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.     

In vivo and in vitro effects of Rhizopus extract on body growth and steroid production in masu salmon, Oncorhynchus masou Brevoort

This study investigated the in vivo and in vitro effects of Rhizopus (filamentous fungus) extract (RU) in masu salmon Oncorhynchus masou Brevoort. Underyearling fish were fed with RU for 16 months. Monthly changes in body growth, gonadal maturation and serum levels of sex steroids were monitored. Gonads were also incubated at 0, 1, 10, 100 and 1000 μg RU mL⁻¹ Leibovitz's L‐15 medium for 18 h. The levels of steroids in serum and cultured medium were measured. It was determined that RU‐fed immature and mature males, when compared with control groups, showed significantly higher body growth during spring, summer and the spawning period. Similarly, immature RU‐fed females showed significantly higher fork length and body weight in autumn, spring and summer. Furthermore, RU‐fed males showed significantly higher levels of serum testosterone (T) and 11‐ketotestosterone (11‐KT) levels in the pre‐spawning season, and 17α, 20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) in the spawning season. In vitro RU incubation of gonads showed a dose‐dependent and significant increase in T, 11‐KT, oestradiol‐17β and DHP release in the medium. It appears that the causes of enhanced body growth and increased steroid production herein observed in salmonids are the physiologically active substances that may be present in the mycelium of the fungus.     

Sex organ extracts and artificial hormonal compounds as sex pheromones to attract broodfish and to induce spawning of Chinese black sleeper (Bostrichthys sinensis Lacépède)

Ovarian, testicular and seminal vesicle extracts of mature Chinese black sleeper (Bostrichthys sinensis Lacepede), synthetic steroids 17α‐progesterone (17α‐P), 17α,20β‐dihydroxy‐4‐pregnen‐3one (17α,20β‐P) and prostaglandins PGE₂ and PGF_2α were used in an attempt to attract broodfish and to induce spawning. Furthermore, 17α‐P, PGE₂ and PGF_2α levels were determined in extracts, and PGE₂ and PGF_2α levels were determined in holding and spawning waters. The results showed that ovarian extracts attracted more males than females to enter artificial nests, while testicular and seminal vesicle extracts attracted more females than males. The highest percentage of spawned nests were found when 17α,20β‐P and PGE₂ were administered to the nests, while the largest egg numbers and the mean highest fertilization rate were observed when PGE₂ was added. In ovarian extract, 17α‐P level was higher than levels in testicular or seminal vesicle extracts. The PGE₂ levels were significantly (P<0.05) higher than PGF_2α in the ovarian, testicular and seminal vesicle extracts. The PGE₂ and PGF_2α levels in spawning waters were higher than those in holding waters. The PGE₂ levels were greatly significantly (P<0.01) higher than PGF_2α in spawning and in holding waters. The results suggest that the sex organs of B. sinensis contain 17α‐P, 17α, 20β‐P, PGE₂ and PGF_2α and that 17α‐P, 17α,20β‐P and PGE₂ may act as sex pheromones in this species, attracting both male and female conspesifics to spawning sites and inducing spawning. Among the compounds tested, PGE₂ was the most effective sex pheromone for induction of spawning in B. sinensis.     

Response of Male Blue Catfish,Ictalurus furcatus,and Male Channel Catfish,Ictalurus punctatus,to Female Channel Catfish Given Pheromonal Steroids or Prostaglandin

The effects of the putative hormonal pheromones 17α, 20β‐dihydroxy‐4‐pregnene‐3‐one (17,20β‐P), 17,20β‐P‐20‐glucosiduronate, and prostaglandin F‐2α (PGF‐2α) injected into female channel catfish, Ictalurus punctatus, were investigated to determine whether male channel catfish and blue catfish, Ictalurus furcatus, could be attracted to the injected females. Females were distributed into traps placed in ponds containing either male channel catfish or blue catfish. Traps were checked six times in a 96‐h period. Males were 17.9 times more likely to be captured with a PGF‐2α‐injected female than with an ethanol‐only injected female, or a 17,20β‐P‐injected female, and 3.5 times more likely to be captured with a PGF‐2α‐injected female than with a 17,20β‐P‐glucosiduronate‐injected female. Males were 6.0 times more likely to be caught between 48 and 96 h post‐injection than between 12 and 24 h post‐injection. These results suggest that the overall best pheromone to attract blue catfish and channel catfish males is PGF‐2α at 48–96 h post‐injection.     

Comparative analysis of reproductive performance between spring and autumn forms of Persian sturgeon,Acipenser persicus,Bordin, 1897: with an emphasis on sex steroids and milt quality

To compare the reproductive performance of spring and autumn forms of Persian sturgeon males, Acipenser persicus, the relative abundance of spermiating and non‐spermiating males, milt quality, sex steroids and cortisol were investigated after pituitary preparation (PP) treatment and at the time of spermiation. Our results showed that higher numbers of spring males are spermiated after PP treatment than autumn individuals. The autumn spermiating males had higher and lower values of sperm density and duration of motility than spring males respectively. The milt volume was higher in spring males than in autumn individuals. The percentage of motility was statistically equal in both the groups examined. In both forms of brooders, the serum levels of testosterone (T), 11‐ketotestosterone (11‐KT), progesterone (P), 17α, 20β, 21‐trihydroxy‐4‐pregnen‐3‐one (20βS) and cortisol (C) increased after PP treatment, although such increases did not occur in non‐spermiating males. Our results showed the probable involvement of 20βs, P, T, 11‐KT and C in the final maturation of Persian sturgeon. In addition, it was demonstrated that the spring form of Persian sturgeon shows better reproductive performance than the autumn form in terms of a response to artificial induction and milt quality.     

Controlled reproduction in Anguilla anguilla (L.): comparison between spontaneous spawning and stripping‐insemination approaches

This study aimed to compare the fertility of eggs between artificially matured female silver eels that spawned spontaneously and those that were spawned by manual stripping. The effects of the two methods of spawning on ovulation and fertilization rate were also investigated. For this purpose, 18 wild female European eels captured in Bonello lagoon (North Adriatic Sea) were carp pituitary extract‐injected to undergo sexual maturation and ovulation; a final injection of 17,20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) was administered when at least 30% of the oocytes were fully transparent. After the DHP‐injection, nine eels were transferred to a new closed recirculating aquaculture system, where they were housed with spermiating males (sex ratio 4/1) to allow spontaneous spawning (SPT‐group); the remaining nine eels were transferred to a 250 L tank and ovulation was checked at four‐hourly intervals by manual stripping (STR‐group). The number of eggs per female in the SPT‐group was significantly greater than that in the STR‐group. Furthermore, fertilization rates in the SPT‐group were notably higher than those observed in the STR‐group. Significantly, the best performances were obtained among eels in which at least 50% of oocytes were fully transparent at the time DHP was administered. We conclude that the fertility of eggs from spontaneously spawning eels is superior to that of eggs acquired by strip‐spawning and artificial fertilization.     

Brain steroid contents in the catfish Heteropneustes fossilis: sex and gonad stage-specific changes

Neurosteroids are those which are synthesized in the central nervous system independently of supply by peripheral endocrine glands. In the present study, brain contents of the steroid hormones, estradiol-17β (E(2)), testosterone (T), corticosteroids, and progestins were investigated in both male and female catfish Heteropneustes fossilis in prespawning (vitellogenic) and spawning (post-vitellogenic) phases using ELISA or HPLC. The data show that the measured steroid hormones showed both stage-specific and sex-related variations. Brain E(2) was significantly higher in males in the prespawning phase and in females in the spawning phase. Testosterone was significantly higher in males in comparison with females in the prespawning phase. Cortisol was significantly higher in the prespawning and spawning phases in males than in females. Corticosterone level was low in the brain. 21-deoxycortisol and deoxycorticosterone were significantly higher in the prespawning phase than in the spawning phase. Male brain recorded the highest concentration of deoxycorticosterone. Progesterone (P(4)) was high in the prespawning phase and low in the spawning phase in both sexes. Levels of 17-hydroxy-4-pregnene-3,20-dione and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-DP) and the metabolites of P(4) were the highest in females in the prespawning phase. The stage-specific and sexual differences in the content of the steroids suggest their biosynthesis in the brain, which may have implications in brain functions, in addition to reproductive regulation.     

Reproductive cycle of the Amazonian planktivorous catfish Hypophthalmus marginatus (Siluriformes,Pimelodidae)

We evaluated the annual process of oocyte and ovarian development of the planktivorous Amazonian catfish, the mapará (Hypophthalmus marginatus), aiming to support captive reproduction for domestication. A total of 149 females were captured from the Tocantins River at the Tucuruí Dam (3°49'55"S, 49°39'9"W) in 13 sampling events. For each individual, we evaluated ovary histology and plasma steroid concentrations. Two annual reproductive cycles, with similar characteristics, including a long period of rest, a short vitellogenic stage and a well‐defined spawning season from November to March, were described. A 17β‐estradiol (E₂) rise and a 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) peak were associated with vitellogenesis and spawning season, respectively, in the first cycle but not in the second reproductive cycle. In conclusion, the studied species presents a reproductive cycle similar to that of other migratory total spawners; however, unusually for this group of fish, there were three (but not two) batches of vitellogenic oocytes in “in maturation” and “mature” stage ovaries, pointing to the possibility of more than one spawn during the spawning season.     

Gonadal Stage and Sex Steroid Correlations in Siberian Sturgeon,Acipenser baeri,Habituated to a Semitropical Environment

Stages of gonadal development, in association with plasma concentrations of the sex steroids 17β‐estradiol (E2), progesterone (P4), testosterone (T), and 11‐ketotestosterone (11‐KT), were investigated for a single time point during a natural breeding season in 7‐yr‐old Siberian sturgeon, Acipenser baeri Brandt, exposed lifelong to a warmwater environment. Among females, examination of gonadal tissue showed variation in ovarian stage, with 12.5, 47.5, 22.5, and 17.5% of females found at Stages 2 (previtellogenic), 3 (early vitellogenic), 4 (mid‐vitellogenic), and 5 (migratory nucleus), respectively. Although patterns varied among the hormones, plasma concentrations of E2, T, and 11‐KT became increasingly elevated in females as maturation progressed. On the basis of histological criteria, males were classified as either premeiotic (quiescent) or meiotic and 50% of the males sampled were found at each stage. Significant elevations in circulating concentrations of plasma E2 and T were observed in meiotic versus premeiotic males, and there was a rise in plasma 11‐KT concentration that approached significance (P = 0.056).     

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.     

Sex differences in circulating steroid hormone levels in the red drum, Sciaenops ocellatus L.

Steroid profiles of cultured and captive red drum (Sciaenops ocellatus L.) were investigated to evaluate the potential use of circulating sex steroid levels as a tool for gender identification in this species. Cultured 18‐month‐old fish were maintained on a 120‐day shortened photothermal cycle to induce precocious maturation. Additionally, wild‐caught fish were maintained in captivity under simulated natural photothermal conditions from late spring to early fall. Circulating 11‐ketotestosterone (11‐KT) levels were significantly higher in males compared with females during the early stages of gonadal growth in both cultured and captive fish. Plasma testosterone (T) levels showed a similar trend; however, the differences were significant only when males were already producing sperm. 17β‐estradiol (E₂) concentrations were low in males and females before gonadal recrudescence but increased significantly with the progression of vitellogenesis in females. These results show that a test using a minimum concentration of circulating 11‐KT could be developed to differentiate between sexes in the early stages of gonadal maturation in red drum. Moreover, plasma E₂ concentrations could be used to identify vitellogenic females. The two steroids considered together could help avoid possible error in gender identification due to unusually high levels of certain steroids encountered in some individuals.     

Capture and handling stress affects the endocrine and ovulatory response to exogenous hormone treatment in snapper, Pagrus auratus (Bloch & Schneider)

Sexually mature female hatchery‐reared snapper, Pagrus auratus (Bloch & Schneider) were captured from sea cages by handline and injected at first capture (control) or 24 h after capture, transport and subsequent confinement (delayed injection) with either saline, luteinizing hormone releasing hormone analogue, human chorionic gonadotropin, or 17α‐hydroxyprogesterone. Blood was sampled before hormone treatment and again after 168 h, and fish were checked daily for ovulation. Plasma levels of 17β‐estradiol (E2), testosterone (T), 17α, 20β dihydroxy‐4‐pregnen‐3‐one (17, 20βP) and cortisol were determined by radioimmunoassay. The ovulatory response was assessed from the proportion of fish ovulating, ovulation volume, egg quality and fertility. A delay in injection resulted in significantly lower plasma E2 and T levels in response to hormone treatment, smaller ovulation volumes, and poorer egg quality than in control fish. The results are consistent with the generally inhibitory effects of stress on reproduction in fish, and confirm the requirement to treat fish with hormones designed to induce ovulation, as soon as possible after capture and disturbance.     

Cortisol and testosterone accumulation in a low pH recirculating aquaculture system for rainbow trout (Oncorhynchus mykiss)

Steroids accumulate in recirculating aquaculture system (RAS), although explanatory factors for such accumulation are still poorly explored. This study investigated the effect of water exchange rate and pH in six replicated RAS on the concentration of the stress hormone cortisol in rainbow trout blood plasma and in the holding water and of the sex steroids testosterone, 11‐ketotestosterone (11‐KT) and 17,20β‐dihydroxypregn‐4‐en‐3‐one (17,20β‐P) over a 70‐day experimental period. Three combinations of water exchange rate and pH were used each treatment, with two replications: (i) high water exchange rate (±1700 L kg^?1 feed) and neutral pH (±7.3), (ii) low water exchange rate (±500 L kg^?1 feed) and neutral pH (±7.3) and (iii) low water exchange rate (±500 L kg^?1 feed) and low pH (±5.8). Plasma cortisol concentrations at day 70 were higher (24.4 ± 9.5 ng mL^?1) for fish kept at low pH when compared to fish kept at neutral pH (12.0 ± 0.1 and 8.7 ± 0.2 ng mL^?1). Water cortisol and testosterone concentrations at day 35 were higher at low pH than at neutral pH, whereas water 11‐KT and 17,20β‐P did not differ among treatments. At day 70, there were no significant differences between low and high pH. These results demonstrate that low pH contributes to increased plasma cortisol concentrations and to its accumulation in water, possibly indicating a stress response to low pH. The higher concentration of testosterone but not of the other sex hormones point to unspecified reproductive effects that need further investigation.     

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.     

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.     

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 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.     

Influence of gossypol from dietary cottonseed meal on haematology, reproductive steroids and tissue gossypol enantiomer concentrations in male rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) males were fed, during a 9‐month period, five experimental diets where fishmeal proteins were gradually replaced with cottonseed meal (CS) proteins (0, 25, 50, 75 and 100%; diets 1–5, respectively). This study was carried out to evaluate the action and tissue concentrations of gossypol. Growth performance of fish was not affected with the increasing levels of CS in the diets. Haemoglobin concentration and haematocrit significantly decreased in fish fed 100% CS compared with other dietary treatments. Gonadosomatic index, plasma sex steroids (testosterone, 11‐ketotestosterone and 17,20β‐dihydroxy‐4‐pregnen‐3‐one) and sperm characteristics (concentration, motility, protein concentration and lactate dehydrogenase activity) were not negatively affected by increasing levels of CS. For the first time, a comprehensive study of gossypol concentrations, total and (+) and (?)‐enantiomers, in several tissues (liver, blood plasma, spermatozoa and seminal plasma) was performed. The concentrations of both (+) and (?)‐enantiomers significantly increased with increasing levels of CS in the diet. The highest concentrations were found in the liver of fish fed diet 5 (185 ± 18 μg g^?1). In blood plasma, the concentrations of total gossypol were 10 times lower than the one found in the liver, but 10 and 100 times higher than the concentrations in the spermatozoa and seminal plasma, respectively. In all tissues studied, the concentration of (+)‐enantiomer was higher than the (?)‐enantiomer. The ratio (?)‐enantiomer/total gossypol did not change significantly with the increasing levels of CS in the diet. The results of the present study indicate that CS can be used over a period of 9 months to replace fishmeal proteins completely without compromising growth and reproduction of rainbow trout males.     

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.     

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E₂), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E₂ levels in females increased rapidly from low values in October (< 0.1 ng ml⁻¹) to peak levels of 3.7 ng ml⁻¹ in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E₂ levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml⁻¹ in November, and peaking again at 3.3 ng ml⁻¹ just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml⁻¹, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml⁻¹ by November, remained elevated throughout the winter, and peaked at 2.8 ng ml⁻¹ I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml⁻¹, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml⁻¹. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.