Effects of Temperature upon Water Turnover in Fish Ponds in Northern Thailand

Patcharawalai Sriyasak,Niwooti Whangchai,Louis Lebel,Jongkon Promya,Chanagun Chitmanat

doi:10.4236/ijg.2013.45b004

Abstract

Fish culture in earthen ponds is an important source of income for farmers in northern Thailand. Water quality in ponds has strong impacts on fish production farmers’ return and is sensitive to weather and climate. Low levels of dissolved oxygen in fish ponds are major cause of mass mortality. Stratification with depth in ponds followed by rapid turnover or exchange of surface and bottom water can expose fish to dangerously low dissolved oxygen levels. The main purpose of this study was to observe the effects of weather on stratification and subsequent water turnover in fish ponds in northern Thailand, especially in the winter and rainy season, when stratification was expected to be most severe. Temperature and water quality measurements were made in fish ponds at 18 farms with depths ranged from 0.8-2.0 m and size of 0.16-0.64 ha. Measurements were made during January and May 2013. Fish farm pond sites were divided into two groups based on elevation above sea level: low ( 400 masl) and categorized into 3 types of farming: commercial, integrated and subsistence. In lower elevation sites, water turnover occurred at night between 22.00 and 02.00 in winter and between 18.00 and 02.00 in rainy season. At higher elevation, turnover occurred in ponds between 20.00 and 22.00 in winter and between 14.00 and 18.00 in rainy season. Turnover was slower in the lower elevation than in higher elevation zones and generally occurred earlier during the rainy season than in the winter. Mean DO in winter was significantly higher (p<0.05) than in rainy season, whilst water temperature and amount of ammonia-nitrogen during the rainy season was significantly higher (p<0.05) than in winter. Turnover improves distribution of dissolved oxygen through the water column and minimizes organic matter accumulation. Cloud cover during the rainy season may have contributed to limit oxygen production and thus may have significantly affect water quality in ponds. Fish farmers should consider more explicitly the role of temperature and cloud conditions when managing dissolved oxygen levels in their fish ponds. Therefore, efficient pond aeration or pond mixing strategies for reducing stratification still plays an important component for providing sound pond management in tilapia production ponds.

Highlights

Tilapia fish culture in earthen ponds is expanding dramatically in Thailand [1]
Mean air and water temperatures decrease with mean elevation across the climate gradient of sites selected for study (Figure 1)
Altitude affects the temperature of the air because air pressure gets lower as the altitude increases and so does inversely affect pond water temperature as well

Summary

Introduction

Tilapia fish culture in earthen ponds is expanding dramatically in Thailand [1]. Prolonged extreme hot weather followed by a heavy rain disturbs the surface water to cool lower temperatures where the cool heavy water layer sink to the bottom floor due to gravity can cause turnover of water in ponds [6,7]. Stratification with depth in ponds followed by rapid turnover or exchange of surface and bottom water can expose fish to dangerously low dissolved oxygen levels subjecting them to stress and vulnerability to diseases. Tilapia fish culture in earthen ponds in northern Thailand can be divided into three categories: commercial, integrated (with pig or chicken) and subsistence. Sensitivity to lower dissolved oxygen in different culture systems causes different levels of risks of mortality from changes in weather and water turnover. The main purpose of this study was to measure the effects of weather on stratification and subsequent water turnover in fish ponds under different

Objectives

Methods

Results

Conclusion