Short communication Determination of the surface area of a fish B O'Shea 1,2 , A J Mordue-Luntz 1 , R J Fryer 2 , C C Pert 2 and I R Bricknell 2 1 Department of Zoology, School of Biological Sciences, University of Aberdeen, Aberdeen, UK 2 Fisheries Research Services Marine Laboratory, Aberdeen, UK Keywords: calculation, Lepeophtheirus salmonis, model, non-salmonids, salmonids, surface area. Surface area availability could influence the number of parasites a host can support (Tucker, Sommer- ville & Wootten 2002). Parasitic infections would be expected to show an increase in infection intensity with an increase in host size due to the larger surface area available for settlement (Dogiel, Petrushevski & Yu 1958). For example, Hanek & Fernando (1978) reported an increase in parasitic Monogenea and Copepoda with host, Lepomis gibbosus (L.), age (and size inferred). Higher absolute numbers of the salmon louse, Lepeophtheirus salmonis (Krøyer), were also found on larger salmon by Tucker et al. (2002). Jaworski & Holm (1992) devised a surface area model to calculate motile L. salmonis density in eight defined regions in fish of varying sizes. Defined regions combined body-surface area with fin-surface area. They concluded that larger salmon had higher L. salmonis intensities due to the larger skin surface availability. Tucker et al. (2002) refined this work to allow the fin-surface area to be assessed independently of the body as L. salmonis is known to preferentially settle on the fins of fish (Bron, Sommerville, Jones & Rae 1991; Grimnes & Jakobsen 1996; Tucker, Sommerville & Wootten 2000). However, Tucker et al. (2002) noted that their study of fish surface area was limited by the image analysis used in calculating the surface area of a two-dimensional object. Consequently, a new method was devised in this study for measuring the surface area of a fish, taking its three-dimensional shape into account. It would give a more accurate measurement of surface area than earlier methods across a wider range of fish sizes. Mathematical equations for a range of fish species could subsequently be derived allowing the surface area of a fish of a known weight to be estimated. Similarly, a preliminary 3D-model has also been recently reported by Hamre (in Glover, Skaala, Nilsen, Olsen, Teale & Taggart 2003; Glover, Hamre, Skaala & Nilsen 2004) and was developed using stereology methods. A wrap method adapted from Bell, Davidson & Scarborough (1961) and Jaworski & Holm (1992) was used to determine the surface area of a fish. Healthy fish across a range of sizes and species with intact fins (Table 1) were processed to determine the surface area of the fins and body. Atlantic salmon, Salmo salar L., rainbow trout, Oncorhyn- chus mykiss (Walbaum), and sea trout, Salmo trutta L., were hatchery-reared stock from the FRS Marine Research Unit, Aultbea, on the West coast of Scotland. Cod, Gadus morhua L., and Atlantic halibut, Hippoglossus hippoglossus (L.), originated from the Seafish Aquaculture Research Unit (now Viking Seafarms Limited), Ardtoe, Scotland and were maintained at Aultbea prior to use. Saithe, Pollachius virens (L.), were rod caught from Loch Ewe, Aultbea and also maintained on site prior to use. For each fish, weight and fork length (salmonids) or total length to the caudal peduncle (non- salmonids) were noted. All fins were dissected, laid Journal of Fish Diseases 2006, 29, 437–440 Correspondence Prof A J Mordue-Luntz, Department of Zoology, School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK (e-mail: a.j.mordue@abdn.ac.uk) 437 Ó 2006 Crown Copyright