The diseases of the native fauna of the United States including nonindigenous diseases were addressed by two major international symposia: The Symposium on Diseases of Fish and Shellfishes (Snieszko 1970) and The Symposium on Wildlife Diseases (Page 1975). The proceedings summarized the status and the effects of worldwide nonindigenous diseases on fishes and wildlife (Bogel and Abdussalam 1976). Since then, new information has been published (Sindermann 1990a,b). Dobson and May (1986) discussed the patterns of invasions by pathogens and parasites.
A summary of the introductions and transfers of parasites and bacterial and viral pathogens by finfishes was completed by Ganzhorn et al. (1992). Not only fishes or eggs may be infected, but the water and the containers may also be contaminated and serve as vehicles for the introduction of pathogens. The chance of establishment of the pathogens depends on the biology of the organisms, the fate of the shipment, and the presence or absence of appropriate hosts. The detection of a pathogen for the first time in a specific geographic location does not necessarily indicate a recent introduction but a major outbreak or increased surveillance. Illegal or undocumented movement of an organism or a natural migration frequently complicates attempts to determine the source of a pathogen in a new geographical area.
Many infectious diseases of fishes are caused by bacterial pathogens (Ganzhorn et al. 1992). Some pathogens exist in a carrier state and may therefore easily be transferred to new geographic areas despite fish-disease surveillance. In the carrier state, the bacteria exist in the host without any detectable pathology and at concentrations that are below the detection level of routine examinations. In addition, some host species and intermediate hosts may not be routinely inspected for fish diseases (Ganzhorn et al. 1992).
Imported viruses may have severe impacts on intensively cultured fishes because viral fish diseases are often untreatable. Some viruses can survive for extended times outside their hosts, some can exist in a carrier state or as latent infections and are not easily detected, and some can be vertically transmitted from progeny by eggs from infected parents (Ganzhorn et al. 1992). Only recently were techniques developed to detect and identify viruses.
Many introduced diseases have been transferred around the world, and their origins are difficult, if not impossible to determine (Granzhorn et al. 1992). The probability of establishment decreases with the complexity of the life cycle of a pathogen.
Several attempts to list the internationally transferred fish parasites have been made (Malevitskaya 1958a,b; Reichenback-Klinke 1961; Kulakovskaya and Krotas 1961b; Hoffman 1967; Hoffman 1970; Bauer and Strelkov 1972; Volovik et al. 1974; Bauer and Hoffman 1976; Gratzek et al. 1976, 1978; Hoffman 1981a), but the records are probably incomplete (Hoffman and Schubert 1984). To identify the established species of nonindigenous pathogens in Florida, we contacted several fish diagnosticians who are familiar with fish diseases in Florida. However, we were unable to determine from Hoffman (1967) and Hoffman and Schubert (1984) which nonindigenous species are presently in Florida. Most, if not all pathologists identify the pathogens to only genus level, which suffices to recommend suitable treatment but not to determine whether the genus is nonindigenous or native. This is particular true of genera with worldwide distributions. Some diagnosticians felt that many species listed by Hoffman (1967) were in fact indigenous to the United States. Some expressed concern that identifying the nonindigenous pathogens in Florida results in more regulations for Florida's aquaculture industry by irresponsible regulatory agencies whose personnel do not understand diseases or epidemiology. However, most basically agreed that many warmwater fish diseases elsewhere in the United States had at one time or another appeared in Florida, especially, when the fishes were under stress. The diagnosticians generally agreed that any pathogen that is host specific to an exotic species is probably also exotic. Some agreed that some pathogens that now occur in other countries may have been transported with exported fishes from the United States. The lack of a national system to prevent the movement of infected warmwater fishes between regions of this country--such as exists for coldwater fishes--is partly responsible for the spread of the pathogens (Hoffman 1970). Many pathogens do not appear until the fishes are under stress from handling, crowding, poor nutrition, or poor water quality (personal observation).
A 1977 survey of 46 comprehensive necropsies of pet fishes in Florida revealed 59% of all fishes carried pathogenic bacteria, 44% had ecologically related diseases, 35% carried protozoan, 28% carried trematodea, 13% carried nematodea, 2% carried dinoflagellates, 2% carried hirundinea, 2% carried crustacea, 2% carried insecta, and 2% had hereditary abdomalities (Meryman 1978). More than 95% of the new infectious fish diseases in Florida are found in newly imported shipment of fish (Meryman 1978). Meryman (1978:234) stated that "The leniency of United States fish health inspections and inadequate research funding has caused a lack of information on diseases in the Florida pet fish industry."
Hoffman and Schubert (1984) pointed out that significant damage to wild fishes from any parasite is usually difficult to demonstrate, but the number of parasites tends to increase and parasites become pathogenic when the host fishes are placed in intensive culture or in confined areas (crowded) such as aquariums or tanks or are transferred to other countries where they are not already present. Host-specific, nonindigenous parasites will probably not become a problem for other species in the country in which they are newly introduced (Hoffman and Schubert 1984). However, parasites such as protozoa (other than blood inhabitants), monogeneans, leeches, and parasitic crustacea that require no intermediate hosts could continue to exist in the exotic species and become a problem if cultured intensively. In their countries of origin, most parasites, however, are adequately controlled Hoffman and Schubert (1984). Parasites that need alternate hosts (trematodes, cestodes, nematodes, acanthocephalans) probably do not survive if the alternate host is not present in the new country. Many non-host-specific parasites have already been transferred to other countries (Hoffman and Schubert 1984). Some are dangerous and should always be eliminated from all shipments.
Gratzek (1980) presented an overview of the diseases of ornamental fishes. He reported that most (60%) aquarist who discontinue keeping fishes do so because the fishes die. He identified common problems with keeping ornamental fishes and stated that the treatment of diseased fishes is the most common problem. Each important disease and parasite of cultured fishes was illustrated and described to aid the aquarist with identification. Aldridge and Shireman (1987) discussed the common diseases and parasites of cultured fishes in Florida and provided information sources for the identification and treatment of common fish diseases.
Based on Hoffman (1970) and Hoffman and Schubert (1984), the introduced nonindigenous pathogen species in the United States are protozoans (12), trematodes: monogenea (24), trematodes: digenea (2), cestodes (1), nematodes (2), copepodes (2), acanthocephalians (1), and isopodes (2). Many have become parasites of indigenous fishes and are now in fishes in Florida. The following information about the nonindigenous pathogens in the United States was taken from Hoffman (1970) and Hoffman and Schubert (1984). Species that are marked with an asterisk are believed to have been introduced into Florida because the pathogen is host specific to introduced nonindigenous fishes in Florida or the biology of the species is similar to that of already established other species or was recently imported (Table 2). Published information on the continued presence of many of these species in Florida is not available. Many pathogens were first discovered when an outbreak occurred, and clear evidence that a pathogen was recently introduced is also not available. Many times the pathogen is only identified to a taxonomic level, frequently to only genus level, to facility an appropriate treatment or control--if one exists. Because one genus may contain indigenous and nonindigenous species to the United States, determination of the status of a pathogen as native or indigenous is difficult. Published details on introductions of the subsequently described species is rarely available.
Protozoa
Dermocystidium koi Hoshina and Sahara 1950. This parasite was in the skin of the common carp (Cyprinus carpio; including Koi carp) and is native to Japan. This parasite has also been in common carp from Korea and in Koi carp in the United States (Migaki et al. 1981).
Ichthyophthirius multifiliis Fouquet 1876. This parasite probably originated in Asia (Hoffman 1970, 1981a) and, because of the lack of host specificity, has been transferred by many fishes throughout the temperature zone. This species is not only a serious problem in hatcheries and in fish farms but is also a major problem in pet stores and in aquariums. It costs thousands of dollars each year for treatment of affected fishes and destroys large numbers of fishes. Economically, this is the most destructive freshwater- fish parasite and its transfer should be denied to places where it is now absent (Hoffman and Schubert 1984). This species is on fishes in Florida.
*Mitraspora cyprini Fujita 1912 (Hofferellus; Sphaerospora cyprini). This parasite causes kidney enlargement and death of goldfishes in Japan (Ahmed 1973, 1974). It has been reported from carps from the Amur River (Bykhovskaya-Pavlovskaya et al. 1962) and from goldfishes from the United States (Hoffman 1981a, 1981b).
Myxosoma cerebralis (Plehn 1904). This species is restricted to the Family Salmonidae and is not believed to be in fishes in Florida.
*Oodinium pillularis. The origin of this species is unknown, but it is believed to be nonindigenous to the United States (Hoffman 1970). It is cosmopolitan and in many fish species (Reichenbach-Klinke 1961).
*Pleistophora hyphessobryconis Schaperclaus 1941. This species is a destructive muscle parasite of ornamental fishes including goldfishes (Dykova and Lom 1980). Most reports are from Europe, but in the United States it has been seen in Metynnis spp. from Brazil (Hoffman and Schubert 1984) and Paracheirodon innesi from South America (Hoffman and Schubert 1984).
*Protopalina symphysodonis Foissner, Schubert, and Wilbert 1979. This species was shipped from Bangkok to Europe and into the United States. Small numbers of it are in the intestines of adult Symphysodon, but often many are in fry and seemingly kill them (Hoffman and Schubert 1984).
*Sphaerospora carassii Kudo 1919. This species is a gill pathogen of goldfishes, common carp, and grass carp in Europe (Molnar 1979). It has recently been found in goldfishes in the United States (Hoffman and Schubert 1984).
*Spironucleus elegans Lavier 1936. This species is a close relative of Hexamita spp. and in the intestines of many ornamental fishes, particularly in South American cichlids (Family Cichlidae) . It often kills fry of Pterophyllum and Symphysodon. It readily invades tissues when Capillaria pterophylli, which damages intestinal mucosa, is present. Spironucleus elegans is often seen in Europe and North America and probably worldwide (Molnar 1982).
*Trichodina reticulata Hirschmann and Partsch 1955. This parasite of goldfishes was described from Europe but probably originated in Asia (Hoffman 1970). It has been on goldfishes in Arkansas (Hoffman and Schubert 1984), Alabama, Mississippi, Louisiana, Georgia, Kentucky, South Carolina (Wellborn 1967), and Pennsylvania (Lom and Hoffman 1964).
*Trichodina subtilis Lom 1959. This parasite was on the gills of goldfishes and other fishes in Eurasia (Lom and Haldar 1977) and in the United States (Lom and Hoffman 1964; Hoffman 1978).
*Trichodinella epizootica (Raabe 1950, Sramek-Husek 1953). This species was probably moved from Asia to Europe on the gills of goldfishes (Hoffman 1970) and other fishes (Lom 1970; Lom and Haldar 1977; Hoffman 1978) and to the United States (Lom and Hoffman 1964; Hoffman and Schubert 1984). This dangerous parasite has seemingly become widely distributed (Hoffman and Schubert 1984).
Some protozoans, Ichthyophthirius multifiliis, Ichtyobodo necatrix, Chilodonella cyprini, C. hexasticha, and certain trichodinids are among the most damaging parasites of fishes and should never be transferred. Possibly equally dangerous new species will be found during transfer of exotics. However, because of the many completed shipments of exotic fishes, the appearance of comparable new problems is unlikely (Hoffman and Schubert 1984)
Monogenea (gill and skin flukes)
Many monogenetic trematodes have been transferred with their hosts (Hoffman 1970; Bauer and Hoffman 1976). They are easily transferred because no intermediate host is necessary. Some destroy their hosts, but most are specific for one species of fish or for two or more closely related species. Nevertheless, transfers to new locations are undesirable (Hoffman and Schubert 1984). Because of high host specificity, most Monogenea do not spread to other fish species when they are introduced with their hosts into a new habitat. But they may become more dangerous to their hosts in the new surroundings (Hoffman and Schubert 1984). Monogenea of food fishes have also been transferred to many countries, mostly in the temperate zone--Asia, Europe, and North America-- where fish culture has increased. Such transfers were reviewed by Hoffman (1970) and Bauer and Hoffman (1976). Monogenea of ornamental fishes have been transferred throughout the world. They usually do not attack other fishes, but transfer should be avoided because the parasites of many tropical fishes have not been thoroughly studied (Hoffman and Schubert 1984). The number of parasites that were introduced into the United States is unknown. Hoffman (1970) listed nine species that are known to have been transferred: Anacanthorus anacanthorus, Dactylogyrus anchoratus, D. vastator, D. wegeneri, Gyrodactylus bullatarudis, G. elegans, Urocleidoides reticulatus, Urocleidus crescentis, and U. orthus.
*Anacanthorus anacanthorus, A. brazielensis and A. neotropicalis have been on the gills of the redbreasted piranha (Serrasalmus nattereri), which was introduced into the United States from South America (Mizelle and Price 1965).
Anacanthorus brevis (Mizelle and Kritsky 1969a). This species was taken from the gills of Brycon melanopterus. It was transferred from Brazil to the United States (Hoffman and Schubert 1984).
Archidiplectanum archidiplectanum (Mizelle and Kritsky 1969b). This species was taken from the gills of Gnathonemus petersi. It was transferred from western Africa to the United States (Hoffman and Schubert 1984).
*Cichlidogyrus spp.This parasite was on the gills of Tilapia spp. and was transferred from Africa to United States in 1960 on T. mossambica (Hoffman 1970).
Cleidodiscus amazonensis, C. piranhus, and C. serrasalmus. This parasite was on the gills of the redbreasted piranha that were transferred from South America to United States (Mizele and Price 1965).
*Dactylogyrus anchoratus Dujardin 1845; Wegener 1857. This parasite was on goldfishes. It probably originated in Asia and was transferred to the United States (Price and Mizelle 1964).
*Dactylogyrus extensus Mueller and Van Cleave 1932. This parasite was on the gills of common carp. It has been transferred from Europe to the United States and Israel (Paperna 1964).
Dactylogyrus vastator Nybelin 1924. This species was on the gills of goldfishes. It probably originated in Asia (Price and Mizelle 1964).
*Dactylogyrus wegeneri Kulwiec 1927. This parasite was on goldfishes and was probably transferred from Europe or Asia (Price and Mizelle 1964).
Dactylogyrus minutus. This parasite of the common carp is well known in Europe and in Central Asia and has been found in the United States (Hoffman and Schubert 1984).
Dactylogyrus baueri and D. formosus. Both parasites are on the gills of goldfishes and were transferred from Japan to the United States (Rogers 1967).
*Gyrodactylus cyprini (Diarova 1964). This species is a parasite of the common carp and is well known in Europe and Central Asia. It occurs in the United States (Rogers 1968).
*Gyrodactylus elegans. This species is a parasite of the goldfish, probably originated in Asia, and then transferred to Europe and to the United States (Malmberg 1962).
Heteronocleidus gracilis was on the gills of Colisa labiosa (Mizelle and Kritsky 1969b) and probably transferred from India to California (Hoffman and Schubert 1984). There is no record of it in Florida.
Longihaptor longihaptor was on gills of Cichla ocellaris (Mizelle and Kritsky 1969a) and was transferred from Brazil to the United States (Hoffman and Schubert 1984).
*Pseudacolpenteron pavlovskyi is a parasite of the common carp and was transferred to Israel and the United States (Hoffman and Schubert 1984).
*Trianchoratus acleithrium Price and Berry 1966. This parasite was taken from the gills of Helostoma rudolfi and was imported from Malaysia into the United States (Mizelle and Kritsky 1969a).
*Urocleidoides amazonensis (Mizelle and Kritsky 1969a) was on the gills of Phractocephalus hemiolopterus and was transferred from Brazil to the United States (Hoffman and Schubert 1984).
Urocleidoides catus (Mizelle and Kritsky 1969a). This parasite was on the gills of Phractocephalus hemiolopterus and was transferred from Brazil to the United States (Hoffman and Schubert 1984).
Urocleidoides megorchis (Mizelle and Kritsky 1969a) attacks the gills of Sorubim lima and was transferred from South America to the United States (Hoffman and Schubert 1984).
Urocleidoides reticulatus Mizelle and Price 1964. This parasite was on a guppy (Lebistes reticulatus) and was transferred from Trinidad to California (Mizelle and Price 1965).
*Urocleidoides robustus. This parasite was on the gills of Symphysodon discus (Mizelle and Kritsky 1969a) and transferred from Brazil to the United States.
Urocleidus crescentis and U. orthus. These parasites were on the gills of redbreasted piranha and were transferred from South America to the United States (Mizelle and Price 1965).
Trematoda, Digenea
Manter (1963) believed that the intestinal trematode Crepidostomum farionis of salmonids was transferred from Europe to North America in trout and became established (Hoffman and Schubert 1984). Because this pathogen is restricted to salmonids, it is not established in Florida.
Bolbophorus confusus. This Eurasian strigeid trematode probably came to the United States in a stray pelican, its natural final host (Hoffman 1970). Hoffman and Schubert (1984) found it in fathead minnows (Pimephales promelas) that were shipped from South Dakota to Arkansas. This species has not been seen in Arkansas since its reported introduction and may not have become established. No record of this species in Florida could be found, but fathead minnows are frequently shipped into Florida from Arkansas as bait, and the trematode could have been introduced into the state.
Cryptocotyle lingua. This species has been in coastal marine fishes in the United States. It was probably carried by European snails on ships from Europe to the East Coast of the United States about 100 years ago (Sindermann and Farrin 1962).
Cestoda
Cestodes require at least one and often two intermediate hosts. Although this requirement complicates relocation of parasite species, some have been transferred.
*Bothriocephalus opsarichthydis (B. acheilognathi, B. gowkengensis). This pseudophyllaeid cestode was introduced into the United States with the importation of grass carp and acquired a new host, the common carp. The common carp is infected between the ages of 2 months and 3 years because it feeds on microcrustaceans, the intermediate host of the parasite (Hoffman and Schubert 1984). Since its initial introduction, the cestode has been reported in cultured bait minnows--the golden shiner (Notemigonus crysoleucas) and the fathead minnow (Pimephales promelas)-- in North America. Later Hoffman (Fish Farming Experimental Station, U.S. Fish and Wildlife Service, Stuttgart, Ark., unpublished data) found it in mosquitofishes (Gambusia affinis; Hoffman and Schubert 1984). It presumably traveled by air shipments in grass carp from Asia. Since then, it has been in mosquito fishes in North Carolina and in California. W. Rogers at Auburn University (Hoffman and Schubert 1984) found B. opsarichthydis in channel catfishes, but it is rarely in a nonplankton feeder. Recently, Hoffman and Schubert (1984) found it in an American endangered fish, the Colorado squawfish (Ptychocheilus lucius), from a fish hatchery in New Mexico.
Nematoda
*Philometra sanguinea (P. carassii). This parasite is a specific parasite of goldfishes and infects the blood vessels of fins (Vismania and Nikulina 1968). It was presumably transferred from Japan to North America by fish hobbyists (Hoffman 1970).
*Camallanus cotti. This species, originally described from fishes in Japan (Fujita 1927), became established in ornamental fish culture and turned up in Malaysia, Europe, the United States, and Australia (Stumpp 1975).
Copepoda and Branchiura, Parasitic
*Argulus japonicus Thiele 1900 Linnaeus. This branchiuran has been transferred to Africa (Fryer 1960), Ceylon (Kirtisinghe 1964), Israel (Paperna 1964), New Zealand (Hine 1975), and North America (Cressey 1978). Although seemingly lacking host specificity, it is usually on goldfishes and on common carp. It also occurs in Japan and China (Yamaguti 1963).
*Lernaea cyprinacea Linnaeus 1758. This devastating copepod has been reported from many species of freshwater fishes and from frog and salamander tadpoles in Africa, Asia, Europe, Israel, Japan, Eurasia, and the United States. In the [former] U.S.S.R., it is known as Lernaea elegans and as a host-specific parasite of goldfishes; however, most parasitologists know it as L. cyprinacea. It probably originated in Asia and spread with the goldfish trade (Hoffman 1970).
Isopoda
Artystone trysibia. This species was imported from Colombia, South America, into the United States in Corydoras. It burrows into fishes and lives in the wound hole (Hoffman and Schubert 1984).
*Lironeca symmetrica (often reported as Livoneca). This species was imported on ornamental fishes from South America to the United States. It has become an established parasite and damages many exotic fishes (Herwig 1976).
Acanthocephala
*Polyacanthorhynchus kenyensis Schmidt and Canaris, 1967. Juvenile forms of this parasite have been in the liver of Micropterus salmoides and Tilapia spp. This species was probably transferred from South America to North America (Schmidt and Canaris 1967).
