Effects of Maternal Growth on Fecundity and Egg Quality of Wild and Captive Atka Mackerel

Tradeoffs in energy allocation between growth and reproduction can result in variation of the reproductive potential in fish with differing growth patterns.  Spawning biomass is often used as a proxy for reproductive potential, based on the assumption that fecundity is directly proportional to body weight.  We examined variation in the reproductive potential of Atka mackerel (Pleurogrammus monopterygius) by studying the effect of differential growth and condition patterns on fecundity, atresia, and egg energy.  Fecundity and egg energy were determined from two geographic areas, Seguam Pass and Amchitka Island, and compared to those of fish held in captivity.  Atka mackerel showed distinct growth and condition differences with weight at length and length at age being the highest for captive fish, intermediate at Seguam Pass, and smallest at Amchitka Island.  Realized fecundity showed captive fish spawning 7 batches, fish from Seguam spawning 6 batches, and fish from Amchitka spawning 5 batches on average.  For wild fish, potential and realized fecundity at length or age was significantly higher at Seguam Pass than at Amchitka whereas the fecundity at weight relationship did not differ by area, suggesting weight as a better predictor of fecundity than length or age.  Atresia and batch fecundity by length or weight did not differ by area, suggesting that variation in fecundity was better explained by variation in batch number, not batch size.  Oocyte dry weight of captive fish was higher than for wild fish, whereas batch order did not significantly affect oocyte dry weight. Increased potential fecundity, realized fecundity, and oocyte quality in Atka mackerel females was strongly related to body size, indicating that growth differences and maternal feeding success impact fecundity and oocyte quality of Atka mackerel.  Therefore changes in growth and condition patterns need to be taken into account to accurately estimate reproductive potential for this species.