The electro-receptive lateral line system appeared early in the evolutionary history of fish.Sturgeons,members of the primitive Chondrostei group,are known for their electroreceptors(ampullae of Lorenzini)on the head,which are thought to be sensitive to weak electric fields in aquatic environments and involved in feeding,mating and migration.Here,we report the results of a set of behavioral and electrophysiological experiments designed to determine the function and characteristics of the electrosense in cultured sturgeons.The results showed Sibe-rian sturgeon(Acipenser baerii Brandt,1869)feeding striking at bio-electric fields produced by living feed-fish enclosed in a gel chamber and at the corrosion field produced by metal rods.With an electric stimulus that mim-ics the bio-electric fields produced by living prey,the relative discharge rate of electrosensory neurons in the dorsal octavolateralis nucleus(DON)was modulated by and phase-locked to sinusoidal stimulus and some units showed selectivity for dipolar direction in white sturgeon(Acipenser transmontanus Richardson,1836).This is the first study to provide the empirical evidence correlating with electrosensory behaviors and electrophysiolog-ical responses in cultured sturgeons,and suggesting that electrosense does play an innate role in feeding behav-ior of sturgeon.We believe this will have important implications for protecting sturgeons in the wild.
When faced with danger,pufferfish react with both a fast-start escape response and inflation behavior.The neural basis of these stress responses in the pufferfish has not been described.The present study reveals that during inflation behavior,the buccal cavity expands and compresses as a pump to control the direction of water flow and draws water in and out.The inflation involves a series of major anatomical modifications of the head.The greatly enlarged first branchiostegal ray and its associated hyohyoideus abductor muscle are the key mechanisms responsible for this behavior.The nerve branch innervating the hyohyoideus abductor muscle is highly developed,and its central origin at the motor nucleus of the VIIth cranial nerve was revealed by tract-tracing using the carbocyanine dye DiI.The central connections from its origin were found to be several motor nuclei in the medulla and the spinal cord,the nuclei of cranial nerve III and IV in the mesencephalon,and the pretectalis superficialis and periventricular preoptic nuclei in the diencephalon.Both the sympathetic cells and the parvocellular part of the periventricular preoptic nucleus might play a neuro-endocrine role in the rapid movement of the buccal cavity during puffing behavior in this species of pufferfish.The central circuit revealed by this study is hypothesized to mediate the C-start escape behavior and puffing behavior.
