Fish Medicine PDF

Fish medicine Marie Kubiak BVSc CertAVP(ZM) CertAqV DZooMed MRCVS RCVS Recognised Specialist in Zoo and Wildlife Medicine WAVMA Certified Aquatic Veterinarian Learning objectives Recognise common conditions affecting pet aquatic animals.  Describe appropriate diagnostics methods to achieve a diag...

Fish medicine Marie Kubiak BVSc CertAVP(ZM) CertAqV DZooMed MRCVS RCVS Recognised Specialist in Zoo and Wildlife Medicine WAVMA Certified Aquatic Veterinarian Learning objectives Recognise common conditions affecting pet aquatic animals.  Describe appropriate diagnostics methods to achieve a diagnosis.  Describe appropriate interventions.  Describe appropriate control measures for prevention and to treat conditions.  Fish taxonomy (simplified!)  Teleosts › Bony fish › Classic tank and pond fish  Elasmobranchs › Cartilaginous fish › Sharks, rays, guitarfish › Rare as pets  Even less common pets! “Pet” fish: Temperate freshwater  Goldfish (Carassius auratus) › Small carp species › Require basic conditions  30l of water per fish  1 square foot of air surface per fish  Can be reduced with aeration  Ideally maintain at 18-20C but can survive a wider range of temperatures  Ponds preferable to tanks if deep enough to avoid freezing  Feed on crustaceans and plants or pelleted food  Koi carp (Cyprinus carpio) › Ornamental fish › Two hundred years of selective breeding › Up to 3ft in length › More sophisticated environments needed     Large ponds of 1.5m depth Filter with biological and physical filtration Aeration Commercial diets  Vitamin C required  Carotenoids to maintain coloration Common issues  Water quality failings › Increases in ammonia, nitrates or nitrites NH3 ↔ NH4+ Ammonia ↔ Ammonium Ions O2 Oxidisation by Nitrosomonas spp Bacteria NO2Nitrite O2 Oxidisation by Nitrobacter spp Bacteria NO32Nitrate Used by aquatic plants N2 Denitrification to Nitrogen Gas Removed by water changes Causes of spikes Failure to prepare and mature a tank and filter  Overstocking  › Can be gradual as fish grow/breed Failure of a filter  Overload of organic material  › Overfeeding › Algal or plant bloom › Dead fish Consequences  Ammonia increase › Irritation of skin  Discomfort  Ulceration  Increased risk of skin infection › Gill epithelial hyperplasia  Secondary effects on oxygenation causing respiratory signs  Reduced osmosis and ammonia excretion › General debilitation due to chronic stress  Nitrite increase › Increased nitrite absorption › Haemoglobin oxidised to methaemoglobin › Hypoxia due to reduction in oxygen transport › Pale tan mucosa and gills  Nitrate increase › Rarely clinical in itself › May affect eggs and fry › Facilitates algal and plant bloom  Secondary drop in oxygenation Management of water quality  Water changes › 30-50% of tank of pond volume Add zeolite to bind ammonia  Reduce organic load  › Remove algae and plants › Reduce feeding  Improve oxygenation › Aerate water › Cool or shade water if hot weather Longer term  Identify and manage cause › Allow filter maturation › Increase filter capacity › Reduce stocking of plants or fish Low oxygen saturation  High biomatter load › Algae, fish, decomposing vegetation › Plants overnight when CO2 production continues and no O2 is produced  High temperatures › Oxygen saturation decreases with temperature Clinical signs  Die off › Typically early morning when O2 is lowest Fish gathering at points of aeration  Signs of chronic stress  › Ulcerative skin disease › Mortality of already compromised fish Diagnosis  Measure oxygen saturation at sunrise Management Remove biomass  Increase aeration  Decrease stocking density  Provide shade/cool water  Monitor nitrogen processing  › Ammonia and nitrites also increase due to common factors Ulcerative skin disease  Parasitic › Protozoa e.g. Ichtyopthirius multifiliis (Ich)  Small white spots and irritation of fish › Gyrodactylus skin flukes › Dactylogyrus gill flukes › Argulus lice › Lernea anchor worm  Bacterial › Aeromonas spp most common › Range of environmental bacteria can be opportunistic invaders  Primary bacterial infection rare › Commonly secondary  Trauma  Damage to skin barrier e.g. high ammonia  Viral › Cyprinid herpes  Can be ulcerative but typically presents with raised plaques  Fungal › Typically secondary › May be ulcerative › Can also present as “fluffy” growths Approach to ulcerative skin cases   Assess pond/tank side where possible Test water parameters › Ammonia, nitrites, oxygen    Assess individual fish for gross lesions and macroscopic parasites Collect swab samples for culture Collect scrapes for cytology/parasitology › Examine immediately if possible Treatment  Medication for specific cause › In main tank/pond or in isolation tank  Consider adding low dose salt to reduce osmotic stress › 1-2g per litre Manage water quality carefully  Reduce stressors  Medication administration  Orally › Compound into pelleted or gel food Injections  In water  › Dissolve/dilute › Bypass filtration system Short term dips of higher concentration  Temperature affects dosing requirements and frequency  Swim bladder disorders Altered buoyancy  Secondary concerns  › Inability to feed › Abrasions Who is affected?  Elasmobranchs, some bottom dwelling teleosts (e.g. flounders) and some pelagic teleosts (e.g. tuna) lack a swim bladder › No swim bladder issues possible!  Physoclistous species › Marine teleosts › Cichlids › Bass and sunfish  Gases diffuse into the swim bladder from rete mirabile (“gas glands”)  Physostomous species › Koi and goldfish › Catfish › Salmon and trout › Tetras A pneumatic duct connects the oesophagous and swim bladder  Bacteria, foreign bodies or food can enter the swim bladder  Koi have a rete mirabile as well as a duct  Infection or anatomical disruption alters swim bladder filling  Altered buoyancy suggestive  › Can also be due to GI disease, neoplasia, granulomas or ascites  Radiographs highlight swim bladder alterations in position, size or shape Diagnosis  Cause of changes needs identification › Radiographs or ultrasound to check for mass or fluid displacing the swim bladder › Aspirate for culture and cytology  Treat based on findings › Systemic antimicrobials › Instill directly into swim bladder Feed larger food items to trigger opening of pneumatic duct  Remove hazards from enclosure  Guarded prognosis  Notifiable Disease  Spring viraemia of carp › Petechial haemorrhages of skin, gills and eyes › Exophthalmos › Pallor › High mortality  Koi herpes virus › Anorexia, lethargy › Gill necrosis › Skin pale patches › Erratic swimming › High mortality  If suspicious contact APHA for advice and testing “Pet” Fish: Tropical freshwater Common in homes and businesses  Require similar consideration to goldfish tanks  Beware mixing aggressive species  Provide plenty of cover for all fish  Common conditions Water quality issues  Fin rot (similar pathology to ulcerative skin disease)  Conspecific and intraspecific trauma  Mycobacterium marinum  Lymphocystis  White spot (Ich)  Fungal skin disease  Velvet (Piscinoodinium)  Hole in the head (Hexamita)  White spot (Ich) Protozoa: Ichthyophthirius multifilliis  Protozoa are less than 1mm in size and appears as fine white dots over the skin  › Cause secondary dermatitis › Increased mucus, ulceration › Gill damage also possible  Treatment: › Over the counter copper based water treatment › Ultraviolet filtration of water › Raise temperatures to 30C over 48-72hrs › 1g/l salt added into water Mycobacterium marinum  Seen across all fish species › Can cause ulcerative skin disease › Visceral granulomatous form  Lethargy, anorexia, loss of condition  Coelomic distension Identified on biopsy of skin lesions or histopathology of granulomas at post-mortem  Impossible to eradicate from a shoal  Depopulate, disinfect, dry out tank  Quarantine new fish for 2 months  Hole in the head Affects cichlidae (cichlids, discus and Oscars)  Presents as shallow ulcers on the head and sides  Due to Spironucleus flagellated protozoa  Mortality low but may be part of chronic stress or co-morbidity with higher mortality  Metronidazole can be given in food or in water but recurrence is occasionally seen   In catfish Edwardsiella ictaluri causes head ulcers “Pet fish”: Marine tropical More challenging to maintain  Salinity requires regular monitoring and maintenance  Run with sump and surplus water  Species often more fragile  Often more visually striking displays  Common diseases Water quality issues  Cryptocaryon (similar to Ich)  Marine velvet (Amyloodinium)  Lymphocystis  Lymphocystis (Iridovirus) Affects marine angelfish, butterfly fish and clownfish  Also affects cichlids (brackish/freshwater)  Viral infection causes fibroblasts to balloon in size  Hypertrophied cells of 1mm diameter are visible as white dots  Disfiguring but mortality is low  Lesions recur spontaneously but relapse is possible at times of stress  Accept endemic lymphocystis or cull affected animals 