PRELIMINARY RADIOGRAPHIC OBSERVATIONS OF VERTEBRAL CHANGES IN DISCUS ( SYMPHYSODON DISCUS)

Discus ( Symphysodon discus) maintained in aquaria are held in a wide range of water parameters and subjected to many different feeding regimes. In a pilot study, four groups of discus (mean length 12.1 cm, mean weight 57.3 g) were submitted to a radiographic examination to assess the skeletal structure of the vertebral column under defined environmental conditions. Water temperature was 30°C for all groups. Two groups were held at <28.6 mg/L calcium (Ca) and two at 50.0-78.6 mg/L Ca within the ambient water. One of each water quality group was fed a commercial discus diet while the other two groups were kept on a plain beef-heart diet, creating a total of four separate groups. In the case of the beef heart group, dietary Ca content (g/kg) was 0.06 and phosphorous (P) content 2.06, leading to a Ca : P ratio of 0.03, whereas in the commercial diet group a Ca content of 20.1 g/kg and P of 7.36 g/kg resulted in a Ca : P ratio of 2.7. Magnesium (Mg) contents of the beef-heart diet were 0.21 and of the commercial diet 1.69 g/kg. Six fish were submitted to radiography at the beginning of the experiment as a control. After 16 wk of the above diets and environmental conditions, radiographs were taken from all fish (six per group) and evaluated by three independent persons using a scoring system. Alterations were found in all groups. The results of this pilot study give reason to scrutinize rearing and keeping conditions of this fish species.