Genetic Control of Juvenile Life History Pattern in Chinook Salmon (Oncorhynchus tshawytscha)

Abstract

To investigate the genetic basis for the difference in photoperiod responses between juvenile ocean-type and stream-type chinook salmon (Oncorhynchus tshawytscha), we conducted two crossing experiments and exposed the progeny to either a short- or long-day photoperiod for 10 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.