THE INFLUENCE OF A FISH EXUDATE ON 2 CLONES OF THE HYBRID DAPHNIA-GALEATA X HYALINA

Two Daphnia clones were isolated from different day depths during the period of diel vertical migration and were tested for their life-histo ry responses to a fish exudate released by juvenile perch. Animals wer e exposed to fish exudate every 24 or 48 h. Both clones responded to t he exudate by exhibiting earlier maturation and larger sizes of first clutches, which resulted in higher rates of population increase. Also, neonates were smaller in the presence of the exudate. It was found th at the clone isolated from a deeper day depth ('migrating clone') was less sensitive to the exudate than the clone isolated from the surface waters, which was presumed to be non-migrating. The non-migrating clo ne responded by having smaller neonate sizes and smaller sizes at matu rity than the migrating clone. The non-migrating clone responded to th e fish chemical when it was exposed to it every 24 or 48 h, whereas th e migrating clone only responded to the exudate if exposed to it every 24 h.