510 U. S. BUREAU OF FISHERIES 



item in the diet of the lake fish after they had attained a size of 

 about 12 inches. Up to this size plankton Crustacea formed about 25 

 per cent of the food. From this it is evident that the larger cut- 

 throat trout consume considerable numbers of forage fish where they 

 are available. Stomach examinations of 46 fry of this species showed 

 a great variety of diet, with the larvae of Chironomous forming the 

 most important item. 



OYSTEB INVESTIGATIONS 



During 1930 investigations relative to various phases of oyster 

 culture were carried out along the Atlantic and the Pacific coasts, 

 the staff of the investigators being more or less evenly distributed in 

 different oyster-producing sections. In New England waters the 

 headquarters for oyster investigation remained, as in previous years, 

 at the Fisheries Laboratory at Woods Hole, where work on physi- 

 ology of spawning has been continued. Cold Spring Harbor Bio- 

 logical Station, on Long Island, was selected as a suitable place for 

 an experimental study of the control of starfish. The Beaufort 

 (N. C.) laboratory served as the headquarters for South Atlantic 

 investigations, which w^ere greatly expanded during the last year and 

 extended from North Carolina to Florida. On the Pacific coast a 

 study of the life history and cultivation of the west coast oyster, 

 Ostrea lurida^ was continued. Thanks to the cooperation with the 

 Washington State Department of Fisheries and Game, a small but 

 well-equipped laboratory located in the center of the oyster industry 

 near Olympia was made available for the bureau's investigators. 

 In cooperation with the State authorities of Oregon and California, 

 a survey of local oyster bottoms and experiments on oyster culture 

 were made. 



PHYSIOLOGY OF SPAWNING 



A study of factors that control spawning is of paramount impor- 

 tance for the successful cultivation of oysters. 



The results of the large number of experiments with O. mrginica 

 carried out by Dr. P. S. Galtsoff from 1927 to 1929 show that no 

 spawning occurs below 20° C, whereas the same specimen can be 

 induced by sperm to sj)awn as soon as the temperature has been 

 brought above 20°. In a few instances it has been noticed that oysters 

 spawned at 27.5° without being stimulated by sperm. Inasmuch as 

 in those cases unfiltered water was used, the possibility of its con- 

 tamination with sperm was not excluded. In the experiments with 

 O. glgas it has been found that a ripe female can be induced to spawn 

 by a temperature of 30° C. The question naturally arises whether 

 the same results could not be obtained with the other species. During 

 the summer of 1931 experiments were carried out at Woods Hole 

 with ripe 0. virginica> which were kept in aquaria at a temperature of 

 about 20°. To avoid possible contamination the water used in the 

 experiments was filtered through a layer of asbestos about three- 

 quarters of an inch thick. The results of the experiments indicate 

 without any doubt that ripe females can be induced to spawn by 

 placing them in water having a temperature from 24.5° to 30° C. At 

 31° the females usually close their valves and remain closed until 

 the temperature drops to 30° or 29° C. 



