154 



Part III. — Twenty-third Annual Report 



VII. — A NOTE ON THE HATCHING OF THE CRAB {CANCER 

 PAGURUS). By H. Chas. Williamson, M.A., D.Sc, Marine 

 Laboratory, Aberdeen. 



In the summer of 1902 a quantity of the fry of the edible crab was 

 distributed in the sea off the coast of Aberdeenshire. 



Nine berried crabs (breester, pea-parten) were obtained chiefly in the 

 neighbourhood of Aberdeen. They were kept in two concrete tanks 

 until the larva? hatched out. Shelter was afforded the crabs in cavities 

 formed by building stones up on the sand-covered bottom of the tank. 

 When the fry hatched out it was attracted to the glass front of the 

 tank, from which side the light entered, and when present in quantity 

 the fry formed a thick white cloud. The young crabs were drawn off 

 into the carboys by means of a syphon. All the fry of the crab 

 deposited near Fraserburgh and Findochty was in the first zoea stage. 

 The crab fry was disposed of as follows : — 



August 6, 1902. — About 1 million set free about 1 mile north of 

 Fraserburgh. 



August 7, 1902. — About 2 millions set free about § mile off 

 Gairnbulg. 



August 19, 1902. — About 1 million set free about f mile off St. 

 Combs. 



September 15, 1902. — About j million set free about f mile north of 

 Findochty. 



The method of estimating the numbers of crab fry was as follows. 

 The fry that was set free was provided by nine berried crabs, and at the 

 low average of half a million eggs to each crab, should number 

 4 1 millions. The proportion of this total set free at each of the four 

 above-mentioned places was apportioned approximately by the number of 

 carboys required for the consignment. 



The crabs hatched out in August, September, and October. The 

 vitality of the crab fry was tested in the following manner. Crab fry 

 were crowded into a glass jar. The water was heated to 17 j° C, and 

 then allowed to cool. Next forenoon the majority was alive and lively. 



On one of the journeys the water in one of the carboys was cooled to 

 about 7° C. The crab fry in this carboy did not, at the end of the 

 journey, appear to be in any better condition than those which had been 

 filled with water at the temperature of the hatchery. 



The crabs which furnished the fry were kept alive when the hatching 

 was finished, and some lived until the spring of 1905. The history of 

 the members of the 1902 group throws some light on certain of the 

 problems of the life-history of this species. It has been already outlined.* 



In January 1903 two of these crabs were dissected; one had died, 

 the second was killed. In the former the ovary was white, with a very 

 slight pink tinge. There were a few red eggs in a bunch near the 

 oviduct. The eggs were degenerating ; they were disorganised internally. 



* Vide Williamson. " Contributions to the Life-histories of the Edible Crab (Cancer 

 pagurns) and of other Decapod Crustacea, &c." — Twenty-second Annual Report of the 

 Fishery Board for Scotland, Part III., 1904. 



