Skeletonema costatumを餌料とするアコヤガイの飼育について

抄録

Rearing of the yearling pearl oyster, Pinctada martensii (DUNKER), of 24-26mm. in average shell hight (see Table 1), were tried mainly on the diet of Skeletonema costatum, during two months from April 13 to June 13, 1963. A series of six glass vessels (see Fig. 1), A-F, each containing sea water of about five liter and equipped with a filter bed, circulating and aerating apparatus, was set in a thermostatic box kept within a range 20-23°C. The culture sea water was changed daily with fresh ones. Ten individuals of the oyster were put in each culture vessel.
Food plankton was prepared in the medium shown in Table 2. 1000, 500, 200, 100, 50 and 20ml. of suspension containing 200×10⁴ cells per ml. of plankton were daily supplied in dropping within one or two hours into culture vessels respectively, after being diluted into one liter with fresh culture medium. In the culture period of 62 days the oysters were fed for 39 days with Skeletonema costatum and for 9 days with Nitzschia sp.
The growth of shell was estimated by following measurements:
1) Increase in whole weight of the oysters weighed submerged in the sea water. The density of soft part of the oyster is almost alike to that of sea water, therefore the increase in under water weight will present the increase in shell weight (see Fig. 3).
2) Increase in volume of shell, calcalated by the formula, shell hight×length×width (see Fig. 4).
3) Weight of marginal part of the shell, which was formed in the course of the experi-ment (see Fig. 5).
4) Weight of old part of the shell measured at the end of the experiment by initial shell volume, which will present the growth of shell valves in thickness (see Fig. 6). They make sigmoid curves against the plankton supply in logarithmus.
The growth of soft part of the oyster was estimated by measuring, the dry weight of whole meat and adductor muscle by last volume of the shell. They make approximately linear relation against the food supply in logarithmus (see Fig. 7, a and b). From these results, the followings are considered;
A) Skeletonema contatum is useful as food for the pearl oyster.
B) To maintain the initial condition of the oyster the plankton supply of 20×10⁴ cells×(39/62-48/62) per day seems necessary.
C) The growth rate of the oyster is the greatest when the plankton supply was 10⁸ cells per day. The amount would make a concentration of 2×10₅ cells per ml., if the plankton was added at a stretch. But in the experiment it was supplied in dropping within one or two hours, therefore the plankton concentration would be much lower than the upper figure. The food supply in a greater concentration seems of no effect to raise the growth rate.