Notes on some fishes associated with the Antarctic krill. II. On Xenocyttus nemotoi ABE, and again on Neopagetopsis ionah NYBELIN

Abstract

Since the description of Xenocyttus nemotoi ABE in 1957,there have been but a few records of this oreosomatid fish. Recently it is taken from time to time along with the Antarctic krill, and 29 specimens have been received for study. Their size varies very little, standard length being 113mm to 180mm. This species is now known to occur off Patagonia as well. They are thought to be the young of a much larger fish. Their diet is copepods. In the absence of the holotype of its close ally, Pseudocyttus maculatus GILCHRIST, it is thought advisable to discuss the relationships of Xenocyttus with the other members of the Oreosomatidae and Zeiformes in the future. The flesh of three specimens of Xenocyttus nemotoi measuring some 150mm in standard length contains water (84.2%), crude protein (9.6%), crude fat (3.8%) and crude ash (1.1%). The subcutaneous tissue is fairly hard, and its heat conductivity is ca. 0.60 (kcal/m・h・℃) as against ca. 0.65 in the flesh. Many specimens of Neopagetopsis ionah NYBELIN have been collected since the publishing of the previous paper of this series. It is met with oftener than Xenocyttus nemotoi at fishing grounds of the Antarctic krill. The number of branchiostegals is oftener 9 on either side. At times it is 8 on either side, or 9 on one side and 8 on the other. The young take the Antarctic krill as food, but one larger specimen trawled at depth in the Ross Sea contained Pleuragramma antarcticum BOULENGER in the stomach.