Eel larvae caught in the mid North Atlantic and along the continental slope off the Portuguese coast are studied together with samples of glass eels caught just before entering fresh water along the Dutch and French coasts. During their migration from the mid Atlantic towards the continental slope the mean length of the larvae investigated increased from 56 to 66 mm, while the mean diameter of their otoliths increased from 0.17 to 0.23 mm. The animals from the mid Atlantic had three complete growth zones in their otoliths, while the majority of those from the continental slope had four complete growth zones. The specimens from the mid Atlantic show typical larval aspects as e.g. position of the anus and reaction to preservation, this in contrast to most of the animals caught along the continental slope. In 70% of the latter the position of the anus is varying and they turned completely opaque after preservation in alcohol; the remaining animals showed all typical larval aspects. In the glass eels the numbers of growth zones varied from two to six complete ones, about 40% of the animals having four or more growth zones in their otoliths. The results indicate that the variation in age found in the glass eels most probably comes into existence along the continental slope, where a number of larvae lag behind in metamorphosis. The growth zones in the otoliths seem to represent completed regular growth cycles which are supposed to be annual.

Bijdragen tot de dierkunde

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Naturalis journals & series

van Utrecht, W. L., & Holleboom, M. A. (1985). Notes on eel larvae (Anguilla anguilla Linnaeus, 1758) from the central and eastern North Atlantic and on glass eels from the European continental shelf. Bijdragen tot de dierkunde, 55(2), 249–262.