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Effects of Dietary Calcium and Phosphorus on Growth, Food Conversion, Bone Ash and Hematocrit Levels of Catfish¹

The University of Georgia Agricultural Experiment Stations and The Skidaway Institute of Oceanography, Post Office Box 13687, Savannah, Georgia 31406

Channel catfish (Ictalurus punctatus) fingerlings were fed diets containing varying dietary levels and ratios of calcium (0.5 to 2.0%) and phosphorus (0.5 to 1.2%). Results from two studies indicated that the available phosphorus requirement of catfish is approximately 0.8% of diet. In both experiments gains were maximal in fish fed diets containing 1.5% calcium and were reduced when higher levels were fed. This hypercalcemia effect could not be prevented by adjusting the Ca/P ratio by the addition of phosphorus to the diet. A phosphorus deficiency characterized by reduced growth, poorer food efficiency and lower bone ash and hematocrit levels occurred in fish fed 0.5 or 0.6% available phosphorus. The absence of a growth response to 0.4% supplemented phosphorus in the form of calcium phytate suggested that catfish are not able to fully utilize phytin phosphorus. Bone ash values from skull and vertebrae samples indicated that the calcium requirement for maximal bone mineralization may be higher than that for optimal growth.

KEY WORDS: • calcium • phosphorus • catfish • growth

¹ This investigation was financed by a contract from the Georgia Game and Fish Commission and the Department of Commerce, National Marine Fisheries Service, under Public Law 88-309, Project no. 2-84-R. Part of the matching funds for this aid-to-state project was provided by a grant from Gold Kist, Inc.

Manuscript received 10 November 1972.