— 219 ^ 



üf life of the elvers ceases. Whether they now go up into fresh water or remain 

 in the sea they keep always at the bottom. After May no eel-fry have as yet been 

 taken pelagically in the sea. 



At the beginning of summer (May, June) the great majority of the elvers in North 

 Europe are therefore metamorphosed, and it is only after this that they begin to feed 

 and to grow both in thickness and length, but the growth may be so slight in the first 

 year, that it cannot always be determined from the length alone, whether an elver taken 

 for example in early spring belongs to the previous year's spawning or the one before 

 (thickness and pigmentation can however decide the question. With regard to how much 

 the elvers grow in this, the first, year we know nothing for certain, and we are far from 

 being able to determine how old a young eel of say lO cm. is. Possibly the growth is 

 very different at different places, and it is further probable that the males grow slower 

 than the females. New and detailed investigation is required before we can say anything 

 definite regarding this. 



It has been mentioned, that the great majority of the elvers are metamorphosed in 

 the beginning of summer, whether they live in fresh water or in the sea. The , meta- 



in development. This holds, for example, for the lo elvers (length 65 — 70 mm.) taken by Professor G. Ü. Sars 

 at Hvitings Island in Norway in July 1872 and mentioned on p. 215. These are preserved at Christiania Zoo- 

 logical Museum, but 1 have been able to examine them, thanks to Prof. Collett. Even the still pelagic 

 glass- eels taken in the centre of the North Sea and at Iceland at the end of April appeared to be 

 relatively far on in development, towards the end of Stage 5, a good deal of pigment relatively being already 

 present. 



With regard to the Danish North Sea coast, the conditions appear very clearly from the data given below, 



published by A. C. Johansen in his paper already cited (Medd. Kom. Havunders., Fiskeri, Bind I, No. 6, 1905). 



I. March 24 — April 15, 1905. The North Sea. 84. elvers caught from the "Thor" have an average 



length of 70*56 mm. The pigment is developed only on t h e tip of the tail and sometimes on the 



head. 

 II. April 26 — May 6, 1905. Brackish and nearly freshwater at Esbjerg (W. coast of Jutland). 288 



elvers have an average length of 71 "44 mm. The pigment only developed on the tip of the tail 



an d the head. 



III. May 9, 1905. Rivulet at Maade brick-manufactory, Esbjerg (W. coast of Jutland). 90 elvers have 

 an average length of 70*29 mm. In the majority of the specimens a slight pigmentation appear 

 over the whole dorsal region. In a few specimens the pigment is restricted to the tip of the tail 

 and the head. 



IV. May 22, 1905. Same locality as III. 261 elvers have an average length of 69'i5 mni. The 



dorsal region and the sides are now distinctly pigmented. Only in 6 specimens the pigment 



is restricted to the tip of the tail and the head. 

 V. June 2 — 3, 1905 Nymindegab (W. coast of Jutland). Slight brackish water. 314 elvers have 



an average length of 67*92 mm. The specimens are distinctly pigmented. 

 VI. June 14—17, 1899. Rivulet at Ribe (W. coast ofjutland). 118 elvers have an average l(;ngth 



of 65*70 mm. The specimens are distinctly pigmented. 



This shows that in the beginning of May the eel-fry already had pigment on the whole of the dorsal 

 aspect, and at the end of this month both the back and the sides were distinctly pigmented. 



Taken on the whole, the great mass of the elvers are pigmented at the end of May. This does not 

 mean, that no colourless glass-eels at all are to be found in the sea in the summer-time after the majority are 

 already pigmented and quite metamorphosed. That some at any rate can be found in June or perhaps even 

 later we know, for example, both from Couch and Cunningham (English Channel). But it is just as certain 

 on the other hand, that by far the great majority are at this period in Stage 6 or even further 

 forward in development. 



28* 



