WHAT CAN FLATFISH ONTOGENIES TELL US ABOUT PELAGIC AND BENTHIC LIFE-STYLES

Eye migration, asymmetrical pigmentation, and a 90 degrees rotation in posture are developmental changes that unify all flatfishes and facil itate a transition from a pelagic to a benthic existence. Settlement p laces the fish in new environmental conditions which may require diffe rent types and levels of performance for survival compared to those ne eded in the water column. Since structure and performance vary as a co nsequence of ontogeny, it is likely that natural selection has acted o n the ontogeny of flatfishes differently from fishes that do not settl e (pelagic fishes) to provide different survival skills by the time fl atfishes settle. This paper provides examples of quantitative methods for comparing fish ontogenies in the context of three predictions: (1) different flatfish species undergo settlement at a common ontogenetic state; (2) they have a common set of skills at settlement that differ from those of pelagic species of the same ontogenetic state; and (3) skills or features that appear earlier in the ontogenetic program of f latfishes than in pelagic fishes suggest attributes that are important to survival in a benthic habitat. Preliminary comparisons suggest tha t flatfishes map have accelerated development of their mechanosensory system relative to pelagic species. Firm conclusions about ecologicall y important differences between the pelagic and benthic habitats deriv ed from analyses of ontogenetic events will require more kinds of data from a broader selection of species.