, irrespective of prelarval age (P > 0.05). Schooling behavior was significantly weakened under D conditions (indicated by asterisks; P < 0.05). However, though they exhibited weakened schooling behavior, a considerable number of prelarvae participated in rheotactic schools under D conditions, whereas non-rheotactic schools almost disappeared. Each mean ± SD is based on at least triplicate counting by two observers, and statistical evaluation was carried out by analysis of variance (ANOVA) followed by Duncan’s multiple range tests