39 



Resumé: 



The age and growth of the eel can be determined. 



Bj' means of the measurement-method it has been determined, that the 

 eel wheu it reaches a size of 18 cm. and begins to take on scales, has hved in 

 our waters 2 years, reckoned from the time that it arrives here as montée (glass- 

 eel, elver) on its early migration. 



By means of the method of scaleinvestigation the age of the scaled eels 

 can be determined. 



Fig. 1 shows that the scale of the eel consists of a central zone — and the 

 youngest 1-year old .scale consists only of this — outside which is fonnd a number of 

 concentric zones or rings, distinctly marked off both from the central zone and from 

 each other. — Sometimes one or more zones are not formed as rings, bnt only 

 as caps at the ends of the longitudinal axis of the scale. 



These zones are anuual rings. 



That they mav be annual rings is based on the periodicitj' in the life of 

 the eel with changing growth-periods (summer) and resting stages (winter) duriug 

 which the eels do not grow. 



That they probably are annual rings may be concluded from a compari- 

 son with the scales of gadoids (and other fislies), wliere a similar structure points 

 in this direction. 



That they really are annual rings is proved bj' following the growth of 

 the scale through a growth-period ; it is laid dovvn, grows and the growth ends, or: 

 a concentric zone is laid down, grows and the growth ends. 



The growth of the scale begins in June or as a rule first in July and is 

 ended at the end of September — sometimes (as in silver eels) the growth ends 

 somewhat earlier, seldom later. 



The scales are oldest (first laid down) at the lateral line on the centre of 

 the side, and for investigation should be takeu from close over the lateral line a 

 little in front of a line from the anus perpendicular to this. 



The age of the scales (in years) is found by counting the zones. 



The age of the eel is therefore = the age of the scale + 2. 



