DIETARY ZINC REQUIREMENTS OF CHANNEL CATFISH, ICTALURUS-PUNCTATUS, SWIM-UP FRY IN SOFT AND HARD WATER
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The minimum dietary zinc requirement of channel catfish swim-up fry was determined in soft (< 1 mg/l as CaCO3) and hard (> 100 mg/l as CaCO3) water. Purified egg-white diets supplemented with 0, 20, 40 or 80 mg Zn/kg were fed to swim-up fry for 6-8 weeks. Weight gain, whole-body ash, wholebody zinc and calcium, survival, mortality due to handling stress, and spinal deformities were determined. Channel catfish fry fed the basal diet in soft and hard water had decreased whole-body zinc levels and increased whole-body calcium levels. Fry in soft water generally had lower whole-body ash and calcium as well as a higher incidence of mortality and spinal deformities than fry in hard water. The minimum dietary zinc requirement of channel catfish fry grown in hard water was determined to be approximately 20 mg Zn/kg diet; whereas fry grown in soft water had a requirement between 20 and 40 mg Zn/kg diet. The greater zinc requirement of fry in soft water did not increase survival or decrease mortality from handling to the levels of fry reared in hard water. Results from this study indicate that environmental calcium interacts with dietary zinc and may influence growth, survival and tissue mineralization of channel catfish fry. 1992.
