AbstractSpermatozoa of the rainbow trout,Salmo gairdneri, were demembranated with Triton X‐100. The demembranated spermatozoa showed vigorous motility in the reactivation solution containing Ca2+at the concentrations below 10−8.5M in the presence of cAMP. The motility was lost at 10−8M Ca2+or more. The shape of the immotile flagella in the presence of high concentration of Ca2+was not uniform: Some showed the cane shape and some were almost straight. The change in Ca2+concentration of the extraction solution did not alter the motility of the reactivated spermatozoa. These results were different from those obtained from the sea urchin spermatozoa. When the concentration of cAMP was changed from 0.5 to 100 μM, the concentration of Ca2+for converting the motile to immotile state was not altered. Thus, it is likely that the Ca2+‐dependent regulatory system of flagellar movement is independent of the cAMP‐induced initiation mechanism, which is assumed to require the transient influx of Ca2+in rainbow trout s
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