64, Bull. Eur. Ass. Fish Pathol., 35(2) 2015 ȱĜ¢ȱȱǰȱ ȱȱ¢ȱ¡ȱȱ Gyrodactylus cortiȱȱȱȱ ȬȱǻAnarrhichthys ocellatus) S. R. M. Jones1*, D. A. Thoney2ȱȱǯȱ ǯȱ¢2 1 ęȱȱǰȱȱȱȱǰȱřŗşŖȱ ȱ¢ȱ ǰȱǰȱȱǰȱşȱŜŝȱǲȱ2Vancouver Aquarium, ǯǯȱ¡ȱřŘřŘǰȱǰȱȱǰȱŜȱřŞȱ Abstract Gyrodactylus corti is a parasite which causes disease and elevated mortality in captive populations ȱȱ ȬȱǻAnarrhichthys ocellatusǼǯȱ¡ȱȱǰȱ ȱȱ¢ȱ¡ȱ ȱȱȱĜ¢ȱȱȱȱȱ ȱ¡ǯȱ¡¢ȱȱȱȱȱ ǻŗśŖȱȱŘŖŖȱȦǼȱ ȱȱȱȱȱȱĜȱȱ ȱ ȱ¢ȱȱȱ ȱ¢ȱ ȱȱ ȱȱȱǯȱȱĜ¢ȱȱ ȱȱǻśȱ ȱŞȱȱǼȱ ȱȱȱȱȱǰȱȱĴȱȱȱȱȱȱȱ řŖȱȱȱȱ¢ȱ¡ȱǻŗśŖȱȱŘŖŖȱȦǼǯȱȱĜǰȱȱȱǰȱȱȱ¢ȱȱȱȱǯȱȱȱ¡ȱȱȱ¡ȱ ȱȱ ȱǻŗşȱȬȬȱ¢ǼȱȱŗŜȱ¢ȱ ȱĜȱ ȱȱȱ ȱȱǻřŖȱǼǯȱȱȱȱȱG. corti ȱȱȱ Ȭȱ ȱȱȱȱȱȱ ȱǯȱ Introduction Gyrodactylus (Monogenea: Gyrodactylida) is a ¢ȱȱȱȱȱȱȱ ȱȱȱ¢ȱȱȱȱȱȱ ęȱȱȱȱȱȱȱȱ¢ȱ ¢ȱȱȱęȱȱ ȱȱȱǯȱ The parasites are viviparous hermaphrodites ȱȱȱ¢ȱȱ and can rapidly increase in numbers leading ȱ¢ȱȱǯȱȱȱǯȱǻŘŖŖşǼȱ ȱŞŞȱȱȱȱȱ¢¢ȱ ȱȱȱȱ¢ȱ¢ȱȱ captive host populations (Thoney and Hargis, ȱ£ȱȱȱȱĜ¢ȱ- ŗşşŗǲȱȱȱǯǰȱŘŖŖŞǼǯȱ ȱęȱȱ and the host-parasite system. The therapeutic ȱȱȱȱȱȱȱȱ making them more susceptible to damage ȱȱȱȱȱ ȱȱ ȱěȱȱȱȱȱȱȱ stress response and acute toxicity to structural ȱ¢ȱȱǯȱ ȱǰȱȱ sideration should be given to site conditions ȘȱȱȂȱǱȱǯȓȬǯǯ Bull. Eur. Ass. Fish Pathol., 35(2) 2015, 65 ȱěȱȱȱ ȱȱȱ impacts on respiration, mucus production and ŘŖŗŘȬŗřǯȱȱȱȱȱęȱ ȱ monitored at least twice daily and mortalities ¢ȱȱ¢ȱǯȱȱȱ ȱȱȱȱȱȱǯȱ ȱěȱȱȱȱȱȱ gyrodactylosis in aquaculture are required. ȱęȱ ȱ£ȱȱȱȱ ȱ ȬȱǻAnarrhichthys ocellatus) occurs in ǯȱȱȱȱȱȱȱȱ¡ment is provided in Table 1. Fish were reared ȱĚ ȱǰȱǰȱȱ ȱ ȱ ȱȱȱȱęȱȱȱ ȱȱȱ ȱȱȱǯȱȬ ȱȱ¢ȱȱȱȱȱ ȱȱȱȱȱ¢ȱ ȱ ȱȱȱȱȱȱȱȱ- prior to treatments. Temperature and dissolved uaculture. Gyrodactylus cortiȱ ȱęȱȱ ȱȱȱȱȱȱ Ȭȱȱȱ ¡¢ȱ ȱȱ¢ȱȱȱȱȱ experiments (Table 1). Mean ambient salinity at the Steinhart Aquarium in San Francisco, ȱŘşǯŜƹŖǯŗȱȬȬȱǻǼȱǻȬȱ ȱǻ£ȱȱ ¢ǰȱŗşŜŝǼǯȱȱ ǰȱȱ ȱęǰȱ ǰȱ ¢ǰȱȱȱȱ¢¢- Ǽǯȱȱ ȱǻŖȱǼȱ ȱȱȱ ȱ ȱȱȱȱȱ with the ambient seawater to create the brackish water treatments in Experiment (Exp.) 3. sis associated with elevated mortality were ȱȱȱ Ȭȱȱȱ ȱǻǯǯǼǰȱǯȱȱ Ȭȱȱ ȱȱȱȱ ȱęȱȱ G. corti and shown, using morphological and a commercial black cod diet (Taplow Feeds, ǰȱǯǯǼǯȱȱ ȱ ȱȱŘŚȱȱ molecular data, to be related to G. perlucidus ȱȱȱǻZoarces viviparus) and (Z. v. Infection ȱȱȱȱ Ȭȱ ȱȱȱ ȱȱȱȱȱ¡ǯȱŗȱȱȱ elongates), G. errabundus ȱZ. viviparus, and G. ȱȱȱȱȱȱȱ¡ǯȱŘȱ anarhichatisȱȱȱ ȬęȱǻAnarhichas ȱřǯȱ ȱȱĴȱ¡ǰȱÊȱ Ȭȱ lupusǼȱȱĴȱ ȬęȱǻA. minor) (King et were placed into a mesh cage in the source tank. al., 2014). The present research describes a labo- ȱęȱȱȱ ȱȱȱǰȱ ¢ȱȱȱȱȱ¡ȱȱ A. ocellatus to G. cortiȱȱȱȱĜ¢ȱ ¢ȱ ȱȱȱȱȱȱȱ ȱǻȬȱǼǰȱȱȱ ȱ¢ǰȱ ȱȱ¢ȱ to the biosecure aquarium at DFO-CAER and ¡ȱȱȱǯȱ randomly distributed into experimental tanks. Materials and methods Parasite counts were made at three times: prior ȱ¡ȱȱęȱȱȱȱ Fish ȱÊȱ Ȭȱ ȱȱȱȱ ǻƽŗŘǼǰȱ ȱ¡ȱȱȱȱ- Vancouver Aquarium and treatment trials were ȱǻƽŗŖǼȱȱȱȱęȱȱȱ conducted at the Fisheries and Oceans Canada, ȱ ȱ ȱ ¡ǯȱ ȱ ¡ǯȱ ŗȱ ȱȱȱȱȱȱ ǻȬǼȱȱȱȱȱęȱ ȱŘǰȱȱęȱȱȱȱȱǻƽşȱ per treatment) were randomly sampled and in Exp. 3, two survivors per tank were sampled ȱȱ ȱ Ĵȱ ȱ 66, Bull. Eur. Ass. Fish Pathol., 35(2) 2015 Table 1.ȱ¡ȱǰȱ ȱ ȱȱȱȱȱȱȱǯȱȱ groups included a seawater control. Experi- Duration Temperament (days) ture1 (°C) Dissolved Oxygen1 (mg L-1) Initial ęsh mass1 (g) Formalin Salinity2 H2O2 (exposure time) 1 12 ŞǯśƹŖǯŖŘ 7.3±0.03 33.3±2.5 150 ppm (60 min) 150 ppm (30 min) 0 ppt (5 min) 2 26 ŞǯśƹŖǯŖŗ 9.1±0.07 60.1±10.1 200 ppm (60 min) 200 ppm (30 min) 0 ppt ǻŞȱǼ 3 16 ŞǯśƹŖǯŖŚ3 10.2±0.11 42.3±5.9 --- --- 30–15ppt4 1 Mean ± standard error; 2ŖȱȱȱŗŖŖƖȱęȱ ȱ ǲ 3ȱȱȱȱ ȱ ȱŝǯŘǚǲȱ ȱȱŘȱȱȱȱȱȱ¢ 4 ǻƽŞȱȱǼǯȱ ȱȱȱ were mounted on glass slides, stained with ȱȱǻŘŖŖȱȦǼǰȱȱ survivor was weighed then individually placed haematoxylin and eosin, cover-slipped and examined using a compound microscope (Zeiss ȱȱȱȱřŖȱȱȱ£ȱ Axio Imager) equipped with a digital imaging system (Axiocam MRc5). ǻřŖȱȦǼȱȱȱȱȱȱȱ ȱȱȱǯȱȱȱȱ the solution containing the detached parasites were placed into an improved Neubauer hae- Experimental design The study design and conditions in the three ¢ȱǻ ȱęǰȱ ǰȱǼȱ experiments are summarised in Table 1. A ran- ȱ¢ȱ¡ǯȱȱȱȱ £ȱȱȱ ȱȱȱ¡ǯȱŗȱȱ parasites recorded in the ruled area was then used to estimate mean intensity (MI, parasites ȱȱęǼȱȱȱȱ¢ȱ ǻ ǰȱȱȱȱȱęǼǯȱȱȱ Řȱȱ ȱŗŖȱęȱ ȱȱȱȱȱŗŘȱ ǰȱȱȱ ȱ ȱȱȱȱȱ ȱȱ ȱȱȱȱęȱȱ ȱȱȱǻ ȱǰȱlin, H2O2ȱȱ Ǽǯȱȱȱ ȱŗŘŖȱ ȱǰȱęȱȱȱ ȱȱ died during an experiment. ¡¢ȱ ǯȱ ȱęȱ ȱȱ by aerated bath immersion and were monitored Histology ¢ȱȱȱęȱ ȱ£ǰȱ ¢ȱȱȱȱȱȱ¡ǰȱȱ indicated in Table 1. Formalin was obtained ȱȱȱȱȱ ȱ¡ȱȱę¡ȱȱ ȱȱřŝƖȱ¢ȱȱǻǼȱ ŗŖƖȱȱěȱȱȱȱ- and hydrogen peroxide was antiseptic grade ȱȱŘŚȱȱŚŞȱǯȱ¡ȱȱ ȱȱ (3%, Exact, Superstore). The chemicals were to 70% ethanol and dehydrated in an alcohol gradient, cleared in xylene, embedded with diluted in seawater to the desired concentration. ȱęȱ ȱȱȱȱȱ ȱ¢ȱȱȱǰȱȱȱęȱ¢ȱ- Ĝȱȱȱȱřȱȱśȱΐǯȱȱ Bull. Eur. Ass. Fish Pathol., 35(2) 2015, 67 Figure 1.ȱȬȱǻAnarrhichthys ocellatusǼȱȱ ȱȱ ȱGyrodactylus corti Arrows illustrate ȱĴȱȱ¢ȱǯȱ ¡¢ȱȱǯȱ ȱȱȱȱ¡ǯȱ ȱ¡ǯȱřǰȱȱ ȱȱŗśȱȱęȱ ȱȱȱȱ ȱ¡¢ȱěȱ ȱȱ ȱ ȱěȱȱȱȱ¡ǯȱŗȱȱŘǯȱ ȱȱǯȱȱ£ȱȱȱ ȱ ȱȱȱȱȱȱȱ ȱ¡ǯȱřǰȱȱȱ ȱȱ ȱ ȱ ȱŘȱȱǰȱȱ ȱȱěȱ representing both seawater and brackish water in temperatures, salinity, and dissolved oxygen treatment groups. Brackish water was obtained were determined using the Mann-Whitney rank ¢ȱȱȱĚ ȱȱ ȱȱȱ ¢ȱȱȱȱ¢ȱȱ¡¢ȱ sum tests. Percent cumulative mortality data in all experiments were analyzed by 2-way 19 ppt (see Figure 3). The experiments were ¢ȱȱȱǻǼȱȱȱ terminated when mortalities in at least one data (arcsin square root), to examine possible ȱȱŞŖƖǰȱȱȱȱȱ ȱ ȱȱȦȱ- in Table 1. ȱǻȱěǼǯȱ¢ȱȱ ȱȱ ȱȱȱ¡ȱěȱ ȱ ȱěȱȱ ȱȱ ȱ ȱ ȱȱǯȱȱ ȱȱęȱ treatments groups in Exps. 1 and 2 were determined using the Kruskal-Wallis one way anal¢ȱȱȱȱǰȱ ȱ¢ȱȂȱ ȱȱ ȱǯȱȱȱȱ Ȧȱěȱȱȱ¢ȱȱǻǁŖǯŖśǼǯȱ tests also were used to examine temperature and ȱȱ¢ȱ ȱȱȱ SIGMASTAT (SPSS, Chicago, Illinois) and sigęȱȱȱȱȱȱ ȱǀŖǯŖśǯ ŜŞǰȱǯȱǯȱǯȱȱǯǰȱřśǻŘǼȱŘŖŗś Results ȱ ¡ǯȱ ŗǰȱ ȱ ȱ ȱ ęȱ ě- among treatments or tank replicates in either ȱȱȱǻǁŖǯŖśǼǯȱȱȱŗŗȱ¢ȱ ences among treatments or tank replicates in exposure in the source tank, parasites were either temperature or dissolved oxygen (DO) ǻǰȱǁŖǯŖśǼǯȱȱȱȱ ȱ ȱȱȱȱęȱǻȱŘǼǯȱ- approximately 21 days old and Gyrodactylus cortiȱ ȱȱȱȱȱęȱǻȱ ŘǼǯȱ ȱ ȱȱ ȱȱȱ ȱŖƖȱȱȬȱȱŗŖǯŖȱƹȱśǯŞƖȱȱ ȬǰȱśŖǯŖȱƹȱŗśǯřƖȱȱ 2O2-treated ¢ȱȱ ȱȱȱȱȱ ȱȱȱ¡ǰȱȱ ȱȱ ȱ¢ȱȱǻǯȱŗǼǯȱȱȱȱ ęȱȱȱȱ ȱ ȱȱ ȱŘȱȱşȱȱęȱȱ ȱǰȱ ȱŞȱȱşȱȱ ȱ ǰȱȱȱȱşȱ to severe edematous swelling and truncation ȱǰȱȱ ȱ ȱǯȱ seawater controls and all 9 treated with H2O2. ȱǰȱ ȱ ȱȱę- mulative percent mortality over 26 d ranged ȱŝŖǯŖȱƹȱŗŖǯŖƖȱȱȱ ȱǯȱȱȱ ¢ȱěȱ ȱȬȱȱ ȱȱ¢ȱȱŗŘȱȱ ȱȱ ȱę¢ȱ ȱǻǀŖǯŖśǼȱ ȱȱȱȱęȱǻŗŜǯŝȱƹȱŜǯŝȱƖǼȱ ȱ ȱȱȱȱřȱǯȱȱ ȱ ȱęȱȱȱ¢ȱǻŚŖǯŖȱƹȱśǯŞƖǼȱ ȱȱȱǰȱȱ ȱę¢ȱ Ȭȱȱȱȱ ȱę¢ȱ lower than in the controls (Table 2). The MI in the H2O2Ȭȱȱ ȱȱę¢ȱ ěȱȱȱȱȱȱȱ the seawater controls. Similar trends among IDs were observed. lower (p<0.05) than the H2O2 and control groups, ȱ ȱȱȱȱȱǻŞŖǯŖȱƹȱśǯŞƖȱ ȱŞřǯřȱƹȱřǯřƖǰȱ¢Ǽǯȱȱȱȱȱ ȱ¡ǯȱřǰȱȱ ȱęȱěȱ between the brackish water and seawater con- the experiment, parasites were present on all ȱęȱȱ ȱȱ¡ȱȱ trols in temperature, DO, and salinity (p<0.05). ȱȱ ȱǰȱȱ ȱřȱȱşȱ ¢ȱȱȱȱȱȱŘşǯŝȱƹȱŖǯŗȱȱ ȱǯȱ ȱȱȬȱȱ ȱŗŞǯŞȱƹȱŖǯŜȱȱǻȱŘǼǯȱȱ ȱȱ ȱę¢ȱ ȱȱ ȱȱ in the seawater controls and H2O2Ȭȱęȱ ȱ ȱȱȱǻŝǯŗśȱƹȱŖǯŗȱǚǼȱ ȱȱȱȱǻŗŖǯŝȱƹȱŖǯŗȱȦǼȱȱȱ ǻȱŘǼǯȱ ȱȱȱ Ȭȱ ȱȱǻŞǯśȱƹȱŖǯŖŚȱǚǰȱȱŗŖǯŘȱƹȱŖǯŗȱȦǰȱ ęȱȱ O2Ȭȱęȱ ȱę¢ȱ respectively). Cumulative percent mortality ěȱȱǯȱȱ ȱȱ - ȱȱŗŜȱȱ¡ȱ ȱę¢ȱ Ȭȱęȱ ȱę¢ȱ ȱȱ ȱ¡ȱǯȱ ȱ ȱȱȱ higher (p=0.003) in seawater controls compared ȱęȱȱȱ ȱǻŝŗǯŝȱƹȱŞǯŞȱƖȱȱŘřǯřȱƹȱ Ĵȱȱǰȱ ȱȱ¡ȱȱ śǯŞȱƖǰȱ¢ǼȱǻȱŘǼǯȱȱȱȱȱȱ ȱ Ȭȱęǰȱ ȱ ȱȱ ȱȱę¢ȱ ȱȱȱȱ¡ȱ ȱęȱǻȱŘǼǯȱ ¡ǰȱȱ ȱȱȱȱŞȱęȱ 2 ȱ¡ǯȱŘǰȱȱ ȱȱęȱěȱ ȱȱȱ ȱ ȱȱ- examined in both groups. The MI and DI were ę¢ȱȱȱȱȱȱ ȱȱȱ ȱ¡ȱęȱǻȱŘǼǯȱ Bull. Eur. Ass. Fish Pathol., 35(2) 2015, 69 Table 2. Gyrodactylus cortiȱ ȱ Ȭȱ ǻAnarrhichthys ocellatus) (mean ± standard error). Number ȱȦȱȱ¡ȱǻ ȦǼǯȱ ¢ȱǻȱȱȱęǰȱǼȱȱȱ¢ȱǻȱȱ ȱȱęǼȱȱȱ ȱȱȱȱȱȱȱ¡ǯȱĴȱȱȱ ¢ȱęȱěȱǻǀŖǯŖśǲȱȂȱȱȱǼǯ Treatments I/E Mean Intensity Mean Infection Density Pre-treatment ŗŖȦŗŖ 13.0 x 104 ± 1.47 x 104 4.25 x 103ȱƹȱŖǯŝŞȱ¡ȱŗŖ3 Formalin řȦş 1.67 x 104 ± 0 a 0.57 x 103 ± 0.16 x 103 a Freshwater şȦş 5.00 x 104 ± 0.92 x 104 ab 1.15 x 103 ± 0.25 x 103 a Hydrogen Peroxide ŜȦŜ 23.1 x 104 ± 6.35 x 104 c 6.32 x 103 ± 1.39 x 103 b Seawater Control śȦś 17.7 x 104 ± 5.10 x 104 b 3.24 x 103 ± 0.62 x 103 bc Pre-treatment ŗŖȦŗŖ 4.70 x 104 ± 0.70 x 104 0.97 x 103 ± 0.20 x 103 Formalin ŘȦş 1.67 x 104 ± 0 a 0.16 x 103 ± 0.03 x 103 a Freshwater ŞȦş 6.04 x 104 ± 2.76 x 104 a ŖǯŞşȱ¡ȱŗŖ3 ± 0.45 x 103 a Hydrogen Peroxide şȦş 5.90 x 104 ± 1.50 x 104 a 1.11 x 103 ± 0.26 x 103 ab Seawater Control şȦş 30.4 x 104 ± 6.00 x 104 b 4.51 x 103ȱƹȱŖǯşŞȱ¡ȱŗŖ3 b Pre-treatment ŗŖȦŗŖ 14.3 x 104 ± 2.44 x 104 3.70 x 103 ± 0.65 x 103 Brackish water ŞȦŞ śǯŞřȱ¡ȱŗŖ4 ± 0.55 x 104 a 0.97 x 103 ± 0.10 x 103 a Seawater control ŞȦŞ 17.5 x 104 ± 2.64 x 104 b 2.74 x 103 ± 0.55 x 103 b Experiment 1 Experiment 2 Experiment 3 Figure 2.ȱȱ ȱ ȱ¢ȱȱȱȱ¢ȱȱ Ȭȱȱ with Gyrodactylus corti (Experiment 3). The seawater treatment group were maintained at constant salinity (salinity shown by dashed line) and the brackish water treatment group at declining salinity (solid line). Cumulative percent mortalities are illustrated by U and S, respectively. 70, Bull. Eur. Ass. Fish Pathol., 35(2) 2015 Table 3.ȱ ȱ ȱ ¢ȱ ǽȱ ƽȱ ŗȬǻȱ ȱ ¢ȱ Ȧȱ ȱ ȱ density) x 100%] by treatment in each experiment Treatment Experiment ŗǼǰȱȱȱȱ¢ȱȱȱȱ¢ȱȱ ȱ¢ȱ¡ȱȱȱ ȱȱǯȱ ȱǰȱȱȱęȱȱ ȱ¡ǯȱŘȱȱȱȱȱ¢ȱȱ 1 2 3 ȱȱȱȱȱȱ¡ǰȱ Formalin ŞŘǯř 96.5 --- Freshwater 64.5 ŞŖǯŘ 64.5 despite the higher mean intensity. Thus, the reduced mortality among treatment groups --- 75.4 --- ȱ¢ȱȱȱȱȱȱȱȱ H 2O 2 ȱȱȱȱ¢ȱ¡ȱȱȱ ȱȱȱ¡ǯȱŘǰȱȱ ȱȱȱ ȱȱȱ- ȱęȱȱěȱȱȱȱ ę¢ǰȱȱȱȱĜ¢ȱǻǼȱ ȱ ȱȱȱȱȱ¡ǰȱ- ȱ¢ȱȱǯȱȱȱ ȱ ȱęȱ£ȱȱȱ- ȱ¢ȱ ȱǻȱřǼǯȱ ¢ȱ ȱȱȱȱ ȱȱȱ ȱȱ ȱGyrodactylus salaris (Bakke Discussion and MacKenzie, 1993). ȱ ȱȱęȱ ȱȱȱȱȱȱGyrodactylus ȱȱ ȱǰȱ ȱȱ cortiȱȱȱÊȱ Ȭǯȱȱ- hydrogen peroxide (H2O2) administered three tions were associated with mortality among ȱȱęȱ¢ȱȱȱ¢ȱȱ ȱÊȱȱ ȱȱȱ ȱ ȱ ȱG. corti and associated mortality ȱ ȱŗȱȱŝȱ¢ȱ ȱȱ ȱȱȱ¡ȱȱȱȱ ȱȱ ȱȱĜ¢ȱ ȱ- ȱ Ȭǯȱȱȱȱǰȱȱ ȱ ȱĜǱȱȱȱȱĜ¢ȱ sessed. Reduced respiratory capacity resulting (Table 3) and this treatment consistently elimi- ȱȱȱȱȱȱȱȱ nated detectable parasites. Formalin treatments pathology likely contributed to the mortality. ȱȱ ȱȱȱȱ ȱ ȱȱ¢ȱȱǰȱȱ challenges provided limited control over the Gyrodactylus spp. in laboratory or aquarium ȱȱȱȱȬȱ ȱȱȱ¡ȱȱȱÊȱ Ȭ ęǰȱȱȱ ȱȱȱȱ ȱǻ- eels resulting in variations in challenge levels chmann and Kristensson, 2003; Williams et among the experiments. These variations were ǯǰȱŘŖŖŞǼǯȱ ȱǰȱȱĜ¢ȱȱȱ ȱ¢ȱěȱȱȱȱȱȱ ȱȱȱȱȱȱȱȱ ȱ ȱȱȱȱȱȱȱȱ ȱȱǻ§Ȭ ȱȱ ȱȱęǯȱȱ ȱȱȱ Valtonen, 1996; Buchmann and Kristensson, ȱȱ¡ǯȱŘȱ¢ȱ¡ȱȱȱ 2003; Rowland et al., 2006; Jørgensen et al., 2009). ȱȱȱȱȱȱ ȱ pre-treatment mean intensity, the lower control ¢ǰȱȱŝȬ¢ȱ¢ȱȱȱȱȱ ȱȱȱǻŗşşŘǼȱȱȱĜ¢ȱ ȱȱȱȱȱHaliotrema spp., on golden snapper (Lutjanus johni) mortality (compared with a 2-day delay in Exp. ȱȱǯȱȱ¢ȱ ȱĜ¢ȱ ǻǼȱȱ¡ȱŗȱȱŘȱ¡ȱŞŘƖȱ Bull. Eur. Ass. Fish Pathol., 35(2) 2015, 71 ȱȱȱȱȱȱ ¢ȱȱȱȱȱȱěȱ- tanks (Rach et al., 2000; Bowker et al., 2012). In another study, Gyrodactylus sp. remained ȱȱ¢ȱȱȱȱȱ ȱ ȱȱ¢ȱȱȱȱǯȱ present on green swordtails (ȱ) ȱ O2ȱ¡ȱȱ ȱȱ 2 ǻȱȱǯǰȱŘŖŖŝǼǯȱȱȱȱȱȱ O2 2 ¢ȱȱ ȱȱȱȱȱ ¡ȱȱȱ¢ȱ ȱȱ- being used to treat Gyrodactylus sp. in seawater, ȱȱĜ¢ȱȱȱȱȱ ȱĜ¢ȱ ȱȱȱȱŜśƖȱȱ ȱȱȬȱȱȱȱȱ ŞŖƖȱȱȱ¡ǰȱȱȱęȱ (sea lice, Lepeophtheirus salmonis or Caligus rog- ȱȱ ȱǯȱ ȱȱ ercresseyi) has been documented (Treasurer and experiments, the total cumulative mortality in Grant, 1997; Bravo et al., 2010). Future advances ȱ Ȭȱȱ ȱ ȱ ȱȱȱȱ 2O2, and mortality only ¢ȱęȱȱȱ¡ȱȱlar sodium percarbonate, which dissociates stabilised during exposure to brackish water into hydrogen peroxide in water, as a possible ȱ¢ȱȱȱ ȱ¡¢ȱ treatment against marine gyrodactylids (see Řśȱǯȱȱȱ ȱȱȱȱĜ¢ȱ Buchmann and Kristensson, 2003). ȱ ȱȱȱȱȱȱȱęȱȱ ȱ ȱȱȱȱȱȱȱȱȱȱ ¢¢ȱȱǻȱȱǯǰȱŘŖŖşǼȱ ¢ȱȱȱ¢ȱȱȱȱȱ ȱ ȱęǯȱ ǰȱ¢¢loses are problematic in marine aquaria and The present study emphasised the challenges ȱȱ¢¢ȱȱȱȱ ȱȱǯȱȱȱ ȱȱȱĜȱȱȱ ǰȱȱȱęȱȱ ȱȱ in this research, continued research into the ¢ȱȱȱȱȱȱȱȱ not advised given its toxicological, allergenic ȱěȱȱȱGyrodactylus pis- and carcinogenic properties (Schelkle et al., culentusȱȱȱęȱǻSyngnathus 2009). Alternatively, research into hypo-osmotic fuscusǼȱǻȱȱǯǰȱŘŖŖŞǼǯȱ ȱȱ¢ǰȱ ȱȱȱȱȱȱ ȱ¢ȱȱHaliotrema sp. was reduced on ȱȱ ȱȱřŖȬȱ ȱ promising, possibly in combination with oxi- bath (Seng and Seng, 1992). Those studies also ȱȱ ȱ ȱ¢ȱȱ Ĝȱȱǯȱ ȱȱȱ¢ǰȱȱĜ¢ȱȱ O2 was 2 dizing agents such as sodium percarbonate. 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