Sex determination is crucial for the maintenance and continuity of species. The specification of primordial germ cells and the development of a functional gonad are key steps, but the mechanisms are not fully understood in many organisms, including zebrafish. Germplasm is a component inherited by the primordial germ cells (PGCs) in zebrafish. Germplasm is localised to the Balbiani body, a conserved membrane-free structure found in all vertebrate oocytes, which gives rise to gametes. Germplasm components contribute to the oocyte polarity as well as the germ cell fate. However, to date, only a few mRNAs have been identified as germplasm components. Additionally, it is known the ovary must be actively maintained to keep the female fate, but little is known about how oocytes differentiate. I have identified a novel germplasm and oocyte component called zgc:163014. Here I show that transcripts of zgc:163014 are expressed exclusively maternally, localising to the Balbiani Body in early oocytes and to the vegetal pole in later oocytes. CRISPR/Cas genome editing was used to generate homozygous zgc:163014 mutant females and the mutants show that maternal zgc:163014 is required for oogenesis. Furthermore, maternal zgc:163014 mutant eggs display extra-numerary micropyles (-the opening through which sperm enters the egg during fertilisation-) such that zgc:163014 eggs appear punctured. Thus, I have named this novel gene pinchado (pin), which means punctured in Spanish. Pin protein is conserved across many teleost species and shows dynamic localisation in the centrosome, nuclei and cortex of cleavage-stage zebrafish embryos. pin RNA is bound by the conserved RNA-binding protein Ybx1, and Pin protein interacts with the Actin cytoskeleton through a beta-propeller domain. My work suggests that Pin plays a crucial role during oogenesis and germline development.