In the present study, we aimed to identify masculinized genotypic females of Rhamdia quelen on the basis of the sex ratio of the progeny. Masculinizing diets containing 3 levels of 17α-methyltestosterone (MT; 60, 90, or 120 mg kg -1 ) were administered to R. quelen fry. Thereafter, 5 phenotypic males from each MT treatment were crossed with normal females, and their progenies were sexed. At least 1 male from each treatment group generated progeny with a higher female:male ratio. These males, designated M60, M90, and M120, were crossed again with 3 other normal females to re-evaluate the sex ratio of the progeny. Moreover, a normal male was used as a control. Again, we found a higher female:male ratio in the progeny of M60, M90, and M120. The control male produced 2 sets of balanced progeny and 1 with a lower female:male ratio. Although these breeders did not generate all-female progeny (79.75 ± 7.20% of females), our findings indicate that M60, M90, and M120 can be considered masculinized genotypic females of R. quelen, suggesting the involvement of autosomal genes or polygenic interactions in sex determination.
The objective of this study was to determinate the lethal concentration of dissolved oxygen (DO) over 96 hours of exposure (LC50-96h) for diploid and triploid jundia Rhamdia quelen juveniles. Diploid and triploid fish weighing approximately 4 g were subjected to DO concentrations varying between 0.4 and 1.3 mg O 2 L -1 ; water temperature was maintained at 27°C and pH at 6.3. The LC50-96h for diploids of Rhamdia quelen was 0.535 mg O 2 L -1 , while the value obtained for triploids was 6% greater. These results demonstrated that triploids of Rhamdia quelen juveniles have greater sensitivity to hypoxia compared to diploids.
Monosex female jundiá (Rhamdia quelen) generated through indirect sex reversal may have their growth influenced by the stocking density, which is an important factor for production in fish farming. Since zootechnical data from R. quelen offspring generated by crossbreeding between genotypic masculinized females (neomales) and normal females were never reported, the objective of this study was to compare the zootechnical indexes of neomale and normal male offspring stocked at densities of 500, 1,000 and 1,500 fish m-3 (D1, D2, and D3) for 61 days. The initial mean weight and length of the neomale and normal male offspring were 0.90 ± 0.12 g / 4.94 ± 0.22 cm and 0.80 ± 0.12 g / 4.60 ± 0.37 cm, respectively. A completely randomized experimental design with three replicates was used, with fish stocked in 0.07 m³ tanks. At the end of the experimental period, the data evaluated showed that there were no significant differences between progeny or among stocking densities in terms of survival, weight, weight gain, length, feed conversion or feed consumption. Therefore, neomale offspring presented adequate productive performance during the juvenile stage and tolerated increases in stocking density without performance loss, making the neomales suitable for R. quelen cultivation.
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