Sensory brain areas in three families of deep-sea fish (slickheads, eels and grenadiers): comparison of mesopelagic and demersal species

The sensory brain areas of a sample of <100 deep-sea fish species were studied, and the relative volumes of the olfactory bulb, optic tectum, octavolateral area and gustatory area were determined. In the absence of direct observations on the behaviour of this ichthyofauna these data allow deductions to be made about the kinds of sensory modalities used preferentially in the deep-sea environment. Here, members of three families are compared that have representatives living on or near the sea floor (“demersal”) and in the open water between 200 and 1.000 m (mesopelagic). The findings indicate that both regions present fish with rich and diverse sensory environments. While vision emerges as the dominant sense of the mesopelagic realm, olfaction seems more important on or near the bottom of the sea. However, other sensory modalities supplement these senses in species-specific patterns. Considerations of the phyletic relationships indicate different degrees of pervasiveness. Whilst in slickheads the dominance of vision appears to be a family-related trait, a similar relationship is not found in either eels or grenadiers. By contrast, the common trait in these two families seems to be the greater adaptability to the environment. Published online: 21 August 2002