fattening of oysters (Hinard, 1923). American 

 biologists made similar observations in C. virginica. 

 McCrady (1874) concluded that "diatoms and 

 spores of algae" constitute the food of Carolina 

 oysters; Lotsy (1893) found that in the James 

 River, Va., "oyster lives almost exclusively on 

 diatoms"; according to Smeltz (1898), the natural 

 food of Florida oysters "can be supplemented 

 by . . . the pollen of our pine trees and the bloom 

 of our palmetto", (p. 307) but no evidence vs^as 

 presented that pollens were found in the stomachs 

 or that they can be digested by the oysters. The 

 flourishing and fattening of oysters in Delav^are 

 Bay was attributed by Nelson (1947) to the abun- 

 dance of the diatom Skeletonema, which he called 

 "the most valuable of all diatoms in the food of 

 oysters in New Jersey watei-s." In an earlier 

 paper (1923b) and in the Report of the New 

 Jersey Agricultural Experiment Station for the 

 year 1924 (Nelson, 1925), he emphasized the 

 significance of nannoplankton which "comprise by 

 far the largest part of the food of the oyster" and 

 at times is composed of small flagellates and other 

 minute forms which may comprise 80 to 90 percent 

 of the stomach's contents. Since no plankton 

 analysis was made by Nelson of the Delaware Bay 

 water at the time of the Skeletonema bloom, the 

 conclusion that the species is "the most valuable" 

 requires corroboration. 



Moore (1910) found that eight species of diatoms 

 constituted 98 percent of the total amount of food 

 in the alimentary tract of Texas oysters and that 

 organic detritus also might play an important part 

 in nutrition. Experimental studies of the feeding 

 of oysters made by Martin (1927b) showed no 

 significant differences between the average in- 

 creases in size of young oysters which were fed 

 pure cultures of the diatoms — Nitzschia jmlea, 

 Amphora cojfeaeformis, Nitzschia -poleaceae, Amphora 

 cofeaejormis var. lineata, and one species of green 

 alga, Gloeocystis vesiculo.m. No check was made on 

 the amount of food added to the water and the 

 experiment lasted only 4 weeks. Water was 

 changed only once during this period. Because of 

 the obvious deficiencies in the experimental 

 technique no definite conclusions could be made 

 from these observations. Martin also suggested 

 that zoospores of Enteromorpha and other algae 

 {Ulva, Monostroma, Ectocarpus, and Pylaiella) 

 form an important element in the food of plankton 

 eaters (Martin, 1927a). A comprehensive in- 

 vestigation of the food of the Em'opean oyster 



drfS> G 



Figure 210. — Moore's method for washing out the stomach 

 and intestinal content of the oyster. A — reservoir with 

 sea water; B — canule inserted in the rectum; C — 

 aspirator; D — collecting vessel; E — canule inserted into 

 mouth of the oyster; F — siphon of the reservoir; G^ 

 siphon of the aspirator; O — oyster. Upper insert O — 

 shows the details of the method of inserting canules B 

 and E into the oyster. 



was made by Savage (1925), whose work remains 

 the most valuable contribution to the study of 

 the problem. He used Moore's (1910) method of 

 washing the entire alimentary canal; this technique 

 is diagrammatically shown in figure 210. Two 

 canules are introduced, one into the anus, B, and 

 the wider one, E, into the mouth. Rubber tubing 

 connects the anal canule with the siphon F in- 

 serted in glass container A filled with sea water. 

 The oral canule leads to a small collecting vessel 

 D, which is connected to the aspirator bottle C. 

 By regulating the flow of water from the aspirator 

 C the alimentary canal may be washed out without 

 damaging the digestive tract. The volume of the 

 collected material is measured and the collected 

 microorganisms identified and counted. By this 

 method Savage (1925) sampled at regular intervals 

 the stomach contents of British oysters and analyzed 

 throughout the year the seasonal fluctuations in 

 the abundance of different species of algae. He 

 considered that the following diatoms were the 

 most important food items of the British (Oxford) 

 oysters: Nitzschiella parva, PleurosigmasTp., Coscin- 

 odiscus sp., Rhizosolenia sp., and Melosira sp. 

 The most significant conclusion made by Savage 

 is that the greater part of the food found in the 

 oysters examined by him consisted of organic 



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FISH AND WILDLIFE SERVICE 



