Growth promoters are extensively used in modern aqua farming for promoting healthy growth and productivity. For optimum growth of shrimp, it should be fed with a nutritional diet that contains sufficient essential amino acids, fatty acids, vitamins, minerals. The nutrients present in the feed may not reach shrimp due to various factors.

Economic impact due to EHP and Vibrio diseases

Asia’s combined aquaculture production currently exceeds 99.10 million tonnes and yet despite its 6.58 % per annum growth, it is marred by episodes of disease that continue to result in major economic loss. In India, the gross national loss in the country due to shrimp diseases was estimated as 48717 metric tonnes of shrimp valued at Rs. 1022.1 crores, and employment of 2.15 million man-days.

EHP is an intracellular microsporidian that replicates within the cytoplasm of the affected tubule epithelial cells in the hepatopancreas, which affects mainly cultured shrimp P. vannamei in several southeast Asian countries. The main clinical signs of EHP-infected shrimps are growth retardation, which leads to increased variability of the size, softshells, lethargy, and empty midgut is seen in more advanced stages.

Intensive and semi-intensive aqua farming accompanies several disease problems often due to opportunistic pathogens as evident from general aquaculture. High stocking densities, high food inputs and other organic loads stimulate the selection and proliferation of opportunistic pathogens like bacteria, viruses, fungi, protozoa etc.

White Feces Syndrome

Signs and symptoms of WFS in shrimp:

– Dark discolouration of the gills
– Hepatopancreas and gut become white and pale in colour
– Floating white feces strings
– Slow growth
– Infected shrimps show loose shell

The causes of white feces may include poor quality of feed (presence of anti-nutritional factors or mycotoxins), bacteria (a number of species of Vibrio), algal toxin (cyanobacteria), gregarines, and EHP. All of the factors have been seen to damages the hepatopancreas. When the hepatopancreas, the largest
internal organ in shrimps, is compromised and damaged, we observe “white feces.” Several problems are associated with the WFS, including reduced feeding, reduced shrimp growth, size disparities and chronic mortalities.

Management and control of shrimp diseases

• PCR screening of broodstock before spawning and PCR screening of larvae (PL) before stocking. Larvae through quarantine systems, and stocking of SPF /SPR seeds, filtration and sanitization of water before intake
• Mortalities are precipitated by sudden stress from the changes of wide fluctuation of climatic condition
• Total disinfection and sanitization to the whole culture system before seeing a fresh batch. Improving host conditions through good nutrition and immunostimulation: A number of microbial molecules such as feed additive probiotic, β 1,3 glucans, peptidoglycans, polysaccharides have been shown to stimulate the non-specific immune mechanisms in shrimp.
• Improving environmental conditions: the environment has a greater role and significant impact on shrimp health, growth and production. Most disease problems are triggered by the deterioration of water and soil quality.
• Biosecurity: The strict principles and guidelines of biosecurity to be adapted in individual farms and cluster wise in farming areas.

The Best Management Practice (BMP), quarantine system and good feed management practice are to be followed during the entire culture period to overcome the disease problems in shrimp culture.

Benefits

• Reduces EHP and white feces infection up to 80 % at the infected ponds
• Resolving stunted growth and helps in achieving 9-10 g average weight at 60 DOC, gain in more than 2 g weight/week in shrimp above 80 DOC.
• Increase disease resistance in shrimp preventing secondary bacterial infections
• Uniform shrimp size minimizes the size variability in the ponds
• Reduced in mortalities due to stress factors like temperature, pH, crowing, salinity, ammonia, etc

Uses
Powder application makes it easy to use at the affected ponds with a suitable binder. Recommended uses are 2 kg per metric ton of feed.

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