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The in vitro effects of sodium orthovanadate (Na3VO4), a G-protein activator, on ovulation and prostaglandin (PG) synthesis were investigated in the brook trout (Salvelinus fontinalis) ovary. PGE and PGF levels in incubation medium of either extrafollicular (EF) tissue or follicles were measured by specific radioimmunoassays (RIA). PGE levels in follicle incubates were increased by Na3VO4 at both pre-germinal vesicle breakdown (preGVBD) and preovulatory (preOV) stages. However, an increase of PGF levels in follicle incubates was observed only in preGVBD follicles in the presence of Na3VO4. The preOV follicles spontaneously released more PGF than preGVBD follicles and the level was not affected by Na3VO4 treatment. In contrast, in incubates of EF tissue, Na3VO4 induced dosage-dependent increases in PGE and PGF at either stage. The Na3VO4-stimulated increase of PGE in preOV follicle incubates was significantly reduced by the translational inhibitor, cycloheximide (5 μM), but not by the transcriptional inhibitor, actinomycin (5 μM). PGF levels in preOV follicle incubates were also significantly reduced by cycloheximide and actinomycin in controls, but not in the presence of 0.1 mM Na3VO4. The results suggest that protein synthesis was required for Na3VO4 to increase accumulation of PGE, and in maintaining control PGF levels in preOV follicles. In addition, since PGF levels in preOV follicles were not reduced by either inhibitor in the presence of Na3VO4, a Na3VO4-stimulated increase of PGF levels was unmasked that apparently acts through a non-translational pathway. In vitro ovulation was also significantly increased by 0.1 mM Na3VO4. However, the Na3VO4-induced ovulation was not inhibited by either actinomycin or cycloheximide. The data imply that the mechanism(s) by which Na3VO4 induces ovulation are distinct from that for stimulating PG accumulation. When preOV follicles were incubated with 10 μM forskolin, no stimulatory effect on ovulation, or on PGE and PGF levels was observed. The data strongly indicate that the effects of Na3VO4 on ovulation and ovarian PG levels were not mediated by an increase in cAMP.

The effects of the phorbol ester, phorbol 12-myristate-13-acetate (PMA), and the calcium ionophore, A23187, on prostaglandin E (PGE) and F (PGF) levels were investigated using incubates of brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) ovarian tissue. The combination of PMA (0.1 μg/ml) and A23187 (0.1 μg/ml) synergistically stimulated an increase in PGE and PGF levels in incubates of brook trout follicles obtained from females prior to germinal vesicle breakdown, prior to ovulation and postovulation. The highest levels were observed in incubates of follicles taken just prior to ovulation. By itself, PMA also stimulated PGE and PGF accumulation while A23187 was much less effective. A23187, but not PMA, stimulated in vitro ovulation of brook trout follicles. Both cycloheximide and actinomycin inhibited PGE and PGF accumulation in incubates of preovulatory brook trout follicles stimulated with PMA but these inhibitors did not block ovulation induced by A23187 or PMA/A23187. The effect of PMA and A23187 were tested on the following 3 yellow perch tissue preparations: 1) isolated follicles [free of extrafollicular tissue (EF)], 2) EF tissue, and 3) intact tissue (containing undissected follicles attached to EF tissue). Incubates with all tissue types were performed in the presence or absence of 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-PG, 0.1 μg/ml). PMA (0.1 μg/ml) in combination with A23187 (0.01 μg/ml) stimulated PGE and PGF accumulation in all tissue types though the greatest increase was generally observed in intact preparations. There was a lower accumulation of PGE in intact and EF tissue incubates stimulated with 17,20β-PG and PMA. In addition, in incubates of ovarian tissue from several perch there was a higher accumulation of PGF in intact preparations stimulated by PMA or PMA/A23187 in the presence of 17,20β-PG. The results for both species indicate that phorbol esters (PEs) can stimulate prostaglandin synthesis in follicles and, given that PEs have been shown to stimulate protein kinase C, it is possible that this enzyme is naturally involved in the control of ovarian PG synthesis in fish. It also appears that the stimulation is related to maturational stage in brook trout and steroid stimulation in yellow perch.

SUMMARY. 1 We evaluated survival, growth and time to maturation of the fairy shrimp, Streptocephalus seali Ryder, in the laboratory at various combinations of temperature and water hardness. 2 Both independent factors affected survival and growth of S. seali. Multiple regression analysis and response surface modelling predict that after 4 days, over 80% survival is obtained at temperatures from 14 to 28°C and water hardnesses from 60 to 130 mg CaCO3 1-−1. 3 Growth rates of larvae were often maximum at physicochemical conditions other than those which had promoted maximum rates of survival. For example, after 12 days mean total body length was almost 12 mm in larvae which had been maintained at 34°C (80 mg CaCO3 1-−1): the maximum survival rate had been obtained at 19°C. Total length was directly correlated with temperature at the lowest hardness tested, but not at the other two hardnesses (100 and 120 mg CaCO3 1-−1). At the latter water hardnesses, total length was significantly less at 34°C than at 32°C on all three sampling occasions (4, 8 and 12 days post-hatch). 4 Similarly, developmental stage of larvae correlated well with temperature but larvae reared at 34°C did not develop more quickly than those reared at 32°C. After 12 days, most larvae at the two highest temperature treatments had developed at least to Stage 14 and many were nearly mature; at 17°C most larvae were still at Stage 10. 5 During our study of maturation rate of females we noted that egg production was initiated after completion of fourteen or fifteen moults. Mean time to maturation at 27°C (17.3±2.8 days) exceeded that at 32°C (12.3±2.6days). The minimum time to maturation of a shrimp was 9 days at 32°C.