BIOLOGICAL OBSERVATIONS ON THE HERRING. 637 



Probably it "was only the want of suitable food, bionglit about by filter- 

 ing the water through a cloth, which detained a large number of fish from 

 their normal growth. •The few, however, which passed this ordeal success- 

 fully showed in the most unmistakable manner that they knew how to 

 makeup for their involuntary fasting. This is an interesting observation, 

 because it shows how much the growth of the herring depends on the 

 quantity of food. A still more striking example of rapid growth was 

 exhibited hj a few small sprats which were sent to me from Cappeln on 

 the 20th of August, 1878.* 



These fish, measuring 30 to 35 millimeters in length, reached a length of 

 ggmm jj^ thirty-five days, whilst they were confined. We, therefore, observe^ 

 in a small fish closely resembling the herring a growth of 25"°^ in thirty- 

 five days, or 22°^"^ during one month. It is well known that the growth 

 of all fresh- water food-fish varies very much. But the fact, proved by 

 actual experience, that salt-water fish, like herrings and sprats, are not 

 only retarded in their growth by want of sufficient food, but will make 

 up for lost time as soon as food is more plentiful, must be considered as 

 another proof that fish of different size may have the same age. This 

 will be a welcome statement to those who could not make the occurrence 

 of herrings of all sizes at every season of the year agree with the sup- 

 position of two, or at most three, spawning-seasons. There is at the 

 present time scarcely any doubt that the best-fed fish of the autumn 

 spawning are fully equal in size to fish of the spring spawning — there- 

 fore 6 months older — which have been retarded in their growth, but that 

 these last-mentioned fish can at a later time reach the size which belongs 

 to their age. 



It is likewise certain that the food of the herring is, as a rule, more plenti- 

 ful during some months of the year than during the rest; that, for ex- 

 ample with us, on the shores of the Bay of Kiel, there is a very noticeable 

 lack of pelagian animals towards the end of winter. Our herrings, there- 

 fore, probably grow slower at certain seasons of the year than at others. 



All that can be aimed at is, therefore, to ascertain the average growth, 

 more especially as one year may not resemble the other in this respect. 



Although this treatise was to be confined to the growth of the embryo, 

 I also made a few observations on the growth of the fins, which may 

 find a place here. 



On the 25th day after the fish had left the egg, the dorsal fins began 

 to appear, and on the 33d day 11 distinct rays could be seen. Six 

 weeks after the fish had left the egg, the dorsal and caudal fins in fish 

 measuring 15-19 '"™ had assumed their complete shape ; but in the 

 former some rays were still wanting, whilst in the latter the smaller half 

 of the rays was wanting. The anal fin likewise showed a form resem- 

 bling its definite form very closely. The number of rays in different 

 fish of the same age varied very considerably. The shape of the pec- 

 toral fins had not changed much, and did not by any means resemble 



* Large numbers of these fish appeared about the same time iu the Bay of Kiel. 



