Morphological conditioning of a hatchery-raised invertebrate, Callinectes sapidus, to improve field survivorship after release

For recruitment-limited, severely depleted fishery stocks, stock enhancement may become an important technique in the return of population sizes to sustainable levels. Aquaculture-reared individuals, however, may face some disadvantages upon release into the wild due to differences between natural conditions and the hatchery. The goal of this study was to test whether field survivorship of hatchery-raised blue crabs, Callinectes sapidus, could be improved by simple conditioning steps, taking advantage of phenotypic plasticity in certain traits. This species is currently the focus of a preliminary stock enhancement program in the Chesapeake Bay. Results indicate that unconditioned hatchery crabs had lower survivorship than wild crabs in the field and differed in carapace color and lateral spine length. Both traits were plastic. Carapace color was changeable within 1-2 days, without a molt, upon the exposure of crabs to new substrates. However, colors within the range produced in this study did not significantly affect survivorship in a field or a laboratory experiment. Change in spine length required exposure to predators for 1-4 weeks. Exposure to fish predators resulted in increased spine length, though exposure to adult blue crabs had no significant effect. Crabs with lengthened spines had significantly higher survivorship in both laboratory and field experiments, suggesting that this feature may be one on which to focus large-scale conditioning efforts. Results of this study suggest a level of phenotypic plasticity that may contribute to the blue crab's ability to take advantage of multiple estuarine habitat types. On a more applied level, results of this study suggest that at least some deficiencies in hatchery-raised organisms can be alleviated and would likely lead to improved success and efficiency of stock enhancement efforts. Similar studies on other hatchery-raised invertebrates and finfishes may also lead to improvements in their enhancement programs.