Effects of Non-Spawning Season (yolkless to Early Yolk Formation Stage) Temperature on Growth and Reproductive Characteristics in Hatchery-Reared, Repeat-Spawning Walleye Pollockgadus Chalcogrammus

The effects of water temperature during the non-spawning season (yolkless to early yolk formation stage of the ovary) on the growth and reproductive characteristics of 4-year-old hatchery-reared walleye pollockGadus chalcogrammus(repeat spawners) were examined. Fish were kept in tanks under two temperature regimes (non-controlled: 6.4-17.2 degrees C; cooled: 5.1-15.7 degrees C) from 42 to 46 months post-hatching (non-spawning period) and showed differences in growth (in terms of weight and condition factor) shortly before the spawning period (mostly at the early yolk formation stage of the ovary). The fish spawned spontaneously from 47 to 51 months post-hatching at 5 degrees C. Growth differences were related to egg diameter but not to the timing of spawning. Larger eggs were spawned from fish that had greater increases in weight and condition during the non-spawning season. In contrast, the main spawning period did not vary according to the non-spawning season treatment. These results were compared with the spawning records of 2- and 3-year-old walleye pollock from two previous years, showing that the timing of spawning advances as fish size increases with age. In addition, spawning experience and the amount of energy acquired before the spawning period likely influence egg size.