The following experiment was designed in order to elucidate as of whether CAH is the only factor regulating otolith mineralization in dependence of the gravity vector: A first group of larval cichlid fish (Oreochromis mossambicus) was reared in normal aquarium water at 1g (1g-Aq). A second group received hg (3g, 7 days) as a physical factor to decrease CAH reactivity (3g-Aq). A third group (1g-AZ) was (at 1g) treated with azetazolamide (AZ; 1 g/l), an inhibitor of CAH (the AZ-concentration used resulted in a complete inhibition of CAH as had been proven by a biochemical assessment of enzyme activity). The last group was maintained both in AZ and at hg (3g-AZ).
Both the saccular and utricular otoliths (sagittae and lapilli, respectively) of the 1g-AZ group showed a decrease in otolith growth (surface area) as compared to the 1g-Aq animals (1g-AZ < 1g-Aq). Similar results were obtained when comparing 3g-Aq with 1g-Aq samples (3g-Aq < 1g-Aq). Regarding sagittae, AZ treatment had no significant additional effect on otolith mineralization under hg (3g-AZ = 1g-AZ). In case of lapilli, however, growth received a further reduction when reared in 3g-AZ (i.e., 3g-AZ < 1g-AZ). Thus, in lapilli, hg and AZ added their effects on otolith growth.
This finding clearly indicates that hg does not only act on otolith growth via a regulation of CAH activity.