2.1 Conventional and Organic Culture System
In the present study, Indian major carps were cultured following two different management practices - (a) Conventional Culture System (CCS) (with commercial fish feed and organic and inorganic fertilizer) and (b) Organic Culture System (OCS) (with organic fertilizer and organic fish feed). Each of the above culture practices was replicated thrice. Six ponds existing on the experimental farm, each measuring 0.015 ha, were used in the study. A schematic diagram showing the layouts of the culture ponds for CCS and OCS, organic crop fields and vermicompost unit are presented in Fig. 1. A schematic diagram showing the various inputs used in OCS and CCS is presented in Fig. 2.
In CCS, ponds were fertilized with cow dung at the rate of 1,250 kg ha− 1, 31 kg ha− 1 of urea and 16 kg ha− 1 of triple super phosphate (TSP). In case of OCS, ponds were fertilized with organic compost comprising vermicompost and vermibed-wash at the rate of 12,443 kg ha− 1and 93.33 liters ha− 1 respectively (Chakraborty et al., 2009). Fertilization was carried one week before stocking, followed by biweekly application for the entire duration of the study period. Vermicompost as well as vermibed-wash were distributed uniformly over the water surface of the ponds. The fingerlings of three Indian major carps, Catla, (Catla catla, Hamilton), Rohu (Labeo rohita, Hamilton,) and Mrigal (Cirrhinus mrigala, Hamilton) were stocked at the rate of 10,000 fingerlings ha− 1 with combinations of Catla 40%, Rohu 30%, and Mrigal 30%. Seed stocks of equal size were of good quality and disease free with good growth rate (Xie et al., 2011), while, fish fingerlings were genetic modified organism (GMO) free and genetic engineering free. Stocking was done in the early mornings, generally before 9.30 a.m. when the temperature of water was low. Before stocking, the fish seed was kept in a bath in 2% NaCl solution for 1–2 minute and was well acclimatized to pond water. The mean initial weight of species stocked were – Catla: 25.5 ± 1.09 g, Rohu: 22.5 ± 1.08 g and Mrigal: 21.3 ± 1.06 g. In CCS, commercial feed and antibiotics were used. The commercial fish feed was pelleted feed (2–4 mm diameter) produced by a local commercial fish feed company. In OCS, earthworm and organically grown protein and oil rich crops - soybean and maize were used as ingredients of organic pelleted fish feed. The crude protein content of the organic and conventional feed was maintained at iso-nitrogenous (32% crude protein).
The harvesting of fishes was done through the repeated netting and draining of ponds at the end of 9 months of the culture period. Each species was harvested by draining the ponds. The fishes were recorded for calculation of survival rates and various yield parameters. The harvested fishes from conventional and organic ponds were gathered in different tanks. The sale price of fishes was primarily dependent on weight at the time of harvesting and type of culture provided. The organically grown fish fetched approximately 30% higher price than that of conventionally grown fish. Sale price of conventionally grown fish (non-organic) was US$ 2.17 kg− 1, the average weight being above 600 g (Catla: 630 ± 5.6 g, Rohu: 670 ± 5.5g and Mrigal: 504 ± 5.3 g) and for the organically grown fishes, the sale price was US$ 2.75 kg− 1, where average fish weight was above 700 g (Catla 709.5 ± 4.3g, Rohu 708.4 ± 4.2 g and Mrigal 547.7 ± 4.2g), in local fish market, Kharagpur, West Bengal, India.
2.2 Economic analysis
The economic analysis included (i) determination of expenditure and income; (ii) profit; (iii) payback period; (iv) net present value and (v) internal rate of return. The field trials were carried out on ponds with 0.015 ha area. The returns on such small pond area are very less and at times can be negative also. Therefore, to compare the economics of different alternatives one hectare pond area has been considered. The cost of various items has been suitably scaled up for 1.0 ha area based on the cost involved in 0.015 ha area and making adjustments wherever necessary. In fact, average weight of fish at the same stocking density and under the same management practice is expected to be more in relatively bigger sized ponds with the same depth. In bigger sized ponds, a fish can traverse a greater distance and therefore, exercise more leading to better growth. Therefore, the analysis made based on the yield of smaller ponds is on the safer side. In case of OCS, the area required for vermicomposting unit and organically grown maize and soybean crop are suitably scaled up to meet the demand for one hectare organic fish pond. The costs of various items were suitably scaled up for 1.0 ha area based on the costs involved in a 0.015 ha area. The profit, payback period, net present value (NPV), and internal rate of return (IRR) were calculated for CCS and OCS using the following formulae (Mal, 1995):
Profit = Income - operating cost … (1)
Payback period = Initial outlay (IO)/cash flow … (2)
Internal rate of return (IRR) was calculated by determining the value of the discount rate at which NPV becomes zero.
The cost analysis of CCS and OCS includes two types of costs: (a) Initial Investment cost for creation of facility of culturing fishes and the (b) variable costs involving the maintenance costs of the fishpond, land lease cost, cost of fingerlings, cost of feed, fertilizer and production cost of field crops.
(a) Initial investment
The initial investment includes the cost of (i) pond construction, (ii) water facilities and (iii) vermicomposting unit.
(i) Pond construction
Earthwork for construction of the ponds was carried out by engaging a contractor who executed the work by engaging daily labourers. The work was carried out according to the requirement of the site. As the soil cannot retain water, it was felt necessary to use lining material on the excavated ponds. Therefore, steps were made from ground level to the bottom of the fishpond for better anchoring of the lining material. Prismoidal formula was used to compute the volume of earthwork. The cost of earthwork was paid to the contractor as per the schedule of rates 2010 of the Public Works Department (PWD), Government of West Bengal, India. As per the schedule, the cost of earthwork for first 1.5 m depth (lift) was US$ 0.29 m− 3 and US$ 0.40 m− 3 for next 1.5 m depth. The price of lining includes the cost of lining material and labour wage to spread and bury it with soil. Cross laminated polythene sheet of Sylpaulin make (250 µ thick, 150 g m− 2 weight, UV ray protectable and green in color) was used for lining of the dugout fishpond. The actual price of the Sylpaulin sheet charged by the authorized dealer was considered to compute the cost of lining material. The price was US$ 0.51 m− 2 in 2010. Labour wage required to spread the polythene sheet on the bottom and sides, including the embankment and to bury the same with a soil layer of 30 cm thickness was paid as per the schedule of rate of Government of West Bengal, India, 2010. Before laying the cross laminated polythene Sylpaulin material on the bed of the fish ponds, a sand cushioning was provided to a depth of 20 cm to avoid any rupture. After laying the Sylpaulin material, a soil cover of 30 cm thickness was also provided on the lining material to provide stability to the material and create a natural pond bottom environment for fish culture. The number of labourers required for the job was 5 man-days for sand filling, earth filling and providing lining material in one pond.
(ii) Water facilities
A mini deep tubewell along with underground pipe lines and accessories was constructed for regular water supply to the fish ponds as and when necessary.
(iii) Vermicompost unit
The cost for vermicompost unit included the maintenance costs of the land and building, civil works for vermicompost shed and vermicompost tanks, implements and machinery and others work.
(b) Variable cost
The variable cost included maintenance costs of the fishpond, land lease cost, cost of fingerlings, cost of feed, fertilizer and production cost of field crops.
(i) Fishpond maintenance cost
The Maintenance cost of the fishpond involves the expenditure incurred for repair and maintenance of the embankment. The cost has been assumed to be 2% of the initial investment (Palmer et al., 1982 and Mishra et al., 1998).
(ii) Land lease cost
It was thought appropriate to add the annual land lease cost for the area diverted for the construction of fishpond. The cost was decided based on prevailing lease rate under the revenue district of West Medinipore, West Bengal. The cost was found to be US$ 60.71 ha− 1 year − 1 as per the rate of 2010.
(iii) Fingerling Cost
Fingerlings were purchased from a nearby farm for stocking in the fishponds. The cost of fingerlings varies depending on the size, weight etc. Fingerlings were purchased at 2.17 US$ kg− 1and later released to the fishponds after acclimatizing them in an earthen tank for 40 hours.
(iv) Feed and fertilizer cost
The organic fish feed was prepared in the laboratory with due proximate composition of suitable protein, carbohydrate, fat, ash, etc. Conventional feed were bought from the local feed company and the formulated fish feed cost was only US$ 0.51 kg− 1 at the prevailing cost of inputs in 2010. The chemical fertilizer cost was calculated as per the local market price.