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Growth, nutrient utilization and body tissue composition were investigated in juvenile carp (Cyprinus carpio) fed diets which meet either 100% (100P), 70% (70P) or 38% (38P) of phosphorus (P) requirements. Diet 70MP, in which microbial phytase of 1000 units was incorporated into diet 70P, was made in order to study to what extent growth and P utilization could be improved. Available P in diet was adjusted to 0.64%, 0.44% and 0.24% using monocalcium phosphate (MCP). Diets were fed to fish with an average weight of 10.3 g for 8 weeks. The best weight gain and specific growth rate were found in fish fed 100P (28.5 g and 2.38%), which were not significantly different (P$gt;0.05) from those (27.8 g and 2.34%) of fish fed 70MP. The lowest values (19.7 g and 1.90%) were obtained in fish fed 38P. Feed conversion ratio ranged from 1.06(100P) to 1.43 (38P), the latter showing a difference from other groups. Nitrogen and phosphorus gains in whole body were higher (P$lt;0.05) in fish groups fed diets 100P and 70MP than in the other two groups. The lowest moisture content (71.9%) was shown in fish fed 38P with the highest protein (15.3%) in whole body. Fish fed 70MP showed the lowest lipid content (7.8%), which w as. however, not different from that (8.6%) of 100P groups. Whole body P content of 100P groups (0.54%) was comparable with that of 70MP groups (0.52%), which was, however. not different from those of the other two groups. Ca and P levels in skin and bone were highest in fish fed 70MP. though there were no significant differences among 100P, 70P and 70MP groups. The present results indicated that available P in diet greatly affected both growth performance and composition of whole body, tissue and bone of juvenile carp. And also. it was revealed that microbial phytase could replace 1% of MCP without any significant difference in criteria above-mentioned.
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