FIGHTING MOSQUITOES WITH MINNOWS.

Otago Witness, Issue 3619, 24 July 1923, Page 59

FIGHTING MOSQUITOES WITH MINNOWS.

The use of fish to destroy the larvae of the mosquito in waters where they breed, has been often advised and employed to some extent. A minnow especially adapted to this use, being vigorous, prolific and very hungry for mosquitoes, is now bred on a large scale in California, and it is hoped that its use may relieve mosquito-ridden communities where for any reason crude oil or other means of fighling the pest are not available. Louva G. Lenert, sanitary engineer in charge of mosquito-control for the beard of health of that State, has an article on the use of this minnow in its Weekly Bulletin (Sacramento). Mr Lenert writes as follows : “ ‘Gambusia affinis’ is the name given to a small, surface-feeding top-minnow, whose native home is in the south-eastern part of the United States, ranging from New Jersey southward along the Atlantic seaboard and westward along the entire Gulf coast and as far as Del Rio, Texas, near the Mexican border. It is also found as far north as Tennessee and Missouri. In the South it is frequently spoken of as the ‘Pot-belly.’ “It is well that its name was decided upon before its economic value was learned, otherwise we might have been confronted with a name a yard long, in which an attempt would be made to describe its true worth. There is no way iri which this could bs estimated, but in a small way it can be said to be worth many millions to the Southern States. “It feeds largely upon insects, and wherever it inhabits water in which mosquitoes breed, its principal food consists of mosquito larvae. For the destruction of mosquito larvte it lias been found superior to any other species. Because of its small size it is able to penetrate to very shallow depths, where it is free from the attack of predacious fishes. Great numbers are often found in water less than an inch in depth. In fact, conditions which are ideal for mosquito propagation are usually also suited to ‘Gambusia affinis.’ It seeks its food at the surface, along the edges of ponds, in the marsh grass and swamps, where it is also protected from large fishes. It is not often found in the open waters where gome fish are present. “This fish is vigorous and very hardy. It requires no special environment for spawning, the young being in an advanced state of development at birth. It is very prolific, producing as many as six to eight broods in a season and averages forty young to a brood. Three generations may be represented in a single season. At birth these minnows are approximately one-half inch in total length, and they have been observed to begin their life of larva? destruction when not more than a day old. “Because of its extreme prolification, easy propagation, ability to adapt itself to different conditions and to reach areas not penetrated by other species, exceptional devouring capacity, general habits and living in identical areas with mosquito larvte, ‘Gambusia affinis’ is the most valuable natural agent known for the abatement of mosquito-breeding. “As a control measure these minnows may be introduced in stockponds, cisterns, shallow wells, water-troughs, surface reservoirs. irrigation canals, and similar places where oiling or draining prove impracticable. They are especially useful in the suppression of mosquito-breeding in slowly-moving streams, sloughs and potholes in drainage channels. “The question is often asked why, with such a valuable ally, mosquitoes continue to exist in the Southern States. Perfect mosquito control can be secured in any body of water by planting ‘Gambusia affinis’ therein, provided the area is first properly conditioned. “Nature’s protection of mosquito production consists of algae, debris and aquatic or other dense vegetation. Clean edges and surface free of debris and floating vegetation are of prime importance. Erect vegetation, such as cattails, when not too dense, will not prevent the penetration and control of mosquito-breeding by these minnows. Sufficiently clear, shallow edges are necessary as a protection from game fish when present. “Local ‘hatcheries’ are desirable in every locality where the use of ‘Gambusia affinis’ is anticipated. These should be, preferably, rather small ponds containing some plant growth, free from the natural enemies (game-fish, water-snakes, water-fowls, bait-collectors, etc.) of the minnows, and situated where they will be easily accessible by automobile or wagon.

Only under very exceptional circumstances will it be found necessary to feed them. “In order that every weapon known might be put to use in the control of mosquitoes in California, the State Board of Health in 1922 secured a shipment of ‘Gambusia affinis’ from Texas and established a hatchery in a pond at Sutton’s Fort, Sacramento. Since that date seven local hatcheries have been established throughout the State. The stock on band for this purpose is almost unlimited. Nature’s balance must be remembered at all times, however, and the fact kept in mind that these finny friends can only be counted on for perfect results when proper conditions are met with. They cannot accomplish miracles. •