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Zoothamniosis disease is one of the parasitic diseases found in vannamei shrimp caused by Zoothamnium penaei which usually lives with poor water quality. It causes the death of shrimps both in pond and hatchery. An abundance of Zoothamnium sp. infested the vannamei shrimp this is still reasonable so long as they do not cause high mortality. But, they can also cause problems in shrimp culture when the environmental conditions are poor and suitable for its development. This parasite that attack shrimps in order to determine the factors causing a decline in growth, meat quality and productivity.
This disease causes the shrimp to breathe hard, difficult to move and cannot find food, difficult to moult, inhibit growth, reduced economic value and cause death to 91%. In addition, this disease is a predisposing factor of secondary infection by bacteria and viruses.
Protozoan ectoparasite abundance varies greatly depending on the different physico-chemical conditions of the water bodies. Parasitic groups of protozoans are generally found in environmental conditions that experience instability in the water quality, especially temperature, as Zoothamnium sp. can breed faster in environmental conditions that have a temperature value above 30°C. Giving too much food causes the remaining food to be left in many ponds. This means that the content of the organic matter in the pond is high and spurs on the growth of the parasites which are also able to grow well.

Symptoms

Zoothamnium sp. Infected shrimps show black/ brown gills or appendage discoloration or fuzzy/cottony appearance due to a heavy colony of the organisms. In some cases, the severely affected shrimp die during the molting period.

The base of Zoothamnium forms a circular disc that fuses with the epicuticle but does not penetrate the underlying cuticle or epithelium. Discoloration of the gills is a common symptom of fouling by organisms and also detritus, silt, or iron which are trapped by the fouling organisms.

Treatment

Chlorine and formalin are often used to treat those commensal organisms if shrimp display heavy infection. Changing water is the most preferable management, which stimulates molting of the shrimp in order to reduce the infestation.

Prevention and Control

Prevention and control of the occurrence of surface fouling are usually done through maintenance of good sanitary conditions at the pond bottom and the overall pond area. Organic matters and suspended solids in the pond should be reduced to prevent the attachment of those fouling organisms. This is achieved by changing the water or applying lime.

Black Gill Disease

Black gills, black gill syndrome, black gill disease, or melanization of the gills is symptomatic of several causes of gills disease. Shrimp Black Gill Disease has been one of the most frequent shrimp farming problems and caused many deaths, especially in the late rearing period. There are infectious and noninfectious causes of black gill disease. Infectious causes include Fusarium solani, Vibrios, and Lagenophrys, while noninfectious causes include nutrient deficiencies and exposure to pollutants and contaminants.

A number of abiotic and biotic reasons have been attributed to the black gill in shrimps. Presence of excessive levels of toxic substances such as nitrite, ammonia, heavy metals, crude oils etc. in the culture water may lead to black gill disease. High organic load, heavy siltation and reducing conditions in rearing pond can also cause this disease in shrimps. Attack of certain bacterial, fungal and protozoan pathogens can also cause black gill condition in shrimp.

Causes:

Black gills in shrimp can be caused by several things.

Accumulation of debris in gills: This is usually associated with poor pond bottom conditions. Lack of proper preparation of the pond before stocking, large amounts of black soil, lack of aeration, irregular water change during rearing, and organic contaminants, and nutrtional deficiency could trigger the disease.
Some fungal species including Fusarium solani, Aspergillus flavus, and A. awamori causes disease. This disease is epizootic and can cause mass mortalities. In infected shrimp, the gills have a very dark, deep black colour.
In the initial stages of this disease, the gills turn orange-yellow or light brown. Eventually, the gills turn darker until they are black. Vibrio-related diseases spread rapidly. Bacterial agents including Vibrio harveyi and Photobacterium damselae were reported to cause black gill syndrome.

Symptoms:

Affected shrimps have gills with brown to black discoloration, in acute cases necrosis and atrophy of the gill lamellae may be apparent. The blackening is due to the deposition of melanin at sites of massive haemocyte accumulation, followed by dysfunction and destruction of whole gill processes.
Shrimp comes to surface in spite of sufficient dissolved oxygen in the water
Mortality in severe cases

Prevention:

Absolute control over feeding is very important in preventing black gill.
Use good quality probiotics at regular intervals with optimum dosages. This helps in reducing the organic load and toxins in the pond.
Controlling water colour and preventing excessive blooms during culture prevents algae crash and accumulation of organic matter in the pond.
Provide sufficient aeration to the ponds.

Remedies:

Treatment of the black gill disease depends upon the cause of the disease.

Preventive or corrective measure may be adopted to avoid or reduce the biotic / abiotic factors in the rearing pond to control the disease condition.
If noticed black gill in some shrimps, suggested to change the water more often and also provide more aerators.
Reduce feeding till water quality improves.
Apply good quality oxygen enhancers daily till complete recovery.
Use probiotics to clean the ponds and absorb toxic gases.
Addition of agricultural lime (CaCO3) according to the pH concentration is also recommended.