MANAGING BACTERIAL LEVELS IN OCTOPUS TETRICUS PARALARVAE CULTURE

The increased demand for octopus as a food source over the past decade has resulted in efforts for further research and development into octopus aquaculture. While significant effort has been given to octopus paralarvae rearing around the world, closing the life cycle of octopus still constrains octopus culture's industrial development.

Commonly observed high mortalities and poor growth in early stages of paralarvae development is thought to be associated with nutritional imbalances of live prey and its nutritional profile. However, the true reason or reasons for this bottleneck remain unconfirmed.

Over the past four years, the focus of the Marine Aquaculture group at the Department of Fisheries, Western Australia has been developing culture techniques to improve health and survival of O. tetricus paralarvae and 'bridging the gap' between the free swimming planktonic stage and the stage at which metamorphosis is reached and paralarvae become benthic.

Various techniques have been tested over this period aiming to eradicate and reduce bacterial levels in tanks and within organisms and its impacts on larvae health and survival.          Techniques trialled included formalin treatment implemented to prevent bacterial proliferation, antibiotic Oxytetracycline treatment and elimination of organic matter by larvae passive transfer, siphoning and improvement of tank dynamics.

Aside from monitoring growth rates and survival, histological analysis of internal biological components of paralarvae under various treatment conditions was measured. Particular focus was on the paralarvae's gut function and development. Histological analyses demonstrated some larvae to be found with a filamentous mat of swarming bacteria in the digestive system. The presentation will review these results.