Fig. 4

Representative photographs showing the progressive increase in the corner-gathering behavior of Acipenser gueldenstaedtii prelarvae with age, followed by aggregation into schools. Two different patterns were observable under the present examination conditions. In pattern I (upper), early corner-gathering prelarvae (day 0–day 2) formed directly non-rheotactic schools at the corners (day 3–day 5). Two large schools on day 5 are indicated by arrows. In contrast, in pattern II (lower), the corner-gathering behavior of the prelarvae (day 0–day 3) shifted to rheotactic prelarval aggregation into a rheotactic school (day 4). A non-rheotactic school developed at a corner on day 5, as indicated by an arrow. Temporal patterns for the two patterns in the diel photoperiodicity of the present study are referred to in Fig. 1