GENETIC-CONTROL OF JUVENILE LIFE-HISTORY PATTERN IN CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

To investigate the genetic basis for the difference in photoperiod responses between juvenile ocean-type an stream-type chinook salmon (Oncorhynchus tshawytscha), we conducted two crossing experiments and exposed the progeny to either a short- or long-day photoperiod for 1 0 wk from the time of first feeding. The first experiment examined the photoperiod response of pure and reciprocal crosses among red- and white-fleshed Quesnel River (stream-type) chinook salmon. The second experiment tested the photoperiod response of pure and reciprocal crosses between Quesnel River (stream-type) and Conuma River (ocean-type) chinook salmon. In both experiments, Quesnel chinook salmon fry (both red and white fleshed) sustained a high growth rate and developed a high degree of seawater adaptability only when exposed first to a short-day photoperiod for 10 wk and then to a long-day photoperiod. In contrast, the Conuma River chinook salmon grew rapidly and developed the increased seawater adaptability characteristic of smolts when reared on either photoperiod regime. Reciprocal Conuma-Quesnel hybrids displayed the ocean-type pattern of development, indicating that the photoperiod-independent phenotype is dominant and not under maternal control.