ScienceAsia 32 (2006): 365-370 |doi: 10.2306/scienceasia1513-1874.2006.32.365

Microcystins in Cyanobacterial Blooms from Two Freshwater Prawn (Macrobrachium rosenbergii) Ponds in Northern Thailand

Rattapoom Prommana^a*, Yuwadee Peerapornpisal^a, Niwooti Whangchai^b, Louise F Morrison^c, James S Metcalf^c, Werawan Ruangyuttikarn^d, Arnon Towprom^a and Geoffrey A Codd^c

 
ABSTRACT: The presence of cyanobacterially-produced microcystins (cyclic peptide hepatotoxins) was determined by analysis of Microcystis spp. in scum and water samples collected from a surface cyanobacterial bloom at a giant freshwater prawn (Macrobrachium rosenbergii) farm in Teung District, Chiang Rai Province, in northern Thailand during March to August 2004. M. aeruginasa and M. wesenbergii were the dominant species of cyanobacteria at concentrations between 850,000±190,000 and 302,000±73,000 colonies l-1. Microcystins were present at 0.44±0.020 g kg-1 dry weight with microcystin-LR and microcystin-RR as the dominant microcystin types, accounting for 45% and 48% of the total microcystins detected, respectively. Microcystins in pond water were present at between 2.2±3.0 µg l-1 and 9.4±2.0 µg l-1. Total microcystin concentrations in water seemed to be positively correlated with the number of Microcystis colonies. A decrease of microcystins in water was observed from April to August 2004, which may have resulted from removal by mechanisms not examined in this study. The total microcystin in water was slightly negatively correlated with total culturable bacteria numbers. Microcystis spp. colony number showed a significant negative correlation with soluble reactive phosphorus (r = -0.98, p<0.05). Nitrate-N, ammonium-N and soluble reactive phosphorus concentrations were between 1.2-1.9, 0.85-1.15 and 0.9-1.1 mg l-1, respectively. Phosphorus concentrations were higher than the permitted limit for waste water from a fishery farm (less than 0.4 mg l-1). This study suggested that surface blooms of Microcystis species in cultivation ponds may present a risk for microcystin bioaccumulation in prawns, either directly or via other organisms in the food web.

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^a Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
^b Faculty of Fisheries Technology and Aquatic Resources, Mae Jo University, Chiang Mai 50290, Thailand.
^c Division of Environmental and Applied Biology, Biological Sciences Institute, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK
^d Division of Toxicology, Department of Forensic Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand.

* Corresponding author, E-mail: smartrattapoom@yahoo.com

Received 6 Feb 2006, Accepted 18 May 2006