Andrew J. Mitchell

Prevalence and Pathogenicity of a Heterophyid Trematode Infecting the Gills of an Endangered Fish, the Fountain Darter, in Two Central Texas Spring-Fed Rivers

Abstract Gills of 194 fountain darters Etheostoma fonticola collected from the Comal River in Texas from May 1997 through May 1998 were found to be parasitized with 8–1,524 metacercarial cysts of a heterophyid trematode tentatively identified as Centrocestus formosanus. The intensity of infection varied among three sites on the Comal River. In contrast, of 130 darters from the nearby San Marcos River that were examined, only 4 (3%) were infected, and these had 1–2 cysts per fish. Of 2,279 Melanoides tuberculata snails from the Comal River that were examined, 139 (6.1%) were infected with the trematode. Only 1 snail in 2,241 from the San Marcos River that were examined was infected. The presence of metacercariae in darters was associated with flared opercula, shortened or thickened gill filaments, epithelial hyperplasia, and engorged lamellae. The normal cartilage support of the filaments was distorted and displaced, leading to severe deformities of filament structure. Gill damage was severe and possibly l...

The Public Sector Role in the Establishment of Grass Carp in the United States

Abstract On 16 November 1963, the U. S. Fish and Wildlife Service Fish Farming Experimental Station at Stuttgart, Arkansas, became the first institution to import grass carp (Ctenopharyngodon idella) into the United States. This introduction was the result of at least seven years of effort to find an effective biological control for problematic aquatic weeds. The introduction was in keeping with a strong environmental and political mandate of that day to replace the broad use of chemicals with biological controls. For about 10 years, federal and state agencies and university systems strongly promoted introductions, spawning, and nationwide stocking of the grass carp. In 1966, the USFWS laboratory at Stuttgart, Arkansas, was apparently responsible for the first accidental release of grass carp to the environment. By 1972, grass carp were stocked in open water systems, documented in 16 states, and established in the Mississippi River system. All this occurred before the first private-sector commercial produ...

Spread of an exotic fish-gill trematode

Abstract Centrocestus formosanus, the gill trematode, has caused serious losses among fish raised by tropical fish producers since the early 1980s and is believed to be harmful to wild fish populations, including the federally listed endangered fountain darter (Etheostoma fonticola), in the Comal River near San Marcos, Texas. The parasite appears to infect in many fishes from Hawaii, Florida, Texas, and Utah. The gill trematode has a complex life cycle involving definitive hosts (aquatic birds and occasionally some mammals) and intermediate hosts (aquatic snails and several fish species). In the United States, the green heron (Butorides virescens) and the great egret (Ardea alba) serve as definitive hosts. The first intermediate host, the red-rim melania (Melanoides tuberculatus), an exotic snail, has been found in 15 southern and western states. This snail exhibits resistance to desiccation, molluscicides, and disinfectants and has been documented to out-compete established mollusks. Both the gill tremat...

Histological and Hematological Evaluation of Potassium Permanganate Exposure in Channel Catfish

Abstract A histological and hematological study was performed to evaluate the effect of waterborne exposures of channel catfish Ictalurus punctatus to potassium permanganate (KMnO4). Three concentrations of KMnO4 were chosen to represent one, three, and five times the therapeutic concentrations (0.438, 1.315, and 2.190 mg/L, respectively), based on the KMnO4 demand, for 36 h, which is three times the usual treatment duration. The organs examined were the gill, liver, and trunk kidney. Differential leukocyte counts of neutrophils and monocytes in the blood and plasma enzyme analyses (lactate dehydrogenase and alanine transaminase) were also performed. The gill was the only organ to show microscopic lesions. Fish exposed to the therapeutic concentration of KMnO4 for 36 h had mild hypertrophy and spongiosis in the gills sampled during exposure, but no lesions were noticed 2 d postexposure. Gills of fish exposed to three and five times the therapeutic dose had extensive hyperplasia, epithelial hypertrophy and...

The Effect of Chemical Treatments on Red-Rim Melania Melanoides tuberculata, an Exotic Aquatic Snail that Serves as a Vector of Trematodes to Fish and Other Species in the USA

Abstract The red-rim melania Melanoides tuberculata, a subtropical and tropical snail, is a nonindigenous species that has become established and is spreading in the United States. Of concern is the potential of the red-rim melania to displace native snail populations and to transmit trematodes that cause serious problems. One of these, a fish gill trematode, Centrocestus formosanus, has negatively affected U.S. commercial and wild fish stocks, including some endangered species. The snail has an operculum that can protect it from desiccation and can remain viable for days on dry fisheries equipment. Thus, contaminated fisheries equipment is suspected as one of the ways the snail is being moved from place to place. A study was conducted to find chemical treatments that would kill 100% of the red-rim melania. Thirteen different chemicals and chemical combinations were evaluated at different concentrations and for various exposure periods. Roccal-D-Plus, Hydrothol 191, niclosamide, and Virkon showed promise ...

Importance of Treatment Duration for Praziquantel Used against Larval Digenetic Trematodes in Sunshine Bass

Abstract The effectiveness of praziquantel (Droncit) against yellow grubs Clinostomum complanatum and unidentified, encysted, larval trematodes was tested in infected sunshine bass Morone chrysops female × M. saxatilis male. Praziquantel treatments significantly reduced the total number of live grubs in the fish in most treatment regimes tested. Treatment at 0.25 mg/L for 24 h was as effective as one at 8 mg/L for 8 h. Mature dead and dying metacercaria may have released toxins that killed host fish in some treatments.

The Effect of High Total Ammonia Concentration on the Survival of Channel Catfish Experimentally Infected with Flavobacterium columnare

Abstract Ammonia concentrations in water can affect the severity of Flavobacterium columnare infections in fish. Two trials lasting 7 d each were conducted to determine the effect of a single immersion flush treatment of total ammonia nitrogen (TAN; 15 mg/L) on the survival of channel catfish Ictalurus punctatus infected with F. columnare; the chemical was added while the water flowed continuously through the tanks. Both trials consisted of four treatments: (1) no ammonia exposure and no bacterial challenge (control), (2) ammonia exposure only, (3) bacterial challenge only, and (4) both ammonia exposure and bacterial challenge. Two hours after exposure to ammonia, the highest un-ionized ammonia level was 0.43 mg/L. The percent un-ionized ammonia is based on TAN, temperature, and pH. Caudal fins from three fish in each treatment were sampled at 24 h posttreatment to be analyzed by quantitative real-time polymerase chain reaction (qPCR). No significant difference in survival (mean ± SE) was noted between th...

A Copper Sulfate−Citric Acid Pond Shoreline Treatment to Control the Rams-Horn Snail Planorbella trivolvis

Abstract The rams-horn snail Planorbella trivolvis carries at least two important digenetic trematodes that infect propagated fish species in the southeastern United States. These snails are found in fish production ponds, and there are no proven chemical methods for eliminating them that would not also kill the fish. Application of an aqueous solution of 589 g of copper sulfate and 58.9 g of citric acid per 10 linear meters in a 2-m-wide swath along the pond shoreline produced an effective treatment. This would give an instantaneous treatment rate of about 59 ppm if the water in the 2-m swath averaged 0.5 m deep. In two separate trials, there was a significant difference in snail survival in the treated and sham-treated ponds. Average survival was 2.2% and 0% in the treatment ponds and 63.3% and 77.8% in the sham treatment ponds.

Evaluation of potassium permanganate against an experimental subacute infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus (Rafinesque)

An experiment was performed to evaluate the efficacy of potassium permanganate (KMnO4) as a prophylactic and therapeutic treatment of an experimental subacute infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus. Fish were cutaneously abraded and divided into five treatment groups: (i) challenged by waterborne exposure to F. columnare and not treated with KMnO4 (positive control), (ii) challenged and simultaneously treated with KMnO4, (iii) challenged and treated with KMnO4 at 1, 6 and 9 days post-challenge, (iv) not challenged and treated with KMnO4 at 1, 6 and 9 days post-challenge (first negative control) and (v) not challenged and not treated (second negative control). The dosing of KMnO4 was 2.0 mg L(-1) above the potassium permanganate demand for 2 h duration. The survival of the group challenged and simultaneously treated with KMnO4 (99%) was significantly higher than the positive control (78%) and was not significantly different from the negative control groups. The challenged fish treated with KMnO4 post-challenge had 7% higher survival than the positive control (85% compared with 78%), but that difference was not statistically significant. The results demonstrate that KMnO4 has a clear prophylactic value but probably a marginal therapeutic value once the infection has established.

Effectiveness of Praziquantel Bath Treatments against Bothriocephalus acheilognathi in Grass Carp

Abstract Many states ban the importation of fish infected with the Asian tapeworm Bothriocephalus acheilognathi. Treatment with an effective tapeworm parasiticide prior to shipment would allow fish to be imported that might otherwise be rejected. In this study, extended praziquantel bath treatments of infected grass carp Ctenopharyngodon idella were tested to determine their efficacy against Asian tapeworms. Preliminary praziquantel treatments of 0.7 mg/L or more for an exposure period of 24 h at grass carp densities of 69 g/L were effective in eliminating all tapeworms from 22-g fish. When the treatment duration was lowered to 12 h, a praziquantel concentration of 2.8 mg/L was required for effective treatment. In replicated studies, significantly reduced tapeworm numbers (0–5 tapeworms per treated fish compared with 30+ tapeworms per control fish) were observed following 24-h exposures to praziquantel at 0.5, 0.7, 1.0, and 1.5 mg/ L. Tapeworm elimination occurred only at the maximum concentration of 1.5 ...