Sex Inversion Research Articles

State of gonads in juvenile triploid trout Oncorhynchus mykiss under conditions of South Vietnam after artificial sex inversion

Gonad morphology and structure of sex cells in juvenile triploid trout Oncorhynchus mykiss of the Donaldson breed incubated and reared at a trout plant under climatic conditions of South Vietnam have been studied. Anomalies in the structure of sex gonads and oocyte structure were found, and partial resorption of sex cells was detected. It was shown that sex inversion in triploid (unisexual) fingerlings of rainbow trout passed successfully on the whole since many sex gonads of these fish simultaneously had both female and male sex cells and sometimes were sterile. The connection of anomalies found in the structure of sex system of trout with species rearing under unusual for it climatic conditions and artificial sex inversion is discussed.

Threatened fishes of the world: Mycteroperca microlepis (Goode & Bean, 1880) (Serranidae: Epinephelinae)

Common names: Gag, badejo de areia. Conservation status: Species listed of least concern by IUCN or vulnerable (Morris et al. 2000) and in Brazil is “overexploited” in Sao Paulo State (Sao Paulo 2008). Identification: D XI + 16–18; A III + 10–12; P 16–18; LL 88–96, caudal fin emarginated. Adult females and juveniles are generally brownish grey with dark vermiculations. Males have a distinctive color pattern (black-belly phases) that includes a dark pigment on the abdomen. The maximum length is 120 cm and the maximum body weight is 32 kg (Heemstra and Randall 1993). Distribution: Western Atlantic: North Carolina, USA to the Yucatan Peninsula, Mexico; eastern Brazil and rare in Bermuda. Habitat and ecology: Juveniles occur in estuaries and sea grass beds; adults are usually found offshore on rocky bottom in depths varying from 40 to 100 m. Feed mainly on fishes, crustaceans and cephalopods (Heemstra and Randall 1993). Reproduction: It is protogynous hermaphrodite, with large aggregations in spawning sites (Gilmore and Jones 1992). Females are sexually mature at 5 or 6 year (67 to 75 cm) and sex inversion occurs between 10 and 11 years old (95 to 100 cm). Threats: This is an important grouper in the reef fisheries of the southeast coast of the U.S and in the Gulf of Mexico (Heemstra and Randall 1993) and an intense fishing pressure was responsible for a decline in male population in northern Gulf of Mexico (McGovern et al 1998). It is threatened mainly by overfishing and coral destruction. Conservation action: In Brazil, since 2003, capturing minimum size was established in 30 cm and in Mexico it is included in the federal fishery management plans. Conservation recommendation: Establishment of a non capturing period during the species spawning aggregations; and mass production in experimental fish hatcheries in Brazil (Sanches 2007). Environ Biol Fish DOI 10.1007/s10641-010-9602-4

Threatened fishes of the world: Epinephelus marginatus (Lowe, 1834) (Serranidae: Epinephelinae)

Common names: Dusky grouper, garoupa-verdadeira.Conservation status: This species is listed as endan-gered in the Red List of Threatened Species (IUCN)(Marino et al. 2003; Cornish and Harmelin-Vivien2004). In Brazil, this species was included in the“over-exploitedorthreatenedwithoverexploitation”listof marine resources(Ministerio do Meio Ambiente IN52004) and in Sao Paulo State (Sao Paulo 2008).Identification:DXI+14–16; P 17–19; A III + 8; LL62–73. The pelvic fins are shorter than the pectoral finsand do not reaching the level of the anus. Themaximum length is 120 cm, with maximum bodyweight of 60 kg (Rocha and Costa 1999). Distribution:This species occurs on both sides of the Atlantic Ocean,from the British Isles to South Africa and southwestIndian Ocean in Southern Mozambique and Madagas-car (Heemstra and Randall 1993). Habitat and ecology:E. marginatus is a coastal, demersal species, commonlyfound over irregular rocky bottoms from shallow waterto 50 m deep (Heemstra and Randall 1993). E.marginatus plays an important role in maintaining theecological balance of hard-bottom ecosystems, with thefeeding based on fish and crustaceans (Barreiros andSantos 1998). Reproduction: This species is a protog-ynous hermaphrodite, with reproductive aggregationsand a complex social structure (Zabala et al 1997;Andrade et al. 2003). It becomes sexually mature whenreaching 45 cm and 2 kg, and maturing females occurbetween 3 and 9 kg. The sex inversion happens whenthey reach 9 to 10 years and 90 cm of length (Brusle1985;Marinoetal2001). Threats: Overfishing.Conservation action: Since 2003, in Brazil a minimumsize of capture was established at 47 cm. Conservationrecommendation: Time-area closures and the develop-ment of technologies for sexual inversion and spermcryopreservation (Sanches 2007; Cabrita et al 2009)are

The Effect of Lyophilized Goat Testes Meal as First Feed on the Growth of `Wesafu`: An Ecotype Cichlid of Epe-Lagoon, in Lagos State, Nigeria

A study was conducted to determine the possible sex inversion effect of lyophilized goat testes meal on hatchlings of 'Wesafu'. Eighty-five fish and a control group were treated with the meal for forty days in an indoor facility and subsequently transferred into outdoor cages and monitored for growth, the result of manual sex ratio was not conclusive and gonad examination for sex ratio determination has been suspended until fish are big enough. Some mortalities (35%) were recorded during the treatment periods while the control group was intact (100%). The chemical composition of goat testes meal revealed a useful 47% protein and 1.23% oil and a good complement of mineral elements. After the initial 25day exposure of fish to GTM, there was no noticeable length difference (2.9cm) as compared to the control group (3.5cm). The lengths were also similar at 6.03cm and 6.07cm for GTM and the control group respectively after 25 days in outdoor green water culture. There were some non statistical differences in both weight and length of fish in the two groups with the test group clearly showing improvements in terms of length and weight indicating the influence of male hormone (testosterone in GTM) in maleness of the test group.

Water polluted by 17α-methyltestosterone provides successful male sex inversion of common carp (Cyprinus carpioL.) from gynogenetic offspring

Summary This study investigated the effects of oral treatment and water pollution by 17α-methyltestosterone (MT) on the masculinization of common carp, Cyprinus carpio, gynogenetic offspring. The oral administration of MT results in detectable levels of the steroid in the water of recirculating systems. Both modes of MT administration (oral/water pollution) caused a high level of masculinization (61.5–100%) of gynogenetic offspring of common carp.

Sex ratio control in pink salmon (Oncorhynchus gorbuscha and chum salmon (O. keta) populations: The possible causes and mechanisms of changes in the sex ratio

Long-term changes in the sex ratio have been studied in pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta) populations of Kamchatka and Sakhalin. It has been demonstrated that these changes are an adaptation to population dynamics: an increase in the population size is accompanied by a shift towards a higher proportion of males; a decrease in population size, by a shift towards a higher proportion of females. The correspondence between morphological and molecular characters in populations of the two species has been analyzed in order to determine the mechanism of sex ratio control. In some pink salmon and chum salmon populations, there is a discrepancy between sex identifications based on morphological characters and molecular markers. This discrepancy is assumed to be accounted for by sex inversion mechanisms, which may be population- or region-specific. In two cases, it has been found that the sex ratio discrepancy in populations is related to the numbers of fish in subsequent generations. These findings suggest that sex inversion may be related to population size control.

Growth and reproduction of the gilthead seabream <i>Sparus aurata</i> in Mellah lagoon (north-eastern Algeria)

Gilthead seabream Sparus aurata (L.), a protandrous hermaphrodite, was caught in Mellah lagoon (Algeria) from July 1997 to June 1998. Its age, growth and reproduction were studied. Fish ranged in size from 157 to 610 mm total length and weighed from 60 to 4000 g wet weight. There were fish aged 1 + to 7 + years old in the samples. Direct scale readings were made by counting the number of rings. These were compared with the data obtained by backcalculating the lengths at different ages. These two methods were in agreement and showed that the growth rate of gilthead seabream in Mellah lagoon is very high compared to other study areas. The growth parameters of the Von Bertalanffy equation were: L ∞ = 55.33 cm, K = 0.513, t 0 = - 0.282, with F ’ = 7.359. The fitted length-weight relationship was W = 1.292. 10 -2 L 3.06 . The reproductive season extended from October to January, with a peak in December. Sex inversion occurred at a total length of 44 cm. Sexual maturity was reached at 32.6 cm total length.

Gonadal changes and blood sex steroids levels during natural sex inversion in the protogynous Mediterranean red porgy, Pagrus pagrus (Teleostei: Sparidae)

Changes in gonadal structure and serum levels of sex steroids were investigated during natural sex inversion from female to male in reared populations of the protogynous Mediterranean red porgy, Pagrus pagrus. Four developmental phases were identified by histological observation: female, early transitional (ETr), late transitional (LTr), and male phases. At female phase, a few nests of spermatogonia were observed at the posterior-ventral part of the gonad mainly in females out of the breeding season. At ETr phase, spermatogonial proliferation occurred while perinucleolar oocytes showed signs of degeneration. At LTr phase, seminiferous lobules were formed and spermatogonial proliferation expanded along the ovary which degenerated. All types of male germ cells could be found. At male phase, functional testis underwent active spermatogenesis while small ovarian remnants associated to fat tissue could be detected. Both 17β-estradiol (E2) and estrone (E1) blood levels were significantly lower in fish at transitional and male phases in comparison to breeding females, while levels of 11-ketotestosterone (11-KT) and testosterone (T) gradually increased in the transitional and male phases. In conclusion, the protogynous P. pagrus possess a delimited type bisexual gonad with a medio-dorsal ovarian area and a latero-ventral testicular zone. Sex inversion starts mainly after the female breeding season with an active spermatogonial proliferation. The testis tissues develop while ovarian tissues regress to disappear completely in the functional male. This process is accompanied by a sharp decrease of estrogens levels and a progressive increase of androgens levels. The physiological significance of such endocrine changes is discussed.

Seasonal changes of serum sex steroids concentration and aromatase activity of gonad and brain in red-spotted grouper ( Epinephelus akaara)

Levels of serum sex steroids (estradiol-17β, E 2; testosterone, T; 11-ketotestosterone, 11-KT) in male, female and natural sex-reversing red-spotted grouper ( Epinephelus akaara), and aromatase activity of gonad and brain in both male and female were investigated throughout an annually reproductive cycle. In females, serum E 2 and T peaked during vitellogenesis, but in males and natural sex-reversing fish, 11-KT, T and E 2 reached peak during spermatogenesis. In addition, in females, serum 11-KT levels (monthly means: 0.32 ± 0.03 ng/ml) which were very low did not significantly fluctuate during the annual reproductive cycle. In breeding season, females displayed higher E 2 levels than males and sex-reversing fish, while males and sex-reversing fish showed higher 11-KT levels and, to a lesser extent, higher T levels than females. Furthermore, the changing pattern of sex steroids in males was similar to that in natural sex-reversing fish, and a second peak of serum androgens 11-KT and T appeared in December both in male and natural sex-reversing fish; significantly higher serum 11-KT levels were observed in natural sex-reversing fish than that in females from December to April. In females, but not in males, aromatase activity of brain and gonad demonstrated significantly seasonal changes (exhibiting a peak in breeding season); moreover, aromatase activity in females was higher than that in males. Furthermore, significantly lower aromatase activity in testis was observed in breeding season, in contrast to that in ovary. Taken together, the present findings indicated that changes of serum sex steroids levels and aromatase activity in red-spotted grouper were closely associated with sex inversion. In addition, the present results also suggested that sex inversion in red-spotted grouper peaked mainly from December to March.

Permanent sex inversion in 1-year-old juveniles of the protogynous dusky grouper ( Epinephelus marginatus) using controlled-release 17α-methyltestosterone implants

Long-term treatments (April–June 2004) with 17α-methyltestosterone (MT) and/or human chorionic gonadotropin (hCG) were used to induce precocious sex change in 1-year-old juveniles (mean ± SD body weight of 131 ± 25 g) of the protogynous dusky grouper ( Epinephelus marginatus). The MT treatment was given once a month using controlled-release implants (1.5 mg per implant, ∼11 mg kg − 1 body weight), whereas hCG was injected intramuscularly once a month (MT/hCG group) or every 2 weeks (hCG group). In vitro mean (± SEM) daily and total MT release from the implants was 22.6 ± 5.4 μg day − 1 implant − 1 and 686 ± 113 μg implant − 1 , respectively. In vivo, plasma MT levels of European sea bas ( Dicentrarchus labrax) used as model fish (203 ± 41 g body weight) and given a single MT implant were 18.5 ± 0.5 ng ml − 1 one day after implantation, declined to 9.6 ± 2.7 ng ml − 1 by day 11 and remained stable between 7.9 and 5.5 ng ml − 1 until day 32. Plasma MT levels were significantly elevated (2-way ANOVA, P < 0.01) in dusky grouper juveniles in response to the MT treatment, both 6 and 12 weeks after beginning the treatment. On the contrary, no significant differences (2-way ANOVA, P > 0.05) between MT/hCG-treated and control fish were observed in plasma testosterone (T) or 11-keto T (11-KT). Pituitary luteinizing hormone (LH) content was significantly lower in both the MT/hCG and hCG groups, compared to controls (2-way ANOVA, P < 0.001), while plasma LH was below detection limits in all treatments. At the onset of the experiment all but one fish were already differentiated into females, having ovaries with primary oocytes. No signs of vitellogenesis or sex inversion were observed in fish from the control and hCG groups during the study. On the contrary, the MT implants induced complete sex change after 12 weeks, with the gonads organized in lobules and cysts filled with germ cells at all stages of spermatogenesis, including spermatozoa. This sex inversion was permanent and fish underwent complete spermatogenesis again during the following year. The results demonstrate that the produced MT-implants, but not the hCG injections, were highly efficient in inducing both sex inversion and complete spermatogenesis in pre-pubertal dusky grouper at the completion of their second year in life. Production of male fish at such an early age may dramatically reduce by many years the time required for natural puberty, sex inversion and the production of sperm by dusky grouper reared under culture conditions.

Effects of aromatizable and nonaromatizable androgens on the sex inversion of red-spotted grouper (Epinephelus akaara)

The effects of aromatizable 17α-methyltestosterone (MT) and non-aromatizable 17α-methyldihydrotestosterone (MDHT) on sex inversion in red-spotted grouper, Epinephelus akaara, were investigated. Fish were implanted with MT, MDHT and MT+AI (aromatase inhibitor, AI) respectively for one month. The results showed that the three treated groups turned into transitional stage with intersex gonads, which contained atretic oocytes and spermatogenic germ cells at all stages of spermatogenesis. The controls did not change sex. The gonads of more than half MT-implanted fish were in early transitional stages of sex inversion, whereas those of more than half MDHT and MT+AI-implanted fish were in late transitional stages of sex inversion. No difference in serum estradiol-17β (E2) levels between the controls and the treated groups were observed, whereas 11-ketotestosterone (11-KT) and testosterone (T) levels increased in all treated groups. Significantly lower gonadosomatic index (GSI) and gonadal aromatase activity were observed in the treated groups, which were in accordance with the lower mRNA expression of P450aromA. However, P450aromB mRNA expression increased in the MT group, while it did not change in the MDHT group. These results suggest that the sex inversion of red-spotted grouper by MT and MDHT implantation might be due to the suppression of P450aromA gene expression, and resulting in both the decrease of the ovarian estrogen –secretion, as well as the increase in the 11-KT levels. Furthermore, the main reason for MT being less effective than MDHT might be due to partial aromatization of MT to estrogen.

EST-based identification of genes expressed in the hypothalamus of male orange-spotted grouper ( Epinephelus coioides)

The orange-spotted grouper, Epinephelus coioides, is an important marine aquaculture fish, but its large-scale aquaculture has been hindered by the rarity of natural males because it is a protogynous hermaphroditic fish. Hypothalamus–pituitary–gonad is an important endocrine axis in regulating reproduction and sex differentiation. To reveal the molecular mechanism of hypothalamic physiological functions, we performed the studies on identification of genes expressed in the hypothalamus of male orange-spotted grouper using EST and RT-PCR strategy. A total of 1006 ESTs were sequenced, and 402 (39.96%) clones were identified as known genes and 604 (60.04%) as unknown genes. The 402 clones of known gene products represent transcripts of 181 genes. Moreover, the expression patterns of 26 unknown genes were analyzed in various tissues, such as liver, kidney, spleen, fat, heart, muscle, pituitary, hypothalamus, telencephalon, cerebellum, midbrain, medulla oblongata, ovary and testes. Five different categories of expression patterns were observed from them. Several unknown ESTs, such as DN551996, DN551998, DN552082, and DN552070, were detected to be hypothalamus-specific, brains-specific, or hypothalamus and gonad-specific genes. Interestingly, DN551996, not only exhibiting expression differences between ovary and testis, but also showing sex-dependent differences in hypothalamus of grouper, might play significant role in grouper reproduction or sex inversion. Further functional studies on these genes will provide more information on molecule regulation mechanism of sex inversion in groupers.

Gonadal development, aromatase activity and P450 aromatase gene expression during sex inversion of protogynous red-spotted grouper Epinephelus akaara (Temminck and Schlegel) after implantation of the aromatase inhibitor, fadrozole

In the present study, we implanted 2-year-old female red-spotted grouper, Epinephelus akaara, with a non-steroidal aromatase inhibitor (AI), fadrozole, in the breeding season and examined changes in gonadal histology, serum sex steroids, aromatase activities and P450 aromatase (P450arom) gene expression in gonads after AI implantation. Aromatase inhibitor at doses from 0.1 to 10.0 mg kg−1 BW induced a sex inversion and completion of spermatogenesis up to the functional male phase, but doses of 1.0 and 10.0 mg kg−1 BW AI produced more males than 0.1 mg kg−1 BW AI. Serum estradiol-17β (E2) levels decreased, but 11-ketotestosterone (11-KT) levels increased significantly in all the AI-implanted groups, whereas testosterone (T) levels increased significantly only in the 1.0 mg kg−1 BW AI-implanted group. Aromatase activities and P450arom gene expression in gonads were inhibited significantly in the AI-implanted groups, which was in accordance with the decrease in serum E2 levels. These results suggested the optimal dose of AI to induce sex inversion to be 1.0 mg kg−1 BW. Furthermore, the sex inversion induced by AI may be attributed to the inhibition of P450arom gene expression and aromatase activity and the resultant decrease in the biosynthesis of endogenous E2. Meanwhile, the elevated 11-KT levels were also associated closely with the occurrence of sex inversion in protogynous red-spotted grouper.

Antiestrogens Inhibit Xenoestrogen-Induced Brain Aromatase Activity but Do Not Prevent Xenoestrogen-Induced Feminization in Japanese Medaka ( Oryzias latipes )

In fish, exposure to estrogen or estrogen-mimicking chemicals (xenoestrogens) during a critical period of development can irreversibly invert sex differentiation. In medaka, a male-to-female reversal upon exposure to a xenoestrogen is accompanied by an increase in brain aromatase expression and activity. However, whether this increase is the direct cause of sex reversal is unknown. In this study we further examined the role brain aromatase plays in genesis of developmental abnormalities in response to endocrine-disrupting chemicals (EDCs). Further, the effects of a mixture of apparent antagonistic environmentally relevant EDCs on development were examined to determine if their combined actions could lessen each other’s impacts. To this end, hatchling medaka were subjected in a 2-week flow-through immersion exposure to an estrogen mimic [dichlorodiphenyltrichloroethane (o,p′-DDT)] and to pharmaceutical [fadrozole (FAD)] and environmental aromatase inhibitors [tributyltin (TBT)] alone and in combination. Brain aromatase expression and enzyme activity were measured on exposure days 5, 9, and 14 by real-time reverse-transcriptase polymerase chain reaction and tritiated water release assay, respectively. We recorded sex reversals at sexual maturity by examining the phenotypic and genotypic sex of d-rR–strain medaka. Results indicate that FAD and TBT inhibit aromatase activity in o,p′-DDT–treated fish but do not prevent feminization, indicating that increased brain aromatase activity is not critical to EDC-induced male-to-female sex inversion. The observation that estradiol biosynthesis inhibitors do not block the effect of the xenoestrogen suggests that in the environment, exposure to seemingly antagonistic EDCs does not necessarily lessen the harmful impacts of these compounds.

Age, growth, mortality, reproduction and feeding habits of the striped seabream, &lt;i&gt;Lithognathus mormyrus&lt;/i&gt; (Pisces: Sparidae) in the coastal waters of the Thracian Sea, Greece

Age, growth, mortality, reproduction and feeding habits were analysed for Lithognathus mormyrus collected in the coastal waters of the Thracian Sea from November 1997 to September 1999. Specimens ranged from 42 to 341 mm in total length. Weight increased with size allometrically (b = 3.242) for immature individuals and isometrically (b = 2.960) for males, females and intersexuals. Growth was described by the standard form of the von Bertalanffy growth equation and the estimated parameters were k = 0.21, t 0 = –0.996 and L ? = 309.4. Total and natural instantaneous rate of mortality was found to be Z = 0.79 year -1 and M = 0.61 year -1 . Sex inversion occurred mainly between 210 and 300 mm (4-9 age classes). Males reached sexual maturity at 162.1 mm (2.5 years) and females at 190.40 mm (3.6 years). The spawning period occurred from May to September, while the gamete emission peaked in June-August. Stomach content analysis revealed that L. mormyrus is a carnivorous species feeding on benthic invertebrates, mainly polychaeta and bivalve molluscs. Ontogenetic variation in the diet composition showed that while growing, the fish become more generalist feeders. We also found that in the summer season the fish become more selective feeders.

Population structure and relative abundance of blue cod (Parapercis colias) off Banks Peninsula and in Dusky Sound, New Zealand

Estimates of blue cod (Parapercis colias) relative abundance and population structure were made from potting surveys of Banks Peninsula and Dusky Sound, New Zealand in 2002. Five inshore and two offshore strata around Banks Peninsula, and five strata between the inner fiord and the open coast of Dusky Sound were surveyed. In Banks Peninsula the overall mean catch rate (all fish) was 2.13 kg/pot per h (range 0.04–4.74) and coefficient of variation (CV) was 10.8%. Blue cod from inshore strata were significantly smaller than those from offshore strata, catch rates were lower, and the sex ratio was skewed towards males (inshore 2.2:1, offshore 0.74:1). In Dusky Sound the overall mean catch rate was 2.69 kg/pot per h (range 1.28–8.42), CV was 6.3%, highest catch rates were on the open coast, and overall sex ratio was 0.78:1 (male:female). Blue cod in the 1940s from throughout New Zealand were on average larger than blue cod in Banks Peninsula and Dusky Sound during this survey. Low relative abundance and small size of blue cod from the more accessible inshore areas, is consistent with fishing pressure causing a reduction in size and probably abundance, particularly in Banks Peninsula inshore strata. In Banks Peninsula, sex ratios in inshore areas are skewed towards males, possibly a result of fishing pressure. The results support other studies on protogynous fish species in which the removal of the larger final sex fish (males), promotes sex inversion. The plasticity of the sex inversion means that blue cod may be capable of restoring optimal sex ratios in the natural state, but may over‐compensate with size specific anthropogenic removal of large numbers of individuals that would otherwise inhibit the sex inversion process.

Reproductive cycle and sex inversion in razor fish, a protogynous labrid in the southern Mediterranean Sea

The reproductive biology of the Mediterranean razor fish Xyrichthys novacula was investigated by demographic data and histological analysis of the female, intersexual and male gonads. Specimens were collected by bottom trawl on a monthly basis between June 2000 and July 2001 in a sandy bay in southern Thyrrenian. Gonad histology confirmed that the Mediterranean razor fish is a monandric, protogynous hermaphrodite. Females reached first sexual maturity at 100 mm (LT) and the estimated mean LT at first maturity (L50) was 125 mm. Females exhibited asynchronous ovarian development and multiple ovulations occurred over the spawning period. Vitellogenesis started in early May and spawning occurred from late May until late September. Sexual transition involved a large‐scale atresia of all oocyte stages and a massive degeneration of ovarian tissue followed by primordial germ cells proliferation. Sex change began at spawning time (June) but transitional individuals tended to cluster at the end of the reproductive period (September). They accounted for 17·1% of the population sampled and were found in a broad size range (105–150 mm LT).

Preliminary Assessment of Sex Inversion of Farmed Atlantic Salmon by Dietary and Immersion Androgen Treatments

AbstractDietary and immersion treatments with the androgens 17α‐methyltestosterone (MT) and 17α‐methyldihydrotestosterone (MDHT) were assessed for their efficacy in the masculinization of Atlantic salmon Salmo salar. Dietary treatments with MT at 1 or 3 mg/kg food or MDHT at 1 mg/kg food for 800 degree‐days resulted in 100% masculinization of all female stocks. Single or double immersion treatments of alevins in MDHT at 400 μg/L for 120 min during the period 0–28 d after median hatch resulted in significant masculinization. Immersion treatments were most effective when conducted more than 14 d after median hatch. Two immersion treatments 7 or 14 d apart resulted in masculinization levels of up to 100%, whereas single immersions yielded levels up to 77%. Immersion treatment resulted in the production of significantly more sex‐inverted males with patent sperm ducts than did dietary treatment. The study shows that immersion treatments are simple and effective for androgen‐induced masculinization of Atlantic salmon, that they are suitable for commercial‐scale use in hatcheries, and that they offer advantages in production efficiency over dietary treatments.

Masculinization Of Genetic Females Of The Common Carp (Cyprinus Carpio L.) By Dietary Administration Of An Aromatase Inhibitor

In the present study, we demonstrated the ability of Fadrozole, an aromatase inhibitor, to induce sex inversion of genetically female common carp fry during the critical sex differentiation period. Thirty-day-old female fingerlings with a mean initial weight of 4.0 g (experiment I) and 3.5 g (experiment II) were fed a diet containing Fadrozole for 36 or 50 days, respectively. Not a single male was found in the control groups of both experiments. In experiment I, Fadrozole at 200 mg/kg feed resulted in 58.6% males, while fish receiving 17α-methyltestosterone at 50 or 100 mg/kg feed resulted in only 5-10% males. In experiment II, the efficiency of Fadrozole was dose- dependent; the lower dose of 100 mg/kg caused masculinization in 86% of the treated fry while the higher doses of 200 and 400 mg/kg feed increased the percentage of males to 97%. These results confirm the importance of aromatization during the labile period in common carp since low aromatase activity during this period, regardless of genotype, resulted in masculinization.

Role of steriod hormones in sex change of protogynous wrasse

The endocrine mechanisms of sequential hermaphroditism were investigated in protogynous wrasse, Halichoeres trimaculatus. Administration of aromatase inhibitor and androgen both stimulated sex change, while estrogen suppressed the induced sex inversion. The results suggest that removal of estrogen is a key step to initiate sex change.