Hypothermal effects on survival, energy homeostasis and expression of energy-related genes of swimming crabs Portunus trituberculatus during air exposure.

Previously, dry or semi-dry approach under the hypothermal condition is proved to be an alternative method in transport of live swimming crabs Portunus trituberculatus. However, we wondered whether this method can improve crab survival when temperature is kept as cool as possible. In this study, we hypothesized that there is a thermal threshold below which dry or semi-dry approach (air exposure) could cause crab physiological disruption and therefore aggravate their mortality. To test the above hypothesis, crabs (23°C) were exposed to air at temperatures ranging from 4 to 16°C. Results showed that crabs had a worse survival and vigor at temperatures below 12°C. Then we tested crab energy metabolism to explore the possible reason. It was shown that total adenine nucleotide and adenylate energy charge in gills were remarkably reduced by air exposure of below 12°C. This increased the need for crabs to re-balance energy metabolism, which was indicated by the upregulation of AMPKα and HIF-1α. Meanwhile, there was a significant increase of the expression of Na(+)/K(+)-ATPase, V-type ATPase and HSP90 at temperatures below 12°C, while all treatments shared a similar level of hemocyanin, urate and lactate in hemolymph and expression of cytochrome c oxidase and NADH-ubiquinone reductase in gills. These results implied that dry or semi-dry approach below 12°C could exert detrimental effects on P. trituberculatus, and perturbation of energy homeostasis, which is more related with changes of energy-demanding physiological pathways, is a possible reason of crab death and poor vigor.