Associations between behavioural ontogeny and habitat change in clupeoid larvae

The ontogeny of evasive behaviours was examined in Atlantic menhaden (Brevo ortia tyrannus, Clupeidae) and bay anchovy (Anchoa mitchilli, Engraulidae), with supplemental data for scaled sardine (Harengula jaguana, Clupeidae). Predicted relationships between ecology and behavioural ontogeny were teste d using the different patterns of inshore vs offshore habitat utilization d isplayed by these species. In two of the species, menhaden and anchovy, the roles of vision, mechanoreception, and audition in evasive behaviours were examined ontogenetically and compared to the morphological development of these sensory systems. Anchovy early larvae were more responsive to a preda tory stimulus than were menhaden; sardine early larvae were intermediate in responsiveness. By the end of the larval period most individuals tested in all three species responded. These results matched the pattern predicted b y larval habitat. Ontogenetic trends in reactive distance did not match pre dictions based on habitat for these species but instead appeared to be more dependent upon changes in sensory morphology. In menhaden, ontogenetic cha nges in responsiveness were more dependent upon neuromast proliferation and cephalic lateral-line canal formation, while in anchovy these behavioural changes were more dependent upon ontogeny of the retina. Auditory stimuli w ere not implicated for either menhaden or anchovy in responding to the stim ulus used.