Molt Stages of the Snow Crab Chionoecetes opilio by Observation of Morphogenesis of Setae on the Maxilla

Abstract

Observation of setal morphology of the basal endite of the maxilla is successfully used for defining molt stages of the snow crab Chionoecetes opilio. The basal endite of the maxilla is easily dissected and can be preserved for up to 48 h in a 10-ml vial filled with ambient salinity sea water at 2-3.degree. C, during which time a reliable staging can be ensured. Frozen endites are not suitable for the observations of setal morphogenesis due to a pronounced epidermal retraction and extrusion of new setae. Three molt periods (postmolt, intermolt, and premolt) can be identified. The premolt period is further subdivided into 3 stages (D0, D1, and D3-4). For snow crab, prediction of the beginning of the molting season is critical due to the economic problems encountered by the fishing fleet when low quality molters are found in abundance in the catch. Identification of molt stages by the technique presented in this paper will allow such a prediction and provide a biological basis for fishery management.