The ultrastructure of spermatozoon and sperm production were observed in wolffish (Anarhichas lupus), a species with internal fertilization, from a broodstock. The mature spermatozoon has an elongated head, eccentric flagellum, and comparatively well developed middle piece. Based on the observations of sperm cells with the optical microscope, the mean lengths of spermatozoon head and flagellum were 3.3 and 21.2 μm respectively. A high variability of sperm cell size was observed due to the presence of spermatids and degenerated spermatozoa in the ejaculate. In most males, sperm production was registered throughout the whole year with a peak in December and January. Sperm production decreased to the end of the breeding season. The difference in volumes of ejaculate and sperm concentrations between males kept at two light cycles (18D: 6L and 6D: 18L) was not significant. Features of wolffish sperm are compared with data reported in the literature on other internally and externally fertilizing fish.

This paper presents some features of turbot sperm and compares them with data reported in the literature on other freshwater and marine fish. In captivity, turbot spermiation period lasts 6 months. When compared to other fish species, turbot males are characterized by low values of maximum gonadosomatic index (0.6-0.8%) and are poor sperm producers in terms of volume (0.2-2.2 ml), concentration (0.7-11.0 × 109 spermatozoa/ml) and total sperm number released per stripping (0.2-12.0 × 109 spematozoa). Compared to most freshwater species, the duration of cell movement is long (1-17 min). The spermatozoon of turbot can be considered to be of a primitive type. A very high protein content (8.8 mg/ml) is found in the seminal fluid of turbot. Increasing collection frequency of turbot males, from monthly to fortnightly and weekly stripping, results in the release of successive samples presenting decreasing semen volume and spermatozoa concentration. Similar spermatozoa concentration and total volume of semen produced per turbot, during a 2 month experimental period, are released from males submitted to an annual light and temperature cycle, compared to those receiving a 6 month contracted light and temperature schedule.