Publication Abstract

Plasma concentrations of ovarian steroids in relation to oocyte final maturation and ovulation in female plaice sampled at sea

Plasma concentrations of ovarian steroids in relation to oocyte final maturation and ovulation in female plaice sampled at sea

A.P. Scott, P.R Witthames, R.J. Turner and A.V.M. Canario

Reproductively mature female plaice (Pleuronectes platessa L.) were caught at sea. Blood plasmas were radioimmunoassayed for free: and sulphated 17,20β-dihydroxy-4pregnen-3-one (17,2β-P); free 17β-oestradiol; free and glucuronidated testosterone; and sulphated 5β-pregnane-3α, 17,20β- triol (3α,17,20β-P-5β) and 3α,17, 21trihydroxy-5 (3-pregnan-20-one (3α,17,21-P-5 β).Ovaries were digested with Gilson's fluid and the oocytes counted and sized by an automatic method. Statistical analysis was carried out on the relationship between steroid concentrations and the'percentage ofvitellogenic oocytes remaining inthe ovaries','batch size of hyaline oocytes','degree ofhydration ofhyaline oocytes' and'time of capture'.

Concentrations of free 17β-oestradiol, free testosterone and glucoronidated testosterone were stronglypositively related to the percentage ofvitellogenic oocytes remaining in the ovaries - being at their highest in pre-spawning (stage IV) females (i.e. those in which oocytes were close to fully grown, but had not yet entered the stage of final maturation). In contrast, the concentrations ofthe other four steroids were at their lowest in stage IV females. Free 17,20β-P (the putative maturation-inducing steroid) became only slightly elevated (less than 2-fold)during spawning (i.e. in stage V and VI females with hydrated and/or ovulated eggs). Sulphated 17,20β-P and 3α,17, 21-P-5β became slightly more elevated (3- to 4-fold). However, sulphated 3α,17,20β-P-5 (3 concentrations increased 30-fold and were at their highest in fish in which only 40% of vitellogenic oocytes remained in the ovaries. Sulphated 17,20β-P, 3α,17,20β-P-5β and 3α,17,21-P-5β concentrations were significantly positively related to hyaline oocyte batch size; and free 17,20β-P, sulphated 17,20β-P and sulphated 3α,17,20β-P-5β were significantly negatively to the degree of hydration ofthe hyaline oocytes. None of the steroid concentrations, however, was related to the time of capture. More ovulated females were found in the afternoon than at any other time of the day.

Reference:

A.P. Scott, P.R Witthames, R.J. Turner and A.V.M. Canario, 1998. Plasma concentrations of ovarian steroids in relation to oocyte final maturation and ovulation in female plaice sampled at sea. Journal of Fish Biology, 52: 128-145

A.P. Scott*, P.R Witthames*, R.J. Turner* and A.V.M. Canario

Journal of Fish Biology, 52: 128-145