Accumulation of microcystins in water and economic fish in Phayao Lake, and fish ponds along the Ing River tributary in Chiang Rai, Thailand

Niwooti Whangchai,Redel Gutierrez,Suthida Wanno,Norio Iwami,Korntip Kannika,Tomoaki Itayama,Rattapoom Promna

doi:10.4236/as.2013.45b010

Abstract

This study determined the levels of microcystins in water and fish from Phayao Lake, Phayao Province and selected fish ponds along the Ing River tributary in Chiang Rai Province. Samples were collected monthly for 8 months (January to August 2011 for Phayao Lake, and November 2008 to June 2009 for fish ponds) and were analyzed by HPLC. The highest total microcystin-LR levels in water and fish in Phayao Lake were recorded in April 2010 at 2.60 ± 2.48 μg·L-1 and 0.20 ± 0.03 μg·kg-1 dry weight, respectively. Microcystis aeruginosa Kütz were the dominant species (271.6 ± 72.4 mm3/m3) in the lake. Colony number of Microcystis spp showed a positive correlation with soluble orthophosphate (r2 = 0.77). Similarly, Nile tilapia ponds surveyed along the tributary in Chiang Rai were contaminated with microcystins as well. The highest concentration detected in water was in March 2009 (0.58 ± 0.24 μg·L-1), whilst the maximum concentration in fish was recorded in April 2009 (2.68 ± 0.51 μg·kg-1 dry weight). Microcystis spp. dominated the pond waters and was positively correlated with chlorophyll a (r2=0.80) and soluble nitrate (r2=0.71). The highest concentration of the cyanobacteria was recorded in February 2009 at 4272.5 ± 62.3 mm3/m3. Results showed that total microcystin-LR concentration in fish in Chiang Rai ponds were higher than in Phayao Lake. This study suggested the possible health risks associated with the bioaccumulation of microcystins in fish (Nile tilapia) cultivated in fish ponds along the tributary in Chiang Rai and in Phayao Lake.

Highlights

Thailand is one of the significant exporters of fish fillet in the United States, along with Taiwan, Mainland China and Indonesia
Microcystin-LR (MC-LR) was detected in 29% (7 out of 24) of water sampled from Phayao Lake throughout the survey period
Nile tilapia from the lake which were collected at the same sampling date as with the contaminated water samples, were likewise found to be tainted with toxic MC-LR, which ranged from ND - 0.26 μg· kg-1 dry weight

Summary

Introduction

Thailand is one of the significant exporters of fish fillet in the United States, along with Taiwan, Mainland China and Indonesia. Tilapia is mainly derived from fish farming in cages and ponds either through monoculture or polyculture with other economic fishes such as hybrid catfish. The consumption of Nile tilapia (Oreochromis niloticus) in Thailand is very popular, especially in the northern part where freshwater consumption rate was reported to be up to 32 kg per person per year [2] The Chiang Mai Aquacultural Cooperative (CMA Co-op) reported that demand for freshwater fish in Chiang Mai amounts to 40,000 kg/day [3]. The largest producer of tilapia (approximately 17.71 tons/day of fish products) is in the Upper North, including the Phan District, Chiang Rai Province, where tilapia production is primarily semiintensive based on natural foods derived from fertilizers or animal manure [4,5]. Because the volume of waste discharged into the fish pond is excessive, it results in a rapid growth of phytoplankton (algal bloom) especially during summer, which mostly often rendered the fish with musty off-flavor, or worst, Openly accessible at http://www.scirp.org/journal/as/

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