Thomas M. Brandt

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...

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...

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 ...

Effects of Temperature on Egg Production and Early Life Stages of the Fountain Darter

Abstract Studies were conducted to determine the effects of water temperature on egg and larval production, larval survival, and juvenile growth of the endangered fountain darter Etheostoma fonticola. Adult fish were exposed to water temperatures of 14, 17, 20, 23 (control), 25, 27, and 29°C for 33 d. Egg production was significantly higher (P ≤ 0.05) for fish held at 14, 17, 20, 23, and 25°C than for fish held at 27 and 29°C. Percent hatch was significantly higher (P ≤ 0.05) at 17, 20, and 23°C than at 14, 25, 27, and 29°C. Larval production was significantly higher (P ≤ 0.05) at 14, 17, 20, and 23°C than at 25, 27, and 29°C. Estimated low and high temperatures to produce 50% mortality of larvae (24–72 h old) over a 24-h period were 3.8 and 31.9°C, respectively. Low survival and substantial variation in growth of controls prevented a meaningful assessment of temperature effects on juvenile growth.

Temperature Tolerance of Red-Rim Melania Melanoides tuberculatus, an Exotic Aquatic Snail Established in the United States

Abstract The red-rim melania Melanoides tuberculatus (family Thiaridae), a tropical, nonindigenous aquatic snail, has become established and is spreading in the United States. Concerns associated with the spread of this snail include its potential to displace native snail populations and to transmit trematodes. Of particular concern is the gill trematode Centrocestus formosanus now found in U.S. commercial and wild fish stocks. The snail survives year-round in subtropical ponds and constant-temperature spring runs in Florida and Texas and in geothermal waters of several western and midwestern states. Knowledge of the temperature tolerances of the snail will increase the ability to predict its potential range in North American waters and to control its spread. Under constant temperature conditions in the laboratory, all red-rim melania (15–25 mm shell height (SH)) were killed by exposure to 5°C for 1 d, 9°C for 2 d, 11°C for 8 d, and 13°C for 12 d. At 17°C and 32.5°C, about 10% of the snails died within 27...

Laboratory Spawning and Rearing of the Endangered Fountain Darter

Abstract Survival of the fountain darter (Etheostoma fonticola), a U.S. federally listed endangered species, may depend on captive propagation. Studies were conducted to determine the effect of temperature on spawning and to develop methods for culture. The fountain darter spawned and produced viable offspring in aquaria at 27, 24, 21, 18, 15, 12, 9, and 6°C. The fish also spawned at 3 and 30°C but did not produce viable eggs. Daily egg production of individual fish held at 27, 21, 15, and 9°C was variable. The mean critical thermal maximum for the fountain darter was 34.8°C. Early life stages, 4–14 mm long, were offered a variety of live protozoans, rotifers, and microcrustaceans. Food selection varied with fish size and food size. Fountain darters reached sexual maturity in about 180 d when maintained at 21°C. Three-year-old darters produced viable offspring, and several lived longer than 4 years. Tricaine methanesulfonate was an effective anesthetic at 60 mg/L but was fatal to subadults at 100 mg/L.

Ascorbic Acid Inhibition of Nitrite-Induced Methemoglobinemia in Channel Catfish

Abstract Nitrite-induced methemoglobin concentrations were lower in channel catfish (Ictalurus punctatus) fed a diet containing 7,720–7,950 mg ascorbic acid/kg than in fish fed a diet containing 63 mg ascorbic acid/kg. The lower methemoglobin levels were evident after the fish were fed the higher ascorbic acid diet for 1 week. Fish were exposed to 2.5–5.0 mg nitrite-N/L for 22 h. Ascorbic acid exhibited a protective effect if fish were fed 48 h or less before blood was sampled, but no protective effect was evident if fish were last fed 65 h before sampling.

Experimental Infection of an Exotic Heterophyid Trematode, Centrocestus formosanus, in Four Aquaculture Fishes

Abstract Centrocestus formosanus, an exotic digenetic trematode that was recently found infecting wild fish in Texas, was evaluated to determine whether it could infect four propagated warmwater fish species. Channel catfish Ictalurus punctatus, sunshine bass (the hybrid of female white bass Morone chrysops and male striped bass Morone saxatilis), golden shiners Notemigonus crysoleucas, and fathead minnows Pimephales promelas were experimentally infected with cercariae of C. formosanus. The trematodes were embedded along the gill filament cartilage. Cyst production, cartilage displacement, and hyperplasia of the lamellar epithelium were observed in wet mounts of sunshine bass and fathead minnow gills. These pathological changes also occurred in golden shiners and channel catfish but appeared to be delayed and less pronounced. Histological examination showed that the parasites were encased in cartilage, and distorted areas were evident in the filament cartilage. Because this trematode has the ability to in...

Raceway Spawning of Florida Largemouth Bass: Effects of Acclimation Time and Hormone Treatment on Spawning Success

Abstract Several acclimation periods and hormone treatments were tried to determine their effects on controlled spawning of 2-year-old Florida largemouth bass (Micropterus salmoides floridanus). During the first season, fish were acclimated to raceways for 0–8 weeks before spawning; males and females were separated during acclimation. There was an inverse relationship between the length of the acclimation period and latency of first spawn after the sexes were mixed. The longest acclimation periods resulted in the shortest latencies; however, once spawning began, the rate of spawning (interval between spawns) was similar across treatments. During the second season, unacclimated and 2-week-acclimated largemouth bass were injected with saline, human chorionic gonadotropin (HCG; 4,000 IU/kg body weight) or [D-ala6pro9-N-ethylamide]-luteinizing hormone releasing hormone (LHRH-A; 0.5 mg/kg body weight). Injections of HCG induced spawning quicker, and produced more spawns and fry, than injections of LHRH-A or sa...

Effects of Fluctuating Temperatures and Gill Parasites on Reproduction of the Fountain Darter, Etheostoma fonticola

ABSTRACT We assessed the effects of fluctuating temperature and gill parasitism on egg and larval production of the endangered fountain darter (Etheostoma fonticola). Fountain darters, with and without the exotic digenetic trematode Centrocestus formosanus. were exposed in the laboratory to constant (24°C) and fluctuating (24 to 26°C, 26 to 28°C, and 28 to 30°C) water temperatures for 21 d. No differences were detected between the number of eggs produced (P = 0.78) or number of larvae produced (P = 0.11) between fountain darters with and without trematodes. Total egg production was greatest at 24°C and decreased (P < 0.05) by 42% at fluctuating temperature of 24 to 26°C, 65% at fluctuating temperature of 26 to 28°C, and 99.6% at fluctuating temperature of 28 to 30°C. Likewise, larval production was greatest at 24°C and decreased (P < 0.05) by 63% at 24 to 26°C 99.9% at 26 to 28°C, and 100% at 28 to 30°C. Water temperature (24 to 26°C) that fluctuated within previously considered optimum temperature (< 27°C) reduced the number of eggs and larvae produced by the fountain darter. Results of this study refined maximum optimum temperature requirements of the fountain darter reproduction with water temperatures ≥ 26°C reducing egg production and water temperatures ≥ 25°C reducing larval production.