Meeting Abstract

S3.6  Sunday, Jan. 4  The hormonal control of seawater performance in anadromous fish MCCORMICK, Stephen D.; USGS, Conte Anadromous Fish Research Center, Turners Falls, MA USA mccormick@umext.umass.edu

Anadromy is a life history strategy in which fish move from fresh water to seawater as juveniles and then return to fresh water to breed. Anadromy developed early in vertebrate evolution and is a feature of many basal fishes such as lamprey, sturgeon and salmonids. Downstream migration and seawater entry of juvenile anadromous fish generally occurs during a particular season and developmental stage. Morphological changes such as silvering and physiological changes such as increased salinity tolerance and scope for growth increase performance and fitness in seawater. The endocrine changes that control seawater performance are best known for salmonids. Cortisol and the growth hormone/insulin-like growth factor I act synergistically to increase osmoregulatory ability in seawater. Prolactin is thought to play an inhibitory role, though direct evidence for this is limited. The thyroid axis promotes morphological changes in salmonids, whereas thyroid hormones inhibit metamorphosis in lamprey. The ability of sex steroids (and estrogenic endocrine disruptors) to inhibit seawater performance may be related to their role in promoting movement of adults into fresh water. Photoperiod and temperature regulate these hormones, and inappropriate rearing conditions such as those that may occur in hatcheries can lower seawater performance. Relaxed selection in land-locked populations has resulted in lower levels of growth hormone and cortisol and dampening of traits associated with seawater performance. By integrating developmental and environmental information, the endocrine system induces behavioral and physiological changes that increase seawater performance of juvenile anadromous fish.