Ontogenetic studies of peripheral and central connections of fish taste system

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Various stages of the larvae of sea catfish(Plotosus lineatus), carp(Cyprinus carpio), puffer(Fugu rubripes), flounder(Paralichthys olivaceus) and red sea bream snapper(Pagrus major) were examined histologically to reveal when and where taste buds(TBs) first appear after hatching. The carp, plotosus, puffer, flounder and red snapper first possessed TBs at first, 5th, 10th, 12th, 15th day, respectively. TBs first appeared simultaneously in the lip region and gill cavity for the carp and Plotosus while they appeared only in the mouth cavity for the other species.The developing process of the barbel TBs of Plotosus was examined by electron microscopy. Precursor cells of TB appeared at 2nd day after hatching as round or oval cell mass in the epidermal layer at the tip of dermal protrusions(origin of the barbel). At 4th day, cells increased in number and somewhat elongated apicard. At 5th day, TBs found on the tip of barbel opened to the surface to make a taste pore. Nerve fibers entered in … More to basal part of TB and basal nerve plexus with simple structures appeared. Three types of cells(t-cell, f-cell, basal cell) were obviously recognized by their shape, position and fine structures. After 6th day, T itself became larger as a result of both an elongation and an increase in number of cells. The ontogenetic development of the facial lobe was examined in the Plotosus and carp. Three-dimensional reconstructions of the facial lobe were produced with a NEC PC-9801VM using COSMOZONE 2SA(Nikon). At 12th day after hatching, the five lobules first appeared in the anterior tip of the facial lobe. They were located only in the anterior one third of the lobe. Thereafter, the lobules developed anteriorly until they occupied the anterior two third of the facial lobe. The facial lobe of the carp appeared as a pair structure in the early stage, and then began to fuse each other.This study suggests the pathway of differentiation of the primary facial taste center in teleost fish. The most primitive taste center is a pair of column and their anterior portion corresponds to the facial lobe. The catfish type of facial lobe is obtained by developing the barbel lobules anteriorly and trunk lobule antero-dorsolaterally. The organization of barbel lobules is related to both the number and relative lengths of the barbels. The carp type of facial lobe is obtained by rotating a pair of the facial lobe medially and fusing each other. In this type, the lip and oral epithelium are disproportionally enlarged in stead of the barbels and trunk. Less