REPRODUCTIVE-CYCLE AND PLASMA-LEVELS OF SEX STEROIDS IN FEMALE EURASIAN PERCH PERCA-FLUVIATILIS

From April 1995 to April 1996, the annual reproductive cycle of the Eu rasian perch Perca fluviatilis was studied at the Fishfarming Lindre C enter (Moselle, France). At monthly intervals (at intervals of 10 days during the periovulatory period), 5 females were caught and dissected . From sampled organs, the gonado-, hepato-and viscerosomatic indexes (GSI, HSI, VSI were calculated, oocyte diameters (OD) and the plasma l evels of testosterone (T), 17 beta-estradiol (E-2), 17,20 beta-dihydro xy-4-pregnen-3-one (17,20 beta-P) and protein-phosphorus (PPP) were me asured. After the sexual resting period observed from May to August (G SI < 1 %, OD < 200 mu m, VSI = 4-6 %), oogenesis began in September wh en the water temperature decreased from 26.4 to 14.1 degrees C. The GS I increased progressively until mid March(15 %), then rapidly until sp awning (25 %, OD = 850 mu m) which occurred in April(14 - 15 degrees C ). The plasma levels of T, E-2, 17,20 beta-P and PPP were low during t he sexual resting period. E-2 and PPP levels increased significantly a t the onset of the oogenesis in September, then the E-2 level raised a bruptly in November (3-4 ng . mL(-1)). In December the T level increas ed rapidly to 15-20 ng mt. The testosterone, E-2 and PPP levels remain ed very high until spawning, indicating the existence of active vitell ogenesis. The highest HSI (2.1-2.2 %) recorded in winter confirmed thi s. During the periovulatory period, a peak of E-2 (4 ng . mL(-1)) appe ared, whereas T level diminished. In this study, 17,20 beta-P levels r emained low (0.2-0.6 ng . mL(-1)) and relatively constant. No 17;20 be ta-P peak was observed during the periovulatory period. Sampling at 10 day intervals was probably inadequate to specify the hormonal variati ons related to the final oocyte maturation and the ovulation. (C) Ifre mer-Elsevier, Paris.