Seasonal changes in plasma gonadal steroid concentrations and gonadal morphology of male and female tench (Tinca tinca, L.)

In order to gain a better understanding of the reproductive cycles of male and female tench (Tinca tinca), gonadosomatic index, gonad histology and plasma concentrations of estradiol‐17β (E₂), testosterone, an drostenedione, 11‐ketotestosterone (11‐KT), 17,20β, 21‐trihydroxy‐4‐pregnen‐3‐one (17,20β,21‐P), 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P) and 17,20α‐dihydroxy‐4‐pregnen‐3‐one (17,20α‐P) were measured at the four seasons of the year, plus a further sampling coincident with the peak of spawning in early July. As expected, in both males and females, the plasma concentrations of androgens (excluding 11‐KT in females – undetectable) and C₂₁ steroids were significantly more elevated in the spring and summer (when most gonadal development took place) than in the autumn and winter. The only unexpected finding was that 17,20β‐P and 17,20β,21‐P, the steroids that are normally associated with oocyte final maturation in females and spermiation in males, were found in substantial amounts in both pre‐vitellogenic, pre‐spermatogenic and post‐spawning fish. This suggests that these steroids may have other as yet unidentified roles in this species.     

Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner

The wrasse, Pseudolabrus sieboldi, is a diandric protogynous labrid fish. Spawning is performed by a terminal phase (TP) male and an initial phase (IP) female between 6:00 and 9:00 h daily during two-month-long spawning season. In the present study, to investigate the roles of steroid hormones in the diurnal spermatogenesis of the P. sieboldi TP male, all steroid hormones produced in the testis were identified and the synthetic pathways of these steroids were determined. Furthermore, the circulating levels of the major steroids produced were analyzed throughout a day at 3-hour intervals during spawning season. In the testis, 11-ketotestosterone (11-KT), estradiol-17β (E2), 17,20β-dihydoxy-4-pregnane-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesized as the major metabolites. In vitro steroid biosynthesis experiments showed similar results to the circulation profiles of the major steroids. This study is the first to clarify the complete steroidogenic pathways in the gonads of a diandric protogynous species throughout its life, when combined with the results of the steroidogenesis in the ovarian follicles. This is also the first report of a clear diurnal rhythm of the steroid production corresponding to the spermatogenic process in the testis of a male teleost.     

Effects of temperature on the final stages of sexual maturation in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.)

Maturing male and female Atlantic salmon (Salmo salar L.) were held under three temperature regimes for 10 weeks between September and December: warm (constant 14–16 °C), ambient (decreasing from 11 to 5 °C), and cold (decreasing from 7 to 3 °C). Blood samples were analyzed for plasma steroid levels, and the fish were inspected for the presence of expressible milt (total volume and spermatocrit) and ovulation weekly. Samples of eggs were dry-fertilized with milt stripped from three males held at the same temperatures and incubated until the eyed stage. In females, levels of plasma testosterone (T) and 17β-oestradiol (E₂) dropped as ovulation approached, concurrent with a rapid increase in levels of plasma 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P). In males, levels of T and 11-ketotestosterone (11-KT) peaked 2–3 weeks after the first appearance of expressible milt, while levels of 17,20β-P increased steadily and did not exhibit a definite peak. Exposure of females to cold water amplified and advanced the profiles of all three steroids compared with the ambient group, and increased the survival rates to the eyed egg stage. Cold water had no immediate effect on the male steroid profiles, but later, higher levels of 17,20β-P were evident compared with both the ambient controls and the warm water group, while the effects on 11-KT and T were more variable. Exposure to warm water completely inhibited both milt production and ovulation. Moreover, warm water modulated the steroid profiles of the males with lower 11-KT levels compared with ambient controls and lower 17,20β-P level compared with cold-water-treated males. In females, warm water resulted in total inhibition of the peri-ovulatory peak in 17,20β-P and prevented the normal decline of T and E₂ levels associated with ovulation. The findings of the present study are highly relevant for broodstock management in aquaculture, as well in understanding the impact of climate change/temperature variability on wild salmon spawning.     

Exposure to 17α,20β-dihydroxy-4-pregnen-3-one changes seminal characteristics in Nile tilapia, Oreochromis niloticus

This experiment was conducted to evaluate the seminal characteristics of Nile tilapia males exposed to water‐borne 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20βP). Male Nile tilapia (Oreochromis niloticus L.) were exposed to the steroidal pre‐ovulatory pheromone 17,20βP, added to water at a concentration of 5×10^?9 M. The pheromone‐exposed males had higher sperm volume and concentration. In addition, the spermatozoa contained in the sperm had higher motility and the motility duration was longer than ethanol‐exposed males (control group). The percentage of live spermatozoa was not affected by the treatments. Our results suggest that this pheromone can improve sperm quality characteristics and could become a non‐invasive method for enhancing spawning in Nile tilapia.     

Effects of hemi-castration on plasma steroid levels in two teleost fishes; the three-spined stickleback, Gasterosteus aculeatus, and the Atlantic salmon, Salmo salar

In order to study the possible homeostatic regulation of gonadal steroids in fishes, plasma steroid levels were measured in hemi-castrated and sham-operated nesting male three-spined sticklebacks, Gasterosteus aculeatus, and in mature 2-year old male Atlantic salmon, Salmo salar. Hemi-castration significantly suppressed androgen levels in both species. In sticklebacks, plasma levels of 11-ketotestosterone (11KT) were 56% and levels of testosterone (T) 55% of those found in sham-operated males. In hemi-castrated salmon the levels of 11KT were 63%, and the levels of T were 75% of the levels in sham-operated males. In contrast, levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P) in salmon (not measured in sticklebacks) were not different between hemi-castrated and sham-operated males. The results suggest that, although levels of the steroid 17,20-P were compensated in hemi-castrated salmon, the androgen levels in fish males in full spawning condition are not closely regulated by negative feedbacks. This revised version was published online in July 2006 with corrections to the Cover Date.     

In vitro steroid metabolism during final oocyte maturation in white croaker Micropogonias furnieri (Sciaenidae)

The main steroids produced by three stages ovarian fragments (post-vitellogenic PV, oocytes in GV migration phase Mtg and mature oocytes M) of white croaker were compared. In Mtg and M stages 17,20β-dihydroxy-4-pregnen-3-one (17,20βP), 17,21-dihydroxy-4-pregnene-3,20-dione (17,21P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesised. The specific synthesis of 20βS in Mtg oocytes suggests a MIS role for this steroid.     

The relationship between plasma and ovarian levels of gonadal steroids in the repeat spawning marine fishesPagrus auratus (Sparidae) andChromis dispilus (Pomacentridae)

The relationship between plasma and ovarian levels of gonadal steroids was examined in two New Zealand fish species with multiple spawning cycles of differing length. Snapper (Pagrus auratus) have a daily cycle of oocyte development, ovulation and spawning, whereas demoiselles (Chromis dispilus) spawn over 2–3 days during a repeat spawning cycle of 7–9 days. Ovarian and plasma levels of the gonadal steroids 17β-estradiol (E₂), testosterone (T), 17-hydroxyprogesterone (17P) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured in reproductively active fish captured from the wild. Ovarian levels of E₂, T and 17P changed in relation to spawning cycle and gonad stage in both snapper and demoiselles. E₂ and T levels were detectable at all times, but highest during vitellogenesis in both species. Cyclic changes of 17P occurred in both species, and levels appeared to depend on the rate of conversion of 17P to other hormones. No changes in ovarian levels of 17,20βP were detected in relation to stage of the spawning cycle in snapper; however, ovarian levels of 17,20βP were highest in demoiselles before spawning when fish undergoing final oocyte maturation predominated. Plasma levels of E₂ and T were strongly correlated with ovarian concentrations (r=0.850 and r=0.819 for E₂ and T respectively) in demoiselles but there was poor correlation between ovarian and plasma levels of 17P and 17,20βP (r=0.004 and 0.273 respectively), or between ovarian and plasma levels of E₂, T, 17P or 17,20βP of snapper (r=0.135, 0.277, 0.131 and 0.279). The poor correlation between plasma and ovarian levels of some steroid hormones suggests that plasma concentrations of steroids may not adequately reflect the reproductive status of the fish during short-term cyclic ovarian changes. It is suggested that this disparity is likely to be most marked in species with ovulatory periodicity of short duration.     

Hormonal and pheromonal control of spawning behavior in the goldfish

Species that employ sexual reproduction must synchronize gamete maturity with behavior within and between genders. Teleost fishes solve this challenge by using reproductive hormones both as endogenous signals to synchronize sexual behavior with gamete maturation, and as exogenous signals (pheromones) to synchronize spawning interactions between fish. This dual role of hormonal products is best understood in the goldfish, an external fertilizer with a promiscuous mating system. Female gonadal growth and vitellogenesis is stimulated by 17β-estradiol (E2) which also evokes release of a recrudescent pheromone. At the completion of vitellogenesis, ovarian E2 production drops and plasma testosterone increases, sensitizing the female gonadotropin II (luteinizing hormone; LH) system to environmental cues (temperature, spawning substrate, pheromones). These cues eventually trigger a LH surge that alters steroidogenesic pathways to favor the production of progestins including 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P). Plasma 17,20β-P stimulates oocyte maturation but is also released to the water along with sulfated 17,20β-P and androstenedione to serve as a preovulatory pheromone. This pheromone stimulates male behavior, LH release, and sperm production. At the time of ovulation, females become sexually active in response to prostaglandin F2α (PGF2α) synthesized in the oviduct. PGF2α and its metabolites are released as a postovulatory pheromone that induces male spawning behavior which further increases male LH and sperm production. Androgenic hormones are required for male behavior and LH release. Although goldfish are gonochorists, hormone treatments can induce heterotypical functions in adults. Similar findings in other fish demonstrate that a sexually bipotential brain is not restricted to hermaphroditic fishes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sperm production and quality in brill Scophthalmus rhombus L.: relation to circulating sex steroid levels

The aims of the present study were to characterize sperm quality and to quantify seasonal changes in sexual hormone (testosterone [T], 11-ketotestosterone [11-KT] and 17,20β-dihydroxypregn-4-en-3-one [17,20β-P]) levels in male brill (Scophthalmus rhombus) plasma, as well as to test a more intensive sampling strategy to establish relationships between sex steroid levels and sperm production parameters. Sperm concentration ranged from 0.5 to 3.1 × 10⁹ spermatozoa mL^?1, and changes in sperm quality parameters depending on sampling date were observed. Plasma sexual steroid levels remained high and changed in parallel during the spawning season and afterwards decreased to very low levels in summer. The analysis of annual changes of 11-KT and T ratios suggests that 11-KT can be the main circulating androgen for stimulating spermatogenesis in S. rhombus and that T could be involved in the beginning of spermatogenesis through the positive feedback on brain-pituitary-gonad axis. Finally, daily 11-KT and T levels showed similar patterns of variation in males sampled, whereas 17,20β-P amounts showed somewhat opposite trends. These differences could be related with the different role of androgens and progestin during the spermatogenesis.     

Steroid synthesis in follicular cells and induction of germinal vesicle breakdown in spotted wolffish (Anarhichas minor) oocytes

Incubation of follicular cells from postvitellogenic spotted wolffish ovaries with tritiated steroid precursors revealed that granulosa cells were able to convert 17-hydroxyprogesterone (17-P) to 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and androstenedione. Theca cells had limited ability to synthesise additional steroids from 17-P but converted 17,20β-P to 17,20β-P sulphate. Neither of the two cell layers was able to synthesise 5β-pregnane-3α,17,20β-triol-20-sulphate (3α,17,20β-P-5β-S) which is found in high concentrations in plasma. 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P), 17,20β-dihydroxy-5β-pregnan-3-one (17,20β-P-5β) and 17,20β-P were most potent in inducing germinal vesicle breakdown (GVBD). Sulphation of 17,20β-P resulted in loss of GVBD inducing activity.     

Effects of photoperiod, temperature and GnRHa treatment on the reproductive physiology of Atlantic salmon (Salmo salar L.) broodstock

The present study demonstrates that acceleratedphotoperiod advances ovulation in Atlantic salmon, and that exposure to cold water prior to spawning further advances and synchronizes this process while improving egg-survival. High water temperature inhibited both sperm release and ovulation, whereas a GnRHa treatment overrode this temperature effect in most individuals. A decrease in water temperature seemed to accelerate both ovulation and sperm release, and water temperature modulated the plasma 17,20βP profiles around ovulation and sperm release. The GnRHa treatment markedly increased the volume of strippable milt and the plasma 17,20βP levels in males.     

Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, <Emphasis Type="Italic">Platichthys stellatus</Emphasis>

The present study was designed to examine the potential for inducing ovulation in starry flounder (Platichthys stellatus) using gonadotropin-releasing hormone analog (GnRHa) and human chorionic gonadotropin (hCG) to assess whether starry flounder are differentially responsive to GnRHa and hCG. Female starry flounder were injected or implanted with different doses of hCG or GnRHa pellets to examine their ovulation-inducing potential and effects on plasma levels of testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Blood samples were collected for up to 10 or 25 days post-injection or post-implantation in two separate experiments designed to mimic the early and middle stages of spawning, respectively. Fish treated with the GnRHa pellets (100 µg) showed a significant increase in the total number of stripped eggs relative to the controls. GnRHa administration had no effect on the floating rate or fertilization rate of ovulated eggs in the both experiments, whereas hCG injection affected both of these rates. Plasma T levels were not significantly different between the exogenous hormone-treated and control fish. In contrast, the plasma E2 level was elevated in those fish treated with GnRHa, regardless of injection or implantation, and was accompanied by increased numbers of stripped eggs in both experiments. Treatment with GnRHa resulted in higher 17,20βP levels compared to the controls, and there was a positive relationship between elevated plasma 17,20βP and an increase in ovulated eggs in response to GnRHa treatment. The implantation of starry flounder with GnRHa-containing pellets was effective at inducing sustained ovulation compared to hCG treatment.     

Production, release and olfactory detection of sex steroids by the tench (Tinca tinca L.)

The present study is concerned with pheromone communication in tench (Tinca tinca L.), establishing firstly whether males have a high olfactory sensitivity to some typical teleost sex steroids and prostaglandins; and secondly whether males and females might be able to synthesise and release some of these steroids into the water. The C₂₁ steroid, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was found to give large electro-olfactogram responses with an estimated threshold of detection of 10⁻¹² M. The male tench were equally sensitive to glucuronidated 17,20β-P (10^−11.6 M) but 100 times less sensitive to sulphated 17,20β-P (11^−9.7 M). Preliminary data from cross-adaptation studies suggest that both the free and conjugated forms are detected by the same olfactory receptor(s). Male tench also had high olfactory sensitivity to prostaglandin F_2α (PGF_2α) and 15-keto PGF_2α (11^−11.5 and 10^−11.4 M). They were relatively insensitive, however, to testosterone (T), androstenedione (AD), 11-ketotestosterone (11-KT), 17β-oestradiol (E₂), 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) and 17,20α-dihydroxy-4-pregnen-3-one (17,20α-P). Radioimmunoassays were used to measure the steroids in plasma and water and all samples were processed for the measurement of free, sulphated and glucuronidated fractions. In females, free 17,20β-P, 17,20α-P, free and glucuronidated T, and AD in plasma showed the largest increases in response to injection with mammalian gonadotropin-releasing hormone analogue (GnRHa) or Ovaprim (a mixture of GnRHa and a dopamine inhibitor). Free 17,20β-P was released into the water at the greatest rate. Plasma concentrations of the two conjugated forms of 17,20β-P were also elevated 18 h after the administration of GnRHa, but not by as much as the free steroid. In males, AD and 11-KT showed the greatest increase in response to GnRHa and were moreover released into the water at a higher rate in the treated group than in the control. The data support a possible pheromonal role for free and glucuronidated 17,20β-P. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Annual Reproductive Cycle of the White Bass Morone chrysops

The gametogenic cycle of the white bass Moronc chrysops was characterized for one year at monthly intervals by measuring circulating levels of the sex steroid hormones testosterone (T) and 11-ketotestosterone (11-KT) in males, and 17β-estradiol (E₂) and T in females. Vitellogenin (VTG), the egg yolk precursor, was also measured in female blood plasma. Gonadal status of individual fish was assessed by histological evaluation, measurement of oocyte diameters, and spermintion response. At the onset of vitellogenesis (October), blood plasma levels of E₂ and T were low, but increased significantly as the spawning period (March-April) approached and oocytes attnined their maximum diameter. All stages of oocyte development were observed in mature females, indicating that the white bass is a multiple-clutch, groupsynchronous spawner. Androgen levels increased in males throughout the reproductive cycle and reached maximal levels during the spawning period. The increase in androgens coincided with sperm production and spermintion in males. The circannual endocrine and gonadal development patterns observed in white bass were similar to those of other members of genus Moronc .     

Fertility and motility of sperm from Atlantic halibut (Hippoglossus hippoglossus) in relation to dose and timing of gonadotrophin-releasing hormone agonist implant

In broodstocks of Atlantic halibut, Hippoglossus hippoglossus, male and female gamete production often becomes unsynchronised towards the end of the spawning season—milt becomes very viscous and difficult to express while the females are still producing batches of good quality eggs. Gonadotrophin-releasing hormone agonist (GnRHa) has been shown to stimulate spermiation in a number of fish species. Therefore, we conducted two experiments where male halibut were implanted intramuscularly with pellets containing GnRHa. The effect of the pellets was tested at three periods: before, at the height of and at the end of spermiation. In the middle period, GnRHa was tested at two doses (5 and 25 μg/kg bodyweight). Measurements were made of milt hydration, sperm motility and fertilisation rate. Implanted males began spermiation at least 4 weeks before control males. Both doses of GnRHa increased the fluidity of the milt. This effect lasted for at least 20 days in the low dose group and for 40 days in the high dose group. When applied at the end of the season, GnRHa reversed the normal trend for the milt to become more viscous. GnRHa treatments did not affect fertilisation rates obtained with the sperm. However, towards the end of the spawning season, sperm motility was enhanced in males treated with the high dose of GnRHa (25 μg/kg) compared to controls. As described previously, plasma concentrations of the gonadal steroids, 5β-pregnane-3β,17,20β-triol 20-sulphate and 17,20-dihydroxy-4-pregnen-3-one, were significantly enhanced by GnRHa treatment. Concentrations of testosterone on the other hand decreased when spermiating males were treated with GnRHa. Our data suggest that 17,20β-dihydroxy-4-pregnen-3-one or its metabolites are involved in milt hydration, possibly through affecting ion transport.     

Seasonal reproductive cycle of Waigieu seaperch (Psammoperca waigiensis)

Predictive and reliable parameters of reproductive status are integral aspects of sustainable fisheries and aquaculture management. These parameters are also important for an accurate evaluation of the effects of different treatments on sexual maturation in fish farming. In the present study, we have characterized the seasonal reproduction profile and described changes in sex steroids in relation to gonadal maturation and development in female and male Waigieu seaperch (Psammoperca waigiensis). The experimental period covered a full calendar year (January–December). In males and females, we observed that plasma sex steroid hormones [oestradiol‐17β (E2), testosterone (T), 11‐ketotestosterone (11‐KT) and progesterone (P)] levels showed monthly fluctuations during the spawning period. Particularly, plasma steroid hormone levels were positively associated with gonadosomatic index values. In addition, high levels of plasma steroid coincided with recruitment of oocytes into yolk accumulation in females. The main spawning period occurred between April and October in females, and between March and November in males. The non‐aromatizable androgen, 11‐KT is generally believed to be the active male‐specific androgen in teleosts, and is associated with the process of spermiation, development of secondary sexual characteristics and regulation of male reproductive behaviour in most teleost species. In this study, we found relatively high amounts of 11‐KT in females between May and December, suggesting an integral role in the maturation process, also for the females. A rapid peak in plasma P level was observed in November and suggests significant roles during post‐spawning and/or resting periods in both female and male fish. Furthermore, all oocyte developmental stages were present within the same sampling month and also within the spawning period, demonstrating the gamete group asynchronous developmental strategy. Overall, Waigieu seaperch showed strong seasonality in reproductive development with corresponding sex steroid patterns. The data presented in this study may contribute to the understanding of the reproductive endocrinology of a tropical marine finfish with increasing industrial prospects and sustainable aquaculture of this species in a developing country, such as Vietnam.     

Effect of Oxygen Saturation in Water on Reproductive Performances of Pacu Piaractus brachypomus

Broodstock pacu Piaractus brachypomus as well as their eggs during their embryonic development were exposed to either normoxia (5.5–7.5 mg O₂/L) or hypoxia (2.0–4.5 mg O²/L) conditions. The plasma concentrations of 11-ketotestosterone in males and estradiol-17β in females, as well as that of their precursor testosterone (T) were significantly ( P < 0.01) higher in fish maintained under normoxic conditions than in fish exposed to hypoxia. After ovulation and spermiation induced by hormonal treatments, the plasma concentrations of T and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) significantly ( P 0.05) increased in both sexes under both normoxic and hypoxic conditions. The plasma levels of T and 17,20βP achieved under normoxic conditions were higher than the ones recorded under hypoxia, except for those of 17,20βP in males. Males responded positively to the hormonal treatments, and the concentration of spermatozoa was 10.5 ± 0.8 10⁹/mL under both oxygen conditions. Hypoxia resulted in significantly lower survival of embryos (17.3 ± 28%) in comparison to normoxic conditions (68.5 ± 25%). Moreover, larval deformities were found when exposed to hypoxia (91.6 ± 6%). During embryonic development of this species 4 mg/L of oxygen is tolerated at 26–27 C without negative impact. We conclude that despite the highly adaptable nature of adult pacu to environmental hypoxia, oxygen concentrations below 4 mg/L severely impacted survival of embryos.     

The Effect of Photoperiod on Sexual Maturation,Appetite and Growth in Wild Atlantic Cod (Gadus morhua L.)

An experiment was conducted to examine (a) the effects of photoperiod on timing of sexual maturation (b) the relationship between plasma steroid levels, appetite and growth in male and female Atlantic cod (Gadus morhua L.). Wild caught Norwegian coastal cod were subjected to either a 6L/18D photoperiod typical of January at 60° N-(Short day group) or a simulated natural photoperiod (Normal day group) from June 2000 until spawning started. Appetite of individual fish were measured twice weekly, while weight, length and plasma levels of the sex steroids testosterone (T), 11 keto-testosterone (11-KT) and estradiol-17β (E2) were monitored bimonthly. Cod in the Short day group matured 3 months ahead of the cod in the Normal day group and started spawning in early November. Appetite decreased in both sexes 2–3 months prior to spawning in both groups, but this reduction was stronger among males. In both sexes, length growth was reduced concurrently with the appetite loss. Overall, females had significantly higher somatic growth, put relatively less energy into length growth and had developed larger livers compared to males at the time of spawning in the Short day group. Plasma steroid levels increased in both groups throughout the experiment, reaching peak levels of ca 10 ng ml⁻¹ (T) and 15–20 ng ml⁻¹ (11-KT) in males, and 1.5–2 ng ml⁻¹ (T) and 12–18 ng ml⁻¹ (E2) in females at the onset of spawning. Steroid levels increased more rapidly among Short day cod verifying the earlier onset of maturation. These results confirm that photoperiod is a major cue to maturation in cod and imply that the high cost of spawning for females incur differences in appetite between the sexes.     

Changes of plasma steroid concentrations associated with spontaneous or induced ovulation in yellow perch Perca flavescens

This study examined the changes in plasma steroids during natural (Experiment 1) and induced (Experiment 2) final maturation in yellow perch Perca flavescens. In experiment 1, ovulating yellow perch were stripped of eggs and blood samples collected to determine the concentrations of testosterone (T), estradiol-17β (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Eggs from individual females were weighed and fertilized. Fertilization rate was determined at the embryo eyed stage. In experiment 2, females were randomly assigned to one of the following treatment groups: (1) saline (0.7% NaCl), (2) des-Gly¹⁰[D-Ala⁶] LHRH-ethylamide (100 μg LHRHa/kg), and (3) LHRHa plus 17,20βP (100 μg LHRHa/kg + 2 mg 17,20βP/kg). Fish were injected intraperitoneally with two doses at a two-day interval. Blood was collected prior to injections and at the time of ovulation/spawning and concentrations of T, E2, and 17,20βP (free and conjugated) were determined. In experiment 1, low concentrations of 17,20βP were recorded at spawning. In experiment 2, all surviving fish injected with LHRHa (5 of 5) released their eggs spontaneously during the week following injections. None of the surviving control fish (0 of 5) ovulated during this period, whereas only 1 of 3 surviving fish injected with LHRHa + 17,20βP released eggs. In the control group, concentrations of E2 and 17,20βP did not show significant differences over the experimental period, whereas plasma T concentrations increased significantly. In fish injected with LHRHa, the concentrations of T and 17,20βP increased significantly after the first injection but then declined at ovulation/spawning. It also appears that 17,20βP was conjugated to its sulfated form. Mortality reached 62.5% in the group injected with LHRHa + 17,20βP indicating that this treatment was severe. Thus, LHRHa alone appears highly effective in inducing ovulation in yellow perch. This revised version was published online in July 2006 with corrections to the Cover Date.