Infestations of the Trematode Bolbophorus Sp. in Channel Catfish

SRAC Publication No. 1801

VI January 2003 PR

Infestations of the Trematode Bolbophorus sp. in Channel Catfish

Jeffery S. Terhune, David J. Wise, Jimmy L. Avery, Lester H. Khoo* and Andrew E. Goodwin**

Digenetic trematodes infest many and two intermediate hosts. The Some digenetic trematodes may types of fish and are common in life cycle (Fig.1) begins when the have several different final and cultured fish in areas frequented adult trematode, which lives in the intermediate hosts. Studies to date, by fish-eating birds. In the past, gastrointestinal tract of the however, indicate that the only most trematode infestations in cul- American white pelican (Pelecanus final and intermediate host for tured channel catfish were caused erythrorhynchos), releases eggs that Bolbophorus are the pelican and the by either Clinostomum complanatum are then deposited into ponds ram’s horn snail, respectively. (“yellow grubs”) or Diplostomum when the birds defecate. The eggs Without these hosts the life cycle spathaceum (“eye flukes”). Such hatch to produce miracidia that of the trematode cannot be com- infestations are rarely more than a infest the first intermediate host, pleted. Helisoma nuisance, though severe infesta- the ram’s horn snail ( sp., Many different species of fish-eat- tions of yellow grub may make Fig. 2). The miracidia mature in the ing birds from locations across fish unsuitable for processing. snail and eventually release larval North America have been necrop- Recently, a digenetic trematode trematodes called cercariae. The sied and examined for the pres- identified as Bolbophorus sp. (here- cercariae infest and encyst in fish ence of Bolbophorus. Some of the after referred to only as to form metacercariae (Fig. 3). The birds sampled were from ponds in Bolbophorus) has been reported in life cycle is completed when peli- Louisiana and northwestern commercially raised channel cat- cans eat infected fish and metacer- Mississippi containing severely fish from Louisiana, Mississippi cariae develop into adult flukes. and Arkansas. Evidence indicates that Bolbophorus infestations have Trematode life cycle caused high mortality rates and Pelican decreased production in channel (adult fluke) catfish. The management strategies discussed here for the control of (eggs) Bolbophorus apply to other digenetic trematodes with similar life cycles. Life cycle and vectors (miracidia) As with other digenetic trematodes, Bolbophorus has a complex life cycle involving one final host Channel catfish Ram’s horn (metacercariae) snail (cercariae) *Thad Cochran National Warmwater Aqauculture Center, Stoneville, MS Figure 1. Life cycle of Bolbophorus sp. **University of Arkansas at Pine Bluff infested fish. With the exception of Clinical signs loafing areas, such as lakes, rivers, one case, the adult fluke has been bayous and refuges, and those found only in American white peli- Catfish infested with Bolbophorus with high numbers of ram’s horn 1 1 cans. The adult fluke was found in have small ( /32- to /16-inch) snails. Farmers should scout for a single brown pelican (Pelecanus cysts that can be anywhere in the snails along shallow areas of vege- occidentalis), but it is not known body but usually appear in the tail tated levee banks. Aquatic vegeta- whether this bird can serve as a (Fig. 4). The cysts are white or red tion should be examined for snails viable final host. raised bumps either just under the that may be attached to stems or skin or deeper in the muscle tis- roots. Since this trematode appears to be sue. endemic in the American white If a farm is at risk, fish should be pelican population, the primary An infestation may have no appar- examined, especially if fish have factor in its spread is the presence ent effect on production, or it may decreased appetite that cannot be of these pelicans in a given area. cause extensive mortalities in explained by other diseases or Fish-to-fish transmission of dige- smaller fish. The limited research poor water quality. A small cutting netic trematodes is not possible. that has been done suggests that seine can be used to collect fish Therefore, transferring affected fish Bolbophorus causes massive dam- that have been attracted to an area from pond to pond will not trans- age to the kidneys and to a lesser by some feed. Additional sampling mit the disease to other fish. The extent the liver. In severe infesta- should be done during harvest and trematodes in fish can not com- tions of smaller fish, gross lesions other seining operations. At least plete their life cycle and will die if may look similar to channel catfish 20 to 30 fish should be examined the infested fish is not eaten by a virus disease or enteric septicemia on site; if any samples have possi- pelican. It is also highly unlikely of catfish (distended abdomen ble Bolbophorus infestation, they that enough cercariae could be with fluid in the body cavity and should be submitted to a fish diag- transferred from pond to pond via bulging eyes). Larger fish seem to nostic laboratory for confirmation. equipment or transport water to be less susceptible; lesions are gen- create an economically damaging erally limited to those on the skin Treatments level of infection. and fins. However, larger fish that are severely infested feed poorly There is no FDA-approved treat- and may appear emaciated. ment for fish infested with trematodes. Control is dependent on breaking the life cycle of the trematode. It is impractical to eliminate the free-swimming (miracidia and cercariae) life stages. The only practical treatment is eliminating or reducing the numbers of final or intermediate hosts. Every effort should be made to discourage predation by birds on commercial catfish operations. (See Figure 2. The first intermediate host Figure 4. Channel catfish fingerling SRAC publications 400, 401 and of Bolbophorus sp., the ram’s horn showing cysts with Bolbophorus sp. 402 for additional information.) Pelicans can be extremely difficult snail (left). The ram’s horn snail metacercariae. (Photograph courtesy of Marco Nicovich, Mississippi State to harass from a pond once they should not be confused with Physa establish a feeding pattern. They spp. (right), another common snail University.) feed at night as well as during found in commercial catfish ponds. daylight. Pelicans are protected by Physa is not an intermediate host for Risk assessment federal law; contact the USDA/ the trematode. Because Bolbophorus can be intro- APHIS/Wildlife Services agency duced easily into a commercial to find out about proper control facility by infested pelicans, and methods. because it can have serious effects In addition to keeping birds away on production, farmers in suscep- from farms, breaking the trema- tible areas should take steps to tode life cycle depends on reduc- limit the spread of this condition. ing snail populations with a com- The American white pelican is a bination of chemical treatments, common winter resident in the biological control species, and lower Mississippi Valley, with aquatic weed control. Expensive chemical treatments aren’t war- Figure 3. The metacercarial stage of migrating populations peaking from February through April. ranted in ponds with little or no Bolbophorus sp. Farms that are at the highest risk evidence of ram’s horn snails. If are those near pelican roosting or fish are only mildly affected, con- servative measures will likely Apply chemicals to pond margins reduce snail populations sufficient- only on calm days so that waves ly in affected ponds. However, if a don’t dilute the chemical too farm has quite a few ponds with quickly. Do not treat recently infested fish, all ponds with high stocked fry ponds; fry and small snail populations should be treated fingerlings may not be able to whether or not the disease is pre- retreat from the treated area fast sent in a given pond. Research has enough to avoid direct contact not yet determined whether the with the chemical. severity of infestation correlates to Figure 6. Hydrated lime slurry being the long-term performance of fish. Hydrated lime applied with a pull-behind sprayer. Producers should evaluate feeding Apply dry hydrated lime at a rate response, length of time to harvest, of 50 pounds per 75 to 100 feet of Copper sulfate and mortality rate before making pond bank. Treat a band 3 to 4 feet Copper sulfate is applied at a rate radical management decisions. The from the pond edge or 1 to 2 feet of 10 pounds of copper sulfate key question is: When does the beyond any vegetation that plus 1 pound of citric acid per 250 infestation become so severe that it extends into the pond. At the pre- feet of pond margin. These dry is no longer economically justifi- scribed application rate, the pH materials should be mixed with at able to maintain infested stocks of will increase briefly (10 to 20 min- least 70 gallons of water per 250 fish? Regrettably, there is no sim- utes) within the application zone feet of pond margin treated. The ple answer to that question. but the lime will not affect the finished formulation should be On farms where pelicans usually overall water quality of ponds applied to a 6-foot band around are found, snail numbers should with total alkalinity greater than 50 the pond perimeter. Application be reduced before pelicans migrate mg/L. The material can be applied equipment is similar to that used into the region. Snails also should with an auger-equipped hopper for hydrated lime slurry. Copper be controlled in late summer or mounted on a tractor to help cover can be toxic to fish, so farmers early fall since ram’s horn snails larger areas in less time (Fig. 5). should not treat ponds with less burrow into the mud during win- than 150 mg/L total alkalinity (as ter months. Trematode-infested CaCO3). Ponds smaller than 7 snails that survive the winter can acres should not be treated shed cercariae over several grow- because this recommended rate ing seasons. would exceed rates that can be applied to the whole pond. Using Chemical treatments copper sulfate in ponds with Treating pond margins with heavy algae blooms can also cause hydrated lime and/or copper sul- severe oxygen depletion because fate can be effective in reducing copper sulfate is toxic to phyto- snail populations within the treat- plankton. To minimize the impact ed zone. Chemical treatments will on algal populations, treat half the pond margin one day and the not eradicate snail populations Figure 5. Hydrated lime being applied from a pond, but will reduce the remainder several days later. to a pond with a tractor-mounted number of snails. Snails will eventually repopulate, so treatments auger. Bayluscide¨ will need to be repeated. Bayluscide® or niclosamide is a To be effective, the correct amount Hydrated lime also can be mixed molluscicide used in tropical of chemical must be applied and with water and applied as a slurry. regions of the world to control the the pond margin thoroughly cov- This form of hydrated lime is usu- spread of the human disease schis- ered. The treatments target snails ally prepared at a commercial lime tosomiasis. It is also used in the in a narrow band of water along facility and delivered to commer- Great Lakes region to control sea ® the pond margin. Snails outside cial applicators or individual farm- lampreys. Bayluscide 70 WP (70% this area will not be affected. The ers. The bulk slurry is transferred active ingredient in a wettable chemical should be applied so that to a large holding tank at the farm powder) has been given a Section it penetrates through any aquatic and subsequently pumped to 18 emergency exemption in vegetation. Areas with thick stands smaller tanks for application (Fig. Mississippi until November 2003 of aquatic vegetation should 6). Formulation rates are 4.0 to 4.7 for control of ram’s horn snail in receive additional treatments. pounds of hydrated lime per gal- commercial catfish ponds. It is Aquatic weeds located away from lon of water. At this concentration, applied at a rate of 1.5 pounds per the pond margin should be elimi- apply 20 gallons of slurry per 100 acre-foot of water. Unlike hydrated nated with an appropriate aquatic feet of levee. lime and copper sulfate, ® herbicide before the pond margin Bayluscide is applied to the is treated for snails. whole pond. At the application rates authorized under the exemp- ed time and money in planting Fox, A. C. 1965. The life cycle of tion, this pesticide is toxic to non- soil-stabilizing vegetation along Bolbophorus confusus (Kraus target aquatic organisms such as pond margins may want to evalu- 1914) Dubois, 1935 (trematoda: fish and aquatic insects. Therefore, ate the effectiveness of other snail strigeoidea) and the effects of Bayluscide® is used to control control measures before deciding the metacercariae on fish hosts. snails in ponds where there are no to eliminate these plantings. For Ph. D. Dissertation, Montana fish. Producers should follow all additional information on aquatic State University, Bozeman, label instructions regarding appli- weed control, see SRAC publica- Montana. cation rates, pond draining and tions 360, 361 and 3600. Mitchell, A. J. 2000. Shoreline pond restocking restrictions. Although severe infestations of treatments for aquatic snails Bolbophorus can be economically that carry the catfish trematode. Biological control devastating to a production facility, The Catfish Journal 15(2):10-11. After chemical treatments to this disease can be managed with Overstreet, R. M., S. S. Curran, L. reduce snail numbers, biological the proper prevention strategies. In M. Pote, D. T. King, C. K. Blend methods must be used to control summary, every effort should be and W. D. Grater. 2002. snails long-term. Black carp made to discourage pelicans from Bolbophorus damnificus n. sp. (Mylopharyngodon piceus) reduce feeding in catfish ponds. If peli- (Digenea: Bolbophorieae) from snails in commercial catfish ponds cans are found in a particular the channel catfish Ictalurus at stocking rates of 5 to 20 fish per region, farmers should monitor punctatus and American white acre. Black carp is a nonindigenous fish stocks for infestations and pelican Pelecanus erythrorhynchos species and its use may be restrict- keep snail populations under con- in the USA based on life cycle ed. Consult the proper authorities trol through chemical and biologi- and molecular data. Systematic (a natural resource agency or cal control methods and aquatic Parasitology 52:81-96. Extension personnel) before stock- weed management. ing. Redear sunfish or “shellcrack- Terhune, J. S., D. J. Wise and L. H. er” (Lepomis microlophus) may also References Khoo. 2002. Bolbophorus confusus control snails, but no experimental infections in northwestern evaluations have been done. The Avery J., D. Wise, L. Khoo and J. Mississippi and effects of water redear’s small mouth may restrict Terhune. 2000. New Trematode temperature on emergence of its foraging to juvenile snails, thus in Channel Catfish. Thad cercariae from infected snails. extending the time required to sig- Cochran National Warmwater North American Journal of nificantly reduce snail populations. Aquaculture Center Fact Sheet Aquaculture 64:70-74. #004, Stoneville, Mississippi. Venable, D. L., A. P. Gaude and P. Aquatic weed control Boerger, H. 1975. Movement and E. Klerks. 2000. Control of the Aquatic vegetation creates ideal burrowing of Helisoma trivolvis trematode Bolbophorus confusus habitat for snails and may hinder (Say) (Gastropoda, Planorbidae) in channel catfish ponds using the foraging of species used for in a small pond. Canadian salinity manipulation and poly- biological control. Weeds growing Journal of Zoology 53:456-464. culture with black carp along the margin and submerged Dronen, N. O., M. R. Tehrany and Mylopharyngodon piceus. Journal in the pond should be eliminated. W. J. Wardle. 1999. Diplostomes of the World Aquaculture Society Grass carp (Ctenopharyngodon from the brown pelican, 31:158-166. idella) and aquatic herbicides effec- Pelecanus occidentalis tively control aquatic vegetation. (Pelecanidae), from the The use of grass carp also may Galveston, Texas area, including have restrictions; as with black two new species of carp, consult proper authorities Bursacetabulus gen. n. Journal of about their use and permit require- the Heliminthological Society of ments. Producers who have invest- Washington 66:21-24.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 00-38500-8992 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.