CAN INFECTED CRABS AND SHRIMPS BE TREATED?

Updated: Apr 1

RAS Aquaculture has been active in the aquaculture industry for years where we run a RAS system for mud crab farming and biofloc technology for shrimp farming. Despite all the care and effort to ensure the well-being of the crabs and shrimps, they can still be infected with diseases.


Crabs are one of the crustaceans found to be carriers of disease like White Spot Syndrome Virus which is famously known as WSSV in the aquaculture world. Lightner (2011) said that WSSV can generally be distinguished by white spots with a diameter of 0.5-2 mm found on the surface of the crab. In addition, shell disease is also common among crabs. It is identified as erosion of the exoskeleton due to microbial action. We can see the infection on the crabs’ shell by looking at the discoloration caused by bacteria.


Discoloration on the crab's shell

Disease-free crab shell

We can treat the crabs from diseases through disinfection using iodine. In commercial sales, iodine is mostly sold in liquid form or solution with different concentrations and is in dark brown colour. It does it work by penetrating through the bacteria’s cell walls before killing them. To disinfect the crabs, we need to use iodine with 4ppm concentration and put it in the water/tank for one hour.


Iodine

(Watch this video for clear instructions on how to use the iodine. Iodine disinfection starts at 1:37)


However, we need to pay attention that iodine cannot be added directly to the RAS or biofloc system because both contain beneficial microbes. The iodine will kill all the bacteria including the good ones if we do so. (Important note: WSSV is a virus and no treatment for it is available yet. Iodine treatment is a preventive measure from diseases, not to kill the WSSV virus.)


Moving on to shrimps, common diseases in its production is White Spot Syndrome Virus, Early Mortality Syndrome (EMS)/ Hepatopancreatic Necrosis Syndrome (AHPNS), Vibriosis infection, Hypothermal and Hematopoietic Necrosis (IHHN), Taura syndrome, yellow head disease, etc.


Firstly, we can treat infected shrimps by reducing the feeding. In RAS Aquaculture, since we use biofloc technology for shrimp farming, it develops beneficial microbes that can be one of food sources to shrimp and potentially improve the water quality in the system by converting ammonia to nitrate. Microbial biomass, in conjunction with the biofloc, serves as a great feed supplement and produces active enzymes for the shrimp in the system. Therefore, it can reduce the ‘FCR’ (feed conversion ratio).


Next, use probiotics which is an alternative for antibiotics to control pathogens. Probiotics improve the shrimps’ growth and survival through immune stimulation and resistance against bacterial viral and parasitic infection. Thus, it will escalate their growth.


Probiotic used in RAS Aquaculture

Thirdly, we can use organic acids. For a disease like Vibrio infection, there are many organic acids that we can use to control it. Nonetheless, studies said the most effective way to restrain the Vibrio species’ growth is using formic acid. In RAS Aquaculture, we mix the formic acid with the shrimp pellet with the measurement of 6g/kg feed amount.


Shrimp pellet and formic acid

Lastly, feed enzymes. The enzyme can boost nutrient density by releasing more energy, protein, and minerals for absorption. It also improves the bioavailability of phosphorus and calcium which is good for the shrimps’ growth development. To add, the enzyme increases ingredient flexibility by using more plant-based components while maintaining shrimp performance. The dosage for the enzyme is 0.4g/kg feed amount.



Summing up, indeed we can treat crabs and shrimps infected by diseases. Disinfection using iodine treatment can prevent the crabs from bacteria that affect their shell. Besides adding probiotics, organic acids and SSF to the shrimp feed, we also should take the feeding amount into account.


Reference:


Wiradana, P. A., Mahasri, G., Sari, R. E. R., Marwiyah, U. C., & Prihadhana, R. (2019, February). Identification of white spot syndrome virus (WSSV) in pacific white shrimps (Litopenaeus vannamei) from ponds postexposure to immunogenic membrane proteins (Zoothamnium penaei). In IOP Conference Series: Earth and Environmental Science (Vol. 236, No. 1, p. 012085). IOP Publishing.

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