Diseases are the end result of a complex interaction between a host (aquatic animal), a pathogen and its environment. A host’s resistance to the pathogen varies depending on the shrimp species, strain and genetics.
In order to keep shrimp healthy, water quality must be observed and maintained. This includes dissolved oxygen levels, organic load and turbidity.
Black Gill Disease
This is a very common and serious disease of freshwater shrimp. It is a condition in which the shrimp’s gills change color from white to brown or black due to accumulated fouling on their gills and appendages. Don’t confuse them, though, check here for a crystal black shrimp grading guide. The fouling is caused by organic debris from the pond bottom or dead phytoplankton as well as bacteria, protozoa and fungus.
When the gills become dirty they lose their ability to absorb oxygen, which causes the shrimp to have respiratory failure. They may also have problems with molting or hatching and can even die from this bacterial infection. This disease can be prevented by regular water sample tests and maintaining good water quality, ensuring that the dissolved oxygen level is always greater than 5 ppm and that the pond’s level of organic matter is low.
Symptoms of black gill disease can be observed in the gills of infected shrimp, which will begin to show signs of necrosis. The gills will look dark brown or black with the loss of their normal white color, and there will be a deterioration in their ability to absorb nutrients and oxygen from the water. The shrimp will also become very sluggish and will not move as they normally would.
A histopathological examination of gill tissue from the affected shrimp will reveal a disruption of the central axis of the primary gill lamellae, resulting in their separation, and an accumulation of hematocyte cells with necrosis and melanization at the site of infection. The hematocytes will also show signs of shrinkage and death by karyorrhexis.
Electron microscopy of gill tissue from infected shrimp will demonstrate that the hematocytes are disrupted and have a distorted appearance after fixation and staining, while the ciliate Hyalophysa lynni is visible as a darkened cyst with a distinct outline.
This bacterial infection can be prevented by removing organic waste from the pond bottom and providing good aeration through bubbling or using a diffuser system. It is also important to maintain good water quality and test the dissolved oxygen, ammonia and nitrogen levels regularly to ensure that they are within the healthy range for shrimp.
Shell Disease
The bacteria that cause this disease (Chitinolytic Bacteria) attack the chitin of the shrimp’s exoskeleton and can result in abscesses. The disease also causes poor molting and can affect a shrimp’s ability to grow and reproduce. This disease is common in ponds where water quality is suboptimal. The bacterial infection can be prevented by maintaining good water quality (particularly dissolved oxygen) and removing dead or infected shrimps. Adding aquatic plants that consume excess nutrients and nitrates can also help prevent the disease from developing.
Infected shrimp display abnormal behaviour, jumping out of the water and laying on their sides. They also have a milky white substance on their abdomens. A pronounced flexure in the third abdominal segment is another symptom of the disease. This disease is a huge cause of loss in the shrimp industry, as it severely impacts the health and reproductive success of females. Females with HPM are unable to complete the molting cycle, and if they are unable to molt, their egg production will be significantly reduced.
One of the most important factors for preventing the disease is to prevent the proliferation of spore-forming bacteria by disinfecting the culture facility with chlorine or iodine-containing compounds. The bacterium Enterocytozoon hepatopenaei is a major cause of HPM, and it is transmitted from the shrimp to other shrimp through contaminated feed and faeces. The disease is most often seen in large-scale commercial operations, but can be found in home and community tanks as well.
It is important to be able to identify and treat the various diseases of shrimp because they can have very serious consequences for the industry. This is especially true in the case of epizootic diseases, which are caused by multiple disease causing agents or causes. This type of multifactorial disease causes rapid, widespread, and severe mortalities in the shrimp population. A shrimp pathologist can typically find evidence of a number of different infectious and noninfectious diseases in an epizootic outbreak, including fouling on the gills or appendages, parasites and other organisms, poor body cuticle integrity, high feed conversion ratios, and poor molting frequency.
Microsporidiosis
There are a number of non-infectious diseases that impact shrimp and these include those caused by environmental factors. These include nutritional imbalances, toxins and genetic disorders. Other disease-causing agents can be viruses, bacteria, fungi or certain parasites. These diseases affect the hygienic quality of the shrimp and their market value, thus it is important for farmers to practice good farm management and prevention techniques.
One of the most common shrimp diseases that are found in freshwater and brackish water shrimp farming is Muscular Necrosis. This is a common disease that affects the body muscles of the shrimp and causes them to lose their color. The shrimp also have a milky white appearance and a pronounced flexure at the third abdominal segment. This disease is attributed to high organic loads, nutrient deficiencies and poor water quality.
Another commonly found shrimp disease is Systemic Ectodermal and Mesodernal Baculovirus (SEMBV). This is a virus that infects the gills of the shrimp and causes them to change their coloration. It can also lead to reduced growth rate and low survival rates. SEMBV is a zoonotic disease that can be transmitted from wild shrimp to farmed ones through contaminated water.
The signs of this disease are a decrease in feed intake, lethargy and darkened gills and appendages. The disease can also cause a reduction in the growth of the shrimp, which is why it is called slow grower syndrome.
This disease is characterized by the presence of the microscopic protozoan Microsporadia in the infected tissue and organs. This protozoan can replace the normal tissue and can lead to sterility in female shrimp, turning their ovaries white. This is a very fatal disease for shrimp and can cause mass mortalities if left untreated.
The best way to treat this disease is to use a salt bath. Mix a teaspoon of aquarium salt with 1 cup of clean tank water and soak the shrimp in the solution for 30 seconds to a minute. This treatment can be repeated as needed to cure the disease. Alternatively, you can also use an antibiotic called Tetracycline. However, make sure you are using a prescription drug that requires a vet or doctor’s script to obtain.
White Spot Syndrome
White spot syndrome virus (WSSV) is a lethal disease that affects decapod crustaceans including penaeid shrimp. WSSV can cause high mortalities in shrimp farms, especially if it is spread to new stocking ponds via movements of or contact between infected shrimp or through contaminated water and equipment.
Symptoms of this disease include the formation of white spots on the exoskeleton, with sizes between 0.5 and 3 mm in diameter. These spots are accompanied by a dark brown to black pigmentation of the chitin of the telson or uropods, and also on the gills and tail section. Shrimp infected with WSSV will display a general loss of activity, anorexia and reduced feeding. The bacterial infection may also cause the shrimp to molt abnormally or fail to grow during a molting period, and can even lead to death.
The bacterial disease can be treated with antibiotics such as oxytetracycline. However, it is important to note that this treatment can also kill off beneficial bacteria in the tank, so it is best to remove the problematic shrimp from your main tank and treat them in a temporary hospital tank or bucket for the duration of the treatment.
Another way to prevent this disease is by removing organic waste from the tank, such as uneaten food and debris, and to keep up with regular water changes and to monitor your pond for any signs of infection. Additionally, the use of dried Indian almond leaves or oak leaves can help to protect the health of your shrimps as they contain humic substances which are slightly antibacterial and antifungal.
Keeping good tank hygiene and monitoring your pond for infections are the best ways to prevent common shrimp diseases from occurring, and once they do it can be very difficult to treat them effectively. If you keep up with these practices, and monitor your pond for symptoms of infection regularly, you can greatly improve the overall health and quality of your shrimps.
