Endocrine changes during gonadal maturation and spawning in the orange roughy (Hoplostethus atlanticus Collett), a teleost from the midslope waters off New Zealand.

Orange roughy were sampled at all stages of the reproductive cycle by trawling at depths of 700-1200 m off the coast of New Zealand. Blood samples were collected from live fish, and changes in plasma levels of gonadal steroids were correlated with gonadal development and spawning. Plasma androgens were low in spent and regressed fish of both sexes and increased during gametogenesis to peak early in the spawning period at 6.6 and 9.4 ng.ml-1 for males and females, respectively. Androgen levels dropped to near basal levels over successive days during the first week of spawning in both prespawning and ovulated or spermiated fish. Falls in plasma androgens were not accompanied by increasing levels of plasma 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta P) which remained at or near assay detection limits throughout. 11-Deoxycortisol (11-DOC) was present in the plasma of both sexes but did not change in concert with reproductive development. 17 beta-Estradiol was present in low concentrations (maximum 0.9 ng.ml-1 plasma) in recrudescing females, whereas estrone was detectable but not elevated at any stage. 17 alpha-Hydroxyprogesterone was not detectable in the plasma of any fish at any time. It is suggested that neither 17 alpha,20 beta P nor 11-DOC were active as maturation-inducing steroids (MIS) in orange roughy and that androgens may act as MIS. If the recorded fall in androgens was due to synthesis of another steroid from a common precursor, then the unidentified steroid does not appear to have been involved in stimulating final gamete maturation, but may have some action in initiating spawning behavior.