Some Experimental Fish Hosts of the Strigeid Trematode Bolbophorus confusus and Effects of Temperature on the Cercaria and Metacercaria

Abstract

Experimental studies were conducted on the digenetic trematode, Bolbophorus confusus (Krause, 1914) Dubois, 1935, to test host specificity in fish and the effect of temperature on the cercaria and metacercaria. Typical infections followed laboratory exposures of the following fishes: Salmo gairdneri, Salmo trutta, Salvelinus fontinalis, Prosopium williamsoni, Pimephales promelas, Hybopsis gracilis, Rhinichthys cataractae, Catostomus commersoni, Pantosteus platyrhynchus, Lepomis macrochirus, and Gambusia affinis. Cercarial penetration occurred in Ictalurus punctatus and Cottus bairdi, but metacercarial development was atypical. Maximum cercarial penetration of fish occurred between 66 and 85 F. Invasive ability was markedly reduced between 55 and 65 F and very few penetrations occurred below 54 F. Metacercariae developed rapidly at 70 F. No metacercarial development was found in fish exposed to cercariae at 70 F and then held at 40 to 42 F. Some metacercariae were observed to develop normally when fish treated in the above manner were returned to 70 F, after being held at 40 to 42 F for 1 month. Water temperature apparently plays a major role in the distribution of the metacercaria of B. confusus (common only in one lake) in southwestern Montana. The digenetic fluke Bolbophorus confusus (Krause, 1914) Dubois, 1935, is established in Meadow Lake in southwestern Montana (Fox, 1962). Although this fluke is reported to be common in Europe, the metacercaria had not been previously reported in North America. It has not been found in other lakes in the Meadow Lake vicinity. In Europe, Dubois (1938) reported the metacercaria of this paarsite in the following fishes: rudd (Scardinius erythropthalmus), id (Idus idus), bream (Abramis brama), flat bream (Abramis blicca), northern pike (Esox lucius), perch (Perca fluviatilis), and mullet (Mugil saliens). He reported the final hosts to be the pelicans Pelecanus onocrotalus and Pelecanus crispis in Europe, and the white pelican (Pelecanus erythrorhynchos) in North America. In Meadow Lake, the metacercariae are found in rainbow trout (Salmo gairdneri), brown trout (Salmo trutta), arctic grayling (Thymallus arcticus), longnose sucker (Catostomus catostomus), and white sucker (Catostomus commersoni). Fox (1962) observed a marked difference in the number of B. confusus metacercariae Received for publication 17 February 1965. * This study was supported by Grant AI-05055-03 from the U. S. Public Health Service, NIH, Bethesda, Maryland. Contribution from the Montana State University Agricultural Experiment Station Project No. MS-844 Paper No. 684 Journal Series. found in brown and rainbow trout from Meadow Lake. All brown trout examined were infected with an average of 194 cysts per fish. Cysts were found in 25 of 30 rainbow trout examined and averaged only 34 per fish. The difference in the degree of infection between the trout and the fact that B. confusus metacercariae are not reported in fish from nearby lakes, formed the basis for this investigation. The objectives were to study the host specificity of B. confusus metacercariae in fish and to find an explanation for the prevalence of the parasite in Meadow Lake fish. Although the snail host and cercaria of B. confusus were not known at the time the parasite was found in Meadow Lake, the complete life cycle has since been determined by Fox (1965). It is briefly as follows: the adult fluke is found in the anterior intestine of the white pelican. The eggs pass out with the feces into the water and hatch after about 15 days. The resulting ciliated miracidia penetrate the planorbid snail, Helisoma trivolvis. Sporocysts develop in the snail producing large numbers of cercariae. After leaving the snail, the cercariae penetrate fish and encyst in the musculature as metacercariae. When eaten by a pelican, the metacercariae develop to patent adults within a few days. MATERIALS AND METHODS Numerous attempts were made to collect snails (Helisoma trivolvis) from Meadow Lake in the spring and early summer of 1963, but none were