Aspects of the early life history of the European conger eel ( Conger conger ) inferred from the otolith microstructure of metamorphic larvae

Abstract

The life cycle of the conger eel (Congerconger L.) is still fairly unknown, especially its larval leptocephalus phase. The morphology, biometry and meristic characteristics of 184 metamorphosing conger eel larvae collected from the Minho River, northern Portugal, between December 1998 and April 1999 were analysed. The total number of myomeres, the general body morphology and the pigmentation pattern of leptocephali are in agreement with the corresponding data found by other authors for this species. The sagitta microstructure of 90 specimens was viewed by scanning electron microscopy. The numbers of daily increments obtained in the otolith's countable zone were between 205 and 324. The final part of the countable zone is characterised by a sharp increase in width of the daily increments (transition zone), followed by a peripheral diffuse zone. In the diffuse zone no narrow circumscribed rings are visible, which prevents an accurate estimate of the duration of metamorphosis. The data indicates that the size variation of metamorphosing leptocephali is large, suggesting that their hatching time must be variable. Our data also show that the largest larvae, in later stages of metamorphosis, arrive first to the northern Portuguese coastal waters.