Shrimp farming and water quality conditions in Phuket, Thailand

The shrimp farming industry in Muang and Ta-lhang District was characterized and a preliminary assessment of the potential impacts on water quality in the coastal zone of Ban-Chi-Lao, Phuket, Thailand were done from February to June 2003. A total of 29 randomly selected shrimp farmers were interviewed. Water samples were collected from four shrimp ponds and the adjoining coastal area and chemically analyzed based on salinity, pH, temperature, transparency, TSS, Chl-a, DO, BOD, NH3-N, NO2-N, NO3-N, TN, ortho-P and TP. Descriptive statistics and correlation analysis were done using SPSS. The shrimp farmers were primarily male from Phuket and had a college degree. Most of large-scale respondents owned the land and had longer experience than the smaller scale. Sex, educational attainment, experience of respondents and farm scale had no relationship with farm productivity and profitability. However, experience had a positive relationship with farm scale. Large-scale farms had the highest productivity, and incurred the highest production cost. Medium- and small-scale farms had higher profitability than the large-scale farm. Compared with the recommended stocking densities for shrimp farming, the general stocking rate in the study area is rated excessive. As a result, there is tendency towards over feeding which could lead to a water quality degradation, reduced survival rates, and increased possibility of shrimp disease outbreaks, hence, low production. This chain of events might explain the diminishing shrimp production currently experienced in Phuket. Use of some dangerous chemicals and prohibited antibiotics by farmers might have a potential health risk for humans. The intake and coastal waters satisfied the coastal water quality standards for temperature, pH, DO and NH3-N. The pond water pH and DO were within the acceptable ranges for shrimp production. Pond water temperature, TSS, secchi transparency and salinity did not meet the optimum ranges for shrimp growth. The discharge water was of acceptable quality based on the pH, BOD, NH3-N, TN and TP standards for effluent water from aquaculture, except TSS. In the overall, shrimp farming does not seem to degrade the quality of the water used in shrimp ponds and afterwards released into the coastal area. Since this study was done during the transition period from the dry to the wet season only, it is essential that the same assessment be carried out at other times of the year in order to get the annual trend. To achieve sustainable shrimp farming development, it is recommended that the stock density be reduced and better quality of broodstock be used