Effect of different dietary vitamin B12 levels on their retention in the body of zebrafish Danio rerio and on the gene expression of vitamin B12 binding proteins

Zebrafish Danio reiro were fed a diet with 59 μg vitamin B12 kg−1 feed (59B12) and a diet with 5 μg vitamin B12 kg−1 feed from 36 dpf (days postfertilization) to 80 dpf. There were no differences in growth or signs of anaemia; however, 5 μg kg−1 was not enough to maintain whole‐body vitamin B12 stores. Transcription of genes related to vitamin B12 absorption and transport was measured. Zebrafish orthologues were found for haptocorrin (tcn1), transcobalamin (tcn2), cubilin (cubn), amnionless (amn) and megalin (lrp2), but not for intrinsic factor (gif) or transcobalamin II receptor (cd320). Dietary vitamin B12 did not affect transcription of tcn1 and tcn2 in the proximal intestine, in the distal intestine or in the liver. No expression of the vitamin B12 receptors was detected in proximal intestine and liver in the studied fish. However, cubn and amn were expressed in the distal intestine but were not affected by diet. In conclusion, 5 μg kg−1 vitamin B12 gave no clinical signs of deficiency, but was not enough to maintain the whole‐body vitamin B12 storage. The selected dietary vitamin B12 levels did not differentially regulate expression of genes coding for proteins involved in vitamin B12 absorption and transport.