Undersøkelser over forholdet mellem spiss- og bredhodet ål og deres næring
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The material dealt with in this paper contains 975 specimens of fresh-water eels from the Norwegian Skagerrack Coast. Of these specimens 674 (9 males, 665 females) were yellow eels collected in the sea near the shore; the rest, 301 specimens, were taken in lakes and rivers near the town of Arendal. Of the latter group 150 specimens (35 males, 115 females) were silver eels, 48 specimens (females only) were yellow eels, and 103 specimens were young ones of indeterminable sex. Attention is especially drawn to the two different types of yellow eels, viz. broadheaded and narrowheaded ones. The measurements (external head proportions in relation to total length and thickness of the body) show a marked difference between the extreme specimens of the two types, but also that they are well combined by intermediate forms. Cranial measurements of young eels show the same variation as the external head measurements in larger eels. By counting the vertebrae in typical specimens no difference in this character was found between the two types. By changing from yellow eel to silver eel the body increases very much in thickness; measurements show that this fact is sufficient to account for the relatively narrower head in the silver eel. The size of the eyes by changing from yellow eel to silver eel increases by 62 per cent in the males, 39 per cent in the females. The analysis of the stomach content of the eels from the sea shows that crustaceans, and partly small fishes, are the most important food animals. To a certain degree the broadheaded eels prefer fish, the narrowheaded ones crustaceans. In fresh water insect-larvae of different kinds together with small snails constitute the main food of the eels.
SerieFiskeridirektoratets skrifter, Serie Havundersøkelser
vol 5 no 8