Behavioral Epigenetics: A Mechanism for Differences Between Wild and Hatchery Salmonids?

There are few discussions so contentious as those concerning hatchery and wild salmonids. There is significant disagreement at every level, from the definitions of the terms “wild” and “hatchery” to the possible management implications of decisions based on those definitions. These terms have various legal, legislative and administrative definitions. In some cases those definitions depend upon local jurisdictions or international conventions, or perhaps the intention of the hatchery production. A very large number of descriptive papers have documented a litany of differences between hatchery and corresponding wild salmon. Some of those differences appear to persist over generations of fish following earlier hatchery rearing experience. Similarly, a large number of reports have suggested, or documented, a variety of interactions between wild and hatchery salmonids, typically to the detriment of wild individuals. There is a continuing history of production of hatchery salmonids over the past 100 years, with current releases of more than 5 billion fish into the North Pacific Ocean. There have been numerous attempts to identify the causes of the differences between hatchery and wild fish, and to manipulate those differences for management purposes. Recent pedigree studies have demonstrated persistent fitness differences resulting from hatchery rearing that can persist over subsequent generations in fish that spawn in the wild. I propose that a possible candidate mechanism for this effect is the well-established principle of behavioral epigenetics. Examples from a number of vertebrate species have shown persistent behavioral differences across generations as a result of environmental effects on parents or grandparents. I will review data that can be used to test the predictions of the hypothesis of behavioral epigenetics as the mechanism responsible for differences between wild and hatchery salmonids.