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Of 1250 scallops sampled from four areas over a 16-month period, 387 (31%) were infected by the trematode Bucephalus sp. Parasitized gonads reached their maximum weight in January, 3 months after non-parasitized gonads had reached their maximum and 2 months after the normal spawning period. In the same month, cercariae first appeared within the sporocysts. They were present for the next 5 months during which time the weight of the gonad and muscle decreased. The muscle weight returned to and exceeded the weight of controls in September-October, a time when cercariae were not being produced and when normal unparasitized scallops were spawning. The characteristic red colour of parasitized gonads occurred at all times of the year. It was not related to the stage of maturity of the parasite.
Sanders et al. (Mon,) studied this question.