Rise of Black Spot Disease

On an average, native fish of Aanchar lake show 40% BSD infection, while as fish of Dal lake and Manasbal lake show 15% and 11% of infection, respectively.
Rise of Black Spot Disease

The ecological systems are continuously being subjected to turmoil by anthropogenic acts. The alteration in the environment also stimulates changes in the distribution and behavior of parasite and vectors. Animal health is deeply related to the changing pattern of environmental condition. For example, environmental biologists are convinced that global climate change could harm fish health. In a recent study, it have been confirmed that some parasitic worms are using enhanced temperatures to increase their chances of survival at the cost of the fish population it uses as hosts. It is still early to say whether such phenomenon is prevailing in all geographical regions of the world. The altered environmental conditions of water bodies in Kashmir Himalaya has been a great concern for the quantic resource managers, and in recent decades researchers have found positive correlation between enhanced eutrophication with the rise of parasitic infection of fish. The rise of Black Spot Disease (BSD) in recent years in native as well as in some exotic fish species in the water bodies of Kashmir Himalaya has also a correlation with the deteriorated water quality. 

 Black spot disease is named as diplopstomiasis or fluke disease and has been reported to infect marine as well as freshwater fish. The term "Black Spot" refers to the formation of small cysts (black pigments) in the skin, eyes or muscles around the parasite. However, according to Kurochkin and Biserova (1996), BSD is basically a symptom in the form of black cyst caused by certain parasite species in freshwater and sea fishes. There are several species of trematodes which are responsible for the Black spot disease at global level. At present, more than 50 species have been recognized which cause similar types of symptoms in different fish species. The infection of black grub in fish of Kashmir Himalaya is caused by the metacercariae of the trematode Posthodiplostomum spp. or Neascs vetesta. The most affected fish species belong to genus Schizothorax and Crossochilus. In last ten years, the maximum infection level of BSD has been reported in Schizothorax niger, Schizothorax escinus and Crossochilus diplochilus. 

It was previously reported that BSD has little effect on the health of fish and even heavy infestations of these worms was considered to have little damage to the fish. However, recent research has shown that heavily infected fish may experience blood loss, skin loss, physiological stress and even death also occur in some cases. In some extreme cases, heavy infection of black spot may blind the fish. The skin of fish may sometimes look unusual if there are heavy black spots on the skin and, sometimes fish may lose its aesthetic look. However, it is pertinent to mention that there are natural white or black spots on the body of fish which should not be confused with diplopstomiasis or fluke disease. 

 The abundance and prevalence of BSD has increased over the years, especially in the lentic water bodies of Kashmir. The pattern of infection indices in past ten years reflect that black grub is showing more association with highly eutrophic environment (Zargar et al., 2013). The intensity and abundance of infection is also rising across the eutrophic pollution gradient and can be a major concern in future for the concerned authority. On an average, native fish of Aanchar lake show 40%  BSD infection, while as fish of Dal lake and Manasbal lake show 15% and 11% of infection, respectively (From authors research). It has been also reported that black grub is the dominant parasite in the highly eutrophic lakes of Kashmir with reference to prevalence (%) and intensity. As per predictions, we may experience more of these fluke diseases in fish of our water bodies as there is exponential increase in the organic loading. 

Signs and symptoms

  It is important to know about the important symptoms of BSD so that proper action can take by the fishery resource managers. People in general and customers in particular should be aware about the diseased fish. The major symptoms are as follows:

15. Small black pigmented spots on skin, fins, tail, snout and tail

16. Small black smudges on fish

17. Live fish shows scratching against surface

18. Behavioral changes can be also observed in fish 

 Black grub prevention and treatment

   It is very difficult to manage this disease under natural conditions. The oligotrohication or recovery of highly eutrophic lakes into moderate eutrophic lakes is one way to prevent the spread of this disease. Rehabilitation of natural fish can be wise step for preventing black grub from spreading to other locations. For fish farm managers, it is important to be very careful while adding a new fish. This disease generally easy to cure in the fish farms. There are number of treatments available which can used to treat this disease from the spread. 

There is urgent need to look into factors which are responsible for the spread of such type of diseases and steps should be taken to prevent the mass scale rise of such infections on the native fish. As we are looking for "Holistic Native Fish Strategy", there is urgent need to take steps to manage the spread of diplopstomiasis and other fluke diseases of fish. 

(The views expressed in the article are authors own and does not necessarily reflect views of the Institution or the organization with which he is associated)

Author is  SERB-DST Fellow, Department of Zoology, CUK, Sonwar Campus,

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