Time-marking methods for scanning electron microscopy in goldfish otoliths.

To produce time marking on otoliths for scanning electron microscopy, young goldfish Carassius auratus were treated with one of the following: tetracycline, ammonium chloride, Diamox, sufocation, starvation, or cold shock. Of those, tetracycline, 1% ammonium chloride and 7 days' starvation produced almost no special markings in the otoliths (lapilli). Didmox (200mg or 500mg/kg) and 30 minutes' suffocation tended to leave markings in the otoliths. However it seems difficult in nature to separate these markings from other check rings formed by unknown events before and during the experiments. The intraperitoneal injection of 3% ammonium chloride also produced a stress marking but this treatment resulited in a high mortality of 50%. Cold shock (23 to 4.2°C) produced a well-defined marking in the otolith and it was easy to discern this marking from other kinds of check rings. The formation rate of the first-order rings in the otoliths was calculated as 0.94 per day by using the experimentally induced markings.