Notes From the Plymouth Aquarium. II

Abstract

As known from ancient times, Electric Rays (Torpedo) have the power of giving severe numbing shocks, and it has repeatedly been stated that this power, which is electrical, is used both as a means of protection and for paralysing prey. That the shock is used in the capture of prey seems never to have been definitely proved. Indeed Roule (1935, p. 161) expresses the opinion that the electric shock is not used for securing food and even doubts that it is normally and effectively used as a means of defence. There appears to be no detailed account of the manner in which Torpedo feeds, but the ninth edition (1925) of the Guide to the Aquarium of the Zoological Station at Naples mentions (p. 106) that the Electric Ray rises from the mud to throw itself against approaching mullet (Mugil), and that the mullet, overcome by fright and electric shock, fall to the ground to be eaten. This very short and incomplete account was not seen until after the following paragraphs had been written.Both Torpedo nobiliana Bonaparte and T. torpedo L. occur from time to time off Plymouth, the former being by far the commoner, and both have been kept in our aquarium tanks. They are sluggish fishes, spending most of the time lying still on the bottom, occasionally swimming for short spells. They swim by sculling with the tail, which has a large caudal and two dorsal fins. This mode of swimming differs strikingly from that of normal rays, which undulate the pectoral fins and trail their tails' it resembles the swimming movements of Rhina squatina (L.), another fish with a sluggish disposition and, as noted below, some other resemblances to Torpedo.