Soil and Water Quality Management in Aquaculture

N Soranganba *

Fish Fair and Fish Crop Competition 2011 at Hatta Kangjeibung on 27 Oct 2011 - Pix by Bullu Raj

Introduction : Good bottom soil and water quality are vital ingredient for any successful aquaculture practices. Although such problems are related to site characteristics bottom soils have undesirable properties viz acid sulphate, high organic and excessive porosity etc. Similarly, the water may have poor quality, viz highly acidic, rich in nutrient and organic matter, high in suspended solids or polluted with industrial or agricultural chemicals.

Water Quality Management : Fish being aquatic being are more prone to disease and are difficult to control. The equilibrium of disease, environment and fish health are important any change in the equilibrium leads to “stressed” and becomes vulnerable to disease which have influences on growth and survival.

Dissolved oxygen : The optimum dissolved oxygen (DO) content of pond waters is in the range of 5 ppm saturation level. Aeration is a proven technique for improving DO availability. Any sort of agitation improves the DO content and among which paddle-wheel, aerators aspirators are most common.

Temperature : Temperature sets the pace for metabolism and biochemical reaction rates. The optimum temperature range for cold water and warm water fishes are 140C-180C and 240-300C respectively. Temperature can be adjusted to optimum level in controlled condition like hatcheries but difficult to adjust in large water bodies. Operation of aerator helps in breaking thermal stratification while planting of trees gives shades.

Turbidity : Several factors like suspended soil particle, planktonic organisms and organic matter contributes to turbidity. Measured using Secchi disc the optimum visibility range from 40-60 cm. it can be controlled by application of organic manure at 500-1000 kg/ha, gypsum @ 250-500 kg/ha or alum @25-50 kg/ha.

Ammonia : Fish are very sensitive to unionized ammonia (NH3) and optimum range is 0.02-0.05 ppm in the pond water. The same is reduced in the case of high DO and high CO2. Aeration, healthy phytoplankton population removes ammonia from water. Addition of salt @ 1200-1800 kg/ha reduces toxicity. Formalin are also use in certain cases. Biological filter may be use to treat water for converting ammonia to nitrate and then to harmless nitrate through nitrification process.

Hydrogen sulphide : Fresh water fish pond should be free from hydrogen sulphide because at concentration of 0.01 ppm fish lose their equilibrium. Frequent exchange and increase of pH through liming can reduces its toxicity.

pH : pH is a measure of hydrogen ion concentration in water and indicate how much water is acidic or basic. Water pH affects fish metabolism, physiological process, toxicity of ammonia, hydrogen sulphides and solubility of nutrient thereby well-being and fertility. pH at the range of 6-9 is best for fish growth and can be increase by application of lime. Agriculture gypsum may be applied to correct alkaline pH.

Total Alkalinity : Ideal range from 60-300 ppm as CaCO3 and it can be treated with lime. Less than 20 ppm leads to fluctuation and more than 300 ppm may become unproductive due to limitation of carbondioxide availability.

Total hardness : It should be greater than 40 ppm because it helps to protect fish against harmful effect of pH and metal ions. Low hardness can be treated with lime.

Carbon dioxide : Pond water should contain low concentration of free CO2 (

Bottom Soil Management : Bottom soil is considered as the chemical laboratory of the pond. However, suitable soil quality problem are common in aquaculture, and therefore, many methods are used for purpose of improving pond soils.

Texture : The nature and the properties of the parent material forming the soil determine the soil texture. An ideal pond soil should not be too sandy to allow leaching of the nutrients or should not be too clayey to keep all the nutrients absorbed on to it. For sandy soil, heavy dose of raw or composed farmyard manure varies from 10000 to 15000 kg/ha/year is required.

Soil acidity : The soil may be acidic, alkaline or neutral but the ideal range for soil pH is 6-8. Acid ponds do not respond well to fertilization and liming is the only way to improve water quality with acid soil and it is the soil that must be corrected for lasting effect, rather than the pH of the water.

Bottom soil oxidation : When the redox potential is low at the soil surface, hydrogen sulphide and other toxic microbial metabolites diffuse into the pond water. Sodium nitrate (NaNO3) can serve as a source of oxygen for microbes in poorly oxygenated environment in which the redox-potential will not drop low enough for the formation of hydrogen sulphide and other toxic metabolites.

Drying pond bottom : Evaporation of water from soil pores and cracking of soil during drying enhances aeration and favour microbial decomposition of soil organic matter. Excessive drying makes soil too dry for microbial activity, so a period of 2-3 weeks is adequate. Tilling with a disk harrow also improves aeration but compaction is required before refilling to reduce erosion.

Sustainable Pond Productivity

Nutrient removal : It is possible to precipitate phosphorus from pond water by applying sources of iron, aluminium or calcium ions. Alum (aluminium sulphate) or ferric chloride are commercially available of which the former is cheap and widely used. Alum @ 20-30 ppm is more suitable in alkaline water (>500 ppm) and gypsum (calcium sulphate) @ 100-200 ppm is better in low alkaline water.

Plankton removal : Copper sulpahte @ 1/100 of the total alkalinity is recommended for reducing phytoplankton abundance and blue-green algae in particular.

Chlorination : It is possible to disinfect bottom of empty pond and waters in newly filled and unstocked ponds by applying chlorine products @ 1ppm or more of free chlorine residual. The residuals will detoxify naturally in a few days so that ponds can be stock safely.

Liming : Liming should be always done depending upon the pH of the water and the soil. As the health of the soil determines the nature of the pond water, pH of the water can be taken as reference to determine appropriate dose of application