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8. Discovery of a fully ripe male of the common eel 



I shall here mention a Danish eel, which the late Professor A. Feddersen has kindly 

 given me for examination, and which in several regards is somewhat remarkable. 



The eel (see Plate XIII) is 34 cm. long and a male. It was caught on the 1st of 

 September 1903 in Praestö Fjord in South East Sealand (consequently in quite shallow 

 water) and has since been preserved in spirits. The abdominal cavity has been opened 

 before the specimen was placed in spirits, and all the internal organs are excellently 

 preserved. 



The eel is a typical silver eel (migrating eel) with all the colours distinctive of this 

 stage and other characteristics (cf. Petersen, 1896, 1. c. p. 13—18). Thus the pectoral fins 

 are deeply black and very pointed, the colour of the body (so far as preserved) partly 

 black, partly with a silver sheen and the snout pointed. What is most striking amongst 

 the external characteristics, however, is the extraordinary size of the eyes, their horizontal 

 diameter being ca. 10 ram.'. 



The most peculiar thing about this eel is, however, the correspondingly great devel- 

 opment of the sexual organs. Whilst the folds of the testes in the common silver eel 

 (migrating eel), according to the investigations of Petersen (1. c. 1896, p. 17) and others, 

 as also my own observations, do not exceed 3 mm. in breadth, they are in the present 

 specimen much larger and thicker. The largest folds, which are found furthest forward 

 in the abdominal cavity, have for example a breadth of ca. 18 mm. and a length of 

 ca. 11 mm., whilst those in the middle of the testes are ca. 9 mm. in breadth and 

 ca. 10 mm. in length (they have here thus a somewhat different form being more circular). 

 In other ways the folds have here not the uniformity in size commonly the case, but 

 some by reason of the enormous development of the majority have remained quite small 

 and repressed. 



To ascertain whether the testes of this apparently ripe eel contained ripe spermatozoa, 

 I applied to a specialist in histology, Cand. Aug. Brinkmann, who kindly submitted the 

 specimen to a closer examination in the desired direction. In a letter of Dec. 17th, 1905 

 Mr. Brinkmann writes the following: 



"At the request of Dr. Johs. Schmidt I have submitted two portions, taken from different 

 places in a well developed eel-testis, to a close microscopic examination. This showed, 

 that the tubuli were everywhere filled with quite developed spermatozoa, and the specimen 

 must therefore be regarded as fully ripe sexually." 



The great interest of this eel lies in the fact of its being the first fully ripe specimen 

 of the eel as yet found and because it has thus enlarged our knowledge of the natural 

 history of this fish. But is does not bring us nearer to the solution of the question of 

 the normal propagation of the eel and it seems to me rather to be an exception, which 

 proves the rule, that is: that the eel does not spawn in shallow water. As so many 

 years have been spent in the search for ripe eels, before we have succeeded in finding 

 one, which was fully ripe, this seems to me to show conclusively, that we have not sought 



■ Grassi and Calandruccio (I.e. 1897, p. 16) give the following measurements of specimens, thrown up 

 from the bottom of the sea (deep water) 



Males: length 34^/2 cm., the horizontal (and vertical) diameter of the eye 9 mm., 



length 33^/2 cm,, the horizontal diameter of the eye 9 mm. (vertical a little smaller). 

 Female: length 48^/2 cm., the vertical diameter of the eye jo mm. (horizontal a little more). 



