FISHERY RESEARCH.

Timaru Herald, Volume CXXV, Issue 18636, 4 August 1930, Page 16

FISHERY RESEARCH.

ADDRESS TO ANGLERS. AGES ANL FOOD OF FISH. Addresses to anglers wer? delivered on Saturday evening by Professor Percival. of Canterbury College, and Mr A. W. Parrott, of the New Zealand Fishery Research Committee, on the subject of research w T ork among fish. There was a good attendance, and the president of the South Canterbury Acclimatisation Society; Mr T. R. Mackay, presided. In introducing Processor Percival and Mr Parrott, the chairman expressed the opinion that the setting up of his Research Committee to j’vcesthmte the position of fish and fish food was a leally good thing, and tney were fortunate in being able to get Professor Percival and Mr Parrott to address fishermen on these important matters. Personally h.» did not think that the fish were as big nov. T as they used to be. Whether this w’as due to ; lack of food or to something in the I food consumed by the fish, he did not j know, but he considered that this was I what Professor Percival and Mr Par- | rott were going to fil'd out if possible. ! Professor Percival said, at the out--1 set. that recently an organised attempt had been made to fatten fish. Mr Parrott had made a start, “but we are not the people who are going to do ail the work," said Professor Percival. “A good deal of the work will be done by the fishermen who out. and in the course of their expeditions make observations, because the nature of the work makes it impossible for those investigating these questions to be in several places at once. So far as the food is concerned, this is one of what has turned out to be a series of lecturei in an educational programme.” I problem of the habits and foods of fish was not a problem concerned with a single science, but of all sciences: and the title w’hich he gave to these talks was the “Economics of the Stream.” Fishermen w r ere more interested in the streams than in the lakes, and so far as he was personally concerned his i knowledge was more extensive with streams than with lakes.

The Professor then proceeded to deal with the speed of streams and the effect upon fish food, and the effect upon the fish of the varying supplies of food according to the spcoU 4' which rivers flow. Trout stream? contained a more or less high percentar ? of oxygen, and the organic matter in the water was burnt up by the water ir. the stream. If trout from a strearn had every organism that was found in that stream in their stomach contents, it was to be surmised that that stream was lacking in sufficient quantities of trout foods, but if. on the other hand, trout showed a preference for certain foods, they had not eaten, and other aquatic organisms that were known to be fairly plentiful in that stream, then it might be concluded that the food supply was plentiful. There was evidence that trout recognised a difference in palatability between different foods. A long series of observations would show that although the fish take both foods, nevertheless when they had a choice they more often take one rather than the other.

Professor Percival said the important point was that there must be a variety of food for the fish if these were to be healthy and a strong growth | promoted. He illustrated lantern slides i disclosing various forms of organisms upon which trout feed. He also dealt I with the question of the liberation of fry, saying that when liberated in small numbers the young fish appeared to do better than when liberated in larger j numbers. In connection with fishing research, they would of necessity be i dependent upon the rest of the world : for solutions of problems and for knowledge to be applied in the work now undertaken, and which would be of benefit in solving questions which were of importance to those interested in fish culture and preservation. Age Determination. Mr Parrott addressed the meeting on the question of the age determination of fish by their scales. He said that the ascertaining of the ages of fish by their scales had become in recent years reduced to an exact science. The theory was that the narrow zones of closely arranged ridges were formed in winter or the cold season when growth was at a minimum, and the broad zones of less closely arranged ridges were produced in summer in the warm season; and the number of zones would give an accurate record of the number of years through which the fish had lived. They had now to determine the limitations and the exceptions to this general rule. What was really known about the formation of these so-called winter and summer bands was this: That the growth of the fish was periodic. Its intensity at any particular time was directly affected by temperatures and feeding, though to what relative extent by each of these factors w f as not yet known. As a general rule growth wfis fastest during the early and immature stages of the fish, and apparently did not entirely cease on the attainment of maturity, but continued in less and less degree as the fish became old. Illustrating by a graph, Mr Parrott said it would be observed that the trout had their scales covered all over, or in part with a series of concentric ridges on thickenings wliich probably served as a stiffening or supporting tissue. Ridges were produced at the growing edge of the scale. They had a tendency to be produced concentrically from the centre of the scale, and at a certain distance from each other. The distance between the ridges was determined by the rate of growth at the time. If the scales of a young trout w’ere examined, it would be seen that these ridges were laid down regularly as growth proceeded. After a certain time, usually at the end of the first year, the new' ridges were formed in incomplete rings, and wexa on the whole close together, btm otherwise resembling their predecesg sors. These were known as winte# bands. The absolute number of ridges had been stated by old observers to afford ah acurate index of the age of the fish. According to some the estimation of the age of a salmon, not only in years but in complete months, was a simple mathematical matter, namely by counting the total number of ridges and dividing by sixteen. It had since been found by a careful study of the scales taken from different parts of the fish’s body, that great variations occur in the number of ridges which appear to follow a general rule of increasing to the adipose fin. and then diminishing towards the tail. After answering a number of questions the lecturers were accorded a hearty vote of thanks by acclamation.