WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2025 65 Catla (Catla catla), rohu (Labeo rohita), tilapia (Oreochromis niloticus) and pangasius (Pangasius sp.) are some of the most suitable species for aquaculture in an abandoned coal pit. One abandoned coal mine led to the creation of a huge water body having a maximum depth of around 300 feet. Due to the high depth, fish are being reared in both submerged and floating cages. Fish production of 2 tons of fish per cage has been attained with the culture of pangasius and tilapia. Physicochemical Properties and Heavy Metal Concentration in Coal Pits One of the major concerns with aquaculture in mine pits is related to the accumulation of heavy metals in the muscle of the fish and the potential risk to human health if the fish is consumed. The human body needs trace heavy metals, but many poisonous heavy metals such as lead, mercury, aluminum, arsenic, cadmium, nickel and copper can cause hazards to human health (Singh 2014). Thus, it is important to set standards to monitor the water quality parameters and metal concentration in both water and fish. Several water quality parameters, including pH, hardness, suspended solids, temperature, dissolved oxygen, alkalinity, and others have been shown to influence the speciation, and thus bioavailability of metals. For example, at low pH, the toxicity of copper is higher as it tends to be present as a free ion. Acid rock drainage and pyrite have been described as major environmental liabilities to reduce the water pH, which cannot be corrected with lime application. In the presence of oxygen, pyrite reacts with water and forms sulfuric acid, occasionally lowering pH values to 4 or less. Innovative Methods to Enhance Water Quality Some abandoned coal mines lead to the creation of huge water bodes that are difficult or impossible to treat. However, for smaller water bodies various methods can be applied to remove heavy metals. Biosorption is an effective and eco-friendly technology that reduces the concentration of heavy metals in pits (Staszak et al. 2024). This method is based on the utilization of various agro- and plant-generated waste, aquatic plants (e.g. Eichhornia, Azolla) and microbial biomass. Biosorption is an independent method; a wide variety of tools, such as rice and wheat husks, activated carbon, agricultural waste, bananas and citrus peels, and green-synthesized nanoparticles can be effectively used for biosorption. Growth of algae blooms scavenge the water of dissolved zinc, copper and cadmium. Liming is another method to improve the water quality parameters and increase pH up to the desired level, but the quantity of lime required depends upon the pH of the water. Application of lime not only increases the pH of the water but also reduces the suspended particles and improves the productivity of these water bodies. This also reduces the bioaccumulation of heavy metals in fish muscle by reducing the culture period. Case Study (I): Fish Farming in Coal Mine Pit at Surajpur, Chhattisgarh Surajpur is one of the districts of Chhattisgarh, situated 334 km away from the state’s capital city, having a total geographical area of 2,786.76 km2. Surajpur, Korba and Korea are wellknown for having large coal reserves, contributing a significant quantity to the total coal supply of India. An abandoned coal pit covering 10.50 acres and stretching 1.75 kilometres, filled with water and resulted in a huge body of water having a maximum depth of 350 meters. South Eastern Coalfield Ltd of CIL initiated efforts to convert the abandoned coal mine to yield promising benefits in Chhattisgarh. To utilize the abandoned coal pit for incomegenerating activities district administration came up with the idea of fish farming through submerged cage culture and boating. During 2018-19, SECL provided financial help to start a boating facility and 32 submersed cages for fish culture on an experimental basis to generate sustainable livelihoods for locals. A cooperative society was formed, named “Mahamaya Fisheries Society” for fish culture and “Shiv Shakti Mahila Gram Sanghathan” to manage the boating facility. The members of the cooperative received training on capacity building and skills. The society has earned Rs 15 lakh selling 17 tons of fish. Heavy metal concentrations in the coal mine water in Surajpur were evaluated, with concentrations of Fe and Zn found to be highest, followed by Mn, Cu, Ni, Hg and Co, in that order (Table 1). When humans consume fish contaminated with such heavy metals, these substances can interfere with enzymatic activities (Ismail and Moustafa 2016, Prasetiyono and Syaputra 2018), but the concentration of heavy metals is typically lower in fish muscle because it is not actively accumulating heavy metals (Bahnasawy et al. 2009). Nile tilapia (Oreochromis niloticus) is cultured in a cage in the coal mine water body; however, the growth rate of fish is somewhat reduced when compared to normal ponds and reservoirs and they require a longer time (7-8 months) to achieve marketable size (CONTINUED ON PAGE 66) FIGURE 2 (A). Growth rate of tilapia in cage culture in abandoned coal mine. Chhattisgarh. FIGURE 2 (B). Growth rate of tilapia in cage culture in abandoned coal mine. Chhattisgarh.
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