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Case studies

Kinked Back


Lately I came upon quite a few instances of this kinked back phenomenon. Normally it is one fish per pond and the owners are baffled by this overnight occurrence. Careful detective work is necessary to determine the cause. There are various reasons for pond fish to develop a kinked back and all possible causes should be considered before appropriate action can be implemented, even if it just to ensure the safety of the rest of the collection. Kinked back/scoliosis is caused by a variety of causes, none of which is infectious. Normally, the reasons, for kinked back/scoliosis are one or a combination of the following:

Vitamin C deficiency. Vitamin C is essential in the diet of Koi. It provides resistance against illness as well as boosting tissue repair. Vitamin C not only supports immunity, it is also a very powerful biological antioxidant which protects the body cells against the baneful action of free radicals.  Also, vitamin C prevents skeletal deformities, promotes normal growth, prevents negative effects of environmental stress, aids in wound healing, lessens toxicity due to environmental contaminants and enhances the natural immunological defence mechanisms against bacterial infection. In short, Koi need vitamin C to survive and all indications are that they are significantly helped by vitamin C in high doses when undergoing stress. Until recently, vitamin C deficiency was rife among Koi because regular vitamin C (ascorbic acid) is easily damaged during the fabrication process (heat treatment) whilst also being quick to lose its action when stored. Recently, a new type, phosphorylated vitamin C has become available which is far more stable as well as being resistant against the heat treatment it is subjected to during the extrusion process. It is important for Koi feeds to be produced incorporating this new, more stable vitamin C. The most widely recognized symptom of Vitamin C deficiency in fish is scoliosis and/or lordosis, although many times these symptoms are manifestations of other problems that will also be discussed. When confronted with a single Koi that developed a kinked back it is normally an indication of some other problem, but when quite a few Koi in the collection, develop a kinked back, especially over time, it is worth-while to investigate the food that is normally fed to the collection. Make sure that the type of food contains a high level of vitamin C and also check the manufacturing date. The best preventative measure is to present a mix variety of food to the Koi collection and to ensure that the food is as fresh as possible. The occasional treat of green lettuce, orange and lemon will be enjoyed by the Koi and will add to their vitamin C intake.


The next possible cause may be an overdose with Organophosphates, like Fenthion, Trichlorfon, or Malathion to name but a few. This can cause kinking of the body due to hyper contraction of the muscles. A side effect of these drugs on the fish is to prevent relaxation of muscles, and this may kink, or break the fishes back. It is therefore necessary to consider whether insecticides were sprayed in the vicinity of the pond or whether a careless neighbour has sprayed something recently. Also consider the possibility of run-off water entering the pond, which may contain pesticides.

The third possible cause may be trauma. The muscles of Koi and other teleost fish are assorted in bands called 'somites'. When a somite is damaged, by Intra Muscular injection technique, for example, or a sharp blow, the somite may die which then shrinks, and kinks the fish, especially when swimming. It may straighten at rest. It is fairly common to see a group of young fish with several "broken back" fish in the group. People tend to worry that it may be a dietary deficiency because several fish may exhibit the symptoms. The chances are however good that during harvesting or packing someone netted many fish at a time and carried them in the net, all piled up. Koi skeletons are NOT weight bearing structures and are rather fragile to damage, especially those fish at the bottom of the net. Drastic temperature changes during early developmental stages are also thought to be responsible in some cases. 


The fourth possible cause may be electrocution through an electrical fault or lightning. In many cases the owner of the pond may not even be aware that electrocution took place until he notice the effect in the pond. Electrocution should be suspected when a pond has one or more fish with this broken back appearance and a history of an appliance malfunction, a tripped breaker or thunderstorm preceding the appearance of the kinked back problem. If this has shown up suddenly, there are several possible causes, but usually this is caused by a lightning strike or electrical discharge into the water from a damaged electrical appliance. Even a minute current just before the Ground Fault Interrupt trips, will be sufficient to cause damage to the nearest fish. Unlike vitamin C deficiency in which case the fish is simply kinked or bent looking, the fish that has been “hit” may be lying on their side in a catatonic state, or may be lying very still at the bottom of the pond. In this initial stage there is no pronounced curvature of the body, but the fish may experience severe ballast problems and will struggle to get to the surface. The spastic way a fish swims after being electrocuted is the most telling when diagnosing the problem. Even if it intends to swim just a few inches, it will be in a jerky, spastic way, right across the pond as if frightened. Over the next few days the fish will develop more and more severe contractions of the body, both when swimming and when at rest. Any stimulation causes the fish to dash about in a severely contorted fashion. Eventually the fish develops a permanent S-shape even when at rest. There is no specific treatment for electrocution. When you discover a fish that has been electrocuted, the following may apply:

 When it is a big fish, kinked, right side up, with normal buoyancy, the kinking may worsen and the curvature can become more severe over time. These fish have more mature musculature and are growing more slowly. They recover more slowly.
 When it is a small fish, kinked, right side up, with normal buoyancy the kinking almost always resolves to 95% of normal, swimming will probably return to normal. Recovery times are normally six to eight weeks. You can see improvements within a week, but it's gradual and recovery may not be complete.
 When it is a big fish, laying over and sinking, the prognosis is extremely poor. These fish cannot equilibrate and they end up being unable to support their body mass nutritionally. Such a fish end up beating the "downside" eyeball out of the socket as it tries to swim.
 When it is a small fish laying over and sinking, it is still a poor prognosis. This fish may be able to eat enough to survive for a time, and perhaps equilibrate, but may not recover and die a slow death.
 When it is a big fish with the right side up, but on the bottom, it may have a swim bladder full of water. It will survive as long as it is able to feed but will eventually develop ulcers similar to “bed sores” and regular treatment will be necessary. There is a specialised procedure wherein the bladder can be tapped, guided by Ultrasound, and the water removed from the air bladder and a mixture of air and antibiotics inserted, but I have never witnessed an attempted, let alone a successful procedure.
 When it is a small fish, right side up but sinking, it may not be worthwhile to try and save the specimen as it may never fully recover.

Drastic temperature changes during early developmental stages are thought to be responsible in some cases. Some authorities maintain that various contaminants may also be responsible in some instances. 

As stated in the beginning of the article, carefull detective work is necessary to determine the real cause of the deformity.

Updated 1 July 2010 

Last Updated on Thursday, 01 July 2010 09:45