Evaluation of two species, Cobia and Giant Grouper, as alternative species to farm in the WSSV affected areas of South East Queensland

Abstract

In 2016/17, the Rocky Point Prawn Farm, along with other farms in the Logan River region of south-east Queensland, was severely affected by a white spot disease outbreak caused by the exotic white spot syndrome virus (WSSV). Measures enforced to eradicate WSSV resulted in a complete loss of stock and a ban on prawn production within the Logan River and wider Moreton Bay area until May 2018. As a result, Rocky Point Prawn Farms (RPPF) elected to investigate the feasibility of finfish aquaculture as an alternative to prawn farming. The current project was undertaken to assess the potential of two finfish species, Cobia (Rachycentron canadum) and Giant Grouper (Epinephelus lanceolatus) as alternative aquaculture candidates for the Rocky Point Prawn Farm and potentially other aquaculture enterprises. The study was developed and led by RPPF with assistance from The Company One (TCO) and the Department of Agriculture and Fisheries (DAF), with staff from the Bribie Island Research Centre (BIRC) and ran from March 2017 until June 2018. In the study, the commercial performance of each species was assessed when cultured in both indoor tank systems and outdoors in cages. Culture facilities at two of RPPF’s production sites included a former prawn hatchery building which housed the indoor tank-based production, and an outdoor landlocked saline lake which contained cages. Cobia fingerlings were produced at BIRC and Giant Grouper fingerlings were supplied by TCO hatchery in Cairns. All fingerlings were initially grown in indoor tanks under controlled temperature conditions and later some were transferred to outdoor cages to assess their performance in both winter and spring/summer. Fish were fed once or twice per day and water quality data was collected daily. Weight and health checks were conducted monthly and any mortalities were removed from tanks or cages daily. The data were used to calculate key production parameters of feed conversion ratio, growth rate and survival throughout the production cycle. Both species were grown to harvest and sold into the domestic market. The production and market information generated by this project provided a framework to evaluate the relative costs and benefits of the two species within the range of production methods and strategies available to RPPF, and guidance towards future investment and optimising production in the future.