Common Conditions in Freshwater Aquarium Fish Fish Are the Largest and Most Species-Rich Group of Vertebrates, Numbering 60,229 Species and Subspecies

Home , Columnaris, Dropsy (fish disease), Fin rot, Substrate (aquarium), Swim bladder disease

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Common conditions in freshwater aquarium fish Fish are the largest and most species-rich group of vertebrates, numbering 60,229 species and subspecies. Given there is such a plethora of species, fish have adapted to a wide range of aquatic environments – from the oceans to desert puddles, and from deep-sea hydrothermal vents to glacial mountain lakes and streams (Weber, Sonya Miles 2013). This article focuses on cold and tropical freshwater fish that are kept as pets. BVSc CertAVP(ZM) MRCVS

Sonya qualified from Bristol In this author’s experience, University in 2013. After there are a large variety of beginning her professional pathogens that can affect career in small animal practice, freshwater fish. Stress she now works at Highcroft and subsequent immune Exotic Vets where she sees a suppression – invariably wide variety of species. She caused by poor water has a special interest in reptile quality – often underpin the medicine and surgery, but enjoys pathogenesis of many of all aspects of being an exotic these ubiquitous organisms. species veterinary surgeon. Underlying causes should, therefore, always be Sonya runs North Somerset investigated and corrected Reptile Rescue in her spare time. (Roberts et al, 2009; Roberts- Sweeney, 2016).

Unlike mammalian patients, Figure 1. A blood sample being taken from the caudal vein in a fish. samples taken for culture and sensitivity testing in freshwater to cause infections and, as ensuring that the head is also fish should be cultured at such, first-choice antibiotics removed and the remaining room temperature (22°- should target them (Roberts- wound treated with a 25°C). Blood agar is a good Sweeney, 2016). suitable antiseptic, such as medium and the organ of iodine, to prevent secondary choice for sampling in cases For ease of reference, infections (Roberts et al, of a systemic infection is the conditions are dealt with 2009; Andrews et al, 2005). posterior kidney. However, in below in alphabetical order. recent studies, blood culture Potassium permanganate results have shown good Anchor worm bathing or chitin inhibitors correlation to kidney samples This parasite (Lernaea) affects – such as lufenuron (0.1- (Roberts-Sweeney, 2016). cold water fish and embeds 0.2mg/L) prolonged In this author’s experience, into muscle, from where it can immersion – are also samples taken with sterile penetrate the internal organs effective; but they can kill precautions from the caudal (Andrews et al, 2005). Clinical non-target invertebrate vein are suitable (Figure 1). signs include inflammation species if they are in the at the site of attachment and same environment The treatments involved ‘glancing’ – the behaviour (Roberts et al, 2009). with many of the conditions when fish rub themselves should include a thorough on objects. Any treatment water should assessment and correction be disposed of safely and not of environmental conditions Individual parasites should allowed in natural waterways (Roberts-Sweeney, 2016). be removed with tweezers, (Roberts et al, 2009). 1.0 Antimicrobials should hours* be considered when bacterial infections are “Stress and subsequent immune implicated. These can be given parenterally, orally or suppression – invariably caused by *Suggested Personal & Professional as a bath treatment, with poor water quality – often underpin Development (PPD) parenteral treatment being the most effective. Gram- the pathogenesis of many of these FISH negative bacteria are the most common type of bacteria ubiquitous organisms”

Columnaris disease Clinical signs are cotton-like Dropsy (‘Malawi bloat’) Basic treatment consists of (‘mouth fungus’) proliferative lesions located There are many causes correcting any underlying This highly contagious in the perioral, periocular, of dropsy ranging from stressors and improving condition is caused by fin, dorsum and tail regions bacterial (Aeromonas) and husbandry. In the author’s Flavobacterium columnare (Roberts et al, 2009; viral infections to metabolic experience, repeat 1 per cent and the external signs are Roberts-Sweeney, 2016). and nutritional disorders aquarium salt water bathing often misdiagnosed as fungal In the author’s experience, (Andrews et al, 2005). In this until the condition has lesions (Roberts et al, 2009; these lesions can progress author’s experience, stressed/ cleared can be affective; and Roberts-Sweeney, 2016). to ulcerations. Lethargy and immunocompromised fish, oxytetracycline bathing daily anorexia may also occur kept in poor conditions, often for 10 days has been used In this author’s experience, and, if the gills are affected, have a high mortality rate. (Roberts et al, 2009). secondary bacterial respiratory disease. infections common; and Clinical signs include a Fish fungus poor husbandry and stress Basic treatment consists swollen coelomic cavity, Many species of owing to over-stocking of oxytetracycline bathing protruding scales with a opportunistic fungal are regularly implicated daily for 10 days (Roberts ‘pine cone’ appearance organisms are involved, (Roberts-Sweeney, 2016). et al, 2009). In the author’s (Figure 2) and anorexia Saprolegnia being the most experience, repeat 1 per (Andrews et al, 2005). common (Roberts-Sweeney, Diagnosis is made using ‘wet cent aquarium salt water Biochemistry and 2016) and their spores are mounts’ of affected areas bath until cleared can haematology, as well as ubiquitous in aquariums, and direct microscopy to be effective. Systemic culture sensitivity and especially if there is decaying differentiate between bacterial antimicrobials may be imaging, can help organic matter. Fish have an and fungal organisms needed in more severe determine the underlying increased risk of contracting (Roberts et al, 2009; Noga, infections (Andrews definitive differential. a fungal infection if the 2010). Flavobacteria are thin et al, 2005). mucous layer covering the rod bacteria with a gliding or The recommended treatment skin is damaged (Andrews et flexing motion. They may also In this author’s opinion, is to isolate affected fish al, 2005; Roberts-Sweeney, be arranged in a ‘haystack’ severely sick individuals and provide them with a 2016), particularly as the appearance (Roberts et al, should be culled and dead suitable diet, the best possible result of rough handling and 2009; Declercq et al, 2013). fish removed from the tank. water quality and to correct poor water quality (Groff, underlying environmental 2001). Infection is often deficiencies (Andrews et secondary to other conditions al, 2005). If antibiotics are (Andrews et al, 2005). indicated they should be based on culture and sensitivity. Cotton wool-like grey lesions appear on the skin and fins Fin rot and can progress quickly Fin rot is often secondary to resulting in death. Specific stress and poor husbandry, diagnosis may be assisted and seen alongside other by direct microscopy of conditions (Roberts et al, freshly made smears and 2009). There may be a variety fungal cultures of the lesions of pathogens involved – (Roberts-Sweeney, 2016). Flavobacterium columnare, Fexibacter maritimus, In the author’s experience, Aeromonas, Pseudomonas repeat 1 per cent aquarium and Cytophaga spp – all salt water bathing, until of which are ubiquitous in clinical signs have cleared, aquariums. Fin rot is especially can be effective. Affected common in long-tailed fish should be removed for coldwater fish kept below treatment and attention given 10°C (Andrews et al, 2005). to underlying stressors and poor husbandry. Dead fish Clinical signs include must be removed immediately. discolouration and necrosis of the fins and/or tail, which Traditionally, malachite lead to difficulty in swimming, green has been used in these and anorexia. It should be situations; but this should noted that if the fins/tail are be avoided nowadays as it destroyed to their base, they is considered carcinogenic will not be able to regrow. (Roberts-Sweeney, 2016). Culture and sensitivity of samples taken from lesions ‘Hole-in-the-head’ disease Figure 2. The ‘pine cone’ appearance caused by ‘dropsy’ in a carp. may be useful indicators of ‘Hole-in-the-head’ disease appropriate treatment. (Hexamitiasis) is caused by

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Figure 3a. Figure 3b.

Figure 3a. Multiple neoplastic lesions originating from the integument of a fish. Figure 3b. A fish euthanised as a consequence of an expansible mass (suspected neoplasia) deforming the eye and face. a flagellate protozoan; and whereas the integument is the Septicaemia water – often sinking to the poor nutrition, water quality, most common organ for the Bacterial (Gram-negatives), bottom or floating upside overcrowding, bacterial manifestation of neoplasia viral and fungal infections down – tail curls and the skin infections often contribute (Figures 3a & 3b) (Vergneau- are commonly implicated is prone to trauma owing to to infestation. Tropical fish, Grosset and Nadeau, 2017; and, invariably, linked with substrate abrasion (Figure 5) specifically Cichlids, Discus, Groff, 2014). Accurate poor water quality and high (Weber, 2014). Angelfish and Oscars are diagnosis relies on biopsies or levels of ammonia (Andrews particularly susceptible removal of the mass et al, 2005). Clinically, there Treatment depends on (Andrews et al, 2005). for histopathology. is reddening to unpigmented removing the underlying parts of the body, bulging eyes cause. If it is the consequence Clinical signs include anorexia Treatment success depends on and a distended abdomen, of constipation, then the and lethargy, as well as the degree of tissue invasion, (Wildgoose, 1996). fish should be starved for producing small holes around condition of the fish, and the three days and then fed half the head and flanks (Andrews level of owner commitment Treatment depends on a skinned, cooked pea. If et al, 2005). (Roberts-Sweeney, 2016). the identification of the this doesn’t work and the underlying cause. Antibiotics fish is passing faeces, then Medicated food can be ‘Pop-eye’ (exophthalmia) in the feed, targeting Gram- the underlying cause is likely used to attempt treatment; This clinical manifestation negative bacteria, can work to be infectious. A suitable however, fish suffering with the involving protrusion of well (Andrews et al, 2005); antibiotic (ideally based on condition are often anorexic, one or both eyes has and, in this author’s opinion, cultures) targeting Gram- in which case metronidazole multiple possible causes, keeping the fish hungry will negative bacteria should be or dimetridazole can be added including bacteria, parasites help with dosing if using in- considered (Weber, 2014). to the water. In the author’s and systemic metabolic feed medications. Severely sick opinion, in severe cases disturbances linked to poor fish should be euthanised. Wasting disease (fish TB) euthanasia should water quality (Andrews et This zoonosis is caused by be considered. al, 2005). In this author’s Swim bladder disease Mycobacterium marinum experience, this condition This may be the result of and M. fortuitum, which Neoplasia is often self-limiting and bacterial and parasitic bacteria thrive in aquariums Neoplastic disease in rarely fatal. infections, birth defects, that are over-stocked with fish is less common than organ dysfunction (including poor water quality (Weber, in mammals is and a Affected fish should the gastrointestinal tract) and 2014; Andrews et al, 2005). consequence of genetic, be isolated and any neoplasia (Weber, 2014). It is seen predominantly in husbandry, viral and environmental deficiencies tropical fish. environmental causes must be corrected. Diagnosis relies upon (Vergneau-Grosset and Antibiotics suitable for Gram- history and clinical signs. Wasting disease is of slow Nadeau, 2017). Generally, negative infections may be In the author’s experience, onset with non-specific neoplasms are ectoderm- and administered via injection if imaging techniques, such as clinical signs, ending with endoderm-derived. a systemic bacterial cause ultrasound and radiographs muscle wasting and raised is suspected, and which is (Figure 4), are helpful. granulomatous lesions. Epithelial neoplasms are likely if both eyes are affected Classical signs are an Specific diagnosis depends the most common in fish, (Andrews et al, 2005). abnormal position in the on finding acid-fast staining

organisms in samples taken References from any lesions (Weber, 2014; Andrews et al, 2005). Andrews C et al (2005). The There is no treatment Interpet Manual of Fish Health. available. Affected fish should Surrey: Interpet. 94-181. be culled and submitted for post-mortem. Declercq AM et al (2013). Columnaris Disease in Fish: White spot A Review with Emphasis on White spot is a protozoan Bacterium-host Interactions. infection involving Veterinary Research, 44: 27. Ichthyophthirius multifiliis. It is often seen after a sudden Groff JM (2001). Cutaneous Biology drop in water temperature, and Diseases of Fish. Veterinary when plants carrying the cysts Clinics of North America: Exotic of the parasite are added to Animal Practice. 4(2): 321-411. the aquarium, or if there is poor water quality (Andrews Groff JM(2014). Neoplasia in fish. et al, 2005). Veterinary Clinics of North America: Exotic Animal Practice, 7: 705-756. Principal clinical signs are ‘glancing’, tachypnoea, gasping, Noga EJ (ed.) (2010). Fish disease: clamped fins, and white lesions Figure 4. A lateral radiograph of an anaesthetised fish. diagnosis and treatment (2nd that progress to cover the edition), Wiley-Blackwell, Ames body (Andrews et al, 2005). (IA) (2010), pp. 107-177. Diagnosis is best made using direct microscopy of freshly Roberts HE et al (2009). Bacterial made smears. and Parasitic Diseases of Pet Fish. Veterinary Clinics of North America: In the author’s experience, Exotic Animal Practice, 12: 609-638. this condition is hard to control once established in the Roberts-Sweeney HE (2016). aquarium and can result in 100 Anatomy and Disorders of the per cent mortality unless you Oral Cavity of Ornamental Fish. act fast. Increasing the water Veterinary Clinics of North America: temperature to speed up the Exotic Animal Practice, 19: 669-687. life cycle of the parasite and the addition of aquarium salt, will Vergneau-Grosset C and Nadeau disrupt the fluid regulation of ME (2017). Fish Oncology, the Ichthyophthirius organism. Diseases, Diagnostics and Therapeutics. Veterinary Clinics Conclusion of North America: Exotic Animal Many of the commonly Practice, 20: 21-56. seen conditions in cold and tropical freshwater Weber S (2013). Itchy Fish and fish are the consequence of Viral Dermatopathies: Sampling, environmental deficiencies Diagnosis, and Management of – such as poor water quality Common Viral Diseases. Veterinary and high stocking densities Clinics of North America: Exotic – resulting in a subsequent Animal Practice, 16: 687-703. suppression of immunity; thereby allowing pathogens Weber S (2014). A Veterinary Guide that are often a natural part to the Fish Gastrointestinal Tract. of the environment, to Veterinary Clinics of North America: cause disease. Exotic Animal Practice, 17: 123-143.

Swift assessment of the Wildgoose WH (1996). BSAVA patient, its environment and Manual of Ornamental Fish. 2nd identification of the causative edn. Gloucester : British Small agent are integral Animal Veterinary Association. pp. to successful attempts 109-258. at treatment. Figure 5. A fish that was euthanised owing to persistent buoyancy issues ultimately diagnosed as a swim bladder problem. Note the curled tail and trauma to the skin caused by contact with the substrate.

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