Knowledge of population characteristics, such as reproduction and life history traits, is essential for sustainable fisheries management. Commercially important Venerid bivalves play a significant role in fisheries and aquaculture worldwide, and the reproductive cycle is complex and highly varied across species. One of the only remaining sustainable Katelysia spp. fisheries in South Australia is in Coffin Bay, Eyre Peninsula, and there is limited information known about their annual changes in reproductive condition. Over 12 months, Katelysia spp. individuals were collected from several fishing grounds in Coffin Bay to identify the age, shell size, and time when the peak spawning period occurs for three species. Sexes were assessed microscopically, and reproductive phase determined by dissection to score gonad condition. The ages of Katelysia spp. were determined using acetate peel replicas and counting the growth bands. We identified that there were some idiosyncratic patterns across sites and months around predicted peak spawning times, and the results show location- and species-based differences in the size and age at sexual maturity. These findings will be important for the advancement of the Coffin Bay Katelysia spp. fishery to avoid overexploitation and ensure food security for the future.