Hey all, my amazing other half stopped off at the UoA library yesterday, and got me 3 books by R.M. McDowall. I've now got a huge amount of info on the Giant Kokopu. I'll copy paste (even though there's a lot of it). Hopefully you guys will find it as interesting as I do!
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The Giant Kokopu is the biggest species of Galaxias, not only in New Zealand but in the whole family. It was also the first galaxiid discovered and the first species of freshwater fish found by the pakeha in New Zealand, being collected by naturalists visiting New Zealand with Captain James Cook in 1773. Common names include Maori Trout & Native Trout.
DESCRIPTION:
The Giant Kokopu is a very stout fish, almost square in cross-section, with a long, broad head (length 27-31 percent of S.L.), and a large grouper-like mouth (upper jaw 41-46 percent of H.L.). The jaws are about equal in length, the cleft reaching back to beyond the level of the eyes; the lips are thick & fleshy. The eyes are of moderate size (15-22 percent of H.L.). There is a small group of enlarged canine teeth on each side in each jaw. The fins are well developed with thick, fleshy bases, the dorsal (10-12 rays) and anal (12-15 rays) fins high and rounded, the dorsal fin originating directly above or a fraction in front of the anal fin. The pectoral fins (13-15 rays) are low on the sides. The caudal peduncle is short and very deep, the depth exceeding the length; the caudal fin is long and usually truncated, although it may be slightly concave in small fish. There are 14-17 long gill rakers and two long pyloric caeca. There are 58-61 vertebrae.
COLOUR:
The Giant Kokopu is often dark coloured, a deep grey-brown, although sometimes it is paler, approaching an olive-buff. The head, back and sides, and the fin bases are profusely covered with delicate gold spots, lines, crescents and rings. These tend to be fine spots on the head and back, but are coarser and bolder on the sides. The belly is usually much paler, bluish-grey in dark fish and a light greenish-olive in paler ones. There is a dark bluish-purple blotch above and behind the pectoral fin bases, but in darkly coloured fishes it is not very obvious.
DISTINGUISHING CHARACTERISTICS:
The Giant Kokopu is distinctive as an adult by the gold spots, rings crescents, etc on the sides. It has longer jaws and much longer pyloric caeca than the similar Banded Kokopu. Its equal jaws easily distinguish it from the Shortjawed Kokopu. The young of the Giant Kokopu are not so easily distinguished from those of the Banded Kokopu; however, the bands on the sides of not cross the back in the Giant Kokopu but do in the Banded Kokopu.
SIZE:
Clarke (1899) reported that the Giant Kokopu may grow to at least 580mm and a weight of 2.7 kg. In my experience this species is not commonly found more than about 300mm long.
DISTRIBUTION:
The Giant Kokopu is found all around New Zealand mostly in streams not far from the sea – it does not seem to penetrate far inland. It occurs in streams on the Chatham Islands and also on Great Barrier Island. Thus, although not common, it is widely distributed.
TAXANOMIC NOTES:
Since Stokell (1954) unraveled the problems on nomenclature in this species, it has been known as Galaxias argenteus. As Stokell pointed out, the name argenteus, meaning silvery (Latin), is singularly inappropriate for this fish as it one of the least silvery of galaxiids. Application of this name to the Giant Kokopu is the result of an error made nearly 200 years ago, but the name must now remain as valid. Other names that have been used for this species include G. grandis, G. Kokopu and more often, G. alepidotus. It has been thoroughly confused with at least three other species from time to time. Maori names used for this fish are far from clear from Best’s (1929) description.
BIOLOGY:
Not much is known about the Giant Kokopu. It is found in very variable habitats, often in swamps, swampy creeks, some lakes, and sometime in gravelly streams, but always where there is plenty of cover in the water – logs, tree roots, overhanging branches, flax bushes and raupo – places where it can skulk and hide during the day. It is probably a mostly nocturnal species although sometimes if caught unawares it may be seen out basking in the sun. As a few anglers know, it will sometimes take a bait during the day. In earlier times the Giant Kokopu were more often caught. Graham (1956) and others discuss catching these fish with a hook and worm, which is still one of the easiest ways of catching them in boggy swamps.
The Giant Kokopu is one of the whitebait species. This comes as a great surprise to many people. The whitebait of the Giant Kokopu is not common in the whitebait catch, but it is there nevertheless. Where the Giant Kokopu spawns is not yet known, but, because the ripe adults are found apparently ready to spawn in typical adult habitats, I suspect that they do not migrate far to spawn. The eggs are relatively small, 1-2mm in diameter, and they vary in number from several to many thousands. Spawning occurs in the autumn or early winter, and when the young hatch they must be washed out to sea. They spend the winter in the sea. The whitebait of the Giant Kokopu appear in the whitebait catch rather late in the season, usually in early November when the whitebait run is more or less over. The young fish are 45-50 mm long and almost completely unpigmented. They make their way upstream into typical adult habitats and the once transparent whitebait gradually develop colouration. First they become a dull greenish-grey colour with a silvery-olive belly. Then up to 6-8 pale vertical bands or blotches develop on the sides, but these do not extend over the back. Often it seems that the bands become fewer in number as the fish grow, with only 3-4 in older fish. The once slender whitebait becomes quite stocky and as it grows the pale blotches are replaced by the characteristic markings of the adult. The Giant Kokopu probably takes two or three years to reach maturity and, judging by the large size to which is sometimes grows, must live for many years.
The Giant Kokopu was probably an important food for the Maoris, as it was one of the largest species in New Zealand’s sparse freshwater fish fauna. However, it is difficult to determine how much it was used as a food because accounts of the Maoris’ use of the native fishes by Best (1929), and others, show that there was much confusion between many different species of Galaxias. The Giant Kokopu is reported to have many small bones and a rather eel-like flavour.
In many parts of New Zealand the Giant Kokopu now seems rare. Undeveloped areas, especially the West Coast, are likely to have some good populations of this species, and there are reports of it being abundant in parts of South Otago and Southland, but in populated and agricultural areas few are found. Decline of the Giant Kokopu in developed areas can be attributed largely to loss of cover suitable for the fishes to live amongst. The Giant Kokopu appears to be not compatible with Brown Trout and is found only where trout are rare or absent. I suspect that competition for cover may be important as both trout and the Giant Kokopu are territorial and aggressive. As pastoral development of the New Zealand continues, it is likely that we will see the decline of this species continuing. While there does not seem to be any immediate danger of extinction, the Giant Kokopu should be regarded and treated as a threatened species.
[Taken from New Zealand Freshwater Fishes, R.M. McDowall 1978]
