636 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



a leng'tli of 0.11 to 0.16 millimeter. Sometimes 20 were found in one 

 and the same larva resembling a string- of J&ne beads and filling the 

 whole space from the month to the " sphincter ani." The copepods, at 

 first of the ISTauplius kind, were not quite so frequent among the contents 

 •of the intestinal tube. 



When Professor Heusen and I examined some of these larvce on the 

 10th day after being hatched, we found a small number of colorless and 

 scarcely visil>le particles of blood. 



After the 10th day the number of our young fish, which had so far 

 enjoyed excellent health, began to diminish in a very noticeable degree. 

 Finally their number dwindled down so rapidly that I was afraid my 

 experiment would be brought to a premature close. The fish did not 

 seem to grow much more in length, although some progress could be no- 

 ticed in its transformation from a larva to a definite fish shape. But the 

 length of the largest one on the 4:7th day after impregnation was only 

 12 millimeters, whilst, according to my observations of young herrings 

 raised in the open water of the Schlei, it ought to have been about 17 

 millimeters. An increase of only 3 millimeters during a whole month 

 could certainly not be called a normal development. The intestinal tube 

 was nevertheless filled nearly all the time. 



Hitherto fresh water had been poured into the oval vessel through a 

 thick cloth, so as to keep out any enemies of the herring. I now made 

 a change in this respect, by pouring the fresh water direct into the ves- 

 sel, hoping thereby to give to the young fish more and more varied food. 

 I can of course not decide whether the favorable turn which matters 

 took was owing to this change, but I know of only one cause of the 

 sudden growth of the fish, namely, the largely increased number of 

 copepods. 



By this increased growth during the third and following months the 

 artificially hatch^ fish at the end of the fifth month reached exactly the 

 same size as the herrings of the same age living in the open water of 

 the Schlei — which I have mentioned in a former report. This was further 

 corroborated by a number of young herrings raised in the Schlei simul- 

 taneously with those kept in confinement. 



