Relation between nerve fiber number and pectoral fin regeneration in the teleost.

The number of nerve fibers per unit of amputation surface area has been determined in four teleosts capable of regenerating their fins (Gobius paganellus, Gobius minutus, Ictalurus nebulosus and Fundulus heteroclitus) and in two-non-regenerating ones (Cottus bubalis and Blennius pholis). The number of nerve fibers is about 16 in the non-regenerating fin and varies between 25 and 35 in the regenrating ones. These data, correlated with previous ones obtained on tetrapods, affirm the principle that there is a phylogenetic decline in the quantitative innervation of the vertebrate appendage. Moreover, they show that in the fish a quantitative neuronal threshold must also be satisfied in order for fin regeneration to occur. The threshold, in terms of fiber number, is higher than in the urodele amphibian. However, the fibers appear to be of smaller caliber; and so, the total amount of neuroplasm at the amputation surface which is required for regeneration may be similar to that for the amphibian.