Oogenesis and reproductive cycles have been studied in sculpin species inhabiting four different ecological zones. COTTOCOMEPHORUS GREWINGKI inhabits coastal pelagic zone (20-300 meters), PARACOTTUS KNERI and COTTUS KESSLERI are found in coastal benthic zone (0,1-250 meters), LIMNOCOTTUS MEGALOPS is restricted to underwater steep slope (200-600 meters). In addition some data about the reproduction of 4 species of Baikalian Cottoidei: COMEPHORUS DYBOWSKII, PROCOTTUS MAJOR, ASPROCOTTUS HERZENSTEINI and ABYSSOCOTTUS KOROTNEFFI have been used.

The following general characteristics of oogenesis and reproductive cycles are common to the species studied: (1) they share the same sequence of events in the process of oogenesis; (2) older generation of oocytes develops in a concerted fashion; (3) reserve stock of oocytes is always available; (4) prolonged III stage of gonads maturity and short IV stage.

Some possible means of adaptation of these species to cold Baikalian habitats have been determined. These are: (1) the presence of basophilic zones (or circumnuclear ring) in the oocytes of previtellogenic development during the entire year, (2) stimulation of vitellogenesis of low water temperature, (3) postspawning condition of gonads corresponds to VI-III stage of a gonads maturity: older generation of reserve stock oocytes is represented by trophoplasmatic growth cells developing longer than one year, (4) formation of restricted breeding groups or reproductively isolated populations with particular season rhythms of gonads.

In the shallow water dweller COTTUS KESSLERI due to a warmer water of habitat postspawning gonads are at stage VI-II and older generation of the reserve stock oocytes is represented by previtellogenic cells and previtellogenic oocytes have basophilic zones only in winter.

Morphological sturucture of oocytes is different at P. KNERI and C. KESSLERI (both are near-shore bottom species). The oocyte morphology of P. KNERI is similar to the one of deep-water species. In C. KESSLERI it is closer to the pelagic viviparous C. DYBOWSKII.