Researchers from the Center for Environmental, Fisheries and Aquaculture Science (Cefas), Chulalongkorn University and the Asian Institute of Technology (AIT), have published a scientific review that focuses on pathogens in the cultivation of M .rosenbergii, identifying other hosts for pathogens and outlining how agricultural practices can limit disease transfer. The team noted that since the last pathogen review in 2012, the number of characterized diseases has increased.
In the last 30 years, the cultivation of the giant river prawn, Macrobrachium rosenbergii, has increased exponentially in tropical and subtropical regions of the globe. The demand and consumption of giant river prawns has been increasing in China, India, Bangladesh and Brazil. But the increase in production has been accompanied by disease pressures that undermine the performance of the shrimp, limit the profits of the farms and the commercial potential of the sector. Shrimp farmers and researchers have also noticed the emergence of new pathogens and viruses that are infecting spawners.
The problem with viral pathogens
The researchers noted that the incidence of viral diseases in farmed river prawns is increasing. This is particularly difficult because the viruses do not appear to be host-specific, meaning they can infect both freshwater and saltwater penaeid shrimp species. It also appears that different hosts can transmit viruses between species.
The researchers created a table summarizing the clinical and histopathological signs of the following viral infections:
Bacterial, fungal and microsporidian diseases affecting giant crayfish
M. rosenbergii are also susceptible to opportunistic bacterial infections that can cause a myriad of clinical signs and lead to mortality. Vibrio, Aeromonas and Pseudomonas spp. have been associated with shrimp mortality in both hatcheries and grow-out ponds.
The fungi were the first pathogens identified in M. rosenbergii aquaculture and have been present in crayfish ecosystems since the commercial expansion of the industry. Fungal agents tend to cause lower levels of mortality compared to viral and bacterial infections, but can discolor shrimp, reducing its commercial value. Researchers note that yeast infections are common in the winter months when water temperatures are colder.
Microsporidia infections have been observed in giant crayfish but have not been taxonomically described to date. It appears that many of the pathogens that affect other shrimp species can infect giant crayfish. Many shrimp farmers rely on antibiotic therapies to limit losses on their farms.