C. Biological Investigations. 



a. Observations eoneerning fishes, especially eod (Gadus callarias, Linn.). 



I\ 



^*7^00L0GiCAL investigations of the sea for a practical purpose 

 Z > may be said to date, in the case of our country from the 

 year 1864, when professor Geoeg Ossian Sars started his obser- 

 vations during the Lofoten fisheries. Already the following year 

 Sabs made a discovery greatly calculated to create a sensation, 

 when he proved that the spawn of the cod floats and goes through 

 its development in the open sea. Because however the result was 

 only published in the Norwegian language, this discovery did not 

 attract the attention it deserved. In the years 1864 — 70 Mr. Saes 

 was engaged in studies of the development of the cod-fry and other 

 circumstances relating to the natural history of the cod, the chief results 

 for each year being published in reports to the home department. 

 Mr. Sabs divided the Lofoten fisheries in three phases, the 

 immigration of the shoals on to the banks, the spawning period, 

 and the emigration. The immigration may be said to commence 

 with the month of January, and lasts to the middle of March, 

 which is the actual spawning month for the masses of cod that 

 migrate to Lofoten. The fishing that goes on in the month of 

 April may be generally said to depend on the outgoing shoals. 

 That the main mass of the cod spawn in March is certainly the 

 rule, but this does not prevent the occurrence in the sea of cod- 

 spawn at the end of Febniary, which Sabs emphasizes, and which 

 I have had opportunities of confirming. Further it may also be 

 mentioned in this connection that I have seen female cods having 

 filled roe-bags at the beginning of May, though this is only excep- 

 tional. In the year 1865 Sabs undertook artificial fecundation of 

 cod. After 8 days the fetus could distinctly be seen, and in the 

 course of 18 days the development of the embryo was finished. 

 The experiments showed that only the roe that allowed of being 

 pressed out of the fish by a gentle pressure, was fit for fecundation. 

 Likewise it was proved that even roe of recently died fish retained 

 the power of germination, and that roe having reached a certain 

 stage of development was little susceptible of outward influences. 

 Even if the sea water was considerably deteriorated, and the egg 

 covered with fungoids, the development went on rather undisturbed. 

 Even the recently slipped young ones could stand deteriorated 

 water, but herein an immediate change occurred the moment 

 the yolk-sac was absorbed. When the gill-splits were formed 



the young did not all survive coming into deteriorated water. 

 Concerning the spawning itself, Saes remarks that the females 

 stand at a higher level in the sea than the males, which depended 

 on the circumstance that both roe aud milt rose to the surface 

 after being shed. Also, the micropyle through which the fecunda- 

 tion was performed turned downwards, and the development of the 

 embryo took place at the lower pole. In the winter of 1865 Saes 

 also proved that the haddock, as well as other species, shed floating 

 spawn, and during a voyage in the following summer the mackerel 

 too (scomber scomhnis) was registered on the list of fishes whose 

 spawn shares the fate of the plancton. 



Throughout the years 1866 — 70 Saes applied himself with great 

 vigour to the study of the biology of the cod, and his efforts were 

 crowned with success. At the end of May 1866 he found that a 

 great deal of cod fry had migrated into the bays and sounds on 

 the east side of Skraaven. The length was then (May 20th) 7 — 8 

 mm., and they were swimming about in the surface of the water; 

 the stomach contents were found to consist chiefly of calanidcs. 

 About the 12th of June the plancton was very abundant, and the 

 tiny fry were swimming vividly about, snapping after the small 

 species of calanus. The largest specimen then had the length of 

 24 mm. Gradually the embryonal fin began dissolving into the 

 dorsal and ventral fins, and in the largest individuals there were 

 signs of the barbal thread in the form of a small knot at the 

 point of the lower jaw. A period of bad weather for some time 

 prevented the investigations, and when fair weather returned (June 

 23rd) it was only exceptional that cod fry was to be seen. Alter 

 searching in vain for several days, Mr. Saes (5tli .July) at the 

 fishing station of Brettesnes became aware of a very young fish 

 jotting out from under a jelly-fish (c/i/cmea mfillata). It proved to 

 be a young cod, and by examining a greater number of jelly-fishes 

 he found a great deal of young cods as well as haddocks. From 

 under the disk of cyanea, as well as aurelia, young cods were 

 frequently taken, the largest being about 40 mm. long and having 

 5 — 6 dark crossbands. In the stomach were found specimens of 

 an amphipod (hyperia), which leads a parasitical existence on the 

 jelly-fishes. This circumstance seemed to suggest a reciprocal use- 

 fulness of the young fish and the jelly-fishes. 



