Abstract:Cultivation of pseudofemale largemouth bass (Micropterus salmoides) is a key step in the preparation of
all-male fry. To determine the optimum parameters for the female sex reversal of largemouth bass, establish the
sex induction technique of pseudofemale fish, and prepare all-male fry, juvenile largemouth bass (15 days
post-hatching, 1.00±0.01 cm in length) were fed with artificial compound feed mixed with 17β-estradiol (17β-E2)
or trilostane (TR). The diets of the three experimental groups contained 30 mg/kg 17β-E2, 30 mg/kg TR, and 20
mg/kg 17β-E2+10 mg/kg TR, which were named E30, TR30, and E20TR10, respectively. The feed of the control
group did not contain 17β-E2 and TR, which was named C. The effects of 17β-E2 and TR on the growth
performance, female ratio, and gonadal tissue development of largemouth bass were analyzed after a 60-day
feeding period. At the age of 12 months, the blood and gonadal tissues of pseudofemales in each experimental and
control group were collected to detect the concentration of sex steroid hormones, expression levels of cyp19a1a
and dmrt1, and ovarian development morphology. The results showed that the body length and weight of the E30
and E20TR10 groups were significantly lower than those of the C group (P<0.05), whereas the body length and
weight of the TR30 group were higher than those of the control group; however, the difference was not significant
(P>0.05). The proportions of females in the E30, TR30, E20TR10, and C groups were 100.00%, 0, 100.00%, and
53.33%, respectively. Gonadal tissue sections showed a large number of primary oocytes in the ovaries of group C.
Ovarian cavities, oogonia, and oocytes were observed in the E30 and E20TR10 groups. However, males in the
TR30 group showed no sexual reversals. At the age of 12 months, the proportions of females in the E30, TR30,
E20TR10, and C groups were 100%, 0, 100.00%, and 46.67%, respectively. Tissue sections showed no
pseudofemales in the TR30 group. The ovarian development of pseudofemales in the other experimental groups
was at stage II. The concentration of estradiol and expression of cyp19a1a in each experimental group were
significantly lower than those in the control group (P<0.05). In summary, largemouth bass pseudofemales can be
produced using the hormone concentrations utilized in this study. However, during the breeding period, the
estradiol content and expression of cyp19a1a in the pseudofemale did not reach the levels observed in normal
females, leading to ovarian retardation. This study provides foundation data for optimizing largemouth bass
feminization.
