DISEASE AMONG TROUT.

New Zealand Herald, Volume L, Issue 15265, 1 April 1913, Page 8

DISEASE AMONG TROUT.

NEW THEORY AS TO CAUSE, PARASITE IN FISH FOOD. A DISAPPOINTING SEASON. It is a groat pity to have to record the fact that trout-fishmg in Lake Taupo has undergone serious deterioration. For many years past this lake has enjoyed the reputation of providing the finest angling in the world, on account of the size and quality of the fish, This season, however, numerous fish in the poorest of condition and devoid of any fighting power have fallen to the bait of anglers. Two theories have been advanced to account for the deterioration of the trout in Lake Taupo. The tot is that the fish have become diseased, owing to, a small percentage of those caught having bees found to bo infected with the same worm which has caused a certain amount of trouble at Rotorua, On the other hand, many anglers are of tlte opinion that the enormous natural increase in the trout has overtaken the food supply in the lake, and that the poor condition of the fish is due, in many cases, to semii-starvation. It is also stated that whilst the fish are in this condition they are, more prone to develop any of the diseases to which they are subject. , Worm-infested Kokopu. As, regards the worm theory, the evil has been attributed in the past to shags, but a correspondent' of the HsatAl.©, who has gone closely into thematter, puts forward a new theory sis to the origin of the worm. He descries a worm-infested native fish, the kokopu, which is to be found in Lake Rotoafra, about 20 miles from Tokaanu. This, he states, is about the thickness of a man's finger and from 2tn to 4in long. A number of these fish were inspected by our correspondent a few days ago. He found them all to be infested with a parasitical worm, reddish in colour, threadlike, and about 2in in length. The bodies of the kokopu were lull of these worms, which are identical with those found infesting the trout, of Lakes Taupo and Rotorua. Out of consideration for the native food supply, Lake Rotoaira has not been stocked with trout, and the number of cascades and waterfalls upon the outflowing stream prevent the trout from entering the reserve. There is nothing, however, to prevent the kokopu from migrating into the lower levels of the Tongariro River, and, as it is known to have been one of the staple diets of the trout, it seems reasonable to our correspondent to assume that it is from this fish that the Worm parasite has sprung. As to how the worm has infected the trout he suggests that it may have done so by direct feeding or through shags who have taken the kokopu as food. Testimony of Old Natives. So far as our correspondent has been able to ascertain the Government's fishery experts, who have been investigating the diiseaso in trout, do riot seem to have come across the kokopu. Nevertheless, he states, he has been informed by old natives that it has been worm infested as far back as they can remember. If the kokopu is the actual source of the disease in trout it may . throw a new light : upon the investigation 61 a ■ blight ' that seems .to threaten to extenninate'the trout so* far as sluggish waters are 'concerned* • >'*■■.' Fish in Boteraa and ' Wailratd.•"' To revert to the starvation theory it is worthy of note that : there is an improvement—slight only, butl marked none the less— the fish in Lake Rotorua this year. A number of the spawning fish have been destroyed,/and netting is now checking the increase. In spite of their extraordinary fecundity- the natural increase «5f the trout at. Rotorua can be easily checked at spawning tiime on account, of the small streams "which run into the lake. It is doubtful, however, whether anything can be done in a huge lake, such as Taupo* to curtail the naltural increase. Numbers of trout caught this season in the Waikato River have also proved to bo out of condition. It iu considered that these fish may have been new arrivals from Lake Taupo in search of food, as many of the Waikato River fish are still iu perfect condition.