Cb. Cowey et B. Woodward, THE DIETARY REQUIREMENT OF YOUNG RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) FOR FOLIC-ACID, The Journal of nutrition, 123(9), 1993, pp. 1594-1600
We sought to determine the dietary folic acid requirement of young rai
nbow trout using growth indices supported by measurements of tissue fo
late concentrations. The investigation was conducted with purified die
ts that had, by assay, basal folic acid levels of 0.08 and 0.16 mg/kg
in the first and second, respectively, of two experiments. Each experi
ment was started with fry (initial mean weight, 1.4 and 2.8 g/fish in
Experiments 1 and 2, respectively) and was conducted at a water temper
ature of 15-degrees-C. Experiment 1 lasted 18 wk and Experiment 2 last
ed 16 wk. Recovery tests (of 8 wk duration, performed on fish fed the
unsupplemented diet) and pair-feeding showed that the unsupplemented d
iet led to a folate-specific deficiency condition in which the main he
matological abnormality was the appearance of misshapen nuclei in a sm
all proportion (2.3%) of erythrocytes. Dietary requirements were shown
not to exceed 0.3 and 0.6 mg folic acid/kg (17 and 33 mug/MJ digestib
le energy) for optimizing survival and growth indices, respectively. W
e conclude that the dietary folate requirement of the trout is compara
ble to that of other vertebrates for the purpose of achieving maximal
weight gain.