The Water scorpion (Nepidea)

Nepidae is a family of exclusively aquatic Heteropteran insects in the order Hemiptera.

They are commonly called waterscorpions for their superficial resemblance to scorpions, which is due to their raptorial forelegs and the presence of a long slender process at the posterior end of the abdomen, resembling a tail.

They are sometimes called needle bugs or water stick insects as they are more slender than Nepa and feed primarily on invertebrates, but occasionally take small fish or tadpoles. Water Scorpions are ambush predators, relying upon camouflage when hunting. They lash out with the front legs and subdue prey via salivary fluids injected through the sharp beak. These fluids contain chemicals that tranquilize prey and initiate digestion.

Note; To control the rate of water scorpions, the pond should be very well be filmigated with chemicals before putting the fries into the nusery ponds.