On the feeding habits of oysters.

Abstract

Studies of the feeding habits of oysters have been in progress since the spring of 1919 to determine: (1) the duration of active filtration of water, and (2) the effects of salinity, temperature, light, food content, and turbidity of the water upon the rate and the extent of feeding. The animals were studied while lying on an oyster reef in their natural environment. By means of recording apparatus continuous kymograph records of all shell movements of the oysters for over 2 months were obtained. Water samples were taken at regular intervals of time and tide, and in addition whenever the animals closed completely or opened after a period of closure in excess of 2 minutes. 1

The investigations have been carried on in several different environments, under widely varying conditions, and warrant the following conclusions:

1. With the water temperatures of late spring, summer, and early fall oysters are active throughout most of the day and part of the night. At temperatures above 20° C. New Jersey natural oysters are actively passing water through the gills for an average of over 20 hours out of the 24.

2. A sudden drop in temperature may result in temporary decrease in the daily number of hours of activity.

3. Between 4°–6° C. there is a sharp decrease in the ciliary activity of oysters. Normal feeding occurs above this range, while almost no food is taken when the temperature of the water is below 4° C. Round 2 found active elimination from oysters at 9° C. but no reduction in the number of bacteria at 5° C. until after a period of 5 days.

4. The rate of filtration of water during any given period of time, as deduced from the rapidity and the extent of ejections of accumulated sediment from the mantle cavity, may vary widely independently of the temperature and the turbidity of the water.