The amount of catch for elvers in coastal waters seems to be correlated with temperature. The maximum catch of elvers in the upstream areas has often been found during or several days after daily seawater temperature reaches its lowest in winter. The lowest water temperature ever recorded in an eel habitat is 15-16°C.
Maximum catch has also been observed to occur at the same time when salinity has leveled off and the flow of seawater has reached its maximum. The elvers also become most active during this period at night.
The biological rhythm of elver activity was found to follow the lunar cycle in the coastal waters. The peak catches occur only once a month, about the time of the new moon. On the other hand, a semilunar rhythm of the elvers in the rivers was observed, namely, two peak catches occurred in each lunar cycle, one around full moon, the other around new moon. The semilunar rhythm of upstream elvers also coincided with the spring tide (8).
CULTURE TECHNIQUES Species Cultured
Of the different species of eels in the world, three are valued for its economic importance, namely, the European eel,
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