Temperature selections of Anguilla japonica (L.) elvers, and their implications for migration

Abstract

This study investigated the temperature selections of elvers of the Japanese eel, Anguilla japonica (L.), that had been acclimatized to various temperatures and salinities. The results provide information needed to assess the possible effects of thermal effluents from power plants and of naturally occurring thermal gradients on the freshwater migration and fishery harvest of elvers. A 7.14-m-long plastic pipe (i.d. 11 cm) fitted with two stainless-steel heat-exchange tubes was used for the study. The countercurrent design of the system provided a thermal gradient ranging from 11� C at one end of the pipe to 31� C at the other. Elvers could swim free of obstacles inside the pipe. They were acclimatized to 13, 15, 17, 19 or 21� C before being subjected to the thermal gradient. The distribution of elvers in the pipe was studied during a 24-h period. The results indicate that the temperature to which the elvers gravitated was higher than their acclimatization temperature for acclimatizaion temperatures between 13 and 21�C. The thermal preference of elvers acclimatized to salinities of 10 or 32 did not differ. The temperature- selection pattern of the elvers suggests that thermal effluents from power plants may not adversely affect the immigration of elvers.