Saltwater Readiness, Growth and Survival of Triploid Summer Steelhead Oncorhynchus mykiss

Pressure-induced triploidy is commonly used in aquaculture to sterilize and thereby genetically contain cultured fish that might otherwise interbreed with wild stocks.  For salmonids, this technique has been widely adopted to sterilize resident trout species and pen-reared salmon.  Relatively little research has evaluated effects of triploidy on free-ranging anadromous salmonids, though adult returns for several species have proven discouraging.  The cause(s) for low adult return rates remain(s) unknown, though we and others have proposed several mechanisms, including: 1) failure to outmigrate as juveniles, 2) high mortality during or shortly after migration to saltwater, 3) failure to properly imprint upon and home to natal streams and 4) failure to develop or respond to the physiological cues that trigger adult spawning migration.  Here we examine the second of these hypotheses by comparing the saltwater readiness, survivorship and growth of triploid summer Steelhead Oncorhynchus mykiss to diploid controls.  We found that, following transition to saltwater, triploid summer Steelhead experienced lower survivorship and growth than diploid Steelhead.  These results will inform our ongoing research of triploid Steelhead, aimed to evaluate ploidy manipulation as a conservation tool.