Cultured shrimp farmers of almost all areas, in the past few months, have drastically faced with problems of illness and death in shrimps by which most of them are still confusing with the causes of disease. Samples of shrimps were sent to various service centers but the results were often unlike and eventually made more and more confusion on them. The author therefore tries to compile data and makes a conclusion for the farmers. From the analysis of fundamental causes of disease in many areas, it is found that most of death in shrimps caused by water quality management and pond bottom surface was not relative to the highly variable climate by that time. This is the major cause that makes the infected shrimps showed the symptom or they are easily infected. The appearance of diseased shrimps frequently found in the past period can be classified as follows:
1. White spots on shells of the dead shrimps - This is the problem mostly found since November 2000. The shrimps that showed this kind of symptom were in the range of 20-60 days of age, noticing that some of the diseased shrimps at the pond edge in the morning of the very first days and their sizes were relatively bigger that those therein.Some had dregs and slimes on their shells and some had white spots underneath their shells . The number of diseased shrimps that stayed along the pond edges later increased rapidly but those in the scooping nets look normal and well eating. About 3-4 days after seeing shrimps at the pond edges then firstly found the dead bodies of shrimps on the pond
Causes of illness in Cultured Shrimps and Remedial Protection by Dr. pornlert Janratchakul
bottoms and in the scooping nets. The accumulative rate of death or the severity of disease in each pond was simply different, ranging from 3 days to one week, depending on the number of infected shrimps at start of launch. If a lot of launched baby shrimps were firstly infected they would quickly die when abrupt changes in water quality or temperature. In case of few infected baby shrimps, the infection would be slow and probably no sudden death if there were good controls of water quality and pond bottom surface. This is because the few infected shrimps might not die simultaneously therefore the less or slower chances of epidemic disease ( by eating themselves ) are possible and enable to continue culturing them. Moreover, it was also found that the farmers who used higher salty water in coastal areas tended to face with more severe problems than those who used lower salty water. In such a case, it can be concluded that the death of shrimps was probably caused by infection of white spot virus.
White sport on shells of the dead
shrimp
Pale and no white sport on shells of
the dead shrimp
In case the accumulated waste condition was not so serious or the shrimps were younger than 40 days, they might survive or die just a little if change of water can be done or reduction of pH value in the ponds. The aspects of shrimps are that they swam around in the ponds in the afternoon or evening since the ammonia in the water is more poisonous and the temperature of water is higher.
