Examining Follicular Development in a Hermaphroditic Fish

In female vertebrates, the ovarian cycle has distinct stages indicating follicular and oocyte development; however, the mechanisms and morphology of these stages are relatively unknown. Species capable of adult sex change are interesting because their reproductive system is capable of exhibiting plasticity when clearly defined as one sex and during protogynous transition. Bluebanded gobies, Lythrypnus dalli, are bidirectionally hermaphroditic marine fish. Many mechanisms and behaviors pertaining to protogynous sex change have been investigated, yet morphology of female genitalia and mechanisms of oocyte development is unknown. Here, we found an inverse relationship between the genital papilla length to width ratio and gravidity ratio, an external measure of how distended the abdomen is with eggs, such that a wider genital papilla was associated with more gravid females. We identified that a ‘flattened’ and ‘rounded’ phenotype is associated with a wider opening of the genitalia allowing for more efficient release of mature vitellogenic eggs in gravid females. We further investigated cellular changes occurring within the gonad when we isolated ovaries from females across four stages of gravidity (n=16) and performed cryosectioning, H&E staining, categorized follicles into five different stages, counted, and measured the area of each follicle. We found in later phases of the ovarian cycle there were more follicles in later stages of development and less follicles in earlier stages of development, and follicle stage is positively correlated with area. These findings show Lythrypnus dalli exhibit similar patterns of oogenesis as other Teleosts. Future studies will investigate characterizing male gonads and the role hormones have in stimulating and inhibiting folliculogenesis