Effects of Different Hormones on Sex Reversal of Rainbow Trout ( Oncorhynchus Mykiss Walbaum) and Production of All-Female Populations

Masculinization of Adult Gambusia holbrooki: A Case of Recapitulation of Protogyny in a Gonochorist?

17α-Methyltestosterone (MT) is a synthetic steroid that has been widely used to masculinize many fish species when administered early during larval development, however, reports on its efficacy on adults is limited. To this end, this study investigated the efficacy of MT in the masculinization of the eastern mosquitofish (G. holbrooki) at two adult stages (maiden and repeat gravid females). The treated females were fed control or respective MT incorporated feed (0-200 mg/kg diet) for 50 days. Effects of the hormone on secondary sexual characteristics, internal gonad morphology, expression of the Anti-Müllerian Hormone (amh) gene and sexual behavior of the treated females were investigated. The results showed that MT at the dose of 50 mg/kg feed stimulated secondary sexual character development, upregulated expression of amh, formation of testicular tissue and a shift in the behavior similar to those of normal males, prominently so in treated maiden gravid females. Post-treatment, long-term observations indicated that only two masculinized females reverted back to being females and gave birth to young. Induction of masculinizing effects in most individuals suggests that the sexual phenotype of this species appears to be highly plastic with potential to sex reverse at adulthood. This in combination with its small size and short reproductive cycle could provide an ideal system to explore the mechanisms of sequential hermaphroditism in fish and contribute to genetic control of this pest fish.

Characteristics and Cryopreservation of Semen of Sex-Reversed Females of Salmonid Fish

Sex reversal has been used as a breeding strategy by salmonid fish to produce genetically and phenotypically single sex populations. Production of all-female fish has great importance for the creation of monosex female triploids of salmonid fish, which are valued for their sterility, lack of female maturation, and larger commercial size. Among salmonids, the majority of rainbow trout (Oncorhynchus mykiss) production is based on all-female production with a high proportion of all-female triploid production in Europe. The main aim of this review is to present the recent knowledge regarding sex-reversed females (SRFs) of salmonid fish. We discuss the methods of sex reversal as well as their effects on the morphology and histology of the reproductive tract. We focus on the characteristics of SRF semen as well as the factors determining semen quality. The lower quality of SRF sperm compared to that of normal males has resulted in the need for the artificial maturation of semen. Most importantly, methods of semen storage-both short-term and long-term (cryopreservation)-that can improve hatchery operations are presented with the special emphasis on recent progress in development of efficient cryopreservation procedures and use of cryopreserved semen in hatchery practice. Moreover, we also address the emerging knowledge concerning the proteomic investigations of salmonid sperm, focusing primarily on the proteomic comparison of normal male and SRF testicular semen and presenting changes in SRF rainbow trout sperm proteome after in vitro incubation in artificial seminal plasma.

Seasonal and age-related changes in semen characteristics and composition of seminal plasma in sex-reverse female rainbow trout (Oncorhynchus mykiss) in comparison with normal males

All-male or all-female progeny is preferable in reproduction of fish species. In rainbow trout, all-female progeny is desirable, and the most common and healthful approach is to use sex reversed (SR) females as broodstock by including androgen hormones through the diet at the larval stage. The purpose of this study was to determine the differences and changes of seminal plasma ions (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^-) and pH in 2 to 3 and 3 to 4 year-old SR females, compared with 2 to 3 year-old normal (N) males at the beginning, middle, and end of the spawning season (SS). Additionally, osmolality, spermatozoa concentration, and sperm motility characteristics were determined. Percentages of sperm motility of SR females were negatively correlated with seminal plasma pH and sperm concentrations (r = -0.479 and r = -0.534, respectively, P < 0.05). Seminal plasma pH (7.14 ± 0.05 to 7.40 ± 0.10) in SR females was less than for N males (7.66 ± 0.10 to 8.04 ± 0.10) at all periods of the SS (P < 0.05). The Ca²⁺ concentrations in the mid-SS were 0.74 ± 0.23 mM in N males, 1.09 ± 0.29 mM in 2 to 3 year-old SR females, and 0.83 ± 0.29 in 2 to 3 year-old SR females, without significant differences (P > 0.05). Furthermore, using of 2 to 3 year-old rather than 3 to 4 year-old SR females for reproduction could provide an advantage in terms of sperm motility characteristics. These findings could be useful for not only understanding of SR of semen from sexually reversed females but also for design of a maturation medium both for further studies and aquaculture production.

Total antioxidant capacity, catalase activity, and lipid peroxidation changes in seminal plasma of sex-reversed female and male rainbow trout (Oncorhynchus mykiss) during spawning season

The advantages of gender-related characteristics are used in aquaculture practice to improve production. For instance, all-female stock is preferable than mixed or all-male stock in salmonid culture. The most effective way to obtain all-female populations is the using of sex-reversed (SR) female trouts, genotypically female but phenotypically male, by masculinizing androgen hormones as breeders in artificial insemination. This study was conducted to evaluate changes in the total antioxidant capacity (TAC), protein concentration, catalase (CAT) activity, lipid peroxidation level (LPO; malondialdehyde), and Fourier transform infrared spectra of seminal plasma of SR female and normal (N) male trouts during the spawning season. Seminal plasma TAC values of N male and SR female trouts were determined as 0.015 ± 0.004 and 0.116 ± 0.033 mM of Trolox equivalents, respectively, in the middle of the spawning season. Some regions related to aromatic rings in seminal plasma Fourier transform infrared spectra of SR female trouts differed from N male trouts were indicated to the higher TAC values. At the middle of the spawning season, protein concentrations were determined as 569.5 ± 139.4 mg/dL in SR female trouts and 66.3 ± 22.7 mg/dL in N male trouts. LPO levels in seminal plasma of N male trouts varied from 46.33 ± 12.05 × 10(-3) to 270.02 ± 70.64 × 10(-3) nmol/mg protein, whereas from 13.87 ± 4.98 × 10(-3) to 48.49 ± 17.31 × 10(-3) nmol/mg protein in SR female trouts throughout the spawning. CAT activities of seminal plasma in N male trouts ranged from 0.38 ± 0.26 to 0.47 ± 0.32 kU/mg protein, whereas those values in SR female trouts varied between 0.21 ± 0.10 and 0.43 ± 0.15 kU/mg protein. Moreover, there were the pairwise significant correlations among all variables except between CAT and TAC (P > 0.05). Remarkable correlations were found between LPO-protein (r = -0.922, P < 0.05, n = 190), LPO-TAC (r = -0.859, P < 0.05, n = 98), and TAC protein (r = +0.879, P < 0.05, n = 98). Similar to seminal plasma of N male trouts, TAC values, protein concentrations, and CAT activities in seminal plasma of SR female trouts have shown decline, whereas LPO levels increased toward the end of the spawning seasons. Seminal plasmas of SR female trouts were characterized by higher protein concentrations and TAC values and lower LPO levels than that from N male trouts.

ECOLOGICAL AND EVOLUTIONARY APPLICATIONS FOR ENVIRONMENTAL SEX REVERSAL OF FISH

Environmental sex reversal (ESR), which results in a mismatch between genotypic and phenotypic sex, is well documented in numerous fish species and may be induced by chemical exposure. Historically, research involving piscine ESR has been carried out with a view to improving profitability in aquaculture or to elucidate the processes governing sex determination and sexual differentiation. However, recent studies in evolution and ecology suggest research on ESR now has much wider applications and ramifications. We begin with an overview of ESR in fish and a brief review of the traditional applications thereof. We then discuss ESR and its potential demographic consequences in wild populations. Theory even suggests sex-reversed fish may be purposefully released to manipulate population dynamics. We suggest new research directions that may prove fruitful in understanding how ESR at the individual level translates to population-level processes. In the latter portion of the review we focus on evolutionary applications of ESR. Sex-reversal studies from the aquaculture literature provide insight in to the evolvability of determinants of sexual phenotype. Additionally, induced sex reversal can provide information about the evolution of sex chromosomes and sex-linked traits. Recently, naturally occurring ESR has been implicated as a mechanism contributing to the evolution of sex chromosomes.