Abstract

Minimal dietary pyridoxine requirements of the gilthead bream ( Sparus aurata Linnaeus) were determined. Partially defined test diets containing graded levels of pyridoxine were fed to groups of fish of average initial weight 2.7 g and 70 g. The criteria used to measure pyridoxine requirements were growth, mortality, food conversion, fish behavior, liver alanine aminotransferase (AAT; EC 2.6.1.2) activity and histopathology. At the lowest dietary pyridoxine level used with the small fish (1.15 mg/kg dry diet) and at the two lowest levels used with the bigger fish (1.15 and 1.46 mg/kg dry diet), vitamin deficiency symptoms were evident in all parameters examined. Signs of deficiency were manifested as growth retardation, high mortality, poor food conversion, hyperirritability coupled with erratic swimming behavior and degenerative changes in peripheral nerves. In both experiments, the dietary level at and above which no deficiency signs appeared was 1.97 mg/kg dry diet. Liver AAT activity was a more conservative parameter, indicating pyridoxine insufficiencies in both groups of fish also at the level of 1.97 mg/kg dry diet.

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