Scoliosis

From Fish

Piscine scoliosis is defined as a congenital nutritional deficiency resulting in curvature of the dorsal spine of fish. It is thought that scoliosis in fish is caused by several diverse agents that possibly act on the central nervous system, neuromuscular junctions, or ionic metabolism.

Cause

Skeletal deformities in fish may be caused by pollutants and chemicals, nutritional deficiencies, infectious diseases and genetics. Moreover, some environmental factors such as thermal shock and overcrowding might play a role in the generation of deformities in fish during early growth.

The classical cause of scoliosis, or “broken back disease” in fish is ascorbic acid deficiency. Improvements in feed manufacture, including phosphorylation of vitamin C, and feed storage, have decreased the incidence of nutritionally derived scoliosis. Still, ascorbic acid deficiency must be considered as a possible cause of scoliosis and a thorough review of feeding practices is warranted when evaluating such cases[1].

Less dramatic signs of deficiency include impaired wound healing and immune function. Deformation of gill cartilage, visible on wet mounts of gill tissue, may indicate ascorbic acid deficiency[2].

The organochlorine pesticide Kepone induces scoliosis in the sheepshead minnow. Some effects associated with Kepone-induced scoliosis in these fish are disruption of myotomal patterns, inter- and intramuscular hemorrhage, fractured centra of vertebrae, and death[3].

Clinical signs

Disease manifests itself most often at the larvae or fry stage, more rarely in adult fish. Sometimes spine curvature can be observed in live-bearing females after fry appear, which can be explained by a dramatic change in abdominal pressure. The spine can become curved in any place; sometimes curvature is observed in several places, it can be both vertical and horizontal. As a rule, sick fish will show impaired growth, though they will not exhibit loss of appetite. Scoliosis is fatal only in larvae and several-week-old fry[4].

Treatment

None known. Affected fish should be disposed of if they appear to be suffering.

Avoid inbreeding. From an early age, it is essential to maintain optimal thermal and hydrochemical regimes and provide a balanced diet necessary for the breeding stock. Do not overstock the aquarium and try to prevent traumas, especially at the larva and fry stages. The tank should have enough plants. Add fresh, settled water to the aquarium at least once a week. Water hardness should be only decreased to the level necessary for a particular fish species during spawning, incubation, larvae and fry development.

Fish should be fed based on a percentage of body weight. For maintenance, 0.5-1.0% body weight per day is adequate. Fish should probably be fed at least 5 days per week. The most common mistake made by pet owners is over-feeding their fish, often with resulting degradation of water quality. Occasionally however, owners dramatically underfeed their fish. This is alluded to above. One feeding per day is plenty for most pet animals. Rearing of young stock does require small meals fed more frequently. This is often accomplished using automatic feeders on commercial farms.

References

  1. Roberts, R.J. 1989. Nutritional pathology of teleosts, In: Fish Pathology, R.J. Roberts (Ed).,. Balliere-Tindall, London Pp. 337-362
  2. Merck Vet Manual
  3. Couch, JA et al (1977) Kepone-induced scoliosis and its histological consequences in fish. Science 197(4303):585-587
  4. Fishy portal