Aquatic veterinarians can use much of the same equipment and medications used in any small animal veterinary practice. Most diagnostic tests in fish can be done using standard veterinary equipment, and surgeries performed with instruments typically used for ophthalmic work, such as iris scissors. Radiology equipment, especially digital or dental units, sonograms, endoscopes, and blood evaluating equipment used for other animals work well with fish patients, too. Many small animal drugs are also used in fish medicine, with only a few special medications needed to supplement other veterinary drugs.

Aquatic veterinarians often make house calls to examine fish, but there are also advantages of having clients bring in the fish to the veterinary hospital. Having a client bring a sick fish into the veterinary hospital allows treatment in a quarantine tank where all the conditions can be controlled and properly maintained. Regular daily observations can be made, and appropriate diagnostic tests and treatments performed. Sick fish are isolated from the remaining fish in the aquarium or pond. Once a diagnosis is made, the fish can be properly medicated, and the sick fish can be cared for until it is well enough to return home. Disadvantages include the lack of examination of the remaining fish and the aquatic environment (aquarium or pond) itself; having the owner transport the sick fish in plastic bags, buckets or ice chests to the clinic; and in many cases the unwillingness of the owner to catch and bring in their sick fish.

By making a house call, the fish can be examined in its own environment. The filtration units can be examined and water tests performed on the spot. Apparently healthy fish can be biopsied and checked for early signs of lesions that the owner might have missed. Suggestions on improving filtration, water quality, and fish husbandry are easier to make when the facilities have been visited, rather than having just the owner’s descriptions.

When making a house call, portable diagnostic equipment including microscopes, slides and coverslips, bacterial culturettes, and water test kits must be brought along. A “doctor’s bag” of common medications and antibiotics can be made up for house calls. Some very important pieces of equipment to bring when visiting koi ponds are your own quality long-handled koi nets (many pond owners have only pool skimmer nets!), a plastic container for holding the fish for examination, and chest-high waders!

Drawing blood samples from larger fish, especially koi, can be done from the caudal vein below the spine in the caudal peduncle. Use a 1 ml tuberculin syringe with a 22 or 23-gauge needle of appropriate length. A butterfly catheter can be attached to the syringe to facilitate handling of the needle separately from the syringe. Fill the hub of the needle with a drop of lithium heparin to prevent the blood from clotting. This is preferable to ammonium heparin or sodium heparin, but they can also be used for hematology testing. The ammonium and sodium heparins will affect those blood values if used in samples for serology or electrolyte testing. Ethylenediamine tetra-acetic acid (EDTA) is not recommended to be used to prevent blood clotting in fish blood samples as it may cause erythrocyte lysis.

Some normal values for koi blood parameters, derived from Advanced Koi Care by Nicholas Saint-Erne (2002, 2010) and from Hematology and Clinical Chemistry of Cyprinid Fish by Groff and Zinkl (1999), are listed in the chart below.

Koi Complete Blood Count (CBC)

Normal Range

Red Blood Cells (Erythrocytes)

• Red blood cells (10–13 μm cell length) 1–2 million/μl hematocrit (packed cell volume) 24–35% hemoglobin 8–13 g/dl
• Methemoglobin 4.8–5.6%
• Mean corpuscular volume 202 fl
• Mean corpuscular hemoglobin 49.1 pg/cell
• Mean corpuscular hemoglobin concentration 0.24 g/dl

White Blood Cells (Leukocytes)

• Total white blood cells 5–15 thousand/μl
• Neutrophils (10–15 μm) 750–1500/μl
• Neutrophils (% of total WBC) 12–20%
• Band (immature) neutrophils 0–4%
• Small (mature) lymphocytes (6.6 μm) 3000–12,000/μl
• Small (mature) lymphocytes 65–85%
• Large (immature) lymphocytes (11.8 μm) 0–3%
• Monocytes (10–16 μm) 100–600/μl
• Monocytes 1–4%
• Eosinophils (13.8 μm) 0–150/μl
• Eosinophils 0–1%
• Basophils (13.8 μm) 0–150/μl
• Basophils 0–1%
• Thrombocytes (4.6 x 7.7 μm) 50,000/μl

Serum Chemistries (Serology)

• ALT(SGPT) 20–50 IU/L AST (SGOT) 100–300 IU/L
• Total bilirubin 0.1–0.3 mg/dl
• Alkaline phosphatase 10–20 IU/L GGT 1–3 IU/L
• Uric acid 1–2.5 mg/dl
• Blood urea nitrogen 5–15 mg/dl creatinine 0.2–0.5 mg/dl
• BUN/creatinine ratio 10–20
• Creatinine phosphokinase 14.5 IU/ml
• Glucose 30–120 mg/dl
• Cholesterol 200–400 mg/dl
• Triglyceride 50–500 mg/dl
• Amylase 25–50 IU/L
• Lipase 25–50 IU/L
• Total protein 4–10 g/dl
• Albumin 2–6 g/dl
• Globulin 2–4 g/dl
• A/G ratio 0.7–1.2
• Osmolality 220–420 mOsm/kg
• Calcium 8.5–13.5 mg/dl
• Phosphorus 10–15 mg/dl
• Calcium/phosphorus ratio 0.6–1.3
• Magnesium 3–5 mEq/L
• Sodium 100–140 mEq/L
• Chloride 90–120 mEq/L
• Potassium 4–30 mEq/L
• Na/K ratio 3–30

Radiographs of fish can be taken successfully with standard veterinary radiology equipment. The radiographs can be taken without anesthesia by briefly restraining the fish in a sealed plastic bag with a small volume of water. The fish in the plastic bag can be placed directly onto the film plate or digital sensor, and the bag taped down if necessary to hold the fish in the correct position. Fish can also be anesthetized and then taken out of the water and positioned for radiographs. Gas bladder (swim bladder) abnormalities, spinal deformities, abdominal masses, and occasionally ingested foreign objects can be evaluated using radiology. Abdominal viscera are not easily distinguishable in a radiograph without a contrast medium. A flexible rubber catheter can be inserted orally to place barium or iodinated contrast medium into the stomach or intestines to perform contrast studies on the intestinal tract. The dosage for barium is 5 to 10 mL/kg body weight and the iodinated medium is dosed at 1 to 2 mL/kg. Be careful not to leak barium into the oral cavity and onto the gills, which could impair oxygen diffusion through the gills.

Ultrasound imaging can be performed on fish confined in a small container of water, as the water serves to couple the transducer to the fish’s body, eliminating the need for ultrasound gel. Transducers of 5 to 10 MHz work well for visualization of internal organs at depths up to 13 to 20 cm into the body, with lower frequency transducers producing images at greater depths of tissue penetration. If not waterproof, the transducer can be placed inside a plastic cover (e.g., plastic bag, examination glove, or condom) for protection. The transducer can be held several centimeters away from the fish if it is in the water, and the transducer repositioned until the desired image is obtained. Motion imaging can be used for guided tissue biopsy collection, abdominocentesis (celiocentesis), or pneumocystocentesis.

Endoscopic examination of the oral cavity, gill arches, and the pharynx can be performed by passing the endoscope into the mouth or gill operculum of an anesthetized fish. Flexible endoscopes can be passed through the esophagus into the stomach or intestines. Koi and goldfish have no stomach, but the proximal intestine is elastic and can distend to hold ingesta. Laparoscopy (coelioscopy) can be performed in larger fish to visualize internal organs or take biopsy samples. A small surgical incision can be made through an anesthetized fish’s body wall to insert an endoscope. Coelomic cavity visualization is used to evaluate the liver (hepatopancreas), the gonads to determine gender or reproductive organ development, the presence of adhesions or inflammation, the gas bladder position and status (inflamed, deflated, or fluid infused), or to collect an abdominal swab for bacterial culture. If the coelomic cavity has been insufflated with air during the procedure, the air must be removed to prevent buoyancy problems immediately after the procedure. The small incision can be closed with a simple interrupted absorbable suture, or sealed with methacrylate tissue adhesive.

Commonly Used Medications in Ornamental Fish

• Amikacin - 5 mg/kg IM, IP every 3 days
• Aztreonam (Azactam) - 100 mg/kg IM, IP every 2–5 days
• Butorphanol - 0.1 mg/kg IM for pain control post-surgically
• Dexamethasone - 1–2 mg/kg IM, IP q12h
• Diflubenzuron (Dimilin) - 0.06 mg/L once weekly for 3 doses
• Enrofloxacin (Baytril) - 10–14 mg/kg IM, IP q48h, or PO q24h
• Epinephrine (1:1000) - 0.2–0.5 ml IM, IP, IC
• Fenbendazole (Panacur) - 50 mg/kg orally for 2 days, 2 mg/L water q7d x 3 doses
• Formalin (37% formaldehyde) - 25 mg/L (1 ml/10 gal) in pond every other day
• Florfenicol (NuFlor) - 30–50 mg/kg IM, IP, PO q24–72h
• Furosemide - 2–3 mg/kg IM, IP q12–72h
• Gentamicin - 3 mg/kg IM once only due to kidney toxicity
• Hydrogen peroxide - 250–500 mg/L dip to prevent fungal growth on eggs
• Levamisole - 10 mg/L for 12–24h bath; 50 mg/L for a 2h bath
• Metronidazole - 50 mg/L bath, daily for 3–10 days, 10 mg/g of food daily for 5 days
• Oxytetracycline - 50–75 mg/kg BW, added to food daily for 10 days
• Praziquantel (Droncit) - 5–25 mg/kg IM, IP, PO, 10 mg/L for 6–24h bath
• Sulfadimethoxine-ormetoprim (Romet, Primor) - 50 mg/kg IM or added to food
• Tetracycline - 250 mg/100 g of food
• Trimethoprim sulfa - 30 mg/kg IM, IP, PO q24–48h