Sexual Differentiation and Use of Hormones to Control Sex in Yellow Perch (Perca flavescens)

Morphological and histologial studies demonstrated that estrogens and androgens affect sexual differentiation and can be used to control the phenotypic sex of yellow perch (Perca flavescens). Normal perch larvae of 5–10 mm total length (TL) had paired gonads with no sex-distinguishing features. In normal 16 mm TL perch, the gonads of females had fused into a single sac-shaped organ, while in males the gonads remained paired. Oogenesis had begun in most females of 35 mm TL. Spermatogenesis in males and vitellogenesis in females were first observed at 85 mm TL. Treatment (for 84 d) of perch (initially 20–35 mm TL) with estradiol-17β at 15–120 μg/g diet induced complete germ cell sex inversion in most males. Similar treatment with 17α-methyltestosterone at 1.5 to 60 μg/g diet induced spermatogenesis and the formation of ovotestes in females. Sperm collected from such ovotestes fertilized normal ova, and the resultant offspring were all female. Our findings indicate that in yellow perch: (1) differentiation of the somatic elements of the gonads precedes gametogenesis, (2) gametogenesis begins earlier in females than in males, (3) the attainment of a specific minimum body size (80–100 mm TL) is important to the initial onset of vitellogenesis and spermatogenesis, (4) both estrogens and androgens are probably involved in mediating sexual differentiation of germinal tissues and (5) females are the homogametic sex.