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Spore release was studied in synactinomyxon, aurantiactinomyxon, echinactinomyxon, raabeia and neoactinomyxum type actinosporeans parasitising the oligochaete, Lumbriculus variegatus. Maximum mean daily spore release ranged from 1,461 in a synactinomyxon type to 17,979 in an echinactinomyxon. The latter type showed the maximum daily spore release by an individual worm of 80,000 spores. Synactinomyxon, aurantiactinomyxon, echinactinomyxon and raabeia all showed significantly greater spore release in the summer months. In addition, echinactinomyxon and aurantiactinomyxon types showed significantly greater spore release at 20°C compared to 13 and 4°C. All actinosporean types studied showed a circardian pattern of spore release with maximum numbers shed between 22.00-01.00 h, except in neoactinomyxum where maximum release occurred between 19.00-22.00 h. Myxospore release of Sphaerospora truttae from Atlantic salmon was measured monthly over five consecutive days. Mature spores were first released from 0+ salmon in November and release then peaked in May with a maximum daily estimated mean of over 25,000 spores per fish before decreasing sharply in June to a mean of <20,000 spores. Numbers of mature spores in the kidneys of the same group of fish showed a similar temporal pattern.