The water budgets for some aquaculture systems in three states viz. Andhra Pradesh, Orissa and West Bengal were determined in the present study. The average evaporation and seepage loss from the aquaculture ponds throughout the year in Cuttack, Kendrapara, Jajpur, and Puri districts of Orissa were 164 ± 8.3 and 73 ± 16.5 cm, respectively; 152 ± 10 and 90 ± 16 cm, respectively, in South and North 24 Paraganas, West Bengal; and 182 ± 12 and 110 ± 10 cm, respectively, in Krishna and West Godavari districts of Andhra Pradesh. Evaporation and seepage were significantly (P < 0.05) different between the fish ponds of the three states. Annual rainfall, run-off, and well water addition to the ponds were 178 ± 40, 14.5 ± 3.4, and 156 ± 48 cm, respectively, in Orissa; 166 ± 14, 9 ± 2, and 173 ± 27 cm, respectively, in West Bengal; 120 ± 12, 8 ± 1, and 304 ± 26 cm, respectively, in Andhra Pradesh. Annual rainfall, run-off, and well water addition to the ponds differed significantly (P < 0.05) in the three states. The consumptive water use was 3.34 ± 0.47, 3.35 ± 0.36, and 2.67 ± 0.23 m3/kg, respectively, in Orissa, West Bengal, and Andhra Pradesh. A significantly (P < 0.05) greater consumptive water use was determined for the fish ponds of West Bengal and Orissa compared to Andhra Pradesh.

INTRODUCTION

In spite of the fact that the volume of water on earth (>71% of the earth's surface) is constant, it goes through a continuous hydrological cycle such as transpiration by vegetation, evaporation, precipitation, runoff, infiltration and other natural processes. As a result, rainfall varies around the world, and many areas suffer water shortages. Although the majority of the earth's surface is covered by water, 97% of the earth's water is in oceans, and, only freshwater (about 3% of which 85% is in the form of glaciers) is suitable for living organisms including humans. In recent years the water table has faced serious threats due to rapid population increase, industrial and urban development, over-use, climate change, global warming, shrinkage in glaciers in the Arctic and Antarctic, natural calamities (shifting of precipitation and reduced snow pack), negligence of people to use water responsibly and slow replenishment of natural waters (Kumar 2013; Kurunthachalam 2014). In addition, drastic economic expansion, energy demand and shrinkage of replenished waters are of major concern. Water withdrawals across all sectors including public use (municipal), rural or domestic use, livestock use, irrigation and thermoelectric power generation increased dramatically between 1950 and 2005 in the USA (Kenny et al. 2009).

It is evident that the availability of freshwater is shrinking day by day, so it is important to know the minimum requirement of water for the production of one ton of fish. Thus water budgeting is important for fish production. The water budget for some watersheds has been reported by Shelton & Boyd (1993). Water budgets were also studied for some experimental ponds in Alabama (Boyd 1982; Boyd & Tucker 2012). Green & Boyd (1995) developed a water budget for some ponds in the dry tropics. In all the cases, they had considered evaporation loss, seepage loss, annual rainfall, and water inflow-outflow. Thus, water budgets are useful for the estimation of requirements of ponds that rely on rainfall and runoff as primary water sources and for flow-through pond facilities. Such budgets will also be able to predict whether an existing or potential source will be able to meet the projected water demand of aquaculture facilities, and also to compare the value of available water for different agricultural purposes (Nath & Bolte 1998). So far as aquaculture ponds are considered in India, no report on water budgets for aquaculture practices is available. Keeping these things in mind, the present investigation was conducted to develop water budgets for freshwater fish ponds in three states, Orissa, Andhra Pradesh and West Bengal, of India.

MATERIALS AND METHODS

Different hydrological parameters were estimated in aquaculture ponds in three states. Data were collected from 20 fish ponds in four districts of Orissa, namely Kendrapara, Jajpur, Cuttack and Puri. Twenty ponds were also selected in the two districts of Krishna and Godavari of Andhra Pradesh. Twenty ponds were also selected in the two districts of South and North 24 Paraganas, West Bengal. The farmers are progressive fish farmers. In Orissa and West Bengal, Labeo rohita, Catla Catla, and Cirrhinus mrigala in a ratio of 1:1:1 are cultured and the production levels are 6,000 to 8,000 kg/ha/yr in Orissa and 6,500 to 8,000 kg/ha/yr in West Bengal. In Andhra Pradesh, Labeo rohita and Catla catla are cultured in a ratio of 9:1 and the production levels are 8,000 to 10,000 kg/ha/yr.

One standard rain gauge and an evaporation pan were installed near the ponds and data were collected for a complete year. The initial rainfall is a very important estimation since it helps to fill the pond to the maximum level for the stocking of fish, mainly in the rainy season. This is the case in West Bengal and Orissa. However, in Andhra Pradesh as annual rainfall is comparatively less, the initial filling of the pond is by irrigation waters. Sometimes the initial water supply is achieved only through direct precipitation run-off and well/canal water. The rainfall normally starts in June/July and results in a rise in the water level in July/August. This rainfall is responsible for the initial filling of the ponds .One staff gauge was installed in each pond and water levels were measured periodically and after each rainfall event. The amount of well water added to ponds through the pumps was calculated (Boyd 1982) using the following equation: 
formula
where W = water from well, E = evaporation, S = seepage, O = overflow, H = pond water depth, P = precipitation (rainfall), R = run-off. Values for the above equation were in centimeters of water depth. Rainfall was estimated from the rain gauge at the farm. In the present study, there was also no overflow of water in any of the ponds. Pond water level changes were monitored with properly marked bamboo sticks installed at the middle of each pond to estimate average water depth. The pond dyke was well compacted and had grass cover. About 67% of rain falling on the dyke entered the ponds in run-off (Yoo & Boyd 1994). The equation for determining run-off for a pond is as follows: 
formula
where a = dyke area (m2) and A = pond surface area (m2).

The evaporation from aquaculture ponds was obtained from an evaporation pan in centimeters using 0.81 as the pan coefficient for evaporation (Boyd 1985). The seepage was estimated in centimeters as the difference in the decrease in water level and evaporation. Data on inflows and well water additions were calculated using the above equation and used to prepare water budgets.

One-way analysis of variance with Duncan multiple range tests was applied to find out the significant differences among the different states using the SAS computer software for the means of rainfall, run-off, well water added, evaporation, seepage and consumptive water use.

RESULTS AND DISCUSSION

Inflow and outflow in a fish pond refer to the amount of water which is added to or discharged from a pond through the direct operations of the farmer. The main water supply for these fish ponds is the natural rainfall that occurs seasonally. In the states of Andhra Pradesh, Orissa and West Bengal, rainfall starts during June/July and continues until September. However, sometimes it continues up to October. During this period, the rainfall results in a rise of water level in a pond and is responsible for the initial filling of the ponds. When the water level reaches about 1 m, the pond is stocked. Where there is less rainfall, water is pumped from the ground water supply by use of a well into the ponds to fill them.

In Puri and Kendrapara districts of Orissa, rainfall was the major source to maintain the water depth of the fish ponds, otherwise water inflow through well water was the largest contributor of water to these ponds. The ponds received a total of 232 cm of rain, averaging 0.63 cm/d in Puri over the year. The ponds received a total of 184 cm of rain, averaging 0.50 cm/d in Kendrapara over the year. The ponds received a total of 164 cm of rain, averaging 0.45 cm/d in Cuttack while the ponds received a total of 135 cm of rain with an average of 0.37 cm/d in Jajpur district of Orissa (Tables 14). Overall, the ponds received an average of 178 ± 40 cm of rain, averaging 0.49 cm/d in these districts of Orissa over the year. The ponds in Krishna and West Godavari, Andhra Pradesh received a total of 120 ± 12 cm of rain, averaging 0.33 cm/d over the year (Table 5). The ponds in South and North 24 Paraganas, West Bengal received a total of 166 ± 14 cm of rain, averaging 0.45 cm/d over the year (Table 6). Thus, the ponds received an average of 0.42 cm/d of rain over the year. Significantly (P < 0.05) higher rainfall was measured in the fish ponds of West Bengal and Orissa compared to Andhra Pradesh (Table 7). After the rainy season, winter and summer seasons follow. The winter season is similar to the dry season, with low temperatures while the summer season is dry with very high temperatures.

Table 1

Water budgets for carp culture ponds in Puri, Orissa (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 103 ± 7 10,300 ± 700 
 Precipitation 232 ± 8 23,200 ± 800 
 Run-off 19 ± 1 1,900 ± 100 
 Total 354 ± 16 35,400 ± 1,600 
Outflows 
 Harvest water 110 ± 10 11,000 ± 1,000 
 Evaporation 164 ± 4 16,400 ± 400 
 Seepage 80 ± 2 8,000 ± 200 
 Total 354 ± 16 35,400 ± 1,600 
Production (kg/ha) 6,250 ± 250 
Consumptive water use (m3/kg fish) 3.90 ± 0.20 
Water productivity (kg/m30.176 ± 0.04 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 103 ± 7 10,300 ± 700 
 Precipitation 232 ± 8 23,200 ± 800 
 Run-off 19 ± 1 1,900 ± 100 
 Total 354 ± 16 35,400 ± 1,600 
Outflows 
 Harvest water 110 ± 10 11,000 ± 1,000 
 Evaporation 164 ± 4 16,400 ± 400 
 Seepage 80 ± 2 8,000 ± 200 
 Total 354 ± 16 35,400 ± 1,600 
Production (kg/ha) 6,250 ± 250 
Consumptive water use (m3/kg fish) 3.90 ± 0.20 
Water productivity (kg/m30.176 ± 0.04 
Table 2

Water budgets for carp culture ponds in Kendrapara, Orissa (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 130 ± 10 13,000 ± 1,000 
 Precipitation 184 ± 6 18,400 ± 600 
 Run-off 13 ± 1 1,300 ± 100 
 Total 327 ± 17 32,700 ± 1,700 
Outflows 
 Harvest water 100 ± 10 10,000 ± 1,000 
 Evaporation 176 ± 4 17,600 ± 400 
 Seepage 51 ± 3 5,100 ± 300 
 Total 327 ± 17 32,700 ± 1,700 
Production (kg/ha) 8,000 ± 200 
Consumptive water use (m3/kg fish) 2.83 ± 0.17 
Water productivity (kg/m30.244 ± 0.06 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 130 ± 10 13,000 ± 1,000 
 Precipitation 184 ± 6 18,400 ± 600 
 Run-off 13 ± 1 1,300 ± 100 
 Total 327 ± 17 32,700 ± 1,700 
Outflows 
 Harvest water 100 ± 10 10,000 ± 1,000 
 Evaporation 176 ± 4 17,600 ± 400 
 Seepage 51 ± 3 5,100 ± 300 
 Total 327 ± 17 32,700 ± 1,700 
Production (kg/ha) 8,000 ± 200 
Consumptive water use (m3/kg fish) 2.83 ± 0.17 
Water productivity (kg/m30.244 ± 0.06 
Table 3

Water budgets for carp culture ponds in Cuttack, Orissa (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 192 ± 8 19,200 ± 800 
 Precipitation 164 ± 8 16,400 ± 800 
 Run-off 11 ± 2 1,100 ± 200 
 Total 367 ± 18 36,700 ± 1,800 
Outflows 
 Harvest water 120 ± 11 12,000 ± 1,100 
 Evaporation 157 ± 5 15,700 ± 500 
 Seepage 90 ± 2 9,000 ± 200 
 Total 367 ± 18 36,700 ± 1,800 
Production (kg/ha) 8,000 ± 150 
Consumptive water use (m3/kg fish) 3.08 ± 0.12 
Water productivity (kg/m30.217 ± 0.03 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 192 ± 8 19,200 ± 800 
 Precipitation 164 ± 8 16,400 ± 800 
 Run-off 11 ± 2 1,100 ± 200 
 Total 367 ± 18 36,700 ± 1,800 
Outflows 
 Harvest water 120 ± 11 12,000 ± 1,100 
 Evaporation 157 ± 5 15,700 ± 500 
 Seepage 90 ± 2 9,000 ± 200 
 Total 367 ± 18 36,700 ± 1,800 
Production (kg/ha) 8,000 ± 150 
Consumptive water use (m3/kg fish) 3.08 ± 0.12 
Water productivity (kg/m30.217 ± 0.03 
Table 4

Water budgets for carp culture ponds in Jajpur, Orissa (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 202 ± 8 20,200 ± 800 
 Precipitation 135 ± 5 13,500 ± 500 
 Run-off 15 ± 2 1,500 ± 200 
 Total 352 ± 15 35,200 ± 1,500 
Outflows 
 Harvest water 120 ± 8 12,000 ± 800 
 Evaporation 160 ± 4 16,000 ± 400 
 Seepage 72 ± 3 7,200 ± 300 
 Total 352 ± 15 35,200 ± 1,500 
Production (kg/ha) 6,250 ± 200 
Consumptive water use (m3 /kg fish) 3.56 ± 0.14 
Water productivity (kg/m30.184 ± 0.06 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 202 ± 8 20,200 ± 800 
 Precipitation 135 ± 5 13,500 ± 500 
 Run-off 15 ± 2 1,500 ± 200 
 Total 352 ± 15 35,200 ± 1,500 
Outflows 
 Harvest water 120 ± 8 12,000 ± 800 
 Evaporation 160 ± 4 16,000 ± 400 
 Seepage 72 ± 3 7,200 ± 300 
 Total 352 ± 15 35,200 ± 1,500 
Production (kg/ha) 6,250 ± 200 
Consumptive water use (m3 /kg fish) 3.56 ± 0.14 
Water productivity (kg/m30.184 ± 0.06 
Table 5

Water budgets for carp culture ponds in Krishna, and West Godavari, Andhra Pradesh (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 304 ± 26 30,400 ± 2,600 
 Precipitation 120 ± 12 12,000 ± 1,200 
 Run-off 8 ± 1 800 ± 100 
 Total 432 ± 38 43,200 ± 3,800 
Outflows 
 Harvest water 140 ± 12 14,000 ± 1,200 
 Evaporation 182 ± 12 18,200 ± 1,200 
 Seepage 110 ± 10 11,000 ± 1,000 
 Total 432 ± 32 43,200 ± 3,200 
Production (kg/ha) 10,000–12,000 (11,000 ± 1,000) 
Consumptive water use (m3/kg fish) 2.43–2.92 (2.67 ± 0.23) 
Water productivity (kg/m30.230–0.277 (0.25 ± 0.03) 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 304 ± 26 30,400 ± 2,600 
 Precipitation 120 ± 12 12,000 ± 1,200 
 Run-off 8 ± 1 800 ± 100 
 Total 432 ± 38 43,200 ± 3,800 
Outflows 
 Harvest water 140 ± 12 14,000 ± 1,200 
 Evaporation 182 ± 12 18,200 ± 1,200 
 Seepage 110 ± 10 11,000 ± 1,000 
 Total 432 ± 32 43,200 ± 3,200 
Production (kg/ha) 10,000–12,000 (11,000 ± 1,000) 
Consumptive water use (m3/kg fish) 2.43–2.92 (2.67 ± 0.23) 
Water productivity (kg/m30.230–0.277 (0.25 ± 0.03) 
Table 6

Water budgets for carp culture ponds in North and South 24 Paraganas, West Bengal (mean ± SD)

VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 173 ± 27 17,300 ± 2,700 
 Precipitation 166 ± 14 16,600 ± 1,400 
 Run-off 9 ± 2 900 ± 200 
 Total 348 ± 42 34,800 ± 4,200 
Outflows 
 Harvest water 106 ± 14 10,600 ± 1,400 
 Evaporation 152 ± 10 15,200 ± 1,000 
 Seepage 90 ± 16 9,000 ± 1,600 
 Total 348 ± 40 34,800 ± 4,000 
Production (kg/ha) 6,250–8,500 (8,000 ± 300) 
Consumptive water use (m3/kg fish) 2.84–3.87 (3.35 ± 0.36) 
Water productivity (kg/m30.180–0.240 (0.21 ± 0.03) 
VariablesDepth (cm)Volume (m3)
Inflows 
 Well water 173 ± 27 17,300 ± 2,700 
 Precipitation 166 ± 14 16,600 ± 1,400 
 Run-off 9 ± 2 900 ± 200 
 Total 348 ± 42 34,800 ± 4,200 
Outflows 
 Harvest water 106 ± 14 10,600 ± 1,400 
 Evaporation 152 ± 10 15,200 ± 1,000 
 Seepage 90 ± 16 9,000 ± 1,600 
 Total 348 ± 40 34,800 ± 4,000 
Production (kg/ha) 6,250–8,500 (8,000 ± 300) 
Consumptive water use (m3/kg fish) 2.84–3.87 (3.35 ± 0.36) 
Water productivity (kg/m30.180–0.240 (0.21 ± 0.03) 
Table 7

Comparisons of hydrological parameters and water use in the fish ponds of Orissa, Andhra Pradesh and West Bengal (mean ± SD)

 Different variables
StatesRainfall (cm)Run-off (cm)Well water added(cm)Evaporation (cm)Seepage (cm)Consumptive water use (m3/kg fish)
Orissa 178a ± 40 14a ± 3.4 156a ± 48 164a ± 8.3 73a ± 16.5 3.34a ± 0.47 
Andhra Pradesh 120b ± 12 8b ± 1 304b ± 26 182b ± 12 110b ± 10 2.67b ± 0.30 
West Bengal 166a ± 14 9b ± 2 173a ± 27 152a ± 10 90c ± 16 3.35a ± 0.45 
 Different variables
StatesRainfall (cm)Run-off (cm)Well water added(cm)Evaporation (cm)Seepage (cm)Consumptive water use (m3/kg fish)
Orissa 178a ± 40 14a ± 3.4 156a ± 48 164a ± 8.3 73a ± 16.5 3.34a ± 0.47 
Andhra Pradesh 120b ± 12 8b ± 1 304b ± 26 182b ± 12 110b ± 10 2.67b ± 0.30 
West Bengal 166a ± 14 9b ± 2 173a ± 27 152a ± 10 90c ± 16 3.35a ± 0.45 

Values followed by the same superscripts in a column are not significantly different at the 0.05 levels.

In fisheries and aquaculture, the rainfall excess or deficit is a more important variable than rainfall alone (Boyd 1985; Yoo & Boyd 1994). This variable is the difference in rainfall and pond evaporation measured on a monthly or annual basis. At most pond sites, there will be periods with a rainfall excess, and other times, there will be a rainfall deficit. Annual rainfall excess usually occurs in humid climates and an annual rainfall deficit occurs in arid ones. There are few places in the world where direct rainfall sustains a pond. There usually must be one or more external water sources such as runoff from a watershed, inflow from seepage, or additions from wells or other water bodies. Boyd & Tucker (2012) reported that total rainfall between April and October in Auburn, Alabama was 75.9 cm and average evaporation from pond surfaces was 89.5 cm. By providing storage volume to capture direct rainfall, almost enough rainfall to replace evaporation losses can be captured. This could reduce reliance upon external sources of water and lower pumping costs.

During winter and particularly summer, the addition of water is required for maintaining the water depth (average of 150 cm). The addition of regulated inflow into the pond varied from 103 to 202 cm over the year with an average of 156 ± 48 cm (mean ± SD) in different districts of Orissa (Tables 14). The addition of well water was 173 ± 27 cm in West Bengal (Table 6) while the same was 304 ± 26 cm in Krishna and Godavari districts of Andhra Pradesh (Table 5). The amount of well water added to the fish ponds was significantly (P < 0.05) higher in Andhra Pradesh because of lower rainfall in the state compared to Orissa and West Bengal (Table 7).

Runoff was comparatively insignificant for the fish ponds in these states. The total water input from runoff over the year was 11 to 19 (Tables 14) with an average of 14.5 ± 3.4 cm (mean ± SD) in Orissa while the same was 8 ± 1 cm in Andhra Pradesh (Table 5). The total runoff was 9 ± 2 cm in the fish ponds of the two districts of West Bengal (Table 6). The daily water gain over the year through runoff was 0.039, 0.021 and 0.024 cm, in the fish ponds of Orissa, Andhra Pradesh, and West Bengal, respectively. Run-off was significantly (P < 0.05) greater in the fish ponds of Orissa compared to Andhra Pradesh and West Bengal (Table 7).

Total evaporation ranged from 157 to 176 (164 ± 8.3) cm throughout the year in the ponds of Orissa. Daily evaporation ranged from 0.43 to 0.48 cm/day with an average of 0.45 ± 0.02 cm/d (mean ± SD) from the ponds of Orissa (Tables 14). Total evaporation was 182 ± 12 cm in the ponds of Andhra Pradesh (Table 5) while the same was 152 ± 10 cm in the ponds of West Bengal (Table 6). Daily evaporation was 0.49 cm/d in Andhra Pradesh while the same was 0.41 cm/d over the year from the ponds of West Bengal. Significantly (P < 0.05) higher evaporation was measured from the ponds of West Bengal and Orissa compared to Andhra Pradesh (Table 7). The increase in evaporation was likely related to the reduction in rainfall and hotter and dryer conditions.

Daily seepage loss from the fishponds ranged from 0.14 to 0.24 cm/d with an average of 0.19 ± 0.04 cm/d (mean ± SD) over the year in Orissa (Tables 14). Daily seepage loss was 0.30 ± 0.04 cm/d from the ponds of Andhra Pradesh (Table 5) while the same was 0.24 ± 0.03 cm/d from the ponds of West Bengal throughout the year (Table 6). Seepage was significantly (P < 0.05) different among the fish ponds of the three states and greater seepage was measured from the fish ponds of Andhra Pradesh compared to West Bengal and Orissa (Table 7). Braaten & Flaherty (2000) reported that average pond seepage ranged from 0.23 to 0.69 cm/d, with an overall average of 0.50 cm/d for the shrimp ponds in Chachoengsao, Thailand.

The seepage rate of 31.0 mm/day, reported by Teichert-Coddington et al. (1988) was observed in ponds built in soils with unusually high iron and aluminum content which resulted in a granular soil structure and high permeability. The seepage rate of 1.2 mm/d in the Briggs & Funge-Smith (1994) study was estimated assuming that no seepage occurred from the pond bottoms. In the present study, seepage was calculated for the pond banks only. (As the pond bottoms were resting on the water table, seepage was calculated for the pond banks only). Yoo & Boyd (2012) reported that seepage rate varies greatly among ponds, and that some ponds may lose a considerable volume of water to seepage. They also reported that properly constructed ponds often have seepage rates below 0.1 inches/d (2.54 mm/d), and few seep more than 0.25 inches/d (6.35 mm/d).

Total water use is the amount of water entering into an aquaculture pond through rainfall, run-off, and other natural processes like seepage in, and water added from a well or canal for management purposes. Total water use varied from 327 to 367 cm in a year (throughout the year) in the aquaculture of Puri, Kendrapara, Cuttack and Jajpur districts of Orissa. Total water use was 432 cm in Krishna and West Godavari districts of Andhra Pradesh while it was 348 cm in the districts of North and South 24 Paraganas of West Bengal.

Consumptive water use for an aquaculture pond consists of water losses due to evaporation and seepage. Accordingly, the consumptive water use was 0.67, 0.62, 0.67, and 0.64 cm/d (mean 0.65 cm/d), respectively in Puri, Kendrapara, Cuttack, and Jajpur districts of Orissa (Tables 14). The consumptive use of water was 0.80 cm/d in Krishna, and Godavari districts of Andhra Pradesh (Table 5) while the same was 0.66 cm/d in South and North 24 Paraganas districts of West Bengal (Table 6). These water use rates are comparable to the 0.63 to 0.95 cm/d in eight brackish water shrimp ponds in Chachoengsao, Thailand (Braaten & Flaherty 2000). It was also reported that the water use rates were 1.16 and 0.87 cm/d in catfish ponds in Alabama and fish ponds in Honduras (Boyd 1985; Green & Boyd 1995). The water use rates for coastal shrimp ponds were 0.71 cm/d in Thailand (Briggs & Funge-Smith 1994).

All freshwater withdrawn from ground water by wells should be included as a consumptive use, because this water would not be available to other users of ground water in the area. Although ground water is recharged by infiltration, it is removed sometimes by wells at a rate exceeding recharge. This diminishes the amount of water available from wells in the area. Ground water depletion is usually more serious in arid than in humid climates, but even in humid climates, availability of water from wells may be reduced during the dry season and especially during drought. During high rainfall periods, the rainfall flux could dominate as the water source to the ponds, and regulated water inflow would be less significant. During dry periods, the opposite could be true.

Consumptive water use could also be computed in terms of production. The fish production was 6,250 to 8,000 kg/ha in the districts of Orissa. Consumptive water use was 2.83 to 3.90 (3.34 ± 0.47) m3/kg in these districts of Orissa. The water productivity varied from 0.176 to 0.244 (0.205 ± 0.03) kg/m3 in Orissa (Tables 14). The fish production in Krishna and West Godavari districts in Andhra Pradesh was 10,000 to 12,000 kg/ha. Consumptive water use was 2.43 to 2.92 (2.67 ± 0.23) m3/kg fish. The water productivity varied from 0.230 to 0.277 (0.25 ± 0.03) kg/m3 in Andhra Pradesh (Table 5). The fish production in North and South 24 Paraganas districts in West Bengal was reported to be 6,250 to 8,500 kg/ha. Accordingly, the consumptive water use was 2.84 to 3.87 (3.35 ± 0.36) m3/kg of fish. The water productivity ranged from 0.18 to 0.24 (0.21 ± 0.03) kg/m3 in West Bengal (Table 6). Significantly (P < 0.05) greater consumptive water use was determined for the fish ponds of West Bengal and Orissa compared to Andhra Pradesh (Table 7). It is evident that consumptive water use decreased with the increase of fish production without any negative impact on the environment and could be one option for the lower requirement of consumptive water use.

Aquaculture depends upon a constant supply of water, and the total volume of water used is greater than the consumptive use of water. If freshwater availability reduces under the climate change scenario, then this water budget could play a vital role where water requirements are to be projected in the planning phase of operations before physical ponds exist. This water budget could likely be beneficial in regional-scale planning and evaluation of alternate water uses.

ACKNOWLEDGEMENTS

The authors are grateful to the Director of ICAR-Central Institute of Freshwater Aquaculture for providing the necessary facilities to carry out the present work. The authors are also grateful to the farmers for their generous help for carrying out the present study in their ponds.

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