Peripheral distribution and central projections of the lateral-line nerves in goldfish, Carassius auratus

The lateral-line system of the goldfish, Carassius auratus, is described from the receptor distribution on the body surface to the termination of the primary afferents within the octavolateralis column. Goldfish have a continuous lateral-line canal system which consists of supraorbital, infraorbital, operculomandibular and supratemporal commissural canals on the head and a trunk canal extending the length of the trunk. There is a single neuromast between each 2 canal pores. The total number of canal neuromasts on the head ranges from 74 to 100. On the body the total number of canal neuromasts ranges from 52 to 60. Associated with each canal are populations of superficial neuromasts. There are approximately 1,000 superficial neuromasts on the head which are arranged in clusters or rows oriented perpendicular to the long axis of the associated canal. On the body there are 3-9 superficial neuromasts on each scale. Further, there is a total of 1,000 superficial neuromasts arranged in horizontal lines between the fin rays of the caudal fin. The neuromasts are innervated by branches of four lateral-line nerves. The dorsal anterior lateral-line nerve innervates the supraorbital and infraorbital canals and associated superficial neuromasts. The ventral anterior lateral-line nerve innervates the operculomandibular canal and associated superficial neuromasts, as well as superficial neuromasts on the operculum. The middle lateral-line nerve innervates the postotic canal and a cluster of associated superficial neuromasts. The posterior lateral-line nerve innervates the supratemporal commissural canal and associated superficial neuromasts, as well as the canal and superficial neuromasts on the trunk and caudal fin. Application of horseradish peroxidase to the individual branches of the lateral-line nerves shows that the posterior lateral-line nerve projects to the dorsal portion of the medial and caudal nuclei, whereas the anterior lateral-line branches project to the ventral portion. Lateral-line projections to the magnocellular and descending nuclei of the octaval column were also observed. The projections to the eminentia granularis are also segregated such that the anterior lateral-line nerves project to the anterolateral portion and the posterior lateral-line nerve to the caudal portion. Thus, there appears to be a topographic organization of the lateral-line projections to the lateralis column and eminentia granularis. However, this topography does not appear to be precise as the projections of the branches of the anterior lateral-line nerves overlap extensively, as do the branches of the posterior lateral-line nerves.