Koi (Cyprinus carpio) and goldfish (Carassius auratus) are common ornamental fish kept as pets in ponds and aquaria today. Koi generally have elongated bodies that grow to more than 120 cm long and weigh 35 kg, they can live at least 50 years. Goldfish have short and round bodies that grow to 60 cm long and weigh 2.5 kg or more, they can live 30 years or more.
Diet
Koi and goldfish are omnivorous and can be fed commercially prepared diets specially formulated for these species. They need an easily digestible food, preferably one with a wheat germ base. Below are some information that may be helpful when selecting feed products for your pet fish.
| Nutritional content | Requirements |
|---|---|
| Carbohydrates | Koi and goldfish should only have 25-40% of their diet from carbohydrates. Overfeeding of carbohydrates can cause liver disease. |
| Protein | The best source of protein for fish is fish meal. The only plant source is soy, and this can only make up 50% of the total protein. Most producers use a standard 25-32% protein diet throughout the grow-out period. |
| Fats | Fats are important for energy, insulation and hormone production. Fats should be 15-25% of the total diet. |
| Vitamins | Fish obtain vitamins such as vitamins A, C, D, E and K from their diet. Vitamin A deficiency can lead to skeletal deformities and vitamin C & E are important for immune function. |
| Minerals | Most fish take in water and mineral from their surrounding water so minimal supplementation is required in the diet. One of the main requirements from diet is phosphorus. |
| Color enhancing food | Formula that have color enhancing effects contain carotenoids (pigments). These should be fed sparingly over only a short period of time. |
The particle size of pellets should increase from a fine meal up to about a 1/4 -inch pellet as fish grow. Smaller multiple feedings per day (preferably twice daily) is highly recommended as they lack true stomach. Overfeeding can result in low oxygen levels in water and lead to bacterial or algal blooms, feed an amount which they can consume within 5 minutes per feeding time. Unconsumed feed should always be removed from tank/ pond after feeding. Proper storage of feed is important to keep it fresh, a cool environment with low humidity prevents mold growth, which can be toxic to fish. Levels of vitamins may be reduced and fats can be decomposed in old or expired feeds. Once a bag or a jar is opened, any leftovers should be tossed 6 months later.
Majority of issues in koi are secondary to poor water quality. Stress from poor water quality often leads to poor growth, reproduction, secondary bacterial, parasitic and fungal infections. Ideally, these tests can be performed once a week, but at minimum once a month is recommended.
| Parameters | Ideal values/ range |
|---|---|
| Temperature | 18 to 24 °C |
| Unionized ammonia | <0.05 mg/L |
| Nitrite | <0.05 mg/L |
| Nitrate | <80 mg/L |
| pH | 7 |
Quarantine and Introduction of New Fish
When introducing new fish to an existing school in an aquarium or pond, acclimation and quarantine are essential. Transfer the new fish by floating them in the water within their bag for approximately 10 minutes to allow acclimation to the new water temperature. Quarantine the new fish in a separate body of water for at least 3-4 weeks. Quarantine should be conducted in diluted non-iodized aquarium salt bath, the dilution factor should be calculated based on the volume of water used. Water quality testing should be performed daily. A 25% water change should be carried out weekly, and replaced with diluted salt water. Monitor the behavior and appetite of the new fish throughout the quarantine period. It is recommended to use a net to transfer the fish on moving day, this is to ensure that the water in which the new fish was kept in is not added to the tank or pond the fish is transferred to. Rule of thumb for stocking is for every 5-8 cm of length of koi to have 0.1 square metre of pond surface area.
Clinical Signs
Some abnormal symptoms to look out for include:
The above symptoms suggest an on-going disease process. We recommend a complete physical examination of your koi and goldfish once every year.
Common Medical Conditions and Diagnosis
Parasitic infection
Some of the common crustacean parasites found in koi and goldfish include anchor worm (Lernaea) and fish louse (Argulus). Other digenean parasites such as gill flukes They are also especially prone to protozoan parasites such as Trichodina and Chilodonella. Some of these parasites are visible and can be identified by the naked eye, while others require confirmation by microscopic examination. Chemical treatments are available for treating these parasitic infections. It is important to note that self-treating inappropriately over a prolonged period of time and can result in detrimental consequences such as drug resistance.
Bacterial infection
Bacteria such as Aeromonas salmonicida, Edwardsiellatarda, Pseudomonas and mycobacterium sp., can infect these species. Aeromonas salmonicidacauses ‘goldfish ulcer disease’ or ‘carp erythrodermatitis’, which often results in superficial or deep sores that may kill up to 50% of the fish population. Bacterial disease should be confirmed and differentiated from other diseases that cause similar symptoms through proper diagnostics such as bacterial culture and sensitivity, so that appropriate treatment can be determined.
Water mold and fungal infection
Water mold is one of the most common infections of freshwater fish and are much more common than true fungal infections. Often, a cotton and proliferative growth can be observed in the skin or gills of infected animals. The chance of recovery is usually directly related to the amount of skin or gill infected. Diagnosis can be made via microscopy and appropriate treatment can be administered to treat these infections.
Viral infection
Koi herpesvirus (KHV) and spring viremia of carp (SVC) are of major concerns. KHV affected only koi while SVC affected both koi and goldfish. These diseases are highly contagious and can cause significant mortality. KHV may cause severe gill lesions, sunken eyes, pale patches on the skin, lethargy, respiratory distress and uncoordinated swimming. Fish infected with SVC are often lethargic, they may have exophthalmia (‘pop eye’), pinpoint bleeding on the skin, swollen abdomen, and bloody mucus coming from the vent. Such infections can be confirmed via PCR or ELISA testing.
Tumor growth
Tumor growth in the eye, skin, fins, mouth, gonad or abdomen) is common in koi and goldfish. Genetic, environmental (prolonged exposure to UV light) and concurrent viral infection are some of the factors contributing to tumor growth. Fish with gonadal tumors often present as bloated/ enlarged abdomen. At advanced stages, the space-occupying tumours in the abdomen may compress on the swim bladder, resulting in buoyancy issues. Surgical excision/ debulking, cryosurgery and laser therapy are some of the treatment options that can be performed under anesthesia for such cases.
Other common diseases in fish include:
We provide veterinary medical services specially catered for aquatic species, this includes pond and tank-side services in addition to in-clinic consultations. Based on the overall history and clinical assessment, there is an array of diagnostics and treatments that we can offer to provide proper health care for your aquatic pets. These diagnostics include imaging (radiography, ultrasound scan or computerized tomography (CT) scan), biopsy sampling, fine needle aspiration and histopathological analysis. Often, when a sick fish starts presenting abnormal clinical signs, medical attention should be provided as soon as possible. Delaying proper medical attention and self-treating without a proper diagnosis may be detrimental in some cases. If you believe that your aquatic pet needs medical attention, please do not hesitate to contact us at +65 6803 8344 to find out how we can help!”
