Life after Precocious Male Maturation in a Semelparous Salmonid: A Physiological Perspective in Spring Chinook Salmon

Atlantic salmon are iteroparous; possessing the ability to undergo repeat maturation. Precociously mature males of this species (a.k.a “precocious parr”) are also capable of smoltification and/or rematuration following maturation at age-1.  Pacific Chinook salmon are typically characterized as semelparous; dying after a single spawning event.  However, observations of survival following maturation in males that mature at age-1 (a.k.a. “microjacks”) have been documented, but little is known regarding the post maturation physiology of these fish.  Specifically, it is unclear the degree to which they may either die, resorb their testes and undergo smoltification or partially or completely resorb the testes then remature.   Furthermore, if all these life-history options are possible in a population, in what proportions do they occur under variable environmental conditions?  In this investigation we measured a series of physiological factors including (survival rate, size, gill Na+/K+-ATPase activity, K, plasma 11-KT, whole body lipid, pituitary FSH and LH mRNA, GSI, and testicular histology) in fish following maturation at age-1 that were fed either a high or low winter ration . From our results we conclude that the capacity for rematuration (iteroparity) is very high independent of overwinter nutritional status in this unique variant of the Chinook salmon life history.