Sexual maturation in the Mackerel Icefish, Champsocephalus gunnari, was studied by macroscopic examination of gonads. Evidence in support of the hypothesis that a proportion of mature fish fail to spawn was obtained. Histological examination of ovaries indicates that some ova were undergoing regression and resorption at least two months prior to the normal spawning date. It is concluded that the underlying cause is probably due to a shortage of krill, an important dietary item for Champsocephalus gunnari.
Abstract:
The results are presented of studying icefish vertical migration based on the data of R/V cruises during the seasons of 1982-83, 1983-84 and 1986-87, when this species was highly abundant on the South Georgia shelf. It is revealed that at day time the fish distributes near the bottom and the maximum catches were available at the middle of the light hours of the day. At twilight the fish concentrations migrate into the water column and the catches greatly decrease. The direct observations of icefish vertical migrations provided by means of hydroacoustic equipment are presented.
