- Swim bladder non-inflation is common in hatchery-reared fish and was also reported in angelfish, Pterophyllum scalare L. Fish eggs are routinely treated with disinfectants and exposed to a variety of physical conditions. We studied the effect of these factors on the prevalence of swim bladder non-inflation in angelfish. Hatching and rearing at 26 °C resulted in 8% swim bladder non-inflation, compared to no swim bladder non-inflation at 28 °C. Eggs hatched in the presence of 1, 2 and 5 ppm methylene blue exhibited significant increases in swim bladder non-inflation (11, 9 and 33%, respectively; none in controls). Time of exposure to methylene blue was a key factor. Exposure for up to 1 day post-hatch did not affect swim bladder non-inflation, but exposure from 2 days onwards significantly increased swim bladder non-inflation. Hydrogen peroxide at 250 ppm significantly increased swim bladder non-inflation (65% comparing to 27% in the control). Higher concentrations resulted in 100% mortality. Exposure to acriflavin at 2.25 ppm, but not 1.25 ppm, significantly increased swim bladder non-inflation (75 and 52% respectively; 20% in controls). Chloramine-T did not significantly affect swim bladder non-inflation. Treatment with methylene blue and acriflavin, but not chloramine-T, produced significantly different frequencies of swim bladder non-inflation morphologies compared to control fish. In conclusion, several chemical treatments commonly used in aquaculture and sub-optimal water temperature increase the prevalence of swim bladder non-inflation in angelfish.