This study deals with individual variation in Bradyidius pacificus (Brodsky, 1950) which is one of the most common aetideid copepods of the waters near Kamchatka. Material was collected during spring-summer 2001 in the eastern part of the Sea of Okhotsk. Only data on females of V-VI copepodite stages are presented. Studied was the structure (setation in particular) of individual limbs, rostrum, cephalothorax and abdomen in more than 50 specimens. There were observed 12 variants of the rostrum, up to 5 variants of the structure of individual segments of the antennules, 8 variants of the protopodites of the maxillipedes and up to 3 variants of the structure of the basipodites of the periopods. The rostrum, antennules and maxillipedes were the most variable parts. There were no variability observed of the structure in the maxillules and the antennae. It is shown that the maxillipedes are more variable than it was considered earlier.

The hypothesis of invasion of Alaska pollock (Gadus chalcogrammus) to the Northern Pacific Ocean during the Bering Strait opening is discussed. Alaska pollock, a fish from the family Gadidae, is the most widespread and abundant commercial species in northern part of the Pacific Ocean. It is considered that the northern part of the Atlantic Ocean was the center of formation of Gadids in the Northern hemisphere. Species Gadus morhua and G. chalcogrammus differ on their features of early ontogenesis and requirements to environment conditions. Life history of the Atlantic cod G. morhua depends on the systems of warm currents in the northern part of the Atlantic Ocean. Unlike Northern Atlantic, all space of northwest part of the Pacific Ocean is occupied by the water of subarctic structure mass. The species G. chalcogrammus occurs more deep-water, differ by benthonic spawning (from 100 to 500 m of bottom depth) and embryonic development at lower (about 0ºC), even negative, water temperature at surface. During their development, the eggs drift under the influence of cold currents. Suitability of early ontogenesis of Alaska pollock to severe conditions promoted its survival and a wide distribution in northern part of the Pacific Ocean during evolution.