SCI-TECH & AGRI

Managing aquatic insects in nursery fish pond

ANY BODY of water is invariably explored by a large number of insects, either in their adult or larval stage.

The most common are beetles, bugs and dragonfly nymphs. Among beetles are predaceous diving beetle (Cybister confusus), water scavenger beetle (Sternolophus rufipus) and whirling beetle (Gyrinus). Aquatic bugs are highly predatory.

Back swimmers (Anisops bouvieri) appear in swarms in manured ponds during rainy season and cause heavy damage.

Other predatory members of this group are water storpion (Lacotraphes griseus), giant water bug (Belostoma indicum) and watersick insect (Ranatra filiformis).

Dragonfly nymphs are highly predatory on carp spawn. Proper preparation of the nursery pond is essential for stocking carp spawn.

The best method is to spray oil-soap emulsion over the pond's surface to choke the respiratory tubes of aquatic insects. The spawn and fish food organisms remain unaffected.

Except for oil-soap emulsion other mixtures or emulsion are easily prepared by simple mixing. For making oil-soap emulsion, the soap is mixed with oil and gently heated for sometime with vigorous stirring.

Commercial detergents like `Teepol B-306' are better substitutes for soap in the emulsion. The recommended dose of `Teepol' is 560 ml to be emulsified with 50 kg of mustard oil. These emulsions are applied by spraying over the pond surface about 12-24 hours prior to stocking of carp spawn.

It is the film of the emulsion that is important and hence care is to be taken not to disturb the film for a few hours.

Care should be taken not to apply it when there is a strong gust of wind. Application of malathion at 0.5 ppm or grammexane at 0.01 ppm in the nursery pond also controls the insects .

S. Saurabh, Niraj Kumar and A.K. Choudhary,

Central Institute of Freshwater Aquaculture, Bhubaneswar-751002.