Relationships of Dissolved Oxygen with Chlorophyll-a and Phytoplankton Composition in Tilapia Ponds

This study investigated the relationships among the parameters of dissolved oxygen, chlorophyll-a and phytoplankton composition in tilapia ponds. Each pond (a total of 18 ponds) was sampled once in the dry, winter season between January and March and again early in the rainy season between May and June. The data were analyzed by examining correlations among parameters as affected by season, altitude and culture system. Observations were made at sites located in 5 selected provinces of northern Thailand: Chiangrai, Chiangmai, Phayao, Lampang and Nakornsawan. Mean elevation of these areas range from 25 to 582 meters above sea level (masl) and were categorized into low (400 masl) elevation sites. Ponds were 0.8 - 2.0 m deep, 0.16 - 0.64 ha in area and could be further categorized into high and low input systems.Mean air temperature in winter ranged between 16.5°C - 35.8°C while mean water temperature ranged between 25.5°C - 27.1°C. In rainy season, air temperature ranged between 22.0°C - 37.3°C and water temperature ranged between 29.4°C - 31.8°C. The amount of chlorophyll-a in both seasons were comparable (p > 0.05), but chlorophyll-a in high input system was significantly higher (p 0.05) than in low input ponds. Only weak correlation was found between chlorophyll-a, DOmax and DOmin. Multifactor-ANOVA was used to analyze the difference of total bacteria and filamentous cyanobacteria in ponds based upon elevation, culture systems and season. Result shows that there is a significant interaction observed between elevation, culture system and season (p 0.05). Species diversity and composition of phytoplankton in fish ponds in 2 seasons revealed the presence of 90 genera of phytoplankton under all 7 divisions. Divisions Chlorophyta and Cyanophyta had the most number of genera identified in both seasons with Pediastrum spp., and Scendesmus spp., and Anabaena spp. as dominant genera/genus, respectively.

Influence of Floodplain Area on Fish Species Richness in Waterbodies of the Chao Phraya River Basin, Thailand

River-floodplain ecosystems are in delicate balance and are impacted by even minor changes in water availability. In this study, we surveyed fish assemblages and investigated environmental and landscape parameters in a total of 135 floodplain waterbodies (rivers, diversion canals, ponds, irrigation ditches, paddy fields, and wetlands) in the Chao Phraya River Basin in rainy (September 2014) and dry (March 2015) seasons. Factors affecting fish species richness in each type of waterbody were analyzed using generalized linear mixed models. Floodplain area around each surveyed waterbody was a major factor determining fish species richness in rivers, diversion canals, and ponds in the region. The contribution of floodplain area was equivalent to that of hydrology (current velocity, water depth) and water quality (dissolved oxygen, turbidity) in the waterbodies. The population of juvenile fishes was increased in temporarily connected floodplain waterbodies to main rivers compared with isolated waterbodies, and fluvial and lacustrine fishes were observed in the temporary inundated floodplain waterbodies during the rainy season. The high dependence of fish species richness on floodplain area in the region appeared to be a result of the use of inundated floodplains by fish species to forage and breed. Our results highlight the impact of flood control measures that reduces floodplain area. These measures must be reviewed to ensure the conservation of fish biodiversity in the Chao Phraya River Basin, one of the world’s most threatened floodplain systems.

Survey of Climate-Related Risks to Tilapia Pond Farms in Northern Thailand

Climate is an important factor for aquaculture production. This study aimed to understand how farmers that culture tilapia in earthen ponds perceive and respond to climate impacts. Important climate-related risks identified include extreme temperatures (hot and cold), excessive rainfall, prolonged cloud cover, flood and drought. Site visits and data collection using questionnaires were conducted to identify important factors influencing farm profits, losses, decision to increase or decrease ponds. Special attention was given to knowledge about fish markets and weather and the impacts of weather and climate on fish growth, disease outbreaks and water quality in ponds. Altogether 585 fish farms in four provinces in northern part of Thailand selected to cover a range of elevations above sea level and thus climate were surveyed (Nakornsawan< 100 m, Lampang 100-300 m, Phayao 300-500 m and Chiang Mai > 500 m). Fish farms at different elevations reported different climate and weather-related impacts. In the area where elevation above sea level is < 100 m, farmers were affected more by floods and extreme hot weather which caused fish deaths and stress that reduced feeding and growth rates. Conversely, fish farmers in the area where elevation above sea level is >500 were impacted mainly by drought and cold weather. These conditions also caused disease outbreaks and reduced feeding rates. Farmers responded by reducing the amount of feed supplied and considering non-fish pond or non-farm supplementary occupations as an adaptation strategy. Among non-climate related factors high prices of feed were most commonly identified as a key issue by farmers. The differences among sites at higher and lower elevation provided insights into the kind of changes in risks farmers may face as climate changes that could be helpful in developing adaptation strategies for individual farmers and the sector as a whole.

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

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.

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

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.

River-Based Cage Aquaculture of Tilapia in Northern Thailand: Sustainability of Rearing and Business Practices

Cage-based aquaculture in rivers raises issues of natural resource management more familiar to fisheries management than does aquaculture in fish ponds on private land. Hybrid red and black Nile tilapias (Oreochromis niloticus L) are reared for 4 - 5 months in cages in the upper Ping River in northern Thailand. Observed mean stocking density was 49 ± 16 fish·m-3, feed conversion ratio 1.47 ± 0.43 kg feed per kg fish and yield density 26.6 ± 8.1 kg·m-3. Input costs were dominated by feed (70%) and stock (16%). Most farms borrowed money and participated in contracts. Fish farming was usually a component of a portfolio of household activities but for some a core business. To succeed fish farmers must manage a combination of market, climate and environmental-related risks. Cage-based aquaculture in rivers faces many challenges;further research on farm practices and vulnerabilities, river and water management, and the commodity-chain are needed.

Fish Diversity and Fish Assemblage Structure in Seagrass Meadows at Sikao Bay, Trang Province, Thailand

We investigated the relationship between environmental variables as descriptors of the fish community, in terms of species diversity indices and fish assemblage patterns, in seagrass meadows at Sikao Bay, Trang Province, Thailand. Fish data and water quality parameters were collected from January to December 2012. A total of 10,596 fish specimens of 97 taxa in 48 families from four stations, Kham Bay (7°30'9.21''N, 99°18'7.67''E), Boonkong Bay (7°31'2.49''N, 99°17'40.09''E), Ban Pak Klong (7°36'17.67''N, 99°16'32.89''E) and Sai Cape (7°38'30.19''N, 99°14'49.85''E), were collected using gillnets of three different mesh sizes. The three most diverse families were Leiognathidae, Carangidae and Tetraodontidae, respectively. The dominant species were Atherinomorus duodecimalis, Sillago sihama and Pelates quadrilineatus. Specimens were highly abundant in July and less so in January and species richness was high in July and less so in March. Fish assemblages were classified into two patterns and the average of the Shannon index was 2.7. The environmental parameters in each month were analyzed by one-way ANOVA which did not show significant difference (P > 0.05) of pH, orthophosphate, wind speed and rainfall. Fish diversity and assemblage, and environmental parameters, were categorized into four groups. These could be promoted to local fisheries so that conservation programs cpuld be set up to ensure the ecological sustainability of seagrass meadows.

Microcystin Accumulation in Nile Tilapia, <i>Oreochromis niloticus</i>and Giant Freshwater Prawns, <i>Macrobrachium rosenbergii</i>in Green Water System Cultivation

Phytoplankton including blue-green algal or cyanobacterial blooms frequently occurred in aquaculture ponds. Some cyanobacteria produced cyanotoxins that may accumulate in the food web and eventually in the aquaculture products. In this study, accumulatation of microcystins in Nile tilapia (Oreochromis niloticus) and giant freshwater prawn (Macrobrachium rosenbergii) cultured in green water system was investigated.Nile tilapia was cultured in green water system and fish food;green water system with Microcystis aeruginosa Kützingand fish food and green water system with M. aeruginosa. Giant freshwater prawn was cultured: in green water systems with and without toxic M. aeruginosa. Microcystins of 8.32±0.76 and9.35±1.45μg·kg—1 d.w. were detected in fish cultured in green water system with M. aeruginosa and fish food and in green water system with M. aeruginosa, respectively. Microcystins of 14.42±1.63 μg·kg—1 was found in prawn samples. It implied that aquaculture products were likely to be contaminated with microcystins. This finding is useful for aquaculture in terms of food safety.

Geosmin Sorption on Cyclodextrin Polymers

Geosmin is one of the major causative compounds of earthy-musty odor and taste (off-flavor) in drinking water (lakes) and in farmed fish. In this study, the sorption of cyclodextrin polymers (CDPs) towards geosmin in aqueous solution was investigated. Sorption kinetics, the effect of solution pH and contact time on the sorption capability of α-, β- and γ-cyclodextrin polymers was discussed. Results disclosed that the sorption of geosmin by the CDPs followed the Ho and McKay kinetic mechanism with the liquid film diffusion as the rate-determining step. Both β-CDP and γ-CDP exhibit high removal efficiencies of 93.4% and 96%, respectively, within 240 minutes at 25°C and pH 7, whilst α-CDP was not effective, removing only 40% geosmin, at an initial concentration of 5 μg·L—1and 5 g·L—1of CDP dose. The cyclodextrin polymers can adapt to a wide range of pH from 3.0 to 11.0 for geosmin adsorption with pH 7.0 as optimum. Results indicate that these sorbents demonstrate significant potential in reducing the concentration of geosmin in water that presents taint problems in both drinking water and fish.

太平洋十年涛动对全球地表气温变化的影响足迹

Sea surface temperature modes have been found to modulate anthropogenic global warming rates on annual and decadal timescales,sometimes leading to periods of“slowdown”despite increasing greenhouse gas emissions^([1]).

Forest Restoration Potential in China:Implications for Carbon Capture

Reforestation is an eco-friendly strategy for countering rising carbon dioxide concentrations in the atmosphere and the negative effects of forest loss and degradation.China,with one of the world’s most considerable afforestation rates,has increased its forest cover from 16.6%20 years ago to 23.0%by 2020.However,the maximum potential forest coverage achieved via tree planting and restoration is uncertain.To map potential tree coverage across China,we developed a random forest regression model relating environmental factors and appropriate forest types.We estimate 67.2 million hectares of land currently available for tree restoration after excluding existing forested areas,urban areas,and agriculture land covers/uses,which is 50%higher than the current understanding.Converting these lands to the forest would generate 3.99 gigatons of new above-and belowground carbon stocks,representing an important contribution to achieving carbon neutrality.This potential is spatially imbalanced,with the largest restorable carbon potential being located in the southwest(29.5%),followed by the northeast(17.2%)and northwest(16.8%).Our study highlights the need to align tree restoration areas with the uneven distribution of carbon sequestration potential.In addition to being a biological mitigation strategy to partially offset carbon dioxide emissions from fossil fuel burning,reforestation should provide other environmental services such as the restoration of degraded soils,conservation of biological diversity,revitalization of hydrological integrity,localized cooling,and improvement in air quality.Because of the collective benefits of forest restoration,we encourage that such activities be ecosystem focused as opposed to solely focusing on tree planting.