Otolith resorption induced by anaerobic stress in the goldfish, Carassius auratus

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Abstract
To examine otolith resorption induced by anaerobic stress, 45Ca‐prelabelled goldfish, Carassius auratus, were kept in oxygen‐deficient ambient water (O2 < 0.5 .1 1−1, 26° C) for 2 days and otoliths (asterisci) were analysed for 45Ca retention. In a second experiment, fish were anaerobically stressed for 2 days, and then received a single intraperitoneal injection of 45Ca. They were maintained under stress for one more day and killed to examine 45Ca deposition in otoliths. Plasma was analysed for total and radioactive calcium. Otoliths (lapilli) were examined for stress‐induced check formation by scanning electron microscopy (SEM).Stress significantly reduced plasma calcium levels and the rate of calcium retention in otoliths, which was calculated from the 45Ca specific activity of the plasma. On the other hand, the rate of calcium deposition in otoliths was the same in the stressed as in the control fish. SEM observation revealed that the applied stress resulted in a check formation in otoliths. These results indicate that a 48‐h stress of oxygen deficiency induces calcium resorption in otoliths.