FOOD OF TROUT

Dominion, Volume 22, Issue 71, 17 December 1928, Page 12

FOOD OF TROUT

RESULTS OF RESEARCH

MUCH WORK YET TO BE DONE

A meeting of the board of the Wellington Acclimatisation Society’s Fresh Water Fish Research Fellowship (which is being conducted under the auspices of the Victoria University College) was held last week. There were present: Messrs. L. O. H. Tripp (chairman). Professor H. B. Kirk, Mr. A. E. Hefford (Chief Inspector of Fisheries), and Dr. G. F. V. Anson. Captain G. S. Phillips, Research Fellow, presented a report covering the work of the past year. Professor Kirk, who acts as supervisor, amplified the report, which was reviewed by Mr. Hefford. After a general discussion it was considered that good preliminary work had been done. Captain Phillins made an urgent appeal for more fish stomachs and also some of eels, required for the purpose of elucidating seyeral important problems. The board will meet next in February, 1929.

In giving the result of his investigations into the food of trout Captain Phillips said that judging by the weight of those fish whose stomachs had been submitted to him for examination, the average weight of a caught trout was lib. 9Joz.. and the length 15$ inches. "The condition of the fish from both visual evidence and report is good,” he continued, "nor does there appear to be any signs of devastation by disease or parasites. The scales of about sixty trout, have- been examined and mounted, and show a regularity of growth due to the fact, that the temperature and supply of food varies little throughout the year. This constant rate of metabolism at present hinders the recognition of annual zones and the preparation of statistics correlating age and rate of growth. Further* investigations in the formation and growth, of scales arc being made with the hope that they may throw more light bn this matter. “Trout’are coming buck in places where there were reported to be none or few. in previous years, as is instanced by-the Ohariu. the investigation of which as a. typical poor- fish river was stopped for .that reason. . ■ “A-tempts have been made to get into to'uch with other countries which have done, or are doing, work connected with our problems, viz.. England, Scotland, Norway. U.S.A., and we are corresponding with workers in other parts of New Zealand. How Trout Live. “For-a number, of years, trout in hundreds of thousands have been liberated ill our rivers, and little thought has been given as to how they are to live. For a time, they can live on the country, and in the present ease they have done so. and done so successfully for a long period. But the aquatic food resources, though rich, are not inexhaustible, and every year the present policy continues will worsen the conditions accordingly. “As fur as I can gather, the situation appears to be as follows: Most of the larger trout are either upstream, in wellbushed and inaccessible country, where conditions are more nearly as they used to be’ than' in the transformed accessible areas, or at the river mouths, where food is more varied and plentiful (or where the fish may be sea-run), or in lakes, where, again the food conditions are quite different.

“In the accessible and well-fished portions of- streams and rivers, there are a great number of small trout—occasional reports to the contrary notwithstanding, and in most of—though not all these places—there is plenty of small fish food, such as caddis and mayfly larvae, and the minute gastropod Potamopyrgus. It is probable that these, are insufficient to produce large fish, and it is also probable that there are not sufficient_Qf even these to cope with the present policy of being eaten by two million new trout yearly—in addition to those fish spawned naturally. Accordingly, it would seem highly advisable either to take steps to increase the food supply, or to stop putting out fish. It would be better still to do both. Why not use the hatcheries (enlarged to double the size this year) to rear trout and trout food alternately, or if considered preferable use half of them for trout, and half for trout food? As to what food would be most suitable, that will require considerable investigation. and I should much appreciate an opportunity of examining the stomachs of large fish.” Captain Phillips has also reported on the AVaikanae River, a preliminary survey having been made from October 20 to November 3, that stream being'chosen because of its being “a typical good” trout stream. The bad weather conditions made it impossible to study the behaviour of trout as had been hoped, and the winged stages of trout food were also not in evidence, except rarely. None the less, said Captain Phillips, a considerable amount of work was possible, including the collection of larval forms of insect food and a reconnaissance of the natural features of the Waikanae basin. He noted that the course of the Waikanae was rapid but uneven. The depth was equally so. ’ In one place the water might be ankle deep and ten yards away it might be of too great a depth for a man to stand. The banks varied considerably in character, in places precipitate and towering, elsewhere flat, and in other parts of moderate slope. The coverings of the banks'varied too. Although most of the tributaries of the Waikanae were of-the mountain torrent type, a few' of them (and these meandered in through the meadows in the lower reaches of its course) were slow and placid and choked with watercress, Lemna and Azolla rubra anil vegetation of a similar ecological nature. 'These abounded in crustaceans and also in insect types not met with in the more rapid streams and consequently were quite probably of considerable value in augmenting the diet of the Waikanae trout. Report on Taupo Expedition. “The last ten days of .August,” continued Captain Phillips, "were occupied by an expedition to Taupo to see the stripping at the Government hatchery, and in addition the general conditions of aquatic life, in Dake Taupo and its tributary waters were given such attention as the time and weather allowed. At Taupo, the first water explored was the Waikato, wherein bully, were observed in large quantities. It was remarkable to note that by the Spa, where a number of boiling springs, containing sulphur, alum, and other impurities were emtying into the Tongariro. there were large numbers of bullies, only a few feet away. Either the bully is very adaptable, or the effect of these thermal springs does not appear to be so injurious as has been supposed. In this neighbourhood are large masses of algae, covered with the mollusc potamopyrgus. In Dake Taupo itself, a number cf rainbow trout were noted spawning or preparing to spawn close in shore, near the townside quay. Again the bully was much in evidence, and there were also reported to be smelt and kokopu in the lake; the latter used to be very num erous, and has (according to my informant) been almost exterminated by the trout. A land-locked variety of inanga was seen, and is fairly common in the lake. . ... “Insect life is not much in evidence in the lake itself, though represented fairly in the streams which flow into it, except for various diptera, mostly culicoiilea—one moderately-sized mosquito being especially and unpleasantly noticeable. "The fresh-water dam is present, but was reported as unsuitable as trout, food, and the crayfish apepars to have suffered similarly, though in a lesser degree to the kokopu, and there is some talk of restocking the lake with it. Bully and shrimp have been used lately for restocking the lake and Its streams-by the Denartment of Internal Affairs, which is trying to evolve a policy which will conserve the wonderful fishing in this district. To effect this, it is making n chemical analysis of some of the streams and of the lake itself, tagging n number of fish, taking seqles end statistics of growth, cullin'.: I lie poor fish, and extend lug the operations of the hatchery con-

sidorably. Rainbow trout, only are stripped. though (here are n few brown trout, here too. , , “A mysterious disease, characterised by lhe lippoiirmiee of white spots, has broken nut nntonjr tho gullies, fl nd nnu caused heavy losses, attacking th' young as well as grown fish. As bullies form th<* chief diof of (lie Into Iron!, lhe mifhorilies are tmieli cimeeriio'l. and are haiiug the mallei' investigated. ’