Freshwater aquaculture

Practical 4 - Aquatic insects

4.1. Species

Gyrinus sp.

• Order coleoptera
• Commonly called whilrgig beetle
• Bluish black in colour
• Antenna short, middle and hind legs flattened
• Feeds on vegetable and animal matter
• Harmful to fry

Dytiscus sp.

• Order coleoptera
• Great diving beetle
• Grows to 2.5 cm
• Legs fringed with hair-like structures
• Hind legs flattened
• Feeds on spawn and fry

Hydrophilus sp.

• Order coleoptera
• Silver beetle
• Feeds on spawn and fry
• Carries water droplets at the top of hind legs which appear as silver globules

Notonecta sp.

• Ord. Hemiptera
• Body slightly cylindrical
• Anterior pair of legs leathery at the base
• Hind legs flattened and fringed for swimming
• Found in large numbers in ponds fertilized with organic manure
• Feeds on spawn and small fry
• Common name back-swimmer

Corixa sp

• Ord.Hemiptera
• Dorso-ventrally flattened body
• Tail end blunt
• Forelegs have flat structures
• Body dark greenish in colour marked with dark spots
• Harmful to spawn and fry
• Commonly called water boatman

Gerris sp

• Ord. Hemiptera
• Common name pond skater
• Longer and thinner legs
• Body thin
• Skates on water film
• Not so predatory

Spharodema (water bug)

• Body flat with sucking beak
• Colour brownish to green
• Produces toxic salivary substances which helps to kill fish

Lethoceros sp.

• Giant water bug
• Not so common in culture ponds
• Body flat, oval; brown or dull green
• Forelegs smaller, others long and ciliated
• Highly predatory, feeds on spawn fry and even fingerlings

Ranatra sp. (water stick insect)

• Body much elongated
• Legs long and slender
• Breathing tube long
• First pair of legs used for holding prey

Nepa sp.

• Water scorpion
• Body oval, prothorax broad
• Long spine like structure at the tail which act as breathing tube

Dragon fly nymphs

• Order odonata
• 2 types: short bodied and long bodied
• Found crawling at the bottom of the pond
• Small projections at tail region with mechanism to close and open
• Expulsion of air through pores helps them to propel in water
• Feed on spawn and fry