Mortality of Macrobrachium rosenbergii at larvae stage

Both larvae stages and adults of the giant freshwater prawn, Macrobrachium rosenbergii are subject to disease caused by viruses, bacteria, fungi and parasites. However, none of these appears to be a major problem in production.

An important disease in Macrobrachium rosenbergii hatcheries, whose exact cause is unknown, is referred to as the ’mid cycle disease’ (MCD). Characteristic of MCD-affected larvae is severe atrophy of the hepatopancreas with intraluminal colonies of Gram-negative cocco-bacilli.

As its names indicates, it is most noticeable in the middle of the larval rearing period (days 15-22 when larvae are at stage VI-VII) when heavy daily mortalities may occur. Population mortality form MCD can be quite high, resulting in losses of 90% or more.

Mortalities may even start to become obvious as early as day 10. The disease is recognizable by the larvae becoming bluish-grey and swimming slowly in a spirally pattern, as well as by a reduce rate of consumption of Artemia and poor growth rate.

Early larvae stags are susceptible to virus caused by Vibrio Harveyi. The unique clinical sign of this disease is the luminescence of infected larvae which can be observed at night.

Infected larvae also show fouling, opacity, slow swimming, aggregation and mortality. Mortality may reach 100 percent.
Mortality of Macrobrachium rosenbergii at larvae stage