The Embiotocidae is a family of marine (with one exception) teleosts which is somewhat unique in that all species possess a truly viviparous type of development. The young remain in the hollow ovary of the parent for a period of about five months, during which time they increase in size from 0.24 mm. (fertilized egg) to about 42 mm. (newborn) (Eigenmann, 1890(Eigenmann, , 1894. It was learned while devising a technique for culturing the embryos in vitro (Triplett, unpublished) that, unlike the adults, they are capable of tolerating only very limited variation in the osmotic concentration of the external medium.The object of this study was to learn more precisely how well these animals can regulate to variations in the concentration of the external medium both as adults and during development. In addition, preliminary experiments were performed in an effort to find out why the adults are better able to regulate than the embryos.
Materials and Methods
Experimental animalsCymatogaster aggregata (Gibbons) was the most easily obtained of the embiotocids and was therefore the principal organism used in the investigation. This species is widely distributed over the west coast of North America, ranging from southern Alaska through Baja California (Tarp, 1952). It has been observed in estuaries where the salinity is quite variable (Hubbs, 1917) as well as in bays and along the open coast. Animals used in these experiments were collected by angling from Goleta Pier, Goleta, California.Less extensively investigated were Amphistichus argenteus (Agassiz) and Micrometrus minimus (Gibbons). These species have about the same distribution as C. aggregata, but so far as the authors are aware, they do not enter brackish water. For these experiments they were collected with a beach seine on the campus beach at Goleta, California. Only adults of these two species were used.
MethodsThe general approach was to determine the total osmotic pressure of the serum and the change in body weight after exposure to experimental salinities for periods ranging from six hours to nine days.
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