Molecular markers of yolk sac fry development in nine families of lake trout

Hypoxia delays hematopoiesis: retention of embryonic hemoglobin and erythrocytes in larval rainbow trout, Oncorhynchus mykiss, during chronic hypoxia exposure

In rainbow trout development, a switch occurs from high-affinity embryonic hemoglobin (Hb) and round, embryonic erythrocytes to lower-affinity adult Hb and oval, adult erythrocytes. Our study investigated the early ontogeny of rainbow trout blood properties and the hypoxia response. We hypothesized that hypoxia exposure would delay the ontogenetic turnover of Hb and erythrocytes because retention of high-affinity embryonic Hb would facilitate oxygen loading. To test this hypothesis we developed a method of efficiently extracting blood from individual embryos and larvae and optimized several techniques for measuring hematological parameters on microliter (0.5 - 2.0 μl) blood samples. In chronic hypoxia (30% of oxygen saturation), stage-matched embryos and larvae possessed half the Hb concentration, erythrocyte counts, and hematocrit observed in normoxia. Hypoxia-reared larvae also had 3 to 6 fold higher mRNA expression of the embryonic Hb α-1, β-1, and β-2 subunits relative to stage-matched normoxia-reared larvae. Furthermore, in hypoxia the round embryonic erythrocytic shape persisted into later developmental stages. Despite these differences, Hb-oxygen affinity (P50), cooperativity, and the Root effect were unaltered in hypoxia-reared O. mykiss. The data support our hypothesis that chronic hypoxia delays the ontogenetic turnover of Hb and erythrocytes but without the predicted functional consequences (i.e. higher than expected P50). These results also suggest that the Hb-oxygen affinity is protected during development in chronic hypoxia to favour oxygen unloading at the tissues. We conclude that in early trout development, the blood-oxygen transport system responds very differently to chronic hypoxia relative to adults, possibly because respiration depends relatively more on oxygen diffusion than convection.

Does spatial variation in egg thiamine and fatty-acid concentration of Lake Michigan lake trout Salvelinus namaycush lead to differential early mortality syndrome and yolk oedema mortality in offspring?

Individual variation in fatty-acid and thiamine concentrations were determined in lake trout Salvelinus namaycush eggs collected at two spawning grounds in Lake Michigan. A suite of predictor variables, including spawning location, egg fatty-acid and thiamine concentrations, were used to attempt to explain cause-and-effect in early life stage mortality among S. namaycush families. Lipid and fatty-acid composition of S. namaycush eggs differed between spawning locations. Salvelinus namaycush offspring from south-western Lake Michigan were affected by a high occurrence of yolk oedema, whereas a higher frequency of early mortality syndrome (EMS) was observed among offspring from the north-western part of the lake. Random-forest regressions revealed location as the most influential predictor of yolk oedema mortality, whereas thiamine level in eggs was the strongest predictor of EMS-related mortality. Several polyunsaturated fatty acids were also found to be predictors of both mortalities. There is evidence of spatial variability in egg fatty-acid concentration among S. namaycush in Lake Michigan that, together with diminished thiamine concentration, contribute to low survival of S. namaycush progeny.