Effect of incubation temperature on green sturgeon embryos, Acipenser medirostris

Regulation of river flow and the amount of winter rainfall are the major factors affecting the water temperature of the spawning grounds, for green sturgeon in the Klamath River. During the primary spawning period of green sturgeon, mid-April to June, the water temperature may vary from 8 to 21degreesC. To estimate the potential implications of this modified thermal regime, we examined the survival and development in three progeny groups of green sturgeon embryos from zygote to hatch, at constant incubation temperatures (11-26degreesC). Temperatures 23-26degreesC affected cleavage and gastrulation and all died before hatch. Temperatures 17.5-22degreesC were suboptimal as an increasing number of embryos developed abnormally and hatching success decreased at 20.5-22degreesC, although the tolerance to these temperatures varied between progenies. The lower temperature limit was not evident from this study, although hatching rate decreased at 11degreesC and hatched embryos were shorter, compared to 14degreesC. The mean total length of hatched embryos decreased with increasing temperature, although their wet and dry weight remained relatively constant. We concluded that temperatures 17-18degreesC may be the upper limit of the thermal optima for green sturgeon embryos, and that the river thermal regime during dry years may affect green sturgeon reproduction.