Environmental Determinants of Sex Ratio in St. Lawrence River Northern Pike: Development of a Molecular Sex Identification Tool and Experimentation with Physical and Chemical Variables

Sex determination and gender ratio within fish populations can be influenced by environmental factors and selective mortality and therefore represents an important marker of population health. Despite its value, sex ratio is typically assessed in mature adult fish during the reproductive phase or through internal examination. Gender determination at early stages of development (e.g., egg and larval) presents a challenge because gonads are not identifiable precluding investigation of sex linked biological processes. We propose the development of a molecular diagnostic tool to determine gender at any life stage.  Based on next generation sequencing data, a cDNA library can be developed to produce gender specific transcriptomes whereby male linked markers can be identified.  If successful, the male specific assay will be used in experimental trials to test environmental factors hypothesized to influence expected sex ratios. Northern Pike males are heterogametic (XY chromosomes) and a 50:50 male to female sex ratio is expected, but in the St Lawrence River, ratios exhibit female dominance (25:75).  Specifically, we will investigate temperature, dissolved oxygen, and xenoestrogen treatments on gender for Northern Pike eggs and larvae. Results will be used to enhance understanding of mechanisms driving Northern Pike sex ratio in the St. Lawrence River.