Oocyte recruitment and spawning chronology in pike, Esox lucius, and muskellunge, Esox masquinongy

Abstract

During the reproductive cycle, the progression of oogenesis differs markedly between northern pike, Esox lucius Linnaeus, and muskellunge, Esox masquinongy Mitchill. Both species have group-synchronous ovaries but have different oocyte recruitment strategies. Pike is a single spawner, developing eggs in a single clutch annually, whereas muskellunge is a fractional spawner, producing two clutches of eggs per year. During the spawning period in large female muskellunge, oocyte counts indicate that the second clutch of eggs is equally important to the first. An event portrait of the spawning period for muskellunge is provided, whereby arrival of adults to a spawning site, egg yield, and hatching success agree with the fractional spawner concept. A hypothesis of the temporal sequence of evolutionary relationships in recruitment of oocytes for esocoid fishes is presented. The reproductive strategy of muskellunge belongs to a common esocoid ancestor, whereas that in pike is derived and unique. The significance of this divergence in closely related species remains consistent with the ecological theory that evolution of reproductive strategies is adaptive to diverse environmental conditions.