ACTIVATION OF PHOTORESPONSES OF BRINE SHRIMP NAUPLII INVOLVED IN DIELVERTICAL MIGRATION BY CHEMICAL CUES FROM FISH

The effects of exposure to a planktivorous fish (Atlantic menhaden lar vae) on the photoresponse involved in the descent phase of nocturnal d iel vertical migration of brine shrimp (Artemia) naupliar larvae were measured in a laboratory system that mimicked the underwater angular l ight distribution. Photoresponses were activated by (i) 1 day exposure to menhaden larvae that could and could not feed on brine shrimp naup lii and (ii) water, alone, from which feeding menhaden larvae were rem oved. Thus, chemical cues activated the photoresponses and predator fe eding was not necessary. Since the time course indicated that activati on occurred within 5 min, brine shrimp have a phenotypic response to a zooplankton predator. The active molecules are <500 Da in size.