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Download Mitchell - Fish Medicine: Infectious and Non
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Mark A. Mitchell DVM, MS, PhD University of Illinois College of Veterinary Medicine Non-Infectious Diseases Ammonia: Most commonly observed in new systems More problematic in cold weather Bacteria decreased function Check regularly in the winter Non-Infectious Diseases Ammonia toxicity More problematic with small fish Toxic levels build up faster Toxic levels vary with pH Un-ionized form highly fatal at 0.2 ppm 1 ppb- 0.02 ppm Chronic problems Non-Infectious Diseases Ammonia toxicity Clinical signs Dyspnea Telangiectasia Gill damage Mucous production Gills and body Lethargy Non-Infectious Diseases Ammonia toxicity Treatment Acute toxicity Remove fish to ammonia-free system Lower system pH Chronic toxicity Water changes Correct inciting cause Non-Infectious Diseases Ammonia toxicity Treatment Chronic toxicity Water changes Correct inciting cause Evaluate filtration Often insufficient capacity System burden Fish density Organic load Detritus Diet Non-Infectious Diseases Nitrite toxicity Clinical signs Similar to ammonia Methemoglobinemia Brown blood Muddy gills Diagnosis Test water Blood sample Histopathology Non-Infectious Diseases Nitrite toxicity Treatment Acute toxicity Remove fish to ammonia and nitrite-free water Oxygenate water Increase salt Chloride competes with nitrite at gill 3 ppt Chronic toxicity Evaluate biological filter, stocking density, feeding practices Non-Infectious Diseases Hypoxia Low oxygen levels How can oxygen levels become depleted in a system? Start by thinking about its usage through the system….. What requires oxygen? What is the highest biomass that requires oxygen? Non-Infectious Diseases Hypoxia Low oxygen levels Rare in aquariums because of aeration More common in ponds Oxygen depletion occurs during the hours when the sun is down Phytoplankton biomass can consume huge amounts of oxygen High mortalities noted at dawn or early morning Largest fish typically go first Non-Infectious Diseases Hypoxia Diagnosis Measure dissolved oxygen levels Treatment Acute toxicity Move fish to well oxygenated/aerated water Prophylactically Aerate water- especially at night Manage phytoplankton blooms Reduce nitrogen in system Non-Infectious Diseases Hypercapnia Clinical signs Narcosis Lethargy/depression Slowed respirations Diagnosis Test water, pH Treatment Increase pH Increase oxygen Stop supplemental CO2 Non-Infectious Diseases Super saturation (gas-bubble disease) Nitrogen gas most common Clinical signs Gas bubbles under skin and fins, ischemia and necrosis Diagnosis Physical exam, evaluate water source Treatment Stop supplemental gas (CO2, pumps), evaluate water source (deep well), minimize venturi’s Non-Infectious Diseases Acidosis and Alkalosis Alterations in pH can lead to problems for fish Log scale Small changes are actually BIG changes Fortunately most fish adaptable Immunocompromised/stressed fish less likely to handle pH varies based on native system Non-Infectious Diseases Acidosis and Alkalosis Common causes for pH fluctuations Carbon dioxide: acidic water Heavy plant life- alkaline water Concrete ponds- alkaline water Calcium compounds- pH: 10-11 Seal with appropriate compounds: bituminous based paints Cheaper paints can be toxic Mix in muriatic acid with concrete to prevent leeching Non-Infectious Diseases Acidosis and Alkalosis Signs: Acidosis: darting, jumping from water, increased mucous production, gill hemorrhages Alkalosis: skin and fin erosions, mucous production- milky white appearance Non-Infectious Diseases Acidosis and Alkalosis Diagnosis: test pH Treatment: Remove fish to aquarium/pond with neutral water Titrate pH to appropriate level Non-Infectious Diseases Chlorine Toxicity Addition to water as an oxidizing agent Early 1900’s- cholera and typhoid fever Research with fish 4 ppm fatal within hours 0.2-0.3 ppm- fatal within hours in susceptible species, longer less susceptible species 0.002 ppm can cause chronic gill issues- hyperplasia Flushing of systems as pulse therapy is common Alterations in dechlorination required Non-Infectious Diseases Chlorine Toxicity Signs dyspnea, gasping at surface Diagnosis: water test gill biopsy branchial epithelial hyperplasia Treatment sodium thiosulfate evaluate municipal water treatment schedules Non-Infectious Diseases Hypothermia Clinical signs Listless, clamped fins, non-progressive swimmers Hyperthermia Clinical signs Hyperactive, tachypnea, rapid swimming, ruptured blood vessels Diagnosis Check temperature Return to normal temperature gradually 2-3oF per hour Non-Infectious Diseases Heavy metals Copper, Mercury, Zinc Clinical signs Breaks down mucus coat, gill epithelial changes, anorexia, edema, disoriented, protruded scales Treatment Remove source Increase pH- chelate compounds Increase oxygen levels to assist gas transport Bacteria General considerations: bacterial infections in fish can rapidly become systemic most infections are caused by Gram-negative bacteria most infections are stress mediated poor water quality, overcrowding, poor diet Bacteria Gram negative opportunists Freshwater Aeromonas spp., Pseudomonas spp. Saltwater Vibrio spp. Gram positive opportunists Erysipelothrix rhusiopathiae Ubiquitous Clinical signs: skin ulcers, hemorrhages on skin and fins, sepsis Bacteria Diagnosis: culture incubation temperature add salt for saltwater cultures sensitivity Treatment: systemic antibiotics reduce stress water changes Aeromonas Aeromonas septicemia, red sore Most common bacterial disease of freshwater fish Clinical signs Generalized Pathogen Aeromonas hydrophila Aeromonas salmonicida achromogenes Aeromonas Predisposing factors High temperatures, overcrowding, organic pollution, hypoxia, skin lesions from primary pathogen (Epistylis) Diagnosis Biochemical identification of clinically significant numbers associated with lesion Treatment Initial Oxytetracycline Bacteria Edwardsiella ictaluri “Hole in the head disease” Enteric Septicemia of Catfish 1976 first case 1981- isolated Primary financial losses Seasonal Spring and fall 72-82F (22-28C) Bacteria Clinical signs Decreased appetite “spiraling” and “surfing” Ulcer between eyes Ascites Hemorrhage internally Treatment Medicated feed-Oxytetracycline Vaccine Flavobacterium columnare Clinical signs Erosive lesions of skin and gill Transmission >15C 70ppm hardness is ideal for growth Risk factors Physical injury, low oxygen, organic pollution, high nitrate, high arsenic Flavobacterium columnare Diagnosis Wet mount – flexing or gliding motion Biochemical tests or agglutination Treatment Surfactant baths Potassium permanganate prolonged immersion Copper sulfate Antibiotics Bacteria Streptococcus iniae 1976: FW dolphin 1996: Ontario 4 cases Bacterimic 16 h-2 d Tilapia Hybrid striped bass, RBT, YF turbot Meningioencephalitis Diagnosis Culture Pulse-field electrophoresis Treatment Antibiotics Vaccine Bacteria Mycobacterium M. fortuitum, M. marinum non-motile, acid fast cosmopolitan distribution transmission: oral-fecal, water signs: chronic progressive disease, lethargy, anorexia, skin ulcers, edema, granuloma formation Bacteria Mycobacteriosis diagnosis: squash preps at necropsy or biopsy culture treatment: poor success depopulate, disinfect ZOONOTIC Yersinia ruckeri Enteric redmouth Pathogen Gram negative Pathogenesis Warm water Transmission Fecal-oral Vertical? Yersinia ruckeri Clinical signs Reddening around mouth and head Darkening of dorsum Anorexia Exophthalmia, corneal opacity, blindness, loss of melanin control Diagnosis Clinical signs, anemia, culture Treatment Oxytetracycline Control Avoid carriers (mammals and birds) Vaccine Yersinia ruckeri Water molds Saprolegnia spp. Cosmopolitan considered opportunist, possibly primary invader too associated with stress secondary invader prefer cooler temperatures Water molds Signs: “cotton-growth” on skin ulcers, trauma. can become internalized. Diagnosis: direct saline smear branching non-septate hyphae Treatment: reduce organic load, salt, formalin Atypical Water Mold Ulcerative mycosis, red-spot disease Freshwater or estuarine Clinical signs Usually deep penetrating wound into body cavity Pathogen: Aphanomyces (most common) Evidence that skin damage by Pfeisteria (toxic dinoflagellate) linked to infection Atypical Water Mold Diagnosis Wet mount Culture on corn-meal agar Treatment None proven Improve water quality Limit access to Pfeisteria Viruses Current status Knowledge of epidemiology of many viruses is limited Aquaculture and wild populations: more common Emerging pathogens? Virus diagnostics Historical Cell culture, Histopathology, EM, Serology Current Molecular techniques PCR, cDNA cloning, restriction digestion analysis Viruses Characterizing viral genomes Determine gene organization, protein products, regulatory strategies Generate clones Diagnostic and control methods Generate probes Diagnostics Investigate molecular epidemiology Immunological response and virus-cell interactions Viruses Lymphocystis cosmopolitan iridovirus signs: macroscopic nodules on skin and fins (internal possible) chronic often self-limiting prognosis poor if affects certain areas of the body Lymphocystis Viruses Lymphocystis diagnosis gross examination wet mounts biopsy and histopath treatment: no specific treatment debulk, probably return spontaneous regression Large Mouth Bass Virus Lake Weir, FL (1991) Unexplained die-off Santee- Cooper, SC (1995) 1,000 mortalities Etiology: Iridovirus Identified other centrarchids Ornamental fish-release, escapes Large Mouth Bass Virus Clinical signs Abnormal swimming patterns Loss of equilibrium Epidemiology: Risk factors Adult fish Summer months Affected and unaffected populations Channel Catfish Virus Herpesvirus 1960’s Confirmed 1971 Signalment Young fish <1 year old Clinical signs Decreased appetite Ascites Renomegaly Channel Catfish Virus Transmission Horizontal and vertical (presumed) Direct and indirect contact Not stabile: UVB, mud, chlorine Diagnosis Histopathology and culture Treatment: None, management Adult survivors are reservoir: don’t use as brood stock Infectious Salmon Anemia Orthomyxovirus Norway, 1984 Canada, 1996 US, 2001 molecular differences between regions Clinical signs anemia, leukocytosis, pale gills, ascites, renomegaly Infectious Salmon Anemia Mortality: significant Transmission: direct, indirect Diagnosis Serology RT-PCR Management Cull affected stocks Protozoa Ichthyophthirus multifilis Ciliate (up tp 1.5 mm) Life cycle: trophont on fish--> break off-> tomonts develop on substrate-->theronts released find fish Temperature dependent Diagnosis: skin scrape, gill biopsy Treatment: many available Conclusions
