Analysis of Behaviour and Habituation of Fish Exposed to Diminished Gravity in Correlation to Inner Ear Stone Formation a Sounding Rocket Experiment (texus 45)

The aim of this study was to analyze the time course of the behavioral adaptation to diminished gravity aboard a texus sounding rockrt in correlation with the calcification status of inner ear otoliths. Experimental animals were fish-larvae (Oreochromis mossambicus). The adaptation to the two applied levels of low gravity between 10 -4 g (platform zero-g of the rocket) and 4x10 2 g (diminished gravity obtained by centrifugation aboard the rocket = “zero-g” occurring during parabolic air craft flights) was followed and the difference in the time profiles of adaptation were analyzed. The accuracy of symmetry in individual otolith-pairs (left vs. right side) was versed proportional to the time required for regain to normal swimming behavior in the zero-g phase of the flight, e.g. in normal, coordinated swimming fish the symmetry of otholiths between left and right side is high (less than 0.9 % deviation at 10 -4 g respectively less than 4% at 5x10 -2 g). In those fish which displayed kinetotic behavior the mean relative difference between left and right ear stone is 12.3% in the case of 10 -4 g and 6.2% when 4x10 -2 g were applied. Source of otolith asymmetry, which leads to kineotic behavior are irregular crystallization, differences in growth and unusual adipose of calcium layers. The data give evidence, that nearly all fish were able to sense 4x10 -2 g and more that 60% at 10 -4 g.