SHOOTING TIMES & COUNTRY MAGAZINE – APRIL 29-MAY 5, 1976
BACKGROUND TO SPORT BY FRANK SAWYER
Disease and Stock Trout
This has been a year when reports of fish mortality have been widespread and , if the drought conditions continue, I feel sure there will be many more before spring and summer are through. To see fish dead and dying which have been in your care for several years is a heartbreaking affair and it is only natural to feel strongly and be bitter about circumstances which can bring about such tragedy, when you know it is through no fault of your own.
Some owners many count the cost in terms of replacement value- which in a way one can understand – but it goes far deeper than mere money with those whose lives have been spent in trying to help create and to foster. As you look at the dead and dying a feeling of helplessness comes over you, a feeling that you have let the side down, so to speak, and that the trust placed in you by nature has been misrepresented.
Disease in fish really sickens me. It is bad enough when trouble is caused by poison or lack of oxygen, when death can be clean and quick, but when the dreaded necrotic or fungoid outbreaks occur which bring about a long and horrible existence from which there is no recovery, then you get the thought that you are dealing with something unclean, and with it comes a feeling of revulsion.
Though much of our present-day trouble is caused by lack of water and pollution, still more has come about by the introduction of stew-bred fish, both brown and rainbow trout. Some disease in fish must have been in existence since time began, just as it has with humans and other land life, for this is one of nature’s ways to prevent over-population. But diseases in trout have increased considerably in recent years and it seems to have become far more common since large fish became easier to produce in stock ponds with the comparatively modern method of feeding with processed pellets. Today, trout grow much quicker and larger with this class of food than ever they did 50 years or more ago. At that time with the food then used, it took quite three years to produce a brown trout of a pound in weight. With the modern pellets this can be done easily in two years. With rainbows, the growth-rate is far greater. But is it of brown trout that I write. Are we getting anywhere by boosting the growth so much beyond anything accomplished naturally?
I have always been very doubtful about this. What is more I have often wondered if it is wise to feed trout so that they mature much earlier than nature intended. Does this, in fact, render them more prone to the various diseases? I have also wondered if this feeding with pellets, where the formula is represented with as much as 40 per cent sea-fish meal (or perhaps I should say, sea-fish offal meal), can bring about a texture in the flesh and build of trout, which is something in common with salmon. When the great majority, especially the Pacific salmon, die from fungoid diseases after their first spawning. To say the least, there is little in the formula of the modern processed pellet which has a food value similar to anything one can find in fresh water.
Though many know what it is like to see these stricken fish I feel doubtful if there is anyone yet who can pinpoint the cause. All we are told so far is that these diseases are virus infections and long names for this or for that have been given to determine one from another. Like all scientific jargon, these names are neither easy to spell, nor to remember, but they sound very important and knowledgeable. If knowing them and talking about them could be of help, all well and good, but to my mind it is essential to find out just how such infections start, and a way to prevent them.
In most cases the more deadly of these can be attributed to uncleanliness brought about by overcrowding. Overcrowding is a common occurrence in many of the fish farms at present and, perhaps with the modern method of feeding, there is greater scope for outbreaks of disease to occur. There are few fish farms about the country now where trout, either browns or rainbows, are produced without the aid of chemicals to subdue or prevent trouble of one kind or another. Indeed I feel sure that without such chemicals the mortality would be so great that a few farm owners could make a living. Yet year after year these stock fish are being introduced to fisheries where they are at liberty to mix with wild and indigenous trout which have had no chemical treatment to render them immune.
Many of these stock fish are caught afterwards and a lot show the tell-tale marks. From time to time anglers write to the press about these. There are those with just a stump for a tail, some with pectoral fin missing or with other fins curled and mis-shapen. Many more have short gill covers or healed sores along the flanks. There can be others with deformed backbones. These are some of the lucky ones which have “recovered” through chemical treatment.
But what of the casualties which occur during the artificial lives of these stock fish since the young ones started to feed? No fish farmer is likely to tell you about these or about the continual treatment he has to carry out. In the stew-ponds this can be done, and some control established, but once these fish have been transferred to fishing waters – river, lakes, ponds or big reservoirs – it is an entirely different story.
Much must depend on the condition of the waters into which these stock fish are placed. Sometimes the change over from pellets to natural food and to a more healthy and natural environment can effect a great improvement and no trouble will follow, but in others it can be the reverse. Introduction of any fish into polluted fisheries can lead to trouble but when some of these have already had a disease of one kind or another, or have been in contact with infection, the risk is that much greater. In such cases, only where frequent stocking and concentrated fishing takes place is there any real return. In the great majority of fisheries, where stocking is done but once a year, they are lucky if more than 50 per cent figure in the annual bag. What causes the other half to die – for die they must? There is no other explanation.
