is adequate to promote growth of larvae of 0. edidis 

 but is insufficient for the spat. 



With tlie exception of the toxic Prymnesium 

 parmim, the naked flagellates provided better food 

 for young oyster larvae than the organisms with 

 hea\y cell walls, which can be utilized only by 

 older larvae. The best single foods were found 

 to be Isochrysis galbana, ^fonochrysis Intheri, 

 Chrom.idina ■pleiades, Dicraferia inornata, and 

 some other unidentified species of Dicrateria. 

 Since the cultures used in these experiments were 

 not free of bacteria, the question naturallj' arises 

 whether the marine bacteria ace utilized as food. 

 Davis (1953) states that none of the 13 species of 

 marine bacteria tested by him were used by the 

 larvae. The species of bacteria have not been 

 identified. However, the probability that, larvae 

 nuiy derive a certain amount of food from some 

 bacteria is strengthened by the observation re- 

 ported by Davis (1953) and Loosanoff (1954) that 

 larvae kept in cotton-filtered sea water without 

 algal food continued to grow for as long as 14 to 

 IS days. The role of marine bacteria in tlie feed- 

 ing of oj'ster larvae needs further experimental 

 study. 



Apparently the best results in rearing larvae 

 under artificial conditions are obtained with a 

 mixed food of Isochrysis galbana, Monochrysis 

 lutheri, Chromulina pleiades, and Dicrateria sp. 

 With such a diet and at 30° C, the larvae of C. 

 virginica begin setting between the 10th and 12th 

 days after fertilization; at 24° C, the sibling 

 larvae are ready to set on the 24th to 26th day; 

 at 20° C, only a few of the larvae set by the 3Sth 

 day. Setting of larvae of 0. lurida at a tempera- 

 ture of 22° C. takes place on the 7th day after 

 release of larvae from the brood chamber (Loosan- 

 off and Davis, 1963a). 



Under laboratory conditions in Woods Hole the 

 young larvae of C. virginica are often found on the 

 bottom of vessels entangled in lumps of several 

 individuals. These larvae never recover and 

 usually die within the next 24 hours. Sometimes 

 the larvae of oysters and clams are attacked and 

 killed by a fungus which has been tentatively 

 identified by the workers at the Bureau of Com- 

 mercial Fisheries Biological Laboratory at MiKord, 

 Conn., as belonging to the genus Sirolpidium 

 zoophtorum Vishniac (Davis, Loosanoff, Weston, 

 and Martin, 19-54; Johnson and Sparrow, 1961). 

 There are undoubtedly other bacteria and possibly 

 viruses which inflict epizootic mortality on larval 



populations in the laboratory and in natural 

 waters. 



The technique of rearing oyster larvae has pro- 

 gressed sufficiently to be applicable to practical 

 purposes of oyster cidture. Details of techniques, 

 organization, and operation of a mollusk hatchery 

 are summarized by Loosanoff and Davis (1963b). 



BIBLIOGRAPHY 



Andrews, Jay D. 



1951. Seasonal patterns of oyster setting in the 

 Jamos River and Chesapeake Bay. Ecology, vol. 

 32, No, 4, pp. 752-758. 

 Ber.nard, Feuk. 



1898. Recherches ontogeniques et morphologiques 

 sur la coquille des lamellibranches. Partie I. 

 Taxodontes et anisomyaires. Annales des Sciences 

 Naturelles, Zoologie, serie 8, tome 8, pp. 1-208. 

 BoNNOT, Paul. 



1937. Setting and survival of spat of the Olympia 

 oyster, Ostrea lurida, on upper and lower horizontal 

 surfaces. California Fish and Game, vol. 23, No. 

 3, pp. 224-228. 

 1940. Methods of collecting oyster spat. Trans- 

 actions of the American Fisheries Society, vol. 69, 

 for the year 1939, pp. 263-267. 



BOEISIAK, A. 



1909. Pelecypoda du plankton de la Mer Noire. 

 Bulletin Seientifique de la France et de la Belgique, 

 tome 42, pp. 149-184. 

 Bruce, J. R., Margery Knight, and Mary W. Parke. 

 1940. The rearing of oyster larvae on an algal diet. 

 Journal of the Marine Biological Association of the 

 United Kingdom, vol. 24, No. 1, pp. 337-374. 

 Butler, Philip A. 



1955. Selective setting of oyster larvae on artificial 

 cultch. Proceedings of the National Shellfisheries 

 Association, vol. 45, August 1954, pp. 95-105. 

 Carriker, Melbourne Romaine. 



1951. Ecological observations on the distribution of 

 oj'ster larvae in New Jersey estuaries. Ecological 

 Monographs, vol. 21, No. 1, pp. 19-38. 

 1959. The role of physical and biological factors in 

 the culture of Crassostrea and Mercenaria in a salt- 

 water pond. Ecological Monographs, vol. 29, No. 

 3, pp. 219-266. 

 1961. Interrelation of functional morphology, be- 

 havior, and autoecology in early stages of the 

 bivalve Mercenaria mercenaria. Journal of the 

 Elisha Mitchell Scientific Society, vol. 77, No. 2, 

 pp. 168-241. 

 Chestnut, A. F., and William E. Fahy. 



1953. Studies on the vertical distribution of setting 

 of oysters in North Carolina. Proceedings of the 

 Gulf and Caribbean Fisheries Institute, Fifth 

 Annual Session, November 1952, pp. 106-112. 

 Cole H. A. 



1937. Experiments in the breeding of oysters {Ostrea 

 cdiilis) in tanks, with special reference to the food 

 of the larva and spat. Fishery Investigations, 

 series II, vol. 15, No. 4, 1936, 25 pp. 



376 



FISH AND WILDLIFE SERVICE 



