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fish species, which for the sake of spawning undertakes great migrations to waters totally 

 different from those in which they have gfown up. When this is taken into consideration, 

 we will see, that there is no qualitative, but at most only a quantitative difference between 

 the biology of the eel and that of many other fish in this regard. And even such a 

 quantitative difference is not always present; for example, I may mention that the distance 

 to the spawning places for the eels, which live in South West Ireland, is considerably 

 shorter than the distance, the large cod-shoals, which according to G. 0. Sars occur in 

 summer around Spitzbergen, where they are or have been the object of a fishery from 

 the Norwegian side, must travel to reach the spawning-places in the warm Atlantic water 

 off the coast of Northern Norway. 



A relatively far more striking feature in the biology of the eel than the extent of the 

 spawning migrations is in reality the circumstance, that this fish, which during growth is 

 so distinctly a shallow water fish, descends before the spawning to the great oceanic 

 depths. This is almost unique among the food fishes^ so far as we yet know. 



In this connection I may call to mind that the allies of the eel, the other eel-fishes, 

 several species of which occur within our region of investigation in the Atlantic Ocean, 

 are for the most part true deepwater forms. 



Several adult specimens of the deep-water eel Synaphobranchus pinuattis were taken 

 by the "Thor" in the Afiantic from the bottom at depths of ca. 1500— 2500 m., and 

 further we have taken many specimens of the Leptocephalus-stage of the 5 species pela- 

 gically over great depths, where they often occur together with the larvae of the common 

 eel {Leptocephalus brevirostris). Of these 5 forms, 3 belong to the genus Leptoce- 

 phaliis (e. g. L. Morn'su), 2 to Tïhirus, which is characterized by a long whip-like tail. 

 They are all figured on Plate IX. Of a single species [Synaphobranms pinnatus) we 

 have even found the quite young bottom-stages in about 1000 m. depths to the west of 

 the Faeroes^. 



Synaphobranchus pinnatus "Thor", ' Something similar, though in far less degree, is perhaps the 



Stat. 99 May 22nd 1904 case with the halibut. The earlier annual groups of this fish are 



Number ^^^^ common at Iceland in shallow water (for example from 50 — 20 



■ m.), where the full-grown spawning or spawned fish do not occur. 



These we could only find in deep water (for example 500 — 800 

 o m.), just as the tiny pelagic young halibut were only taken by the 



"Thor" over great depths. Evidently like the eel, the halibut 

 descends to great depths for spawning. The cod and other fishes 

 descend gradually with increasing age to the gi-eatest depths, where 

 they mainly occur. 



^ ^ . 2 The place was 6i°i5' N. Lat. , 9°35' W. Long., depth 



o 970 — 872 ni. 



"Thor" station 99, May 22nd, 1904, 



° In a two hours haul with the youug-fish trawl on the bottom 



54 specimens were taken, whose length can be seen on the accom- 

 panying Table. 



000000000 All these specimens, the youngest of which belonged at least 



to two annual groups, the smallest measuring from ca. 101/2 — ca. 

 121/2 cm., were entirely transformed, had the permanent teeth and 

 were already taking food. 



At m y request Cand. Mag. Ad. Jensen was so kind as to examine 



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