Brain areas in abyssal demersal fishes

Four areas of the brain which receive primary projections from chemical sen ses ([1] olfactory bulb, [2] gustatory area including facial and vagal lobe s), the eye ([3] optic tectum), and mechanosensory, and-hair-cell based sys tems i.e. the lateral line, vestibular and auditory systems ([4] trigeminal and octavolateral regions) have been studied and relative size differences used to make deductions on the sensory preferences of 35 fish species livi ng on or near the bottom of the deep sea. Furthermore the relative volumes of the telencephalon and the corpus cerebelli were determined. Two evaluati on modes were applied: (1) the relative mean of each system was calculated and species with above-average areas identified; (2) a cluster analysis est ablished multivariate correlations among the sensory systems. The diversity of sensory brain areas in this population of fish suggests that the benthi c and epibenthic environment of the abyss presents a rich sensory environme nt. Vision seems to be the single most important sense suggesting the prese nce of relevant bioluminescent stimuli. However, in combination the chemica l senses, smell and taste, surpass the visual system; most prominent among them is olfaction. The trigeminal/octavolateral area indicating the role of lateral line input and possibly audition is also well represented, but onl y in association with other sensory modalities. A large volume telencephalo n was often observed in combination with a prominent olfactory system, wher eas cerebella of unusually large sizes occurred in species with above-avera ge visual, hair-cell based, but also olfactory systems, confirming their ro le as multimodal sensorimotor coordination centers. In several species the predictions derived from the volumetric brain analyses were confirmed by ea rlier observations of stomach content and data obtained by baited cameras. Copyright (C) 2001 S. Karger AG, Basel.