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Aquaculture 184 2000 277–290 www.elsevier.nlrlocateraqua-online
Biofouling of fish-cage netting: the efficacy of a silicone coating and the effect of netting colour
Stephen L. Hodson , Christopher M. Burke, Andrew P. Bissett
CooperatiÕe Research Centre for Aquaculture, Tasmanian Aquaculture and Fisheries Institute, PO Box 1214, Launceston, Tasmania 7250, Australia
Received 8 July 1999; received in revised form 22 September 1999; accepted 27 September 1999
Abstract
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The efficacy of a silicone coating Veridian 2000 to reduce fouling on salmon-cage netting was examined at a salmon farm in Tasmania, Australia. Significantly less fouling occurred on the
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2
. Ž
2
. white silicone-coated netting 1.9 kgrm
compared to uncoated white 7.8 kgrm and black
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. 8.5 kgrm
netting after 163 days immersion. On silicone-coated netting the green alga UlÕa rigida dominated the fouling mass, with smaller amounts of solitary ascidians. In contrast, solitary
ascidians dominated the uncoated black and white netting and accounted for more than 75 of the fouling mass. Netting colour significantly affected the growth and composition of algal fouling,
but had no effect on invertebrate fouling. Cleaning experiments demonstrated that fouling organisms were poorly adhered to the silicone coating and that relatively little effort was required
for their removal. Silicone coatings may provide an effective non-toxic solution to reduce fouling on sea-cages and to increase the ease of fouling removal. q 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Biofouling; Antifouling; Netting; Silicone; Fish cages
1. Introduction
Biofouling on fish-cage netting is a serious problem to mariculture worldwide. It can Ž
rapidly occlude mesh and necessitates the frequent and costly cleaning of nets Hodson .
et al., 1995, 1997 . Fouling significantly impedes the water flow and therefore the Ž
. supply of dissolved oxygen to the caged fish Aarsnes et al., 1990 . Fouled netting also
increases structural fatigue on cages and the fouling communities may harbour disease- Ž
. causing microorganisms Kent, 1992 .
C o rresp o n d in g au th o r.
T el.: q6 1 -3 -6 3 2 4 -3 8 1 6 ;
fax : q6 1 -3 -6 3 2 4 -3 8 0 4 ;
e-m ail: stephen.hodsonutas.edu.au
0044-8486r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 0 4 4 - 8 4 8 6 9 9 0 0 3 2 8 - 2
The prevention of fouling on mariculture structures is complicated by the choice of net material and the dangers of toxins to cultured species. Multi-filament netting
material is an ideal substrate for fouling: it is non-toxic, contains many crevices that can entrap and protect settling organisms, and has a high surface-area to volume ratio.
Although copper-based antifoulants have proved effective on nets, their use is undesir- able because of environmental effects from broad-spectrum metal-based toxins, together
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with consumer concerns that can jeopardise market image Lewis, 1994a . Problems associated with mariculture antifouling have recently received publicity.
The Scottish Environment Protection Authority has found sediments underneath fish Ž
. cages to be seriously contaminated with copper Miller, 1998 . Further, the Norwegian
aquaculture industry is working toward a significant reduction in the use of copper-based Ž
antifouling by the year 2010 Norwegian Pollution Control Authority, personal commu- .
nication . There have been incidents where antifouling has adversely affected fish: in the 1980’s, trials with tributyl-tin on cages caused significant effects to farmed salmon
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Short and Thrower, 1986; Davies and McKie, 1987 and, more recently, boat antifoul- Ž
. ing was implicated in residues within wild fish Kannan et al., 1995a,b .
Internationally, the development of more environmentally acceptable antifoulants is focused on two strategies: the production of ‘‘foul-release’’ surface coatings and
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coatings that release non-toxic compounds that act as deterrents Clare et al., 1992 . The Ž
former strategy is based on a physical surface effect, where low surface-free-energy low .
surface tension prevents adhesion or reduces adhesion strength of fouling organisms Ž
. Lewis, 1994b . Substantial fouling is prevented because large masses slough from the
surface and are easily removed by hydrodynamic forces, such as across a ship’s hull, or Ž
. by light cleaning Schultz et al., 1999 . The most successful coatings are presently based
on silicone elastomers, and often include oil-based additives that further improve fouling Ž
. resistance Lewis, 1994b; Swain and Schultz, 1996 . Coatings based on other materials,
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Ž including fluoropolyurethanes
Bultman and Griffith, 1994 , polyurethanes Lewis,
. Ž
. 1994b and perfluorinated polymers Lindner, 1994 , have also displayed excellent
adhesion resistance. Ž
This paper describes the evaluation of a commercial silicone coating Veridian 2000, .
International Coatings as applied to fish-cage netting. The development, composition and adhesion of fouling are compared between white silicone-coated netting, white
uncoated netting and black uncoated netting. The preferential settlement of fouling species in relation to substrate colour and the adaptation of species to low-surface-free
energy are described and discussed. The flexibility and non-toxic properties of silicone coatings make them highly suitable for fish-cage netting. Results show that they can be
used in conjunction with underwater cleaning equipment, alleviating the need to remove netting from the water for cleaning.
2. Materials and methods
