Mechanical control of Ichthyophthirius multifiliis Fouquet, 1876 (Ciliophora) in a rainbow trout hatchery A.P. Shinn a, * ,1 , S.M. Picon-Camacho a , R. Bawden b , N.G.H. Taylor a,c,1 a The Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK b Pisces Engineering Ltd., Ballochallan, Cambusmore, Callander FK17 8LJ, UK c Cefas, Weymouth Laboratory, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK 1. Introduction The mechanical prevention and control of pathogens is often overlooked, but is long established and has proven to be effective under many different circumstances. Obvious examples include the use of flea/knit combs to reduce the burden of fleas and head lice, mosquito nets to prevent malaria and barrier contraceptives such as condoms to avoid the transmission of many sexually transmitted diseases. Less well known examples also exist to control parasitic infections found in aquaculture. Control of infections by species of Argulus Mu¨ ller, 1785 in carp culture has been achieved through the use of removable substrates upon which the parasite lays its eggs. These substrates are removed and cleaned before the parasite can hatch, thus reducing recruitment to the system (Bauer, 1970; Hoffman, 1977). Control of species of eye fluke, Diplostomum von Nordmann, 1832 and Tylodelphys Diesing, 1850 by mechanical filtration and electrical grids has also been described by Larsen et al. (2005) and Scha¨ perclaus (1992) respectively. Another example is through the dislodgement and removal of mobile stages of sea lice, Lepeophtheirus salmonis (Krøyer, 1837) and Caligus elongatus von Nordmann, 1832, from salmon cages through the use of pump systems (Anon, 1996). Ichthyophthirius multifiliis (Fouquet, 1876) is the greatest cause of disease attributed mortality in the UK trout industry, accounting for an estimated 2–5% loss in annual production (c.360–900 tons), amounting to £2 million in lost revenue (British Trout Associa- tion, personal communication). This ciliate protozoan is highly pathogenic and can cause the disease ‘‘white spot’’ in both wild and cultured freshwater fish (Matthews, 2005). The parasite has a temperature dependant direct life-cycle. An infective theront stage penetrates the epidermis of the fish before turning into the feeding Aquacultural Engineering 41 (2009) 152–157 ARTICLE INFO Article history: Received 9 January 2009 Accepted 1 July 2009 Keywords: Ichthyophthirius multifiliis White spot Mechanical control Protozoan Parasite control Oncorhynchus mykiss ABSTRACT Ichthyophthirius multifiliis, more commonly known as ‘white spot’ is recognised as one of the most pathogenic diseases of wild and cultured freshwater fish. In trout hatchery systems infections can quickly establish and result in high mortality if left unregulated. Current control centres around the use of regular bath treatments with formalin, however, treatments are not always effective and are labour intensive. Environmentally safe, non-chemical alternatives are required. This paper describes the performance of a mechanical system developed to remove cysts from commercial trout raceways. The system consists of two parts: a specially designed suction head connected to a pump that is used to vacuum the bottom of hatchery raceways, and a low-adhesion polymer raceway lining. Following tests on a series of potential linings, the most efficacious product in preventing settlement of cysts was used to line three raceways in a commercial rainbow trout (Oncorhynchus mykiss) hatchery. Over a period of three months, lined raceways were vacuumed on a daily basis. The three control raceways were maintained according to the farms normal husbandry procedures. Approximately thirty fish were sampled from each raceway at fortnightly intervals, and the abundance of the parasite in each raceway determined. The mechanical system led to a significant reduction in the abundance of the parasite in the test raceways, with a mean abundance of 361.88  260.75 parasites per fish in control raceways compared with 1.64  1.59 parasites per fish in the test raceways at the peak of the infection. Additionally fish survival was significantly higher in test raceways over control, with a mean of 84.5% of the stock surviving in the test raceways compared with only 70.6% in the controls by trial end. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +44 1786 467874; fax: +44 1786 472133. E-mail addresses: aps1@stir.ac.uk (A.P. Shinn), sara.picon@stir.ac.uk (S.M. Picon-Camacho), bob@piscesengineering.co.uk (R. Bawden), nick.taylor@cefas.co.uk (N.G.H. Taylor). 1 Joint senior authorship – order settled following a three horse game of Aunt Sally played in The White Hart, Oxford. Contents lists available at ScienceDirect Aquacultural Engineering journal homepage: www.elsevier.com/locate/aqua-online 0144-8609/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaeng.2009.07.002