No. 12. GILPAT.pdf - Marine Institute Open Access Repository

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NDP Marine Research Sub-Programme 2007-201324
NDP Marine Research Sub-Programme 2007-20133. PILOT MONITORING PROGRAMME3.1. Zooplankton Monitoring3.1.1. BackgroundThe negative interactions between gelatinous zooplankton (primarily cnidarians, althoughsometimes ctenophores) and fish in aquaculture appears to be an increasing problem throughthe intensification of aquaculture operations in many coastal areas worldwide. Over the lastthree decades there have been numerous fish kill incidents or health problems in marinefarmedfish that have been associated with gelatinous zooplankton (Purcell et al, 2007). Themajority of problems have occurred with marine-farmed salmonids in northwest Europe;nevertheless aquaculture operations in other regions such as Asia, North America, andAustralia have also been affected (Yasuda 1988; Willcox et al. 2008; Rodger et al. 2011b).Although large-scale gelatinous zooplankton blooms can sometimes be the obvious cause (inthe case of conspicuous scyphomedusae), problems may also be associated with small or nearinvisiblespecies and a lack of sampling and investigation around these events can obscure thecause (Cronin et al. 2004). Furthermore, whilst mass mortality events often get reported inthe literature and the media, associated lower level health problems such as gill disorders arerarely reported despite the scale of the problems in some regions (Rodger 2007). Gelatinousagents that have been previously known or implicated in fish kill events and gill disordersinclude hydromedusae, siphonophores, scyphozoans, ctenophores, and hydroids. The incidentsinvolving each group are outlined below.HydromedusaeA bloom of Solmaris corona (small oceanic narcomedusa) was implicated as the causative agentin the mortality of ~900,000 salmon at Scottish aquaculture sites in August/September 1997(Båmstedt et al. 1998); and again in 2002 when there were around 650,000 mortalities in twodays (Rodger et al. 2011a). The neritic leptomedusa Phialella quadrata has also been implicatedin fish kill events and as a vector of bacterial gill disease. In the 1980’s 1,500 salmon died atfarms on the Shetland Isles, Scotland. Histopathological examination revealed severe epithelialstripping and necrosis of the lamellae, amongst other damage, and some of the fish werereported to have up to 40 P. quadrata in their stomach contents (Bruno & Ellis 1985). Recentresearch has also identified P. quadrata as a potential vector for the bacterial pathogenTenacibaculum maritimum. These filamentous bacteria were found on both the manubrium of P.quadrata and on the gills of salmon from a Scottish salmon farm (Ferguson et al. 2010).However, although there was evidence of bacteria on both the jellyfish and the fish gills, based25
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