SOME RESULTS OF THE INTEKNATIOKAL FISHERY INVESTIGATIONS. 455 



early development of both the fresh-water eel and the conger-eel has 

 always been very imperfectly known. It is now well known that the 

 peculiar flat, ribbon-like, and transparent fishes called " Leptocephali " 

 are the young stages of the fresh-water eels. Leptocephali are very 

 rarely found on the coasts of Britain or Northern Europe ; the few finds 

 that have been made are all recorded in the literature. Nevertheless, 

 every year in the spring and summer enormous numbers of small flat 

 eels of varying degrees of transparency are found all along British and 

 continental coasts. These young eels, or " elvers," are the transformed 

 Leptocephali returning from the sea into the rivers. When the eel 

 approaches maturity it descends the rivers to the sea, assuming as it 

 does so a peculiar coloration, or " bridal dress." In the sea it becomes 

 mature, spawns, and the larva which develops becomes, at an unknown 

 time after the hatching of the egg, the Leptocephalus. Before the 

 latter larva reaches the coasts it undergoes metamorphosis and becomes 

 the " elver." So much has long been known, but the further questions 

 — the character of the eggs, their development and hatching, the 

 development of the larvae, the place and time of spawning, and the 

 duration of the embryonic and larval periods — all have been profound 

 mysteries. The Leptocephalus is, in fact, the first stage in the develop- 

 ment of the eel; that is well known. Of the earlier stages we know 

 next to nothing. What we do know is due to the investigations of 

 Grassi and Eaffaele in the Mediterranean, and may be summed up by 

 saying that the eel spawns in relatively deep and warm water some dis- 

 tance from the land. 



But this lack of knowledge of the spawning habits and development 

 of the eels (both fresh-water and marine forms) is due, without doubt, 

 to our hitherto very imperfect methods of investigation. Given the 

 right form of fishing apparatus and some considerable range in the area 

 over which this is used, and there is no doubt that all stages of the eel, 

 from the developing egg to the Leptocephalus, should be found in 

 abundance. This occurred to Petersen in connexion with the use of 

 the small- fish trawL " The Leptocephali," he says, " will surely be 

 found, I thought, if we seek them in the right time, place, and 

 manner." During a trip to the Faeroe Isles and Iceland in 1904 the 

 Thor had to pass through warm and deep Atlantic water, and on fishing 

 at a station* south-west from tlie Faeroe Isles on May 22nd, 1904, a 

 single Leptocephalus was taken in the young-fish trawl. In 1905 

 Schmidt again succeeded in finding "great quantities of Lcptoccpliahis 

 hrevirostris in the depths of the Atlantic"! Considered both as a con- 

 tribution to the natural history of the eel, and as a fact which is likely 



♦ 61° 21' N. ; 19° 59' W. 



t Meddelelser Komm. Havundersog., Fiskeri, Bd. i. Nr. 5, 1905, \k 5. 



