Tuatara: Volume 14, Issue 1, April 1966
Further Observations on Galaxias Whitebait and their relation to the distribution of the Galaxiidae
Further Observations on Galaxias Whitebait and their relation to the distribution of the Galaxiidae
The Most Widely Recognised Species of whitebait in New Zealand is the juvenile of Galaxias attenuatus (Jenyns) but it is now known that other New Zealand Galaxiidae also have marine whitebait. The whitebait stages of G. attenuatus, G. postvectis Clarke, G. fasciatus Gray, and G. brevipinnis Gunther have been described (McDowall, 1964b) and it was suggested that G. argenteus (Gmelin), because of its similarity to some of these other species, would also be found to have a marine whitebait stage. This paper describes the whitebait of G. argenteus and discusses the relationship between the marine existence of some Galaxias species and the distribution of the family Galaxiidae. The distribution of the Galaxiidae around the southern hemisphere land masses was discussed by McDowall (1964a).
During a survey to determine the composition of the commercial whitebait catch in New Zealand (McDowall, 1965), a sample of whitebait was collected from the Buller River and the fish reared page 13 until pigmentation patterns indicated the species present. This was not a random sample, but was chosen, as far as possible, to exclude G. attenuatus which was well known to have a marine whitebait. G. attenuatus can be distinguished from other Galaxias whitebait by the more extensive trunk pigmentation. One of the survivors of this sample was, in fact, G. attenuatus. The fish were captured by a whitebaiter using a scoop net about half a mile upstream from the mouth of the Buller River and well within the tidal reaches. Eleven fish survived until they were identifiable, and one of these was G. argenteus, strongly suggesting that this species has a marine whitebait. Definite proof that the whitebait of G. argenteus is marine, and not merely estuarine, is lacking. However, in view of the strong evidence that G. postvectis and G. fasciatus have marine whitebait (McDowall, 1964b), and the close relationships between these two species and G. argenteus, it is considered highly probable that the whitebait of G. argenteus is marine.
It is remarkable that the eleven survivors of the sample comprised 5 G. fasciatus. They thus represent all five species of Galaxias known to have marine whitebait in New Zealand. G. argenteus was subsequently identified in many samples from rivers on the west coast of the South Island.
1 G. attenuatus, 1 G. brevipinnis, 1 G. argenteus, 3 G. postvectis and
The Whitebait of G. argenteus
G. argenteus whitebait were found to be more heavily built than the whitebait of other species. Measuring between 50 and 55mm length to caudal fork (L.C.F.), they were deep and thick bodied, with broad long head, a deep caudal peduncle and an expansive caudal fin. The pigmentation of G. argenteus whitebait is similar to that of G. fasciatus and G. postvectis, consisting of rather indistinct dorsal, ventral and mid-lateral series of melanophores, with further melanophores on the head and opercular margins (Fig. 1). Soon after the fish enter fresh-water, pigmentation begins to intensify and the young G. argenteus becomes a dark grey-brown colour, and later 8-10 distinct pale blotches or bands develop on the sides of the trunk (Fig 1). This pattern is quite different from G. fasciatus juveniles in which the bands are narrower and much more numerous, and from G. postvectis in which the bands are dark on a paler body colour.
The adult of G. argenteus has a mass of yellow-gold spots, rings, crescents and lines on the dorsum of the head, the trunk and the fin bases (Fig. 2). These markings are superimposed on the bands of the juveniles, which may still be visible in younger adults, but become obscured in older fish. The body colour of the adult ranges from light brown to dark chocolate.page 14
Marine Associations of the Galaxiidae
Some writers have expressed the view that the family Galaxiidae is primarily a fresh-water one. Stokell (1950) suggested that some form of land connection between the areas of galaxiid distribution was necessary until the Galaxiidae had evolved. Although it has been known for a long time that G. attenuatus has a marine whitebait, it has been thought by some that the marine stage of G. attenuatus is atypical of the Galaxiidae (e.g. Phillipps, 1919). The distribution of G. attenuatus around the southern land masses may be quite recent, but the existence of further species of Galaxias with marine larval stages shows that the marine life of G. attenuatus is not atypical.
The distinctive life-cycle of G. attenuatus, more particularly the persistent shoaling habits (found only in the juveniles of other species) and the characteristic habit of breeding amongst vegetation above normal water levels suggest that G. attenuatus is not a typical galaxiid. Ogilby (1899) drew attention to the distinctness of G. attenuatus when he removed it to the new genus Austrocobitis. The validity of using G. attenuatus to explain the dispersal of the ancestral Galaxiidae is thus doubtful, but the knowledge that page 15 other ‘more typical’ Galaxiidae have marine stages in their life cycles renders it unnecessary to depend exclusively on G. attenuatus as a pointer to Galaxias distribution patterns and means of dispersal.
G. attenuatus appears to be differentiating in several land-locked lakes where the marine larval stage is eliminated. Stokell (1964) described a form of Galaxias (G. parrishi) from Lake Bullen Merri, Australia, and noted another similar form from Lake Colac. The author has specimens of ‘G. attenuatus’ collected from Lake Modewarre in Australia by Mr. D. A. Pollard. This lake is land-locked, and the fish are intermediate in many respects between G. parrishi Stokell and G. attenuatus. In a survey of the coastal dune lakes of New Zealand (Cunningham et al, 1953), specimens of a fish very similar to G. attenuatus were collected from Lake Waiparera, a small land-locked lake near Kaitaia, and these showed differences from G. attenuatus similar in degree to the differences described by Stokell for G. attenuatus and G. parrishi.
The ability to forsake a partially marine life and adopt a purely fresh-water one where circumstances are suitable appears also to be true for G. fasciatus which has been collected from the Kaihoka Lakes, near Collingwood; neither of these small lakes has an outlet stream yet there are large populations of G. fasciatus in them. The similarities in the form and life history patterns of the partially marine G. brevipinnis and the two lake Galaxiidae G. lynx Hutton and G. koaro Phillipps, suggest that these lake species may be derived from a species with a marine whitebait. The marine whitebait is replaced by a lake whitebait with subsequent diversification isolated from the parent stock. It appears that the family Galaxiidae can be regarded as a euryhaline fresh-water family in which there is capacity for adaptation to a purely fresh-water existence when isolated by some barrier from the sea.
Dispersal in the New Zealand Region
The fact that certain species of Galaxias have marine whitebait is reflected in their New Zealand distribution. G. fasciatus is particularly widespread and occurs from North Auckland to Southland on both the east and west coasts of New Zealand; it is also known from the Chatham Islands (Stokell, 1950), the Chicken Islands, Stewart Island (Stokell, 1949), Little Barrier Island, Cavalli Island. Mercury Island, D'Urville Island and Kapiti Island. G. argenteus and G. postvectis are less widely recorded, but this may partially be attributed to the difficulty in capturing these species from the dense cover they live in. However, G. argenteus is known from the Bay of Plenty, Taranaki, Wellington, Wairarapa, Canterbury, Westland, Fiordland, Otago and Southland. G. postvectis is not commonly collected, but is now known from North Auckland, Bay of Plenty, Taranaki, Wellington, Marlborough and Westland. Many of these localities are from the author's records. With further collecting it seems likely that both G. argenteus and G. postvectis will be found in New Zealand wherever suitable habitat is accessible to them.
G. brevipinnis is as widely distributed on the mainland of New Zealand as G. fasciatus. It has been found in North Auckland, Waikato. Bay of Plenty, Hawke's Bay, Taranaki, Wanganui-Manawatu, Wellington, Westland and Otago, and has also been recorded from Kapiti Island (Wilkinson and Wilkinson, 1952). G. campbelli Sauvage, from the sub-antarctic islands of New Zealand is regarded by Stokell (1954 and 1960) as con-specific with G. brevipinnis. G. attenuatus occurs throughout New Zealand and is known from some of the offshore islands and from the Chatham Islands.
Other species are more restricted in their distribution. G. divergens Stokell and Neochanna apoda Gunther occur in the southern North Island and the Nelson-West Coast area; these regions were connected as recently as the Pleistocene glaciations (Fleming, 1962). Galaxias lynx occurs in the mountain lakes of the South Island, and is also recorded by Stokell from Lake Waikaremoana in the North Island. Apart from this apparent anomaly and the cases of G. divergens and Neochanna apoda, all New Zealand Galaxiidae not having marine whitebait are confined to one or other of the major islands, and present data indicate that many have very restricted distributions, e.g. G. burrowsius Phillipps is recorded only from Mid-Canterbury, G. paucispondylus Stokell and G. prognathus Stokell are known only from mountainous Canterbury streams. G. koaro Phillipps occurs only in the thermal lakes of the central North Island.
The much broader distribution of G. attenuatus, G. postvectis, G. fasciatus, G. argenteus and G. brevipinnis appears to be closely page 17 correlated with the fact that they have marine dwelling whitebait. The barriers of physiography and salinity which prevent the dispersal of the non-marine Galaxiidae have not limited the dispersal of the sea-going species, which are widespread in New Zealand lowland streams.
Dispersal in the Southern Land Masses
The hypothesis that the genus Galaxias has been distributed amongst the southern land masses by oceanic routes is supported by the discovery that several species, apart from G. attenuatus, have marine whitebait. The fact that G. attenuatus is present in three widely separated land masses (Australia, New Zealand, South America) shows that its larvae and juveniles are capable of oceanic dispersal, and that this dispersal could have taken place quite recently. The presence of marine larvae in several species now restricted to New Zealand indicates that the family has had a potentiality for oceanic dispersal for a long time, i.e. long enough to allow the evolution of distinct species in New Zealand.
Any doubts about the validity of G. attenuatus as an index for the early distribution of the family are no longer of consequence as more ‘typical’ species of Galaxias support the hypothesis of oceanic dispersal equally strongly. However, although at least three species in Australia (Lynch, 1965) and five species in New Zealand have marine juveniles, only one species is found to occur in more than one faunal region. This suggests that in the past, success in movements of these fishes across these gaps must have been infrequent. Apart from the comparatively recent dispersal of G. attenuatus, all species were apparently dispersed sufficiently long ago to allow divergence to bring endemism to all the other forms of Galaxias in each area. It is possible that some change in the marine life, such as a reduction in the length of the marine stage, has affected the ease with which the marine tolerant Galaxiidae are dispersed.
In the previous paper (McDowall, 1964a) it was suggested that the New Zealand Galaxiidae had Australian origins. If this is the case, then the presence of five species with marine juveniles in New Zealand is probably a result of diversification of Australian form(s) in a New Zealand fresh-water environment almost uninhabited by fish. Because dispersal in the south-temperate region is probably west to east, these marine tolerant New Zealand species would be unlikely to reach Australia. That only one of the five species is known to have crossed the South Pacific from New Zealand to South America is not surprising in view of the great distance involved.
The author is indebted to the following for their assistance: Mr. K. F. Maynard and Mr. G. A. Eldon for collection of specimens; Dr. J. A. F. Garrick, Victoria University of Wellington, Mr. L. J. Paul, Fisheries Research Division, Mr. J. W. Brodie, Acting Director of Research, Fisheries Research Division, Dr. Giles W. Mead, Museum of Comparative Zoology, Harvard University, and Mr. J. M. Moreland, Dominion Museum, for commenting on the manuscript; Mr. D. A. Pollard, Monash University, for Australian Galaxiidae.
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* Present address: Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, U.S.A.