Culture of fish food organisms

Unit 6 - Microworms

6.1.2.Biology and culture of chironomid larvae
After mating in flight the female releases the eggs while skimming the water surface. Their eggs are laid in gelatinous strings with some species having red larvae. Egg numbers can range from 50 to 700. The eggs sink to the bottom where, under tropical conditions, they hatch in 24~48 hours into the next stage - the larva or aquatic stage. The newly hatched larvae are not more than 1 mm long but they can measure up to 10~25 mm when they reach the last stage of the larva period. The larva stage can last from less than 2 weeks up to 7 weeks depending on temperature. Each larva moults four times before it reaches the pupal stage. The pupa is usually formed in the mud tube and it protrudes its head from one end of the tube so that the breathing filaments can be waved about in the water. The pupae emerge to the surface before swimming. They have high reproductive capacity, each female lay about 2300 eggs in one batch which hatch in about three days at temperature (18-22^oC). Those that reach the surface emerge into flying adults after a few hours and immediately fly off to mate, living only a few hours or days. The adults do not feed during their adult existence and mating normally occurs during the night. The entire life cycle can be completed in 2 weeks, although it is common for the life cycle to take longer to complete.