This study examined the effects of ration and temperature on the molt of male adolescent snow crab Chionoecetes opilio (O. Fabricius, 1788). In one experiment, crabs were exposed to 1 of 4 treatments, 2 levels of ration and 2 levels of temperature. In a second experiment, all crabs were fed and a 4-level factor was addressed in which temperature was held constant as in experiment 1 (2 levels) or switched from one level to the other. Food consumption declined significantly and at a similar rate over time at both temperatures, several weeks before molt took place. Larger crabs molted to morphometric maturity in a greater proportion with no influence of ration or temperature. Smaller crabs also molted earlier than larger crabs. Temperature had a marked effect on the timing of molt, with crabs kept at a higher temperature molting 1 mo earlier and crabs exposed to shifted temperatures, molting midway between the two other groups. Body density decreased markedly at ecdysis, but was also influenced by ration and temperature particularly in nonmolters; the effect of ration on body density in nonmolters was highly significant. Ration also had a major effect on the size of muscle and digestive gland and their moisture content. Unfed nonmolters were in poor condition, particularly at a higher temperature, whereas molted crabs had large digestive glands associated with high moisture contents, irrespective of treatment. Timing of the migration of snow crabs to shallow and potentially warmer waters in the spring in the Gulf of St. Lawrence might be determined in part by molt requirements. Cold temperatures provide an energetic advantage during the premolt period, when food consumption decreases, but high temperatures result in an earlier molt and a fast recovery during the early postmolt period.
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Vol. 29 • No. 4