Introduction

Among the fishes collected by the vessels H.M.S. Erebus and H.M.S. Terror while they were in New Zealand waters during the years 1840-41 was a small congrid eel which Sir John Richardson (1848, p. 109, pl. 50, figs. 1–5) described and figured under the name Congrus habenatus. The type specimen was taken in "Cook's Strait", but no more precise locality was given. Since the time of Richardson's account the "little conger" or "silver conger", as the species has come to be known by fishermen and others, has occasionally appeared in seine nets, trawls and fish stomachs from other parts of the New Zealand coast as well as from the Cook Strait area. The silver conger is also well-known in southeast Australia. Such an eel cannot easily be confused with other eels of these regions in view of its remarkably bright silver colouration over the anterior part of the body and particularly the iris making this a most attractive and easily-remembered fish.

Although Richardson's Congrus habenatus is thus well-recognised from Australasian coastal waters there has always been considerable systematic confusion, involving some nine generic names, in the correct name of this animal and related species elsewhere. This paper finally resolves this confusion; but further, early in the examination of numerous specimens of the silver conger from the New Zealand region, it was found that a second, unrecognised species was also present in the area and this is described and figured here.

In the preparation of this paper I have been able to examine 33 juveniles and adults of the two species, most of which were taken in seine nets in Wellington page 16 Harbour while the others were collected mainly by commercial trawls from various localities around the New Zealand coast and from as far north as the Kermadec Islands. I have also been able to examine two glass-eels, still possessing their larval pigment, from Western Australia. These provided a conclusive link between the larval stages and the young elvers of these eels. A great number of larvae of the two species, about 250 in all, representing an almost complete series up to late metamorphosis, were also available. The development and distribution of the larvae are thus now established and have been included in the account to complete the knowledge of the two species of silver conger in the Australasian area.

Proportional measurements were made to the nearest 0.1mm with accurate calipers in the manner I have already described (Castle, 1961, p. 2). Small structures were drawn with the aid of a camera lucida. One adult specimen of each of the two species was stained in alizarin and cleared in glycerine for the purpose of osteological study. Two skulls were examined as hand specimens. In the examination of the leptocephali the first myomere is taken as the one which extends ventrally to the level of the notochord. Myomeres are counted along the midlateral level. Preanal myomeres are those which lie in front of the vertical through the vent and where this cuts across a myomere this is included in the preanal count.

I am greatly indebted to the following institutions and persons who have helped in many ways in the preparation of this account. Firstly, to those institutions which have so generously allowed me to examine leptocephali or adults in their collections (a) the C.S.I.R.O. Division of Fisheries and Oceanography, Cronulla, New South Wales, (b) the Centre d'Océanographie de l'Institut Français d'Océanie, Nouméa, New Caledonia, (c) the Australian Museum, Sydney, (d) the Western Australian Museum, Perth, (e) the Dominion Museum, Canterbury Museum and Otago Museum, New Zealand; secondly, to Mr R. H. Kanazawa, Division of Fishes, U.S. National Museum, Washington, for valuable comments on the distinctions of various genera of eels and for literature; Dr J. C. Yaldwyn, Australian Museum, for examining the type of Congromuraena longicauda; finally, to Prof. L. R. Richardson, Department of Zoology, for his valuable criticisms.