Using light and electron microscopy, enzyme‐histochemistry thin‐layer chromatrography and photometry the functions of the spermatic ducts in salmonid fishes (rainbow trout,Oncorhynchus mykiss, Arctic charr,Salvelinus alpinus; grayling,Thymallus thymallus; whitefish,Coregonussp.) were investigated. During spawning the spermatic duct of the Salmonidae has a high secretory activity: it synthesizes steroids, lipids (triglycerides, fatty acids, cholesterol esters, phosphatidylcholine), monosaccharides (glucose, fructose), proteins and enzymes (acid and alkaline phosphatase, glucuronidase and proteases). It is important for storage and resorption of spermatozoa. Interspecific differences exist in the storage capacity for se