Peripheral mechanisms of tactile sensation in fish.

Touch is a fundamental sensory modality across vertebrates, yet its neuronal basis has been primarily investigated in amniotes. How tactile information is detected, transduced, and encoded in fishes, a diverse group of aquatic vertebrates, remains poorly understood. Here, we focus on the peripheral mechanisms of touch detection in the piscine somatosensory system, integrating anatomical, physiological, and molecular lines of evidence. Existing work reveals broadly distributed slowly and rapidly adapting tactile afferents across fish body regions and species. The terminal end-organs of these afferents have simpler anatomical structures than in amniotes. However, these tactile afferents detect a similarly broad range of mechanical cues, including sustained pressure, transient touch, velocity, and vibrations over a wide frequency range, and use similar encoding and mechanotransduction strategies. This perspective offers insights into general principles of vertebrate touch across aquatic and terrestrial environments and a comparative framework for the evolution of sensory specialization among tactile receptors.