The general objective of the study was to determine modulation of gene expression by environmental factors 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. This experiment was designed as a new type of gravitational experiment which we like to call relative microgravity referring to the fact that the larvae first grow in hyper gravity for 5 days and are then returned to 1g normal gravity for 1 day. Zebrafish embryos were placed on a Large Diameter Centrifuge at 3 hpf brought to a gravitational force of 3 g until 5 dpf. Reference embryos were kept in parallel at 1g (Inc). At 5dpf one batch was left at 3g (3g) one batch was returned to 1g (3g>1g) while a third batch was returned to 1g but left on the axis of the centrifuge (Axe; 3g>Axe). The experiment was repeated 4 times each time with 4 batches of 60 larvae.