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Zoology Publications from Victoria University of Wellington—Nos. 33 and 34

Discussion

Discussion

The twelve leptccephali dealt with above plus the four specimens from the Dana collection giving a total of 16 known specimens of anguillid larvae from the Southwest Pacific contrasts strongly with the richness of collections of this family in other ocean areas. This is the more interesting because the area contains six known species, all of which are common in the freshwaters of the area. There is no uncertainty in sorting these few larvae into long-finned and short-finned categories. Within these groups, four larvae can be identified as the short-finned A. obscura (one specimen) and A, australis (three specimens) since the number page 13 of myomeres is distinctive between the adults of these species, but so far no distinction other than zoogeographic in the sense of the localities at which specimens were taken can be made at the subspecific level for A. australis.

Of the eight long-finned larvae two are here identified with A. megastoma, since these two specimens were taken much further to the north of the observed geographic range of A. dieffenbachi with which the larvae of A. megastoma could be confused. The six remaining specimens belong either to A. marmorata or A. reinhardti although certain differences in morphology and geographical reasons suggest that four of these are A. marmorata and two A. reinhardti.

Although there are no very early larvae in this collection, the smallest being 23.7mm (A. megastoma, it may be significant in determining the location of the breeding areas of the various species that all the smaller larvae were collected to the east of the larger larvae (with the exception of the Dana specimen of A. obscura, 43mm). Taking into consideration the general east-west trend of the prevailing current system in this area it seems likely that the breeding area for these species is well to the east of New Caledonia—that is, between Fiji and Tahiti.

All of these Anguilla larvae were collected in depths of about 100m-200m where the temperature is at least 20°C. and the salinity is about 35.5%o. Conditions such as these are known to occur in the breeding areas of the Atlantic species of Anguilla.

In 11 early elvers of A. australis australis from the New South Wales region Ege (1939, p. 209) records the total length to be 47mm-64mm although the average was about 53mm. Both of the glass-eels described above fall within this range (52.5mm and 57.9mm). Elvers of A. australis schmidti from New Caledonia reach an average maximum of about 50mm, while those of this species from New Zealand reach a much greater average length, about 61mm. As Ege (1939, p. 211) notes, there appears to be no systematic significance in the difference in maximum size between elvers from New Caledonia and New Zealand, but that this is rather "an expression of biological-geographical conditions". A similar condition in which the elvers are relatively large nevertheless also occurs in the other two temperate species of Anguilla in the Pacific. A. japonica Temminck & Schlegel from Japan has elvers which reach about 57mm (Ege, 1939, p. 142) while those of A. dieffenbachi from New Zealand reach about 64mm-70mm. It is possible that the temperate elvers are more distant from the breeding grounds of the adults than are their tropical counterparts, and this may account for their larger average size.