North American Journal of Fisheries Management 29:823–828, 2009 [Article] American Fisheries Society 2009 DOI: 10.1577/M08-207.1

Use of Ice-Water and Salt Treatments to Eliminate an Exotic Snail, the Red-Rim Melania, from Small Immersible Fisheries Equipment

ANDREW J. MITCHELL* U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Post Office Box 1050, Stuttgart, Arkansas 72160, USA

THOMAS M. BRANDT U.S. Fish and Wildlife Service, National Fish Hatchery and Technology Center, 500 East McCarty Lane, San Marcos, Texas 78666, USA

Abstract.—Ice-water and salt treatments were evaluated for disinfection of small immersible fisheries equipment contaminated with a nonindigenous tropical snail, the red-rim melania Melanoides tuberculatus. This introduced species can displace native snails and transmit trematodes directly to fish and indirectly to other animals, including humans. The red-rim melania has a well-developed operculum that protects it from desiccation and allows it to remain viable for days on dry fisheries equipment. Treatments were produced by adding 10 kg of salt and 33.3 kg of ice to 66.6 L of water (salt–ice-water [SIW]) or by adding 40 kg of ice to 32 L of water (ice-water only [IW]) and were tested for various periods (0.17 min to 24 h) to find exposures that would kill 100% of the treated snails. Temperatures produced in the test containers ranged from6.38Cto 2.48C for SIW and from 08C to 4.98C for IW. The survival of snails in saltwater-only (SW) treatments (10 kg of NaCl in 100 L of water) was also tested. Three size-groups of snails were tested: 2–4-, 15–20-, and 30–40- mm shell heights. Exposure periods that resulted in an estimated 0% survival for the 15–20-mm snails were 35.8 min for SIW, 179.6 min for IW, and 423.6 min for SW. The calculated amounts of time (regression analysis) required to kill 100% of the three size-groups of snails exposed to the SIW treatment were 17.8 min for 30–40-mm snails, 35.8 min for 15–20-mm snails, and 67.5 min for 2–4-mm snails.

The aquatic, tropical red-rim melania Melanoides displace native snails and transmit trematode parasites tuberculatus is an exotic snail that is spreading directly or indirectly to fish, birds, and humans (Abbott worldwide and has been found in 16 states in the 1952; Martin 1958; Premvati and Pande 1974; Dundee USA (Abbott 1952; Murray 1971; Amaya-Huerta and and Paine 1977; Nollen and Murray 1978). One of Almeyda-Artigas 1994; Mitchell et al. 2007). The snail these trematodes, the fish gill trematode Centrocestus can survive in waters having a temperature range of formosanus, has caused massive mortalities in cultured about 178Cto328C (Mitchell and Brandt 2005). The tropical fish, resulting in several ornamental fish red-rim melania has an operculum that can cover the growers losing their businesses (Blazer and Gratzek mantle, sealing off the snail and giving it the ability to 1985; Vogelbein and Overstreet 1988; Mitchell et al. withstand several chemical disinfectants and long 2005). In Texas, C. formosanus also infects wild fish periods of desiccation (Dudgeon 1982; Francis-Floyd populations and may have caused some mortality of the 1991). Snails greater than 10 mm in shell height can federally listed fountain darter Etheostoma fonticola in survive up to 8 d of desiccation (Dudgeon 1982) and in its critical habitat (Mitchell et al. 2000). Experimen- unpublished studies by the authors, 2–5-mm snails tally, this trematode can infect several of the major U.S. survived for more than 24 h. The red-rim melania also cultured warmwater fish species, including the channel reproduces parthenogenically, broods its young inter- catfish Ictalurus punctatus, sunshine bass (female nally, readily adapts to different environments, and has white bass Morone chrysops 3 male striped bass M. a hard shell that limits natural predation (Jacobson saxatilis), golden shiner Notemigonus crysoleucas, and 1975; Stein et al. 1984; Dudgeon 1986; Perera et al. fathead minnow Pimephales promelas (Mitchell et al. 1990). 2002). The red-rim melania is important because it can Dip nets and other small fisheries equipment are suspected as one means by which red-rim melania have * Corresponding author: [email protected] been spread to several springs in Texas (Mitchell et al. Received September 22, 2008; accepted December 15, 2008 2007). Aquatic biologists on field collecting trips often Published online May 28, 2009 travel from one site to another in a few hours without

823 824 MITCHELL AND BRANDT disinfecting equipment between sites. It is important immersed, and the mixture remained between 08C and that a quick disinfection treatment be developed that 2.58C in all trials during exposure periods of up to 360 can be used while en-route. Previous studies have min. Temperature in IW trials reached a high of 4.98C examined chemical and hot-water dip treatments for in the 720- and 1,440-min exposures. Another treatment disinfection of nets and other small equipment consisting of a salt–ice-water mixture (SIW) was (Mitchell and Brandt 2005; Mitchell et al. 2007). produced by mixing water (66.7 L), ice (33.3 kg), and These studies indicate that snails survive 1-h baths in NaCl (10 kg). This mixture produced colder tempera- full-strength household bleach, 70% ethanol, 10% tures of 6.38Cto2.48C. The combination rate for the formalin, 10% salt, and a pH of 1–13. All red-rim SIW came from earlier tests of various ice, water, and melania (2–40-mm shell height) placed in a bath of salt combinations; the target was a mixture that would Roccal-D-Plus (alkyl dimethyl benzyl ammonium consistently produce temperatures less than 08C for up chloride and didecyl dimethyl ammonium chloride at to 12 h. Corresponding controls (well water at 20.8– 600 mg/L of water) for 16 h or in 508C water for 2.5 23.18C for IW and 18.0–22.08C for SIW) were run for min were killed. Although these last two treatments each replicate in each test. All IW and SIW treatments were effective, both have limitations. The 16-h Roccal were thoroughly mixed for 1 min via a large paint stirrer dip will probably be too long for some collecting trips driven by a cordless drill before snails were added. and poses a chemical disposal problem; a hot water Mixing of ice and water was necessary to obtain a source is often unavailable. uniform temperature throughout the container. Tem- All red-rim melania (15–20 mm) held in 58C water peratures were recorded during the course of the trials in incubators for 24 h died (Mitchell and Brandt 2005); using HOBO Water Temp Pro v2 temperature loggers therefore, we presume a colder dip treatment using ice (Onset Computer Corporation, Bourne, Massachusetts). (readily available at fueling stations and convenience Two size-groups of red-rim melania (2–4 and 15–20 stores along most highways) would kill the snails in mm) were exposed to IW treatments (exposure periods less than 24 h. Additionally, adding salt further cools of 15, 30, 60, 120, 180, 360, 720 or 1,440 min), and the water–ice mixture and may reduce treatment time three size-groups (2–4, 15–20, and 30–40 mm) were (http://www.waynesthisandthat.com/saltice.html). The exposed to SIW treatments (0.17, 0.95, 1.9, 3.8, 7.5, objective of this study was to find an ice-water or 15, 22, 30, 45, 60, or 120 min). Treatments at all ice-water and salt treatment that would kill 100% of the exposure periods were performed using three or more snails tested within a few hours. replicates with 10 snails/replicate. Exposure periods that killed all snails were repeated with at least three Methods additional replicates to confirm findings. The 10 snails Red-rim melania (shell heights, 15–20 and 30–40 were placed in an aquarium net (10.0 3 12.5 cm) and mm) used in this study were collected from the Comal secured with an overlaid piece of nylon window screen River in Comal County, Texas from July 2006 to May or with an identical net fastened on each side with 6.4- 2008. Snails were shipped to and held at the Harry K. mm binder clips. A string was tied to the net handles Dupree Stuttgart National Aquaculture Research Cen- for ease of retrieval after they were pushed to the ter, Stuttgart, Arkansas (Mitchell and Brandt 2005). bottom of the trash cans for a given exposure period. Testing was also done on juvenile snails (2–4 mm) Lids were put on the trash containers to help maintain recently released (,8 d old) from the brood pouches of the desired temperature. After the exposure period was several 15–40-mm snails. The center’s well water used completed, nets were removed and snails were then in this study had a total alkalinity ranging from 188 to placed into 400 mL of 238C well water in 0.6-L plastic 257 mg/L, total hardness of 86–137 mg/L, and a pH of beakers; the 30–40-mm snails were put into 2,000 mL 7.2–8.0 based on data taken from this and other studies of water in 4-L or 5-L buckets. The beakers were then using the same well water and measured with standard transferred into a 20.0–21.08C incubator for 3 d, after titration methods and a pH/Oxi 340i/SET meter which the viability of all snails was determined. Snails (Wissenschaftlich-Technische Werksta¨tten, Weilheim, with intact mantles that displayed any movement were Germany). considered live. Methods are further described by An ice-water-only (IW) treatment was produced by Mitchell and Brandt (2005). mixing well water (32 L, temperature of about 238C) For the 2–4-mm snails, trials were performed as and ice (40 kg kept 15 h in a freezer at 178Cto above except that these smaller snails were tested in 228C) in a 120-L plastic trash container wrapped with smaller, fine-mesh nets. Snails were placed in the radiant barrier reflective insulation (foil-covered bubble bottom of the nets, and the nets were twisted above the wrap) to help maintain low temperatures. The mixture snails; each net was then clipped at the twist with 6.4- had just enough water to allow nets to be completely mm binder clips to retain the snails during treatments. RED-RIM MELANIA ELIMINATION FROM EQUIPMENT 825

Excel 2003 (Microsoft Corporation, Redmond, Wash- ington) to determine whether a relationship existed between exposure duration and survival of snails. Polynomial regression equations for the various treatments and snail sizes were used to estimate minimum exposure periods needed to kill all snails.

Results There was a near doubling in the amount of time needed to kill all red-rim melania held in SIW as size of snails decreased. The SIW (6.48Cto2.48C) exposure times that resulted in 0% survival, as FIGURE 1.—Percent survival of red-rim melania of three calculated from the regression equations, were 17.8 shell-height size-groups exposed to a salt–ice-water treatment min for the 30–40-mm snails, 35.8 min for the 15–20- (2–4-mm snails: y ¼ 0.0206x2 3.3783x þ 134.19, r2 ¼ 0.91; 15–20-mm snails: y ¼ 0.0494x2 4.2284x þ 88.07, r2 ¼ 0.79; mm snails, and 67.5 min for the 2–4-mm snails (Figure 30–40-mm snails: y ¼ 0.1964x2 9.1643x þ 101, r2 ¼ 0.89). 1). Actual snail survival (1.7%; 1 of 60 snails in each size-group) was observed at 22 min for the 30–40-mm snails, 30 min for the 15–20-mm snails, and 60 min for Testing also was performed to determine the effect the 2–4-mm snails (Table 1). No snails survived of a saltwater-only (SW) treatment on the survival of exposure periods equaling or exceeding 30 min (for snails in two trials. In the first trial consisting of three 30–40-mm snails), 45 min (for 15–20-mm snails), and replicates of 10 red-rim melania (15–20 mm), snails 90 min (for 2–4-mm snails). The same increased were placed in nets as described above and were sensitivity to low temperatures as size increased was exposed for 30, 60, 120, 240, 480, or 720 min to 10 kg obtained when 15–20- and 2–4-mm snails were of NaCl previously mixed as described above with 100 exposed to IW. An exposure time of 180 min killed L of well water (equivalent to 66.7 L of water and 33.3 all 15–20-mm snails subjected to the IW treatment, kg of ice from the SIW treatments) at 16.38C to 20.78C. whereas an average of 73.3% of the 2–4-mm snails The second trial mirrored the first, except that because survived the same exposure (Table 2); more than a of a shortage of snails, only two replicates were 720-exposure min was needed to kill all 2–4-mm snails conducted at 30-min exposures. In both trials, held in IW. corresponding groups of control snails were treated Using IW to obtain a complete kill of 15–20-mm concurrently as above, except without NaCl; the snails required less than half as much time as using temperatures ranged the same as for the treated groups. SW, and using SIW required less than one-fifth of the Survival was assessed as described above. amount of time required when using IW. The Regression analyses were run in Microsoft Office calculated exposure times to obtain 0% survival for

TABLE 1.—Survival of three size-groups (2–4, 15–20, and 30–40-mm shell height) of red-rim melania exposed to salt–ice- water treatments for various periods. Each number represents the number surviving in each of six replicates (10 snails/replicate; the overall percent survival for all six replicats in that group is also presented). Water temperatures in treatments ranged from 6.38Cto2.48C. Temperatures in the control exposures ranged from 18.08C to 22.08C; survival in control snails was 98.8%.

Number surviving by replicate and overall percent Exposure time (min) 2–4 mm 15–20 mm 30–40 mm

0.17 7; 9; 9; 10; 10; 10 (91.2%) 0.95 8; 9; 5; 6; 6; 9 (71.7%) 1.9 10; 10; 7; 7; 8; 6 (80.0%) 10; 10; 10; 5; 8; 8 (85.0%) 3.8 6; 10; 9; 7; 8; 5 (75.0%) 8; 8; 7; 7; 5; 9 (73.3%) 7.5 10; 10; 10; 10; 10; 10 (100%) 8; 7; 10; 4; 6; 5 (66.7%) 6; 4; 4; 1; 3; 4 (36.7%) 15 10; 10; 8; 10; 9; 10 (95%) 5; 3; 10; 0; 4; 3 (41.7%) 0; 0; 1; 1; 0; 1 (5.0%) 22 2; 0; 0; 2; 2; 2 (13.3%) 0; 0; 0; 0; 0; 1 (1.7%) 30 5; 5; 10; 6; 7; 7 (66.7%) 0;0;1;0;0;0(1.7%) 0;0;0;0;0;0(0%) 45 1; 2; 1; 3; 0; 1 (13.3%) 0;0;0;0;0;0(0%) 0;0;0;0;0;0(0%) 60 0; 0; 1; 0; 0; 0 (1.7%) 0;0;0;0;0;0(0%) 90 0; 0; 0; 0; 0; 0 (0%) 120 0; 0; 0; 0; 0; 0 (0%) 826 MITCHELL AND BRANDT

TABLE 2.—Survival of two size-groups (2–4- and 15–20-mm shell height) of red-rim melania exposed to ice-water only (IW) or saltwater only (SW) for various times. Each number represents the number suriving in each of six or three replicates (10 snails/ replicate; the overall percent survival for all replicates in that group is also presented). Treatment temperatures were 0.0–4.98C for IW and 16.3–20.78C for SW; temperatures for their respective controls were 20.8–23.18C and 16.3–20.78C. Survival in control snails was 97.9% for the IW trials and 100% for the SW trials.

Number surviving by replicate and overall percent Exposure time (min%) IW 2–4 mm IW 15–20 mm SW 15–20 mm

15 10; 10; 10 (100%) 30 10; 10; 10 (100%) 10; 10; 10; 10; 10 (100%) 60 10; 10; 10 (100%) 9; 10; 9; 10; 10; 10 (96.7%) 120 6; 8; 8 (73.3%) 9; 10; 9; 9; 10; 9 (93.3%) 180 6; 9; 7 (73.3%) 0;0;0;0;0;0(0%) 240 2; 4; 4; 5; 3; 3 (35%) 360 3; 6; 5 (46.7%) 480 0; 1; 0; 1; 0; 0 (3.3%) 720 0; 2; 0; 0; 0; 0 (3.3%) 0;0;0;0;0;0(0%) 1,440 0; 0; 0; 0; 0; 0 (0%)

15–20-mm snails were 35.8 min for SIW, 179.6 min would probably not be maintained for more than a few for IW (0–4.98C), and 423.6 min for SW (16.3–20.78C; hours. The SIW treatment, which consistently pro- Figure 2). Survival of control snails (all sizes in all duced colder temperatures (2.08C) and required only tests) was 99.1%. 90 min to eliminate snails of all sizes, is more likely to maintain the cold temperatures required to eradicate Discussion unwanted snails on a hot day. Both IW and SIW treatments are easy to set up and The salt in the SIW treatment contributed minimally relatively inexpensive once the insulation, trash can to snail mortality. In the SW treatment, only 6.7% of and lid or large ice chest, cordless drill, and paint stirrer the snails were killed within 120 min. Although the have been purchased. The IW treatment is not temperatures in one SW test dropped slightly below the recommended because it requires a long exposure preferred red-rim melania survival range (17–328C; period (12–24 h) and may not consistently produce a Mitchell and Brandt 2005), the few hours at 16.3–178C cold enough treatment to be reliable. If an IW treatment should have had little effect on survival. No controls is conducted outdoors on a hot day, the colder died while being maintained at the same temperature, temperatures required for red-rim melania elimination and the survival results were similar to another SW test where temperatures (19.7–20.78C) remained within the preferred survival range. The SIW treatment (66.7 L of water, 33.3 kg of ice, and 10 kg of NaCl) is recommended for rapid (2 h) killing of all red-rim melania. An unexpected finding was that larval red-rim melania still in brood pouches of adult snails and naturally released juvenile snails had a higher tolerance to low temperatures than did parental snails. Several larval snails were found alive in brood pouches of dead parent snails (15–20 mm) killed by a 180-min IW exposure; in one dead adult, five larvae were found alive. Three further tests (not part of this study) were conducted to determine some initial survival charac- teristics of the larval snails. A 60-min SIW treatment was performed on 15–20-mm snails to verify the FIGURE 2.—Percent survival of red-rim melania exposed to previous observation; six larvae from 30 dead parent treatments of salt–ice-water (SIW), ice-water only (IW), or snails were found alive. Following another 60-min saltwater only (SW) for various lengths of time (SIW: y ¼ 0.0494x2 4.2284x þ 88.07, r2 ¼ 0.79; IW: y ¼0.0065x2 þ SIW treatment, 64 larval snails were removed from 30 0.7222x þ 80, r2 ¼ 0.99; SW: y ¼ 0.0002x2 0.309x þ 95, r2 ¼ dead parents and placed in freshwater; none had 0.87). survived when observed 3 d later. We retained 30 RED-RIM MELANIA ELIMINATION FROM EQUIPMENT 827 dead parent snails subjected to 180 min of IW to see if 16 h (Mitchell et al. 2007) in a vat is recommended. any larvae would naturally emerge and survive; none Other disinfectants we tested previously, including survived. household bleach, are not effective. The SIW treatment Initially, only tests with 15–20-mm red-rim melania is practical for on-the-road use and should be an were planned, but following the above-mentioned effective, inexpensive, relatively quick method for observations, it became clear that testing with small killing all red-rim melania on nets and other small andrecentlyreleased(,8-d) juvenile snails was immersible fisheries equipment that fit into a 120-L needed and that testing even larger snails (i.e., 30–40 container. Other than a thin coating of salt residue, mm) could yield further important information. The which can be easily washed off after treatment, the results from these tests documented that smaller snails equipment would be free of potentially harmful tolerated longer exposures to both SIW and IW chemicals and should not be degraded by cold treatments (comparing tolerance to different low temperature. An insulated trash container or large ice temperatures was not tested). In general, size and age chest, portable drill and paint stirrer, salt, ice, water, are related but the effect of age on temperature and 2 h are all that is needed to eliminate red-rim tolerance, particularly among small snails (2–4 mm), melania from this equipment. is unclear. We have no explanation for why juvenile red-rim Acknowledgments melania survived subfreezing temperatures for longer The authors thank Tom Ryan, Diego Araujo, Quincy exposures than their parents. Few similarities are Pence, and Catherine Phillips for collection of snails known in the animal kingdom. Hatchling painted used in this study. Special thanks are given to Matt turtles Chrysemys picta are known to survive subfreez- Barnett for setting up and running the ice-water ing ( 108C) temperatures (Costanzo et al. 2000). Cold- treatments and for his help in recording results. We acclimated painted turtle hatchlings exhibited pro- are grateful to Joe Fries, Nathan Stone, and Jerry nounced capacities for super-cooling and resistance to Ludwig for constructive comments and review of early inoculative freezing. They eliminated or deactivated manuscripts. Mention of trade names of commercial endogenous ice nuclei that prevented ice crystals from products or their use to control the spread of exotic forming. Their ability to retain urea, which elevates snails in this publication does not imply recommenda- blood osmolality, helped to maintain circulation at tion or endorsement by the U.S. Department of subzero temperatures. It is possible that juvenile red- Agriculture or the U.S. Department of the Interior. rim melania have similar mechanisms that help Any views in this paper are those of the authors and not maintain their circulation for longer periods at subzero necessarily the views of the U.S. Department of the temperatures, mechanisms not found in larger, pre- Interior. sumably older, individuals. The transfer of red-rim melania with fisheries References equipment is an issue of real concern. Fisheries equipment used at a site where the snail might be Abbott, R. T. 1952. A study of an intermediate snail host (Thiara granifera) of the oriental lung fluke (Paragon- present should be disinfected before further use at imus). Proceedings of the United States National another site. Drying nets for several days should not be Museum 102:71–116. used as a method of disinfection for the red-rim Amaya-Huerta,D.,andR.J.Almeyda-Artigas.1994. melania. Dudgeon (1982) found that red-rim melania Confirmation of Centrocestus formosanus (Nishigori, greater than 10 mm in shell height survived desiccation 1924) Price, 1932 (Trematoda: Heterophyidae) in for up 8 d, but he did not give the upper size of snails Mexico. Research and Reviews in Parasitology 54:99– tested; it is possible that larger red-rim melania would 103. Blazer, V. S., and J. B. Gratzek. 1985. Cartilage proliferation survive even longer periods of desiccation. Where hot in response to metacercarial infections of fish gills. water is available, an immersion in water of at least Journal of Comparative Pathology 95:273–280. 508C for a minimum of 5 min (Mitchell and Brandt Costanzo, J. P., J. D. Litzgus, J. B. Iverson, and R. E. Lee. 2005) would be recommended; this is the most rapid 2000. Seasonal changes in physiology and development disinfection treatment for red-rim melania, damage to of cold hardiness in the hatchling painted turtle fisheries equipment would be minimal, and there is no Chrysemys picta. Journal of Experimental Biology concern of chemical contamination of the environment 203:3459–3470. Dudgeon, D. 1982. Aspects of the desiccation tolerance of when disposing of the treatment water. In a hatchery four species of benthic Mollusca from Plover Cove setting where time for completion of the disinfection Reservoir, Hong Kong. Veliger 24:267–271. process is not an issue or where larger equipment Dudgeon, D. 1986. The life cycle, population dynamics, and requires disinfection, the use of Roccal at 600 mg/L for productivity of Melanoides tuberculata (Muller, 1774) 828 MITCHELL AND BRANDT

(Gastropoda: Prosobranchia: Thiaridae) in Hong Kong. Brandt. 2005. Spread of an exotic fish-gill trematode: a Journal of Zoology 208:37–53. far-reaching and complex problem. Fisheries 30(8):11– Dundee, D. S., and A. Paine. 1977. Ecology of the snail, 16. Melanoides tuberculata (Muller), intermediate host of the Mitchell, A. J., M. J. Salmon, D. G. Huffman, A. E. Goodwin, human liver fluke (Opisthorchis sinensis)inNew and T. M. Brandt. 2000. Prevalence and pathogenicity of Orleans, Louisiana. Nautilus 91:17–20. a heterophyid trematode infecting the gills of an Francis-Floyd, R. 1991. Use of Bayer 73 to control snails in endangered fish Etheostoma fonticola in two central ornamental fish ponds. Pages 467–490 in Aquaculture Texas spring-fed rivers. Journal of Aquatic Animal Report Series. Florida Department of Agriculture and Health 6:283–289. Consumer Services, Tallahassee. Murray, H. D. 1971. The introduction and spread of thiarids in Jacobson, M. K. 1975. The freshwater Prosobranch, Tarebia the United States. Biologist 53:133–135. ganifera, in Oriente, Cuba. Nautilus 89:106. Nollen, P. M., and H. D. Murray. 1978. Philophthalmus Martin, W. E. 1958. The life histories of some Hawaiian gralli: identification, growth characteristics, and treat- heterophyid trematodes. Journal of Parasitology 44:305– ment of an oriental eyefluke of birds introduced into the 323. continental United States. Journal of Parasitology Mitchell, A. J., and T. M. Brandt. 2005. Temperature 64:178–180. tolerance of red-rim melania Melanoides tuberculatus, Perera, G., M. Yong, J. R. Ferrer, C. Arrinda, and O. Amador. an exotic aquatic snail established in the United States. 1990. Effectiveness of three biological control agents Transactions of the American Fisheries Society 134:126– 131. against intermediate hosts of snail-mediated parasites in Mitchell, A. J., A. E. Goodwin, M. J. Salmon, and T. M. Cuba. Malacological Review 23:47–52. Brandt. 2002. Experimental infection of an exotic Premvati, G., and V. Pande. 1974. On Centrocestus heterophyid trematode, Centrocestus formosanus, in four formosanus (Nishigori, 1924) Price, 1932 and its aquaculture fishes. North American Journal of Aquacul- experimental infection in white leghorn chicks. Japanese ture 64:55–59. Journal of Parasitology 23:79–84. Mitchell, A. J., M. Hobbs, and T. M. Brandt. 2007. The effect Stein, R. A., C. G. Goodman, and E. A. Marschall. 1984. of chemical treatments on Melanoides tuberculatus,an Using time and energetic measures of cost in estimating exotic aquatic snail that serves as vectors of trematodes to prey value for fish predators. Ecology 65:702–715. fish and other species in the United States. North Vogelbein, W. K., and R. M. Overstreet. 1988. Life-history American Journal of Fisheries Management 27:1287– and pathology of a heterophyid trematode infecting 1293. Florida-reared ornamental fishes. International Associa- Mitchell, A. J., R. M. Overstreet, A. E. Goodwin, and T. M. tion for Aquatic Animal Medicine Proceedings 19:138.