Responses of channel catfish (Ictalurus punctatus) swim-up fry to dietary calcium in soft and hard water.

1. Responses of channel catfish (Ictalurus punctatus) swim-up fry to dietary calcium in soft (< 1 mg/l as CaCO3) and hard (> 100 mg/l as CaCO3) water were determined by feeding purified egg-white diets containing 0, 0.5, 1.0, or 2.0% calcium from CaCO3 for 8 weeks. 2. Catfish fry fed the basal diet (0.03% Ca) in hard and soft water had lower whole-body ash and whole-body calcium concentrations but higher weight gain and survival than those fed calcium-supplemented diets. 3. Fry in soft water generally had lower whole-body ash, whole-body calcium, and survival, as well as a higher incidence of spinal deformities than fry in hard water. 4. Feeding higher levels of calcium to fry reared in soft water did not increase whole-body calcium levels or decrease spinal deformities to the levels observed for fry reared in hard water and fed supplemental calcium. 5. These data indicate that calcium derived solely from dietary or environmental sources was not sufficient for optimum health of channel catfish fry.