FEEDING OF OYSTERS IN RELATION TO TIDAL STAGES AND TO PERIODS OF LIGHT AND DARKNESS

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Abstract
Studies made in Long Island Sound and Milford Harbor showed that during all hrs. of the flood and ebb the predominating majority of the oysters (Ostrea virginica) contained large quantities of food. The relative quantities of food during the ebb were at least equal to, or sometimes exceeded, those recorded during the flood. The rate of water pumping of oysters indicated that they feed actively at all tidal stages. The vol. of water filtered by the oysters through their gills during 1 hr. may be >1500 times greater than the vol. of the body of the oysters. Within the temp. range of 17 to 28[degree]C the oysters remained open on an av. of 94.3% of the time. During flood they were open on an av. of 93.4% of the time and during the ebb periods, 95.2%. At night the % of oysters with full stomachs was comparable to that of the individuals examined in the day time. During darkness the oysters fed actively. The ay. rate of pumping was not lower than during daylight. No correlation was found between the periods of closure of the shells and darkness. Under favorable conditions, neither tidal changes nor changes in the time of day affected the rate of feeding. The results do not support the theory that the American osyter does not feed late at night and in the early morning, and is relatively inactive on the ebb tide.