Study:Investigation of pale shrimp disease in Pacific white shrimp caused by Photobacterium damselae subsp. damselae in low saline conditions.
In shrimp aquaculture, new emerging pathogens are responsible for causing various diseases. Most of the disease in shrimp farming are associated with multifactorial. Still the specific causes for disease need to be studied well.
In the aspects of prevention and treatment, novel techniques using phages, probiotics, plant extracts, functional compounds are emerging. Eventhough, it is limited in disease curation in shrimp aquaculture.
Today, we will discuss about pathogenicity of non-vibrio in causing mortality in shrimp.
Original publication :
Investigation of pale shrimp disease in Pacific white shrimp caused by Photobacterium damselae subsp. damselae in low saline conditions.
Author: Niti Chuchird, Natnicha Chongprachavat, Wiranya Suanploy, Lalitphan Kitsanayanyong, Putsucha Phansawat, Arunothai Keetanon, Parattagorn Wimanhaemin, Tirawat Rairat
Abstract:
Pale shrimp disease is a emerging disease which cause different levels of mortality in shrimp. In the southern provinces of thailand, one of the study investigated naturally outbreaked pond showing signs of pale colour body. After sampling, they confirmed presence of non-vibrio species Photobacterium damselae subsp. damselae. The isolated pathogen examined for pathogenicity study by immersion and oral challenge and exchibited the same signs and symptoms and also it caused mortality of almost 50% and 90% in challenge models.
Important factors influencing this disease:
- Culture system
- Stocking density of the pond
- Salinity of the water
Among these above mentioned factors, Salinity of the pond is the most influencial parameter to cause this disease. Although, this Photobacterium damselae subsp. damselae is a marine origin strain.
Sample collection and analysis:
Around 200 number of shrimp samples were analysed for diagnosis. Those samples are collected from infected pond located in surat thani province of thailand and the shrimp were cultured in higher stocking densities. Collected samples were further analysed for major diseases causing pathogens including WSSV, IMNV, YHV, AHPND.
Challenge test using filtered homogenate from diseased shrimp:
On other hand, homogenate from diseased shrimp was filtered and performed for challenge by injection method on live shrimp. The clinical signs and mortality was observed over the period of time. This challenge performed to identify whether infected shrimp from pond acquire any virus or not? But at the end of the experiement, it is confirmed that samples from the infected pond did not have any virus.
Different challenge studies on this study:
1.Cohabitation challenge (Feeding of diseased shrimp to healthy shrimp):
To further identify the etiology of disease, cohabitation challenge performed whether diseased shrimp can spread pale shrimp disease or not.
2.Oral and Immersion challenge study:
Photobacterium damselae subsp. damselae strain isolated from the infected pond was used for performing challenge experiements by immersion and oral method. Hepatopancreas from the challenged group, and shrimp from infected pond were taken for bacteria isolation.
Results:
Shrimp from infected pond showed pale body colour with reduced pigmentation. Hepatopancreas from the infected shrimp showed signs of infections. Histopathological signs revealed lymphoid speroids, necrosis, nodule formation, hemocytic infiltrations. Additionally, samples tested for other diseases includes WSSV,YHV,AHPND,IMNV showed negative in analysis.
In cohabitation study, no mortality found in the control and challenged group. But in the other challenged group(immersion and oral method), there is a significant change in pale body colour appeared.
In the immersion and oral challange study using Photobacterium damselae subsp. damselae strain to the healthy shrimp showed pale coloured body as well as exhibited higher mortality compared to control group. This results states that the Photobacterium damselae subsp. damselae can cause pale shrimp disease in low saline water and contributes to the mortality.
This study demonstrated the association between Photobacterium damselae subsp. damselae and pale shrimp disease. Anyway, the detailed research should be focused on the co-infection of this species with other virulant strains. Research on therapautics further needed.
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Regards,
Dhivagar
E-mail: dhivagarfcri2000@gmail.com
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