The effect of methyltestosterone (MT) on sex differentiation and growth in juvenile yellow perch (Perca flavescens).

A study was conducted to evaluate the gonad differentiation of juvenile yellow perch (YP, Perca flavencens) and determine the latest labile period related to hormone treatment. Juvenile fish were subjected to two dietary concentrations of methyltestosterone (MT; 20 and 50 mg/kg feed) for 60 days in three (3) age groups of 38-, 46-, and 67-days post-hatching (dph), where control group were fed with standard commercial feed. Following a 10-month on-growing period, sex phenotypes were determined by gross and histological gonad morphology. Results showed the juvenile YP responded to the exogenous hormone when it was applied at 38 dph for both 20 and 50 mg/kg feed resulting in 100% males. At 46 dph, only 50 mg/kg feed resulted in 100% males. Both MT-treated at 38 and 46 dph significantly differed (P < 0.01) from the expected normal population of male:female (1:1). MT-treated at 67 dph resulted in 37% and 25% intersex fish for both 20 and 50 mg/kg feed dosage groups, respectively. MT-treated at 38 and 46 dph promoted growth and showed significantly heavier mean body weight (P < 0.05) compared to control. The gonadosomatic index (GSI) of MT-treated at 38 and 46 dph was significantly lower than that in control. This study provides the first evidence that juvenile YP can be successfully masculinized when the treatment is initiated at the age of up to 46 dph. The result is important for sex control in aquaculture.

[Selection of vestibular system function in Chinese astronauts].

OBJECTIVE: To examine and evaluate the vestibular function of Chinese astronaut candidates in order to select the astronauts with good vestibular function. METHOD: Fifty-nine male candidates, the fighter plane pilots, participated in the Caloric tests, and 38 pilots among all the candidates experienced the parallel swing and Coriolis acceleration stimuli in tests. The parameters, such as vestibule-autonomic nervous reflex symptoms, electrogastrography (EGG), electronystagmography (ENG), ECG, blood pressure, postural equilibrium ability were employed to evaluate the vestibular function. RESULT: Caloric tests indicated that there were function symmetry on both sides of semicircular canals, as well as normality of visual-vestibular and vestibulo-ocular reflexes in all the candidates. The parallel swing and Coriolis acceleration stimulus demonstrated that there were differences of vestibular functions in 38 pilots. Incidence of I category (stability type) of vestibular function exceeded 52.6%, and II category (relatively stable type) approached 42.1% as well III category (relatively susceptible type) was reported to be 5.3%. CONCLUSION: Vestibular function of astronaut candidates could be evaluated comprehensively and objectively in the present tests. The Chinese astronauts can be chosen from the candidates with stable type or relatively stable type up to standard vestibular function.