Movements of Hoplias aimara during the filling phase of the Petit-Saut dam, French Guyana

Twenty Hoplias aimara were tagged intraperitoneally with radio-transmitters in the Sinnamary River, French Guyana. In November 1993, 13 tagged fish we re released in an area which would be flooded by the Petit-Saut reservoir i mpoundment in mid-1994. Seven other tagged fish were released in January 19 94, 20 km upstream of the upper limit of the reservoir. Hoplias aimara show ed site fidelity: 75% of fish returned to their capture site before the tes t area was inundated. The remaining fish stayed close to the release area. Monitoring during three 24-h cycles before reservoir filling showed that H. aimara has a limited home range, which is less marked in unconstrained rea ches during the wet season (April to August) than in constrained reaches du ring the dry season (September to November). In natural conditions, H. aima ra has a wider home range in unconstrained river reaches than in constraine d river reaches. After closure of the dam, in September and October 1994 (d ry season, low water) more than half of the total H. aimara tagged in the f looded zone migrated upstream following the rise of water. (C) 1999 The Fis heries Society of the British Isles.