A survey on causes of sudden feeding decrease in farmed white leg shrimp (Litopenaeus vannamei) in Boushehr Province

Objective: In September 2007, some shrimp farmers in Boushehr Province reported sever and sudden decrease in daily feeding of ponds. We investigated causes of this problem in 6 affected farms. Method & Materials: we did field observation on affected farms and took 20 samples from 20 affected ponds (each sample was 10 shrimps) for detection of major viral shrimp (WSSV, YHV, TSV, IMNV, IHHNV) by PCR, Nested PCR, RT-PCR with IQ2000 kits. Furthermore, 2 samples of shrimp feed were taken and sent to the laboratory for physicochemical and microbial analysis. Results & Conclusion: At first in field observation, there was no special clinical symptom except for decrease of feeding, empty gut and loose shell. Other shrimp behavior such as swimming and shell color were normal. In the study of environmental changes. we found a sudden decrease in water temperature (29◦C to 20◦C in 2 days ). Other factors such as salinity, turbidity and oxygen level were normal. All results of PCR tests were negative and none of mentioned viruses were detected. The results of feed analysis showed that feed composition was normal accordance with Iranian national standard. We concluded that decrease of weather and water temperature below 20◦C and abrupt change of it was the major problem and caused stress to shrimp. Decrease of feeding was first response to this stress. Finally FCR of affected farms went high and economic loss was heavy to shrimp farmer.