— 2l8 — 



the conclusions to be drawn from the material. I am quite aware, however, that I -have 

 not included everything that has been written on the subject in the different countries, 

 but I hope nevertheless that nothing essential in all the many reports, many of which 

 are in works and papers difficult to be got at, has been omitted. 



1 may first give (a) a general review over the occurrence of the eel=fry in their 

 first year. 



According to our investigations, the greater part of the metamorphosis of the eel- 

 larvae {Leptocephahis brevirostris) takes place out in the Atlantic. Here the larvae live 

 pelagically in the upper water-layers and the ist, 2nd, 3rd and 4th stages of metamor- 

 phosis are then passed through, resulting in the eel-shaped, colourless glass-eel, which has 

 been known for a number oj years (Stage 5). Such colourless glass-eels occur in the 

 sea as early as November' to the west of Ireland near the 1000 meters line, or almost 

 half-way between this and the coast, and in this month they are evidently already on 

 their way towards the coasts. During this migration the glass-eels are usually found close 

 to the surface at night, whilst in the day-time they are as a rule deeper down in the 

 water, even on the bottom in the shallower waters. 



The arrival of the glass-eels on the coast or at" least their ascent into the fresh 

 water has nowhere on the European Atlantic coasts been observed before September 

 (north coast of Spain), and no earlier stage than the 5th ^ has anywhere been found 

 taking part in. this inward migration. This strengthens therefore my opinion, that Stage 4 

 is completed out over deep water in the Atlantic, before the fry have reached the 

 European coasts. 



When the glass-eels have just come into the fresh water, the rest of the metamor- 

 phosis from Stage 5 to Stage 6 (dark, almost non-transparent elvers) often proceeds 

 rapidly (cf Vaillants). Fresh water is by no means however a necessary condition for 

 the completion of the metamorphosis; it at most only hastens it in this regard. Thus a 

 large number of specimens remain in the salt or brackish water at the coasts, from 

 which sooner or later some run up into fresh water, often in company with younger 

 ascending elvers, and others chiefly males never leave the salt or brackish water. When 

 the glass-eels remain in the sea the metamorphosis thus proceeds more slowly, but in 

 May the great mass are metamorphosed, i.e. the body is reduced in length, 

 height and thickness, and the back and sides are covered with dark pigment, that is, 

 they reach Stage 61 Together with the transition to Stage 6 the pelagic mode 



' On the north coast of Spain they occur already from September — October. 



2 I have for example examined several thousands of specimens of young elvers taken about New Year 

 (3rd Jan. 1906) at Bayonne in France. All the specimens were in the 5th none in the 4th Stage (or 6th). 



3 It is certainly true for the elvers coning up last in the season, but that it is likewise true, for example, 

 for the elvers running up on the French coasts about New Year, does not seem proved. That the young eels 

 when they first come up into fresh water rapidly become more pigmented, is indeed certain under all conditions, 

 but how far the other changes accompanying metamorphosis, e. g. the considerable reduction in length etc., 

 really occur more rapidly in fresh water than in the sea, requires further investigation at those places where 

 the ascent occurs very early in the year, for example at South West France or Spain. 



4 Cf. the definite statements of the French and English elver fishermen, that the eel-fry become non trans- 

 parent, dark and hard so that they no longer can serve as food at the end of April (or sometimes somewhat 

 later in the course of May). Further, the eel-fry found in the sea after May are usually metamorphosed. I have 

 for example examined numerous small elvers taken both in the sea and fresh water in summer and autumn 

 (all at the bottom), but all were pigmented on the back and sides and thus in Stage 6 or even further forward 



