Sequeira, V.Couto, ElsaNeves, A.Vieira, A. R.Paiva, R. B.Canario, A.V.M.Gordo, L. S.2019-11-202019-11-202017-050022-11121095-8649http://hdl.handle.net/10400.1/13141Two hundred and seven individuals (103 females and 104 males) of bluemouth Helicolenus dactylopterus (Scorpaeniformes, Sebastidae), a commercially important deep-water species with an unusual reproductive strategy, from the eastern Atlantic Ocean ranging from 13<bold></bold>9 to 37<bold></bold>5 cm total length (L-T) were analysed from September 2011 to October 2012. The analysis included gonad maturity phases and blood-plasma levels of oestradiol-17 (E-2), 11-ketotestosterone (11-KT) and 17,20-dihydroxypregn-4-en-3-one (17,20-P). Results confirmed the existence of an annual reproductive cycle with asynchrony between females and males and a spawning season from January to May. A pronounced peak in 17,20-P in October for both sexes was associated with possible mating behaviour and recent copula. Levels of E-2 increased preceding the elevation of the gonado-somatic index during ovarian growth and were lower during regression and regeneration. The frequency distribution of oocyte-embryonic stages and variation of hormone levels suggest the existence of daily rhythms. Fertilization was detected between 2000-0000 and 0800-1200 h and spawning took place throughout the day peaking between 2000 and 0000 h. The cyclic pattern of sex steroids and ovarian recruitment provides a new insight into the reproductive strategy of this species.engTrout salmo-gairdneriReproductive-cycleOocyte growthFishFecunditySebastesSpermatogenesisScorpaeniformesDelarocheRockfishjournal article10.1111/jfb.13299