CHINESE MITTEN CRAB — PANNING 375 



UTILIZATION OF MITTEN CRABS 



It is evident that efforts should be made to convert into profit these 

 huge masses of mitten crabs caught daily during the main migration 

 period. In Bremen the crabs are boiled and distributed to farmers 

 who feed them to pigs with good success. Many fishermen crush 

 their by-catch of mitten crabs and feed them raw to ducks which under- 

 stand very well how to pick out the soft substance and thrive well on 

 it. In Garz and Gruetz on the Havel, the mitten crabs are ground 

 in large mills, and when this mutage cannot be fed to ducks, it is 

 dumped into the rivers where the young fishes eat it eagerly. This is, 

 of course, unprofitable and consequently experiments have been made 

 for a long time by the "Havel," an association for the protection of 

 fisheries in Gruetz, which would lead to utilization of the mitten crabs. 

 These experiments have yet not been concluded and, therefore, can 

 not be reported on. 



MUTATION OF MITTEN CRABS 



The mitten crabs have reacted to their introduction into a strange 

 environment with some very conspicuous changes in their outward 

 form. Plate 9 shows the three best examples of this change in the 

 form. The changes have taken place principally in two systematically 

 important characters — the rostrum teeth between the eyes and the 

 three pairs of protuberances on the back behind the forehead. 



If one assumes that the mitten crabs were introduced into Germany 

 arouDd the turn of the century, it has required a comparatively long 

 exposure to the new environment for these mutations to take place. 

 No traces of changes were noticed in specimens brought to us in the 

 twenties. In 1932 and 1933 the mitten crab was conspicuously labile 

 in systematically important characters. The rostrum teeth were 

 weaker and seldom pointed but mostly blunt, almost round; the 

 indentures between the teeth were flatter and often shaped very 

 irregularly; the protuberances on the back were fainter and those of 

 both rear pairs seemed to be inclined to fuse. At that time it was 

 barely possible out of a large mass of mitten crabs to find even a few 

 typical specimens to be used as exhibits. Now the mitten crab 

 again has its original form without any deviation from the Chinese 

 specimens brought to me only recently from Shanghai. It seems 

 (more cannot be said) that the original mutation was accompanied 

 by a general fluctuation of those characters which were affected by 

 the change. 



The parts of the foregoing report not based on my original investiga- 

 tions are taken from volume 47 of the Reports of the Hamburg 

 Zoological Museum and Institute (works by Drs. Peters, Thiel, 

 Schubert, Hoppe, and Peters), which I recommend for further infor- 

 mation. 



