Robin M. Overstreet

Synopsis of freshwater crayfish diseases and commensal organisms

Disease agents and pests associated with freshwater crayfish fall into six main categories—viruses, bacteria, rickettsia-like organisms (RLOs), fungi, protists and metazoans. Data and information on specific disease agents and pests from each of these categories are presented in this synopsis. Each agent or group of agents is considered under the following headings—condition, causative agent(s), life cycle/life history, epizootiology, pathology, pathogen viability. Information for the synopsis was obtained from the published literature and from personal contact with internationally recognised experts in freshwater crayfish aquaculture, biology and disease. Data of relevance for import risk analysis are summarised. Import risk analysis is the process by which the risks associated with importation of animals and plants, and products derived from animals and plants, are assessed and managed. Hazard identification is essential and is the first component of an import risk analysis. In 1996, the Australian Quarantine and Inspection Service (AQIS) commenced a review of policy relating to the importation of non-viable freshwater crayfish products, along with a suite of other aquatic animal products. AQIS commissioned a synopsis of freshwater crayfish pests and pathogens for use as a resource document for hazard identification in the formal IRA process.

Parasites of some penaeid shrimps with emphasis on reared hosts

Abstract Information is presented about parasites and commensals of penaeid shrimps, allowing those who rear shrimps and those who are interested in associated organisms of shrimp to have a better knowledge of the organisms that are or may be associated with brown, white, and pink shrimps. It covers common and rare organisms and diseases, primarily in the northern Gulf of Mexico, listing several previously unreported species including an undescribed gregarine, a larval nematode ( Spirocamallanus pereirai ), a commensal nematode ( Leptolaimus sp.), a leech ( Myzobdella lugubris ), a blue-green alga ( Schizothrix calcicola ), a hydroid ( Obelia bicuspidata ), and others. A possible relationship between the peritrich ciliate, Zoothamnium sp., and predilection to mortality following stress is discussed. Comparative data are given for organisms from brown and white shrimp from different ponds and the natural environment between 1969 and 1972 at Grand Terre, Louisiana. Also reported are organisms observed in or on shrimp from floating cages in Alabama and ponds in Florida and Texas, as well as wild stock from Mississippi and Georgia.

SOME PARASITES AND DISEASES OF ESTUARINE FISHES IN POLLUTED HABITATS OF MISSISSIPPI

Diseases that afflict aquatic animals living in waters suspected or known to be polluted are described. The following pollutants are discussed with regard to their effects on the environment and the animals of the estuaries; pesticides, industrial chemicals, heavy metals, and fecal pollution. Microorganisms are discussed with regard to public health and fish health. Transmission of the virus of infectious hepatitis by oysters is emphasized. Parasitic diseases are discussed with regard to life cycle of the parasite, effects of pollution on intermediate hosts, and host specificity. Diseases caused by various helminth and protozoan parasites are described. Nonparasitic diseases discussed are integumental hyperplasia, liver disease, and various neoplasms. (HLW)

Carcinogenicity tests with small fish species

Abstract Development of carcinogenesis bioassays that utilize small fish species is important principally for investigating the causes of neoplasms in wild fishes and for providing alternative or supplementary models to rodent carcinogenicity tests. Availability, economy, latency of tumorigenic response, and ease of maintenance and exposure are commonly cited advantages of small fish species in carcinogenesis bioassays. Carcinogen metabolism and mechanisms of carcinogenesis in several small fish species appear similar to those processes in the more thoroughly studied large fish species as well as in rodents. Recent studies suggest that small fish species are appropriate test models for waterborne carcinogens having a variety of mechanisms. Several small fish species readily develop hepatic and non-hepatic neoplasms following brief static exposures to direct-acting genotoxic compounds such as methylazoxymethanol acetate (MAM-Ac) and N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). Tumorigenic responses appear to be related to species and to various exposure factors. Indirect-acting genotoxic carcinogens such as nitrosamines and polynuclear aromatic hydrocarbons have not been thoroughly tested in small fish species but appear to require longer exposures than direct-acting ones to induce hepatic neoplasms. An especially important potential use of small fish carcinogenesis bioassays is in testing carcinogens that might have epigenetic mechanisms, especially complex mixtures that might affect man or the environment but are difficult to test in rodent models. Preliminary studies indicate that prolonged exposures of up to 6 months to a mixture of halogenated organic compounds result in hepatic neoplasms in two small fish species. To improve their usefulness and exploit small fish carcinogenesis models better, gaps in several areas need to be filled. These include (1) a better understanding of biological and nutritional requirements of test species as related to carcinogenesis, (2) a broader database on neoplastic responses of various species to various chemicals, and (3) development of special exposure methods and standardization of test protocols.

Carcinogenic effects of some polycyclic aromatic hydrocarbons on the Japanese medaka and guppy in waterborne exposures

In this paper, we review studies on the carcinogenic effects of two polycyclic aromatic hydrocarbons (PAHs), benzo(a)pyrene (BaP) and 7,12-dimethylbenz(a)anthracene (DMBA), on the Japanese medaka (Oryzias latipes) and the guppy (Poecilia reticulata). Exposure media were prepared by adding PAHs to water, with and without dimethylformamide (DMF) as a carrier, and passing this solution through various sized filters. The low exposure medium was a 0.45 micron filtrate without DMF that contained less than 5 micrograms L-1 PAH. The intermediate medium was a DMF-mediated 0.45 micron filtrate which contained 30-50 micrograms L-1 of PAH. The high medium was a DMF-mediated glass-fibre filtrate which contained 150-250 micrograms L-1 of PAH. Young fish specimens (6-10 d old) were given a 6 h exposure once weekly for 2 to 4 wk. Both BaP and DMBA induced hepatic neoplasms in the two species, with the medaka being more sensitive than the guppy, and DMBA being a stronger carcinogen than BaP. Liver neoplasms almost exclusively developed after exposure to BaP and the neoplasms were limited to the high concentration exposure, whereas DMBA caused a substantial number of extrahepatic neoplasms as well as hepatic ones, especially in the medaka. Furthermore, all three concentrations of DMBA induced hepatic neoplasms in the medaka and all but the low concentration induced neoplasms in the guppy. These studies demonstrate the carcinogenic effects of two waterborne PAHs on two small fish species following brief exposures to very low concentrations, and support the contention that environmental PAHs can contribute to the occurrence of cancer in wild fishes.

Evolution of the trypanorhynch tapeworms: Parasite phylogeny supports independent lineages of sharks and rays

Trypanorhynch tapeworms (Platyhelminthes: Cestoda) are among the most diverse and abundant groups of metazoan parasites of elasmobranchs and are a ubiquitous part of the marine food webs that include these apex predators. Here we present a comprehensive analysis of their phylogeny, character evolution and host associations based on 10years of sampling effort, including representatives of 12 of 15 and 44 of 66 currently recognized trypanorhynch families and genera, respectively. Using a combination of ssrDNA and lsrDNA (Domains 1-3) for 79 and 80 taxa, respectively, we maintain one-to-one correspondence between molecules and morphology by scoring 45 characters from the same specimens used for sequencing, and provide museum vouchers for this material. Host associations are examined through likelihood-based ancestral character state reconstructions (ACSRs) and by estimating dates of divergence using strict and relaxed molecular clock models in a Bayesian context. Maximum parsimony and Bayesian inference analyses of rDNA produced well-resolved and strongly supported trees in which the trypanorhynchs formed two primary lineages and were monophyletic with respect to the diphyllidean outgroup taxa. These lineages showed marked differences in their rates of divergence which in turn resulted in differing support and stability characteristics within the lineages. Mapping of morphological characters onto the tree resulting from combined analysis of rDNA showed most traits to be highly plastic, including some previously considered of key taxonomic importance such as underlying symmetries in tentacular armature. The resulting tree was found to be congruent with the most recent morphologically based superfamily designations in the order, providing support for four proposed superfamilies, but not for the Tentacularioidea and Eutetrarhynchoidea. ACSRs based on the combined analysis of rDNA estimated the original hosts of the two primary parasite lineages to be alternatively rajiform batoids and carcharhiniform sharks. This fundamental split provides independent support for rejecting the notion that rays are derived sharks, and thus supports the most recent molecular phylogenies of the Neoselachii. Beyond the basal split between shark- and ray-inhabiting lineages, no pattern was found to suggest that the trypanorhynchs have closely tracked the evolutionary histories of these host lineages, but instead, it appears that host-switching has been common and that the subsequent evolution of the parasites has been ecologically driven primarily through overlap in the niches of their shark and ray hosts. Using a relaxed molecular clock model calibrated by means of host fossil data, the ray-inhabiting lineage is estimated to have diversified around the Jurassic-Cretaceous boundary, whereas the shark-inhabiting lineage is estimated to have diversified later, in the Middle Cretaceous. Although the large error associated with the estimated divergence dates prevents robust conclusions from being drawn, the dates are nevertheless found to be consistent in a relative sense with the origins of their major hosts groups. The erection and definition of the suborders Trypanobatoida and Trypanoselachoida, for the major clades of trypanorhynchs parasitizing primarily rays and sharks, respectively, is proposed for the two primary lineages recovered here.

Dose-related carcinogenic effects of water-borne benzo [a] pyrene on livers of two small fish species

Benzo[a]pyrene (BaP) administered by water-borne exposures caused dose-related carcinogenic effects in livers of two small fish species, the Japanese medaka (Oryzias latipes) and the guppy (Poecilia reticulata). Medaka and guppies each were given two 6-h exposures. The first exposure was conducted on 6- to 10-day-old specimens. The second exposure was given 7 days later. The tests incorporated five treatment groups: (1) control, (2) carrier (dimethylformamide) control, (3) low BaP dose (not detectable--4 ppb), (4) intermediate BaP dose (about 8-47 ppb BaP), and (5) high BaP dose (200-270 ppb). Following the high-dose exposure, hepatocellular lesions classified as foci of cellular alteration (altered foci), adenomas, and hepatocellular carcinomas occurred in both species. In medaka, the lesions appeared to develop sequentially with the appearance of altered foci followed by adenomas and then hepatocellular carcinomas. Most lesions in guppies, however, were classified as altered foci although a few adenomas occurred in the early (24-week) sample and hepatocellular carcinomas occurred in the late (52-week) sample. When total lesions were combined, medaka had an 11% incidence at 24 weeks after the initial exposure and 36% incidence at 36 weeks. In guppies, 8% had liver lesions at 24 weeks, 19% at 36 weeks, and 20% at 52 weeks. A single extrahepatic neoplasm, a capillary hemangioma in a gill filament, occurred in a medaka from the 36-week high-dose sample. The results suggest that the medaka and guppy are capable of metabolizing water-borne BaP to carcinogenic metabolites which initiate hepatic tumor development.

Biology and pathogenesis of the coccidium Eimeria funduli infecting killifishes.

Epizootics of Eimeria funduli involved estuarine killifishes (Fundulus grandis, F. pulvereus, F. similis, and F. heteroclitus) in Mississippi, Alabama, and Virginia. All of more than 500 specimens examined of F. grandis from Mississippi during 1977 though 1979 had infections, regardless of age, sex, or season collected. Oocysts occurred primarily in the liver and pancreas, replacing up to 85% of both those organs. Infrequent sites of infection were fatty tissue of the body cavity, ovary, intestine, and caudal peduncle. Living fish did not discharge oocysts. Eimeria funduli is the first known eimerian to require a second host. To complete the life cycle, an infective stage in the grass shrimp Palaemonetes pugio had to be eaten. In 6-mo-old killifish reared in the laboratory at 24 C, young schizonts were first observed in hepatic and pancreatic cells 5 days postfeeding, followed by first generation merzoites by day 10, differentiation of sexual stages during days 15 to 20, fertilization between days 19 and 26, sporoblasts from days 25 to 30, and sporozoites about day 60. Unique sporopodia developed on sporocysts by day 35 when still unsporulated. Temperatures of 7 to 10 C irreversibly halted schizogony. Both schizogony and sporogony progressed slower as age of host increased. When infective shrimp in doses ranging from 1 to 10% of a fishs body weight were eaten, the level of intensity of resulting infections did not differ significantly. Pathogenesis followed a specific sequence, with the host response apparently unable to contend with extensive infections as seen typically in nature and in our experiments. Premunition was indicated. When administered Monensin orally, infected fish exhibited a reduction in oocysts by 50 to 70% within 20 days as compared with untreated fish. Furthermore, infected killifish exclusively on a diet of TetraMin for 3 mo completely lost their infections.

Aquatic pollution problems, Southeastern U.S. coasts: histopathological indicators

Abstract Pollutants cause lesions and affect parasitic infections in numerous finfishes and shellfishes in the southeastern United States as well as in many other parts of the world. The relatively high water temperature in this region may augment the effects of contamination from specific domestic, agricultural, and industrial sources. Because of the lack of detailed cause-and-effect studies in the Southeast, individual toxicants or combinations of toxicants have not been related to specific histopathological conditions. Nevertheless, a variety and abundance of specific and general pathological indications of pollution occur in marine and estuarine species along the southern U.S. coasts of the North Atlantic Ocean and the northern Gulf of Mexico. Among those occurring in several polluted regions are striped mullet with mesenchymal neoplasms; sciaenid and other fishes with lymphocystis; fishes with ulcers, red sores, fin erosion, and granulomas; and crustaceans with shell disease. Other indications include specific cytotoxic, neoplastic, and developmental lesions in addition to specific microbial and metazoan parasites and diseases that occur in animals from specific locations or regions. Improved protocols are needed to distinguish toxicant-induced and toxicant-modified communities, species, individuals, and lesions from those that may be similarly affected by natural environmental factors.

Monogenean infestations and mortality in wild and cultured Red Sea fishes

Hyperinfection by the gill-infesting monogeneanAllobivagina sp. (Microcotylea) caused mass mortalities in juveniles ofSiganus luridus cultured in seawater earthen ponds and holding tanks in Eilat (Gulf of Aqaba, Red Sea). Other species ofSiganus and adults ofS. luridus cultured in the same systems acquired a low intensity of infestation. Most hyperinfected fish were emaciated and anaemic with hematocrit values below 10 %. Skin and mouth infestations by the monogeneanBenedenia monticelli (Capsaloidea) caused mass mortalities in grey mullets (Mugilidae). These mortalities occurred in large individuals in wild populations ofLiza carinata from lagoonal habitats in the Gulf of Suez and in most species of grey mullets cultured in Eilat. The intensity of infestation correlated positively with severity of infestation, and the common sites of infestation corresponded with areas of severe pathological alterations. Spontaneous recovery followed the climax of an epizootic, both for infestedS. luridus and infested grey mullets. Decline in infestation coincided with remission of the pathological signs.