title: Relationships between environmental changes, maturity, growth rate and plasma insulin-like growth factor-I (IGF-I) in female rainbow trout.
abstract: Size reflecting growth rate, energy balance or nutritional status is regarded as an important determinant of the ability of trout to undergo puberty. The relationship of a change in photoperiod, either natural (SNP) or advancing (ADV), with growth, IGF-I and reproduction was investigated in virgin female rainbow trout. Under SNP 63% of the population attained maturity while only 29% spawned 6 months in advance in the ADV regime. Under SNP both size and growth rate in late spring-early summer appeared to determine whether an individual may initiate reproduction while condition factor appeared to be a better predictor in the ADV regime. A complete seasonal relationship between plasma IGF-I, daylength and temperature was demonstrated under natural conditions, and provides direct evidence for the relationship between reproduction and IGF-I. Conversely, trout maintained under ADV exhibited a significantly different plasma IGF-I profile relative to those under a natural photoperiod. Furthermore, IGF-I levels accurately reflected growth rate prior to elevations in sex steroids, suggesting that IGF-I may provide an endocrine signal between the somatotropic and reproductive axes that growth rate and/or size is sufficient to initiate gonad development. In addition, maturing individuals under SNP typically expressed higher circulating IGF-I levels than those that remained immature and may reflect a greater opportunity for IGF-I to act on the pituitary to stimulate gonadotropin production. We observed elevated levels in maturing fish for 3 months under SNP compared to only 1 month under ADV were observed. This may reflect a reduction in the window of opportunity to initiate reproduction under advancing photoperiods and hence explain the reduction in fish successfully recruited.
authors.affiliation: Institute of Aquaculture, University of Stirling, Stirling, Scotland FK9 4LA, UK. jft2@stir.ac.uk
authors.forename: J F
authors.initials: JF
authors.lastname: Taylor
authors.forename: M J R
authors.initials: MJ
authors.lastname: Porter
authors.forename: N R
authors.initials: NR
authors.lastname: Bromage
authors.forename: H
authors.initials: H
authors.lastname: Migaud
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D049628:Body Size / Q000502:physiology* / Q000528:radiation effects; D004777:Environment; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008027:Light; D017686:Oncorhynchus mykiss / Q000097:blood / Q000254:growth & development*; D017440:Photoperiod; D011897:Random Allocation; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology* / Q000528:radiation effects; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D007334:Insulin-Like Growth Factor I