KAKAHI’S CYCLE

Taranaki Daily News, 16 January 1933, Page 10

KAKAHI’S CYCLE

SMALL FISH AS HOST. A FRESH-WATER MUSSEL. The remarkable life-circle of the New Zealand fresh-water mussel, kakahi, is called to mind, states the . Post, by the ' liberation of a number of them in the stream that. runs through Otari Plant. Museum, Wellington, on its way - to the harbour at Kaiwarra. These’ mussels are fairly big. A sample is 3j inches long and about an inch and a-half broad. Kakahi were food for the Maori, but are in these times scarce, and becoming scarcer. .Their liberation at Otari is in pursuance of the project to stock the stream system there with all types of New Zealand freshwater life. The stream has 'contained exotics in the form of trout and perch (the latter probably derived from ova overflowing from the Karori reservoir), but it is not physically suited, in its higher waters, tb angling. The mussels (kakahi) were- liberated by Mr. W. J. Phillipps, of the Dominion Museum, with the assistance of the Director of City Reserves (Mr. J. G. MacKenzie) and the' custodian of Otari (Mr. McKay), also with the approval of the Hon. Botanist to the City (Dr. L. Cockayne, F.R.S.). While it is unlikely that the kakahi will ever become extinct, it is certainly the case that this

mussel is not nearly so common now as in former times, although there are several rivers in the Wellington province

where it is known to exist in fair num- ’ bers. It is hoped that Otari waters will be favourable to its survival and increase. The mussels handled by Mr. Phillipps were sent alive to the Dominion Museum by Mr. W. Fraser, of Feilding; and after the Director (Mr. W. R. B. Oliver) had selected some typical examples for the Museum collection, the remainder were liberated. 'Kawahi’s scientific name is Diplodon menziesi. The sexes are separate and the egg is hatched in the brood pouch

of the female until it reaches a larval stage, called;a glochidium. Later glochidia or .larvae are ejected into the water. Each larva must now come m contact with a srnall fresh-water fish a “bully,” or . a species of Galaxias (a genus which includes native trout), or even a young introduced trout. Each glochidium is armed with two interlocking hooks in the form of a valve. These fasten on to the fish and the glochidium becomes a parasite on the skin, fins or roof of the mouth of the host fish. In this position it becomes encysted by an overgrowth of the skin or mucous membrane of the host, and is nourished by its body juices. While in this condition a metamorphosis takes place, and ultimately a foot arises ,as a median ventral elevation behind the mouth, and on each side of it two papillae appear, the rudiments of gills. The larva is now fitted for free existence. It drops from its host and gradually assumes the adult form and mode of life. Professor E. Percival, of Canterbury College,- Christchurch, has recently . investigated the life history of the South Island kakahi, Diplodon lutulentus. He found the adults in the stony beds of several small lakes in West Canterbury, notably Lake Sarah at an altitude of about 1800 feet. Collections made at the end of November with a tow net trailed slowly about six inches from the bottom contained a large number of glochidia. Professor Percival found that the young of “bully” and native trout (Galaxias) were the hosts for the larvae. ARAWA DREDGES. In the North Island, on certain lakes and rivers, kakahi were classed as an important food of the Maori. Special dredges were constructed by Arawa and other tribes to take this mussel, and at least one North Island lake (for example, Roto-kakahi) has been named because of its former abundance of mussels. Kakahi is also the name of a North Island Main Trunk railway station near fhe Wanganui River.