Mackerel icefish become sexually mature at 3 years of age, with the exception of the southern Scotia Arc where they don’t reach maturity till a year later. Upon sexual maturity, they spawn for 2-3 months yearly. Some populations begin to spawn as early as late February and others do not finish their spawning until as late as September. This variation is the result of the different locations of each population and natural variation from year to year (review article). Feeding conditions serve as a trigger for what proportion of a population spawn each year. Kock (1990) estimated that 10–20% of theadult fish do not spawn each year. This proportion may increase to 60% in those years when krill is scarce atSouth Georgia and the fish suffer from malnutrition. Generally, they greatly reduce feeding directly before spawning. They also move closer to shore before spawning to preferred grounds, with males starting this mild migration about a month before females (Everson et al. 2001). C. gunnari have absolute fecundity typically around 2 – 8,000 eggs with a relative fecundity usually in the order of 5-20. Differences between years have been observed in relative fecundity. These differences may be related to the actual condition of the fish (Alekseeva and Alekseev 1997) which may vary considerably between years and even within a season (Everson and Kock 2001). Relative fecundity sometimes decreased with increasing length and weight of the females, such as in C. gunnari (Alekseeva and Alekseev 1997). Eggs of C. gunnari range from 2.6 to 4.1 mm in diameter (Kock 1981) and are demersal, or exist at the sea floor (Everson et al. 2001). Incubation after fertilization takes approximately 3 months, wich is short in comparison to the other icefish (Duhamel 1995). The hatching larvae are 13-17mm in size (Duhamel 1995). Time of hatching varies by location, and appears to happen for several months (North 1990; Everson et al. 2000a). After hatching, they live as active, pelagic predators of krill, becoming increasingly sedentary with age (Kock 2001).
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