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 neonata to primipara stage in a medium preconditioned with fish (Rutilus rutilus or Perca fluviatilis). Daphnia galeata, the species usually exposed in its natural habitats to fish predators, exhibited reduced juvenile length increments, earlier maturation, and relatively larger clutches of smaller eggs. Such reactions were not found in Daphnia obtusa, a species typical of fish-free localities. Reaction to the fish factor did not include structural changes of the filtration apparatus.