Effect of Netting Materials on Fouling and Parasite Egg Loading on Offshore Net Pens in Hawaii

Parasitic skin flukes, primarily Capsalid Monogeneans, Benedenia sp. and Neobenedenia sp. are a scourge to the marine aquaculture industry worldwide. These parasites infect a wide range of hosts in tropical and temperate waters, causing immediate irritation and stress to the animal and, if levels are left unchecked, can lead to bacterial infections and eventual death. The life cycle and physiology of these two genera lend themselves to exponential growth in fish tanks and seacages. A series of topical chemical treatments can often remedy the problem in land-based containment systems, but topical treatments are less effective in offshore net pens.

Neobenedenia, the parasite of concern in Hawaiian offshore mariculture, reproduces by releasing (up to) several hundred eggs daily (Whittington and Horton, 1996). These eggs are composed of a rugged shell and a long tendril. The tendrils allow the eggs to attach directly to netting or to fouling on the netting. Bathing of contained fish in a chemical compound such as Hydrogen peroxide only removes the infective stage of the parasite from the skin of the fish, leaving unhatched eggs attached to the netting unharmed. These eggs will tend to hatch and re-infect the fish within the net pen. Preventing reinfection requires a significant reduction in the ability of parasite eggs to efficiently colonize the netting material. The virulence of Neobenedenia infection can be greatly reduced by identifying netting materials which inhibit the efficacy of parasite egg colonization.

Several attributes make a netting material more or less resistant to parasite egg colonization. First, is the material porous or contain areas of overlap, such as in a braided rope? The small crevices formed by the strands of a braided rope give egg attachment mechanisms greater purchase. Second, is the material easy to clean? Smooth surface netting materials tend to facilitate easier removal of eggs and fouling with active cleaning methods such as pressure washing. Third, is there an antifoulant compound coated on the netting, or is it made of a compound that has antifoulant properties that will inhibit egg attachment or health?

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Prepared July 17, 2012
By: Jennica Lowell, M.S.
Blue Ocean Mariculture