An investigation into the efficacy of Biokos® in controlling ciliates in laboratory cultures of <i>Saccharina latissima</i> gametophytes

A major challenge faced by kelp aquaculture operations is the control of contaminants, including by marine ciliates. Biokos® is a commercially available treatment for ciliate parasites in fish, in which the active ingredient is a viscosin-like lipopeptide surfactant. This study aimed to determine whether Biokos® is effective at controlling ciliate contamination in Saccharina latissima cultures without impacting gametophytes. Two experiments were conducted. Biokos® was first added to a live ciliate culture, and mortality was compared to a control. Subsequently, Biokos® was added to a culture of S. latissima gametophytes. The growth, density, and reproduction of gametophytes were compared to a control. Biokos® was highly effective at destroying ciliates within 24 h of treatment. We observed no impact on the vegetative growth of gametophytes. However, Biokos® did reduce gametophyte densities and may have had an impact on adherence. Biokos® also induced higher egg and sporophyte production in female gametophytes, potentially as a response to changes in pH associated with the treatment. There is potential for Biokos® to be effective at controlling ciliate contamination in gametophyte cultures, and at this stage, we would recommend treatment at manufacturer-recommended doses, along with appropriate buffering to maintain the pH of the culture. Further research is recommended on the identity of ciliate species contaminating gametophyte cultures and the response of different kelp species to Biokos®. Additionally, we would recommend that Biokos® now be tested in a commercial hatchery setting to identify impacts on S. latissima throughout the cultivation process and to determine optimal dosing procedures.