COMPARISON OF THE RESPONSE OF DAPHNIA-GALEATA AND DAPHNIA-OBTUSA TO FISH-PRODUCED CHEMICAL-SUBSTANCE

Individuals of two clones of two Daphnia species were reared from neon ata to primipara stage in a medium preconditioned with fish (Rutilus r utilus or Perca fluviatilis). Daphnia galeata, the species usually exp osed in its natural habitats to fish predators, exhibited reduced juve nile length increments, earlier maturation, and relatively larger clut ches of smaller eggs. Such reactions were not found in Daphnia obtusa, a species typical of fish-free localities. Reaction to the fish facto r did not include structural changes of the filtration apparatus.