A Gastric Battery for Fish

We previously described, in Transactions of the American Fisheries Society (1965), vol. 94, p. 193-194 “A device for holding objects in the stomachs of fish, consisting of a 1/16-inch plastic rod formed to loop around the isthmus and extend down the gullet into the stomach. This harness was developed to secure an experimental gastric battery, not reported at that time. The battery was intended to power an ultrasonic tracking transmitter. After 20-day trials of seven combinations of metals in an electrolytic solution of 0.5 percent hydrochloric acid, we chose gold and cadmium for the battery plates on the basis of their longevity, primarily, and secondarily on the strength of their power output. The gold-cadmium batteries were constructed by wrapping cadmium and gold foil, separated by a spiraled polyethylene spacer, around the portion of the harness rod that extended into the stomach. The 0.3-millimeter-thick foil plates were about 1 by 3 centimeters; the 0.15- by 1.5-millimeter spacer strip was spiraled with a 5-millimeter space between each wrap. Enameled No. 30 copper wires soldered to the plates served as battery terminals