Sex-reversed Fish Research Articles

Sperm traits and fertilization success of male and sex-reversed female rainbow trout ( Oncorhynchus mykiss)

Sperm motility, density, adenosine triphosphate (ATP) concentration, and fertilization rates of sex-reversed female (XX-male) rainbow trout ( Oncorhynchus mykiss) were compared to those of normal (XY-male) males. The relationships between sperm traits, fertilization rates, and characteristics of individual fish (weight, gonadosomatic index) were assessed. The fertilization rate of sperm stripped from normal males averaged 81% (s.d. 16%). The sperm of sex-reversed females had to be removed directly from the testes and achieved average fertilization rates of 60% (s.d. 13%). Testicular sperm from normal males was motile for shorter periods of time and produced lower fertilization rates than testicular sperm from sex-reversed fish. Fertilization rates were positively correlated with higher initial sperm motility, but not with sperm density or ATP concentrations.

Effect of oestradiol-17beta immersion treatments on sex reversal of mud loach, Misgurnus mizolepis (Gunther)

Mud loach, Misgurnus mizolepis (Gunther), were sex reversed using the immersion technique. Fry were raised in water containing 50, 100 or 200 μg oestradiol-17β I−1 for 1, 2 or 3 weeks. Survival rates decreased as dose and duration of treatment increased: in most instances they were significantly (P < 0.05) lower than those of the controls. Growth rates were unaffected except for fish in the 200 μg I−1 treatments. The 200 μg T−1 treatments for 2 and 3 weeks produced monosex female populations. The 100 μg I−1 treatment for 3 weeks produced 99% females and 1% intersex individuals. Histologically, ovaries of sex-reversed fish were similar to those of normal females. Morphologically, however, they were different in that the ovaries of sex-reversed fish were not connected to the genital pore. The hormone treatments affected the size and morphology of the pectoral fins, which exhibit sexual dimorphism in mud loach.

Hormonal induction of precocious sex reversal in the ricefield eel, Monopterus albus

The present study has evaluated the effects of a salmon gonadotropin-releasing hormone analog (sGnRH-A), the dopamine receptor antagonist domperidone (DOM) and carp pituitary homogenate (CPH) on sex reversal and serum steroid levels in the ricefield eel. Treatment with sGnRH-A alone or in combination with DOM for a 9-week period induced precocious sex reversal of female to male ricefield eel. The gonads of sex-reversed fish contained functional testicular tissue with secondary spermatocytes and spermatids; some primary oocytes were present, but no secondary oocytes remained. Sex-reversed fish treated with sGnRH-A either alone or in combination with DOM had elevated serum testosterone levels and depressed 17 β-estradiol levels which was comparable to the hormone pattern of males which had undergone natural sex reversal. DOM alone did not induce sex reversal but tended to inhibit ovarian development. Also treatment with CPH did not initiate sex reversal but stimulated ovarian development and increased serum 17 β-estradiol levels. These results suggest that the hypothalamo-hypophyseal system may play a significant role in the initiation of sex reversal in the ricefield eel and that GnRH is a key factor in this process.

Sex Reversal of Florida Red Tilapia in Brackish Water Tanks Under Different Treatment Durations of 17-Ethynyltestosterone Administered in Feed

Florida red tilapia (5-to 12-day post-hatching) were raised in 0.53-m3 tanks (stocking density = 5,660 fish/m3) supplied with recirculated brackish water (12 ppt) and fed a diet containing 60 mg 17αethynyltestosterone (ET)/kg diet for different durations: 0, 7-14, 14-21, 21-28, and 28-35 days. Fry were fed daily (0830-1630) to satiation (17-22% biomass) by means of continual automatic feeding. Each treatment consisted of 3-4 replicate tanks. All durations of androgen treatment produced nearly all-male populations (range =94.3-98.1%), with no significant (P> 0.05) effects of treatment duration on growth rates (mean = 15.3% body weight/day) or survival (mean = 37.3%) were observed after 28 days. Fry averages 1.40g after 28-35 days of androgen treatment and consumed 0.206mg of ET per individual. In contrast, fry averaged 0.040g after 7-14 days of androgen treatment and consumed only 0.003mg of ET, or 1.5% of the 28-day total. The results demonstrate the feasibility of reducing the duration of androgen treatment for sex reversal in Florida red tilapia to 7-14 days, in order to minimize hormone consumption, size of sex-reversed fish and to accelerate hatchery throughput. This will minimize risks to consumers; facilitate marketing; and improve availability, transportation, and cost of sexreversed fingerlings to farmers.

Feminization of Oreochromis mossambicus by the administration of diethylstilbestrol

Gonadally undifferentiated Oreochromis mossambicus fry were given different doses of diethylstilbestrol (DES) orally for 11 or 15 days and reared for 70 days. All-female populations were produced at doses >100 μg DES/g diet in both treatments. Mortality increased at higher doses (>500 μg/g). The hormone treatment significantly ( P>0.0005) improved the growth performance of the sex-reversed fish.

The ‘YY’ supermale in Oreochromis niloticus (L.) and its potential in aquaculture

A male Oreochromis niloticus obtained by gynogenesis was found to sire 100% male progenies consistently when crossed with normal females. Evidence suggests that this fish is a ‘YY’ supermale and that its mother was spontaneously sex reversd (XY). Hormone treatment of normal fry followed by progeny testing was used to generate sex-reversed male and female O. niloticus. Intercrosses among these sex-reversed fish, normal males and females, and the supermale result in progeny sex ratios which are consistent with a monofactorial system of sex determination in O. niloticus where males are XY and females XX. However, some exceptional results were obtained suggesting the existence of minor sex-ratio modifying factors. It is shown experimentally that YY males can be used to study sex reversal to female in this species without the need for progeny testing. A programme for the commercial production and maintenance of YY broodstock and its use for the generation of monosex male progenies in aquaculture is discussed.

Histochemistry of Liver Tumors Induced by Diethylnitrosamine and Differential Sex Susceptibility to Carcinogenesis in &lt;italic&gt;Oryzias latipes&lt;/italic&gt;

Liver tumor nodules were induced by the administration of diethylnitrosamine [(DENA) CAS: 55-18-5; N-nitrosodiethylamine] to the fish, Oryzias latipes. A histochemical study showed decreased ATPase and glucose 6-phosphatase (Glc-6-Pase) activities in most of the tumor nodules. Increased ATPase staining and, occasionally, Glc-6-Pase staining were also observed. In some nodules, the distribution of bile canaliculi was disordered, indicating positive ATPase activity. Basophilic and eosinophilic nodules could be discriminated by histologic examination. The observations on serial histochemical and histologic sections revealed extreme heterogeneity in the phenotypes of the nodules. Measurement of the enzyme-altered areas indicated that the development of nodules was more prominent in male than in female fish. Experiments with sex-reversed fish, XX males and XY females, suggested that the sex difference in the susceptibility to DENA does not result from the difference in sex chromosomes but from the difference in sexual phenotypes.

Sex reversal in Betta splendens Regan with emphasis on the problem of sex determination.

To gain insight into the sex-determining mechanism of the Siamese fighting fish, Betta splendens, sex-reversed individuals were bred and the ratios of the spawnings were examined. Sex-reversal of 245 females was undertaken by ovariectomizing them; of these, 104 became sex-reversed. Twenty-three of these latter fish were mated to normal females and eleven spawnings were raised to maturity. These spawnings resulted in all female broods or mixed broods. Were the male fish heterogametic, a view currently held by some authors, no males would be produced in these spawnings. Thus, male heterogamety was not substaintiated in this study. Contrary to other studies, the experimental sex reversal of females is not a rare event since nearly two-thirds of the fish that survived the surgery became sex-reversed. Gross dissection and histological observation of sex-reversed fish revealed a regenerated, unpaired duct which remained after the ovaries had been removed. The tissue of the regenerate was testicular and contained active spermatogenesis. Some alterative methods of sex determination which may apply to the Betta are examined. These include the possibility of two different sex-determining races, the effects of exogenous factors, and a polygenic system of sex determination.