Using Biosecurity and Prevention as Weapons against New Shrimp Diseases

White Spot Syndrome Virus, Early Mortality Syndrome, intestinal parasites... Shrimp farms have been successively hit by major epidemics over the past few years. With their often dramatic social and economic impact these disease outbreaks have forced aquaculture industries to question their everyday management practises. What lessons can be learned from these successive crises?

The specificity of the shrimp's immune system does not allow for effective vaccination. The emergence of new diseases has therefore compelled farmers to adopt innovative coping strategies to maintain growth performance and ensure farm profitability.

Since its inception in 2009/2010, the Early Mortality Syndrome (EMS) has rapidly spread to China, Vietnam, Malaysia and Thailand. More recently, it has crossed the Pacific to Mexico. In infested areas, death tolls have reached such heights that they have significantly impacted the worldwide shrimp supply. However, unlike other recurring pathologies in the industry, the EMS does not actually stem from a virus but from a bacterium, the Vibrio parahaemolyticus (quite common in farms) that has itself been infested by a phage (bacterial virus). As soon as it contaminates a shrimp's organism, this vibrio starts producing a toxin that eventually attacks the shrimp’s hepatopancreas and causes it to degenerate. If EMS hits a pond, it ends up eliminating most of the entire shrimp population. It is very difficult to get rid of this bacterium once it has settled in a pond. Indeed, like many pathogenic bacteria affecting shrimp, it seems that this vibrio has forged resistance to a wide range of antibiotics.

Recently, intestinal parasites such as gregarines, such as Enterocytozoon hepatopenaei (EHP), long known for infesting the intestines of farmed shrimp, have become the subject of renewed attention from experts. Indeed, although they do not cause massive mortalities, these parasites result in delayed growth performance that is detrimental to the farm. In addition, the EHP, long known for parasitizing monodon shrimps, is reported to have widely colonised white shrimp populations in Southeast Asia.

Strategies that have so far been developed for lack of specific remedies are derived from the pharmacopoeia that traditionally applies to terrestrial animals (antibiotics or ant-coccidial). Yet the use of drug molecules in such contexts poses many risks, especially upon commercialization; risks such as finding residues in meat.

There are no miraculous solutions but a set of preventive measures can still be applied to prevent pathogens from filtering through the ponds and to keep animals in a state of optimal health. Veterinary products should only be used as a last resort, after consultation with a specialist. This last point is especially relevant when attempting to prevent pathogenic bacterial populations from developing resistance to antibiotics. For this reason, biosecurity barriers need to be erected at all levels of input (post larvae, feed, water and also vehicles, staff, predators...).

Among the other steps that must be carried out are the regular maintenance of pond water quality (oxygenation control, monitoring of mortality, effective and frequent water sampling, adaptation and fractionation of feed intake) as well as the reasonable use of pharmaceuticals products and feed additives of proven efficiency.

Exchange networks are an extremely powerful tool allowing farmers to find first-line responses in the event of a disease outbreak. These crises have forced aquaculture industries to change their rearing approach by experimenting with new farming methods (mixed farming, changes in production cycles, setting up of crawl spaces, biofloc application). Some producers in infected areas have thus learned from sharing and pooling experiences in their attempt to find ways to handle these multifactorial issues.

Experts from the Techna Group can assist shrimp farmers worldwide in their attempts to monitor rearing performance and the health state of their shrimp populations. For more information, please do not hesitate to contact us!