The general objective of the study was to determine modulation of gene expression by environmental factors specifically simulation of microgravity with a special emphasis on bone formation. For this reason the specific period of treatment was chosen between 5-6 days post-fertilization (dpf) when bone formation and calcification are taking place. Zebrafish larvae were placed at 5 dpf into a clinostat (CLINO) for 24 hours which was shown to simulate microgravity by the specific rotational movements it generates. We show that CLINO exposure causes a clear decrease of bone formation as illustrated by cranial skeleton staining of the bone matrix by Alizarin Red by morphometric analysis of the resulting images. Thus a whole genome micro-array experiment was conducted to identify genes that may be involved in the observed effect on bone formation.