Publication Abstract

Reproductive steroids duringmaturation in a primitive teleost, the Pacific herring (Clupea harengus pallasi)

J. Carolsfeld, A.P. Scott, P.M. Collins and N.M. Sherwood

Concentrations of reproductive steroids were measured n the plasmaof captive Pacific herring, Clupea harengus pallasi, (1) prior to ovulation andmilt production, (2) luring the periovulatory and newly milt-producing period, (3) duringa "ripe" holding period after ovulation and during milt production, and (4)before and after pawning. 17a,20β-Dihydroxyprogesterone (17,20β-P), despite being present only in low concentrations in theinconjugated (free) form (< 10 ng/ml), is likely to be the maturation inducing steroidin females and was associated with the initiation of milt production in males since itslevels are elevated coincidentally with these events. Gucuronated 17,20β-P, free 17α-hydroxyprogesterone 17-P), andfree and glucuronated 3α,17α-dihydroxy-5β,pregnan-20-one (3x,17-P-50)were present in high concentrations (140-250 ng/ml) in periovulatory females and newlymilt-producing males. This steroid pattern suggests that the low levels of 17,20β-P are due to glucuronation andcompetitive conversion of its precuror, 17-P, to free and glucuronated 3α, 17-P-5β. Glucuroated testosterone was theprincipal steroid in preovulatory and premilt-producing fish (200-350 ng/ml), coincidentwith similar levels of glucuronated 11-etotestosterone in males. After ovulation femalesdid of spawn synchronously until 2 months later, which may be partially due to reducedenvironmental cues in the captive situation, while male fish released milt sporadicallythroughout the ripe holding period. Steroidal indicators of readiness to spawn in femalesor males were not detected. Rather, levels of all steroids gradually decreased in ripeholding fish (< 30 ng/ml) to reach even lower levels (< 1 ng/ml) after spawning. Wesuggest that "runniness" of gametes is a distinctive characteristic of femalesthat are ready to spawn, but that this may result from relaxation of sphincter musclesrather than being an additional maturational step.

Reference:

J. Carolsfeld, A.P. Scott, P.M. Collins and N.M. Sherwood, 1996. Reproductive steroidsduring maturation in a primitive teleost, the Pacific herring (Clupea harengus pallasi).General and Comparative Endocrinology, 103: 331-348.