Book Review: Diseases of fish by L. E. Mawdesley-Thomas, K. W. Burris, and J. L. Knuckles et al.
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During the IVth International Conference on Lyme Borreliosis in Stockholm, 1990, a workshop on control of Lyme disease vectors briefly reviewed: basic ecological principles for tick control; biocontrol of ticks; chemical control, including the use of repellents and use of permethrin-treated rodent nest material; tick control by habitat modification; and reduction of tick host availability. It was concluded that, although much research work remains, Lyme borreliosis is to a large extent a preventable infection. Avoidance of heavily tick-infested areas, personal protection using proper clothing, and prompt removal of attached ticks remain the most effective protective measures. Many other prophylactic measures are available and could be efficiently integrated into schemes to reduce the abundance of vectors. However, since the ecology of the infection varies greatly between different localities it may be necessary to apply different combinations of control methods in different endemic regions.
The dot blot assay, modified and adapted for detection of antigens from Vibrio anguillarum in fish tissues, was specific for V. anguillarum and did not react with antigens of V. ordalii , Pseudomonas sp., or Yersinia ruckeri . The blot assay enabled detection of as little as 2.3 ng of a mixture of protein antigens obtained from cell-free extracts of V. anguillarum ; it was about 100 times more sensitive than either the indirect fluorescent antibody technique or bacterial isolation for detecting V. anguillarum in fish tissues.
Studies were performed to determine if increasing water temperatures could control infectious hematopoietic necrosis virus (IHN) disease in sockeye salmon ( Oncorhynchus nerka ). Mortalities could be prevented if the water temperature was raised to at least 18 C within the first 24 hr after infection of the fish and if the fish were maintained at this temperature for 4–6 days. The disease did not recur after the elevated temperature treatment, but the fish would still contract the disease if they were reinfected. Reasons for the protecting action are discussed.
Moving 4–5-in. coho salmon ( Oncorhynchus kisutch ) held in soft (20 ppm CaCO 3 ) water from the relatively light loading density of 0.5 lb/ft 3 to 1, 2, or 4 lb/ft 3 (density index, DI = 0.1, 0.2, 0.4, 0.8) caused significant stress as indicated by loss of feeding behavior, but only minimal physiological disturbances, as indicated by lack of hyperglycemia or hypochloremia. However, moving them to 6 or 12 lb/ft 3 (DI = 1.2, 2.4) caused significant physiological stress which required at least a week for recovery. Smolting coho salmon were physiologically stressed by population densities of 1 lb/ft 3 or more and a subclinical corynebacterial kidney infection was activated. Rainbow trout ( Salmo gairdneri ) (4–5 in.) were physiologically stressed when moved and held at 1 lb/ft 3 or more but retained normal feeding behavior. This indicates that handling and crowding stress will be minimized in softwater areas if densities in fish distribution trucks or in ponds or raceways during disease treatments are held to 0.1–0.5 lb/gal.
A description was given of a gram-negative, peritrichously flagellated, fermentative bacterium that was isolated on numerous occasions from kidney tissues of rainbow trout ( Salmo gairdneri ) afflicted with redmouth disease. Although the bacteria apparently were members of the family Enterobacteriaceae, it was impossible to determine their taxonomic position within the family with certainty. Hence it was recommended that their taxonomic position remain sub judice for the present. As a temporary designation RM bacterium was used. Redmouth disease was transmitted from infected to normal fish through the medium of water.
Surveying for flying squirrels by using traditional techniques produces extremely low detection rates compared with ultrasonic acoustics. Within Pennsylvania, the northern flying squirrel subspecies Glaucomys sabrinus macrotis is state listed as endangered due to habitat loss and parasite-mediated competition by and hybridization with the southern flying squirrel Glaucomys volans . This subspecies is isolated from adjacent populations in West Virginia and New York and has experienced drastic population declines. The discovery and characterization of ultrasonic vocalizations of G. s. macrotis and G. volans , as well as successful field surveys with ultrasonic acoustic detectors in the southern Appalachian Mountains, highlight the potential use of this technique for determining the presence of G. s. macrotis . To confirm the feasibility of using this technique on declining populations of G. s. macrotis sympatric with G. volans , we conducted 108 nights of passive ultrasonic acoustic surveys for G. s. macrotis at six survey sites by using two detectors per survey site ( N = 12 detectors) in June 2017. We considered sites high quality (“high”) or low quality (“low”) based on the number of physical capture records during the past 2 decades and the dominance of boreo-montane conifer tree species in the overstory. We detected G. s. macrotis at four study sites and G. volans at all six study sites. We found higher average probability of detection for G. s. macrotis in high vs. low sites (0.28 ± 0.06 [mean ± SE] and 0.09 ± 0.07, respectively), whereas probability of detection was similar for G. volans between high and low sites (0.13 ± 0.05 and 0.17 ± 0.05, respectively). We also found G. s. macrotis had lower latency of detection at high vs. low sites (2.7 ± 0.8 and 7.83 ± 1.5 nights, respectively) but G. volans did not vary in latency of detection between sites (5 ± 1.6 and 3.8 ± 1.5 nights, respectively). Our study shows acoustics can be successfully used to efficiently survey G. s. macrotis in Pennsylvania, where populations are small and monitoring these populations more effectively is critical to determining changes in persistence due to climate- and disease-induced factors.
An epizootic of type E botulism (Clostridium botulinum) occurred among common loons (Gavia immer) along the Lake Michigan shore of Michigan's Upper Peninsula (USA) during October and November 1983. An estimated 592 dead loons washed ashore along the Garden Peninsula. Type E botulinal toxin was demonstrated in blood samples and stomach contents of dead loons, and in samples of three species of dead fish found on the Lake Michigan shore. We suspect that loons acquired botulism by ingesting sick or dead fish containing type E toxin.
Fish were sampled at the Ed Weed State Fish Hatchery (South Hero, Vermont, USA) in September 1992. Aeromonas salmonicida was common, with concentrations as high as 10 5 to 10 7 colony-forming units per gram of mucus, and readily recovered from most mucus samples obtained from furunculosis-sensitive populations of brook trout ( Salvelinus fontinalis ), lake trout ( Salvelinus namaycush ), and Atlantic salmon (Salmo salar) . The pathogen was the predominant microorganism and accounted for greater than 85% of the total number of bacteria isolated from the mucus of these fish. By comparison, A. salmonicida was recovered only from two rainbow trout ( Oncorhynchus mykiss ), and bacterial frequencies did not exceed 10 3 colony-forming units per gram of mucus. The pathogen was not recovered from the mucus of steelhead ( O. mykiss ) or Rome brown trout ( Salmo trutta ) selectively bred for resistance to furunculosis, even though there was widespread contagion throughout the hatchery and fish were cultured on a common, unprotected water supply.
Lead poisoning was diagnosed in four spectacled eiders ( Somateria fischeri ) and one common eider ( Somateria mollissima ) found dead or moribund at the Yukon Delta National Wildlife Refuge, Alaska (USA) in 1992, 1993, and 1994. Ingested lead shot was found in the lower esophagus of one spectacled eider and in the gizzard of the common eider. Lead concentrations in the livers of the spectacled eiders were 26 to 38 ppm wet weight, and 52 ppm wet weight in the liver of the common eider. A blood sample collected from one of the spectacled eiders before it was euthanized had a lead concentration of 8.5 ppm wet weight. This is the first known report of lead poisoning in the spectacled eider, recently listed as a threatened species by the U.S. Fish and Wildlife Service.
Objective Research has indicated that salmonids raised in a hatchery and stocked into the wild have lower future survival and reproductive success than wild fish. Understanding whether hatchery rearing practices affect populations after stocking can help to maximize the quality, quantity, and economic value of fish stocked for conservation and recreational purposes. The goal of our study was to test whether and to what extent rearing density affects poststocking survival of Rainbow Trout Oncorhynchus mykiss when stocked into a put-grow-and-take fishery. Methods Rainbow Trout were raised for 3 months in the hatchery at two densities (high = 51,948–13,072 fish/m 3 , rearing index 2.0, 1,260 metric units; low = 12,987–3,268 fish/m 3 , rearing index 0.5, 315 metric units). A subset of the fish were PIT-tagged and stocked into Parvin Lake, Red Feather Lakes, Colorado. Recaptures of tagged fish occurred every 2 weeks for the first 2 months poststocking and at 7 and 12 months poststocking. Results At the time of stocking, there were no statistical differences in Fulton’s condition factor, total length, weight, or hepatosomatic index for each treatment. Recapture data indicated that there was no difference in Fulton’s condition factor and hepatosomatic index after stocking. Apparent poststocking survival was higher for fish raised at low density in the hatchery compared with those raised at high density. Conclusions Our study suggests that rearing density affects fingerling Rainbow Trout poststocking survival. Stocking more fish due to fish being reared at higher densities within the hatchery did not result in more total fish remaining after a year in the lake compared with the low-density treatment. Rearing fish at high densities does not provide a benefit of more fish after stocking and may result in more disease risk in the hatchery.
All trematodes which cause infections and diseases in humans (zoonoses) require snails for their first intermediate host. Some have additional intermediate hosts such as crustaceans, fishes and frogs. In this paper I have discussed the use of various procedures for controlling snail populations thereby reducing the population of trematodes whose cercariae penetrate the skin of man, or which are acquired by eating raw aquatic vegetation such as watercress, or which cause pathology in fish. Biological, chemical, and physical snail control techniques are discussed. The most promising molluscucides are copper compounds, Bayluscide, biocidal rubber and molluscicidal bait.
Causes of population collapse and failed recovery often remain enigmatic in marine forage fish like Pacific herring ( Clupea pallasii ) that experience dramatic population oscillations. Diseases such as ichthyophoniasis are hypothesized to contribute to these declines, but lack of long-term datasets frequently prevents inference. Analysis of pathogen surveillance and population assessment datasets spanning 2007–2019 indicate that the age-based prevalence estimate of Ichthyophonus infection was, on average, 54% greater among a collapsed population of Pacific herring (Prince William Sound, Alaska, USA) as compared to a nearby population (Sitka Sound, Alaska, USA) that is relatively robust. During the study years, the age-based infection prevalence ranged from 14 to 44% in Prince William Sound and 5 to 33% in Sitka Sound. At both sites, the age-based infection prevalence declined over time, with an average decrease of 7% per year. Statistical analyses indicated that infection prevalence between the two populations was reduced by regional factors affecting both sites, and that these factors were independent of herring density. Infection prevalence in both populations was positively correlated with herring age and negatively correlated with the Pacific Decadal Oscillation. This study demonstrates how synthesis of environmental, stock assessment, and disease assessment data can be leveraged to elucidate epidemiological trends in diseases of wild fish.
We experimentally infected juvenile chinook salmon ( Oncorhynchus tshawytscha ) with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), to examine the vulnerability to predation of fish with differing levels of Rs infection and assess physiological change during progression of the disease. Immersion challenges conducted during 1992 and 1994 produced fish with either a low to moderate (1992) or high (1994) infection level of Rs during the 14-week postchallenge rearing period. When equal numbers of treatment and unchallenged control fish were subjected to predation by either northern squaw fish ( Ptychocheilus oregonensis ) or smallmouth bass ( Micropterus dolomieui) , Rs-challenged fish were eaten in significantly greater numbers than controls by nearly two to one. In 1994, we also sampled fish every 2 weeks after the challenge to determine some stressful effects of Rs infection. During disease progression in fish, plasma cortisol and lactate increased significantly whereas glucose decreased significantly. Our results indicate the role that BKD may play in predator-prey interactions, thus ascribing some ecological significance to this disease beyond that of direct pathogen-related mortality. In addition, the physiological changes observed in our fish during the chronic progression of BKD indicate that this disease is stressful, particularly during the later stages.
Mycoses of systemic distribution are rarely observed in fresh-water fish in this country. In a recent review of atypical cell growths in fishes, Nigrelli cited the only known instance of a mycetoma in a North American fresh-water fish which occurred in the head of fingerling landlocked salmon from an Idaho hatchery. The fungus associated with this granuloma was characterized by a branching septate mycelium. Rucker reported a streptomycete which was pathogenic to blueblack salmon. This organism produced internal nodules containing masses of hyphae but no inflammatory response. A pathogenic fungus has been observed frequently in marine fish, however, and in both marine and fresh-water fish in Europe. This organism was tentatively classified as a Phycomycete in or near the order Chytridiales and was assigned to the genus and species Ichthyophonus hoferi , later reclassified as Ichthyosporidium hoferi . The graduloma described in this report occurs in fresh-water trout and is apparently caused by a budding, yeast-like form with no hyphae which evokes a tremendous inflammatory reaction. Morphologically, the organism does not resemble the previously described Ichthyosporidium. The lesions were first seen accidentally in sections prepared from a diplobacillus infection of brook trout termed “kidney disease.” Subsequently, the granuloma was observed in three widely separated infections involving the diplobacillus in each instance. The histological material was received in a fixed condition; thus, no cultural data was available and the nomenclature and classification of the mycotic organism were not attempted. The present distribution of the disease, however, with its potential threat to domestic fish populations, seemed to warrant a description and discussion of the disease. Efforts are in progress to culture the organism.
Review of: Microbial Diseases of Fish. Edited by R.J. Roberts, Special Publication No. 9 of the Society for General Microbiology. Academic Press, London. 1982. 305 p. $40.50 (U.S.).
In 1991, the poor physical condition of largemouth bass Micropterus salmoides from Lake Harris, Florida, was associated with the decline of the lake's fishery. The swim bladders of emaciated bass had mild inflammation and ecchymotic hemorrhages. A mycoplasma-like organism isolated from swim bladders was initially believed to be the causative agent. The organism was later identified as Acholeplasma laidlawii by using a fluorescent antibody procedure and was demonstrated to be nonpathogenic. Parenteral injection of the organism into healthy largemouth bass fingerlings produced no signs of disease or difference in growth rate compared with control fish during a 16-month period. Field studies resulted in isolation of A. laidlawii from black crappies Pomoxis nigromaculatus , bluegills Lepomis macrochirus , and redear sunfish L. microlophus , but not from noncentrarchids in Lake Harris or from any fish species in a control fishery (Lake Holly, Florida). The absence of organisms in all emaciated bass, our inability to reproduce the disease, and isolation of the organism from seemingly healthy fish suggest this organism was not pathogenic.
We established a method of directly detecting Clostridium botulinum type C cells, while minimizing spore detection, in the intestinal contents of Mozambique tilapia ( Oreochromis mossambicus ). This technique involved extraction of predominantly cellular DNA from tilapia intestinal tracts and used a polymerase chain reaction assay to detect presence of type C 1 toxin gene. We consistently detected C. botulinum type C cells in tilapia gastrointestinal contents at a level of 7.5×10 4 cells per 0.25 g material or 1.9×10 3 cells. This technique is useful for determining prevalence of the potentially active organisms within a given population of fish and may be adapted to other types of C. botulinum and vertebrate populations as well.