The effects of population and thermal acclimation on the growth, condition and cold responsive mRNA expression of age-0 lake sturgeon (Acipenser fulvescens).

In Manitoba, Canada, wild lake sturgeon (Acipenser fulvescens) populations exist along a latitudinal gradient and are reared in hatcheries to bolster threatened populations. We reared two populations of lake sturgeon, one from each of the northern and southern ends of Manitoba and examined the effects of typical hatchery temperatures (16°C) as well as 60-day acclimation to elevated rearing temperatures (20°C) on mortality, growth and condition throughout early development. Additionally, we examined the cold shock response, which may be induced during stocking, through the hepatic mRNA expression of genes involved in the response to cold stress and homeoviscous adaptation (HSP70, HSP90a, HSP90b, CIRP and SCD). Sturgeon were sampled after 1 day and 1 week following stocking into temperatures of 8, 6 and 4°C in a controlled laboratory environment. The southern population showed lower condition and higher mortality during early life than the northern population while increased rearing temperature impacted the growth and condition of developing northern sturgeon. During the cold shock, HSP70 and HSP90a mRNA expression increased in all sturgeon treatments as stocking temperature decreased, with higher expression observed in the southern population. Expression of HSP90b, CIRP and SCD increased as stocking temperature decreased in northern sturgeon with early acclimation to 20°C. Correlation analyses indicated the strongest molecular relationships were in the expression of HSP90b, CIRP and SCD, across all treatments, with a correlation between HSP90b and body condition in northern sturgeon with early acclimation to 20°C. Together, these observations highlight the importance of population and rearing environment throughout early development and on later cellular responses induced by cold stocking temperatures.