TAMONE, S.L.; DUTTON, J.M.; Univ of Alaska SE: Effect of eyestalk ablation on circulation ecdysteroids in snow crab, Chionoecetes opilio: evidence for a terminal molt.

Snow crab, Chionoecetes opilio are a commercially important crab fished in the Bering Sea and Canada. The management of this species requires a better understanding of their molting biology. C. opilio undergo a morphometric molt to maturity after which it is unclear whether they are capable of further growth. To understand the physiology of growth in C. opilio, we studied the regulation of molting hormones (ecdysteroids) in immature male, mature male and mature female crabs. Steroid hormones known as ecdysteroids regulate the molt cycle of crabs. Elevated ecdysteroids promote premolt during which the new cuticle is synthesized, lost limbs are regenerated, and muscular changes ensue. Ecdysteroids are synthesized by y-organs and are under the inhibitory regulation of the eyestalk neurohormone (molt-inhibiting hormone). In crabs that continue to grow circulating ecdysteroids increase upon eyestalk ablation. In crabs that undergo a terminal molt (will not molt again), ecdysteroid secretion diminishes, as the y-organ atrophies and does not respond to eyestalk ablation. In this study, mature and immature crabs were eyestalk ablated to induce premolt and increase circulating ecdysteroids. Eyestalk ablation had no effect on mature males and females, but increased circulating ecdysteroids in immature males (p < 0.01). This effect was significant 8 days post ablation. Circulating ecdysteroids in mature C. opilio were 100-fold lower than in immature males (1.3 ng/ml vs 124.5 ng/ml). In addition, only immature males developed limb buds in response to limb autonomy further supporting the hypothesis that C. opilio undergo a terminal morphometric molt to maturity.