Environmental cues used in upstream orientation by Parameletus chelifer and P. minor (Ephemeroptera) nymphs; an experimental study

Experiments using a plexiglass Y -maze fluviarium showed that nymphs of Parameletus chelifer and Parameletus minor each used different environmental cues to orient. P. chelifer nymphs reacted to pH while nymphs of P. minor were very sensitive to concentration of dissolved organic matter. The capacity to detect these water quality differences was lost as soon as the nymphs reached seasonally submerged areas suitable for growth at the margin of the river. When nymphs of both species had reached their growing areas, water temperature became the crucial cue for orientation.