H.—ls.

North America for a great many years, but is practically an untouched field for research in New Zealand. Its practical importance in connection with fresh-water-fish culture will be appreciated if one recalls that in the past several vain attemps have been made to introduce into New Zealand the whitefish (Coregonus clupeiformis), the most valuable food fish of the Great Lakes of North America. The last attempts to acclimatize this species were made by the Marine Department when from 1904 to 1907 two million eggs were imported from America each year. " Each shipment of eggs," it was reported, " arrived in first-rate condition, was successfully hatched out (at hatcheries situated at Lake Tekapo in the Mackenzie Country and at Lake Kanieri, Westland), and the fry liberated in the lakes mentioned." Why did not these fry grow up and produce a stock of fish ? The answer has been provided by Professor Percival's examination of the plankton (the minute forms of life) in our lakes. Generally speaking (though of course his investigations have not been exhaustive) he has found in New Zealand lakes (including Lake Tekapo) a remarkable dearth of animal plankton, the principal constituents of which in lakes are the minute crustaceans belonging to the sub-order Cladocera and the order Copepoda. This is the class of food that the whitefish principally depends upon in the early part of its life, its habits and requirements in this respect being somewhat 'similar to those of the marine herring. In its later life it feeds upon insect larvae, small crustacea and other bottom fauna. Without an understanding of the food-requirements of the fish to be acclimatized, and of the possibilities of satisfying them in the environment into which they are to be introduced, any attempt at acclimatizing a new species of fish is pure guesswork—which explains the various failures of past acclimatization enterprises and also indicates the importance of a scientific basis for future policies. Apart from its bearing on the problem of whitefish acclimatization this subject of the investigation of the life in New Zealand lakes has a direct and practical interest in connection with our fresh-water fisheries. It is well known that the trout caught in practically all our lakes at the present time are of smaller average size and sometimes otherwise inferior to those formerly obtained. Without concluding, as some anglers have, that this is always and entirely a a matter of food-supply, one must recognize that for the maintenance of a good stock of big trout the presence of a sufficient and suitable supply of food is essential. It is frequently urged that a lake should be stocked with some kind of small fish to serve as food for the trout. This has sometimes been done ; but rarely, if ever, does the practical fisherman who advocates or practises such an expedient stop to consider how the small fish themselves are going to be fed or whether the conditions will be suitable for their propagation. To be of real benefit to the trout it is necessary that the fodder-fishes should live on organisms that would not otherwise be available, or of which a smaller equivalent would be available, for the nourishment of the trout. They must also be able to maintain their numbers by reproduction and growth in spite of the toll taken by the trout and other predators. Every lake in the country has a potential capacity to provide for the nourishment of a certain amount of fish, the kinds and quantities possible being dependent upon certain fundamental factors which are capable of being ascertained. The basic essential is the presence of the right kind and sufficient quantity of material in solution in the water to provide a fertilizing or nutrient medium for the production of plant-life. The " feed " in water that is analogous to the herbage of the land exists mainly in microscopic form and may be a constituent of the plankton invisible to the human eye or may form a sort of slime on the bottom or on water-weeds. Such microscopic algae provide the nourishment for minute animals and for insect larvae, crustaceans, and molluscs which are preyed upon by larger animals, and thus directly or indirectly may contribute to the nourishment of trout and ultimately feed or otherwise entertain a successful fisherman. The point to be noted is that the trout is the last stage in a succession of steps from food that has been feeder to feeder that will be food. The general problem of this aspect of fish-culture is to ensure that the successive steps are present and correct, so that they may lead with the minimum of loss or deviation to the production of trout or other fish that are desired. Big trout cannot flourish on a diet of microscopic algae nor on the smallest crustacean species, but if there ts present an abundance of Copepoda or Cladocera it is possible to introduce small fish that will make use of them and that will themselves be available as trout-food. If the Copepoda and Cladoeera are not there it is obviously futile to introduce a species of fish that is dependent on them for food. This sketchy reference to the " fish-food chain " of a lake may serve to illustrate the necessity for the investigation of the minute forms of life in the water and of the dissolved contents and other qualities of the water itself in order that the maintenance of a fish-stock may be considered on a scientific and therefore on a soundly practical basis. Professor Percival's spare-time investigations, which are at present a relatively small side-line in the work carried out under the auspices of the Committee, represent only the beginning of the exploration in New Zealand of a very vast field for research that is as essential a basis for progress in fish-culture as the chemistry and microbiology of soils has now proved to be for pointing the way to modern agricultural developments. The expenditure of the Research Committee during the year amounted to £800 14s. Bd., of which £624 represents payments for salaries and wages to three whole-time and .one temporary worker. The ground covered by the investigations would have been more restricted but for the co-operation of acclimatization societies, to whose executives and members the Committee is indebted for assistance to the Field Biologist and for data sent to the laboratory at Canterbury College. It must be recorded with regret that insufficiency of funds has prevented the publication of detailed reports on the work for which a substantial amount of material has now been prepared. A. E. Hefford, Chief Inspector of Fisheries. 4—H. 15.

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