SOME ASPECTS OF OSMOREGULATION IN EMBRYONIC AND ADULT CYMATOGASTER AGGREGATA AND OTHER EMBIOTOCID FISHES

¹ Department of Biological Sciences, University of California, Santa Barbara, Goleta, California

1. The osmoregulatory abilities of adult and embryonic Cymatogaster aggregata were tested by determining serum freezing points and weight changes after exposure to dilutions of sea water ranging between 15 and 100 per cent.

2. Adults were able to regulate in external media ranging between 20 and 100 per cent sea water. The greatest deviations of weight and serum freezing point from the normal occur after one to two days in the experimental media. Regulation in all media is complete at or before nine days of exposure.

3. The ability of embryos to regulate is proportional to their stage of development. The youngest animals tested regulate only in media with values between 25 and 36 per cent sea water.

4. Similar though less extensive experiments were performed with adult Amphistichus argenteus and Micrometrus minimus. The osmoregulatory ability of these species is identical to that of adult C. aggregata.

5. Preliminary experiments using Cl³⁶ as a tracer indicate that the branchial salt secretory mechanism present in the adults is absent or operating less efficiently in the embryos of C. aggregata.

6. Observations on the volume of the gut in different external media indicate that the embryos drink the medium, thus creating an osmotic gradient between the body fluids and the lumen of the gut. The result is dehydration or "edema," depending upon the tonicity of the external medium.