WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2023 33 FIGURE 7. Sorted fish being weighed before marketing. to utilize resources of the entire water body. Indigenous and exotic carps were reared with preferences: the preferred combination included Catla catla as a surface feeder, Labeo rohita as a column feeder, and Cirrhinus mrigala as a bottom feeder. A secondary species combination included Labeo bata and Cirrhinus reba while a third combination included Hypophthalmichthys molitrix, Oreochromis niloticus and O. mossambicus. However, these 1st, 2nd and 3rd combination options were intermixed based on culture feasibility, market demands and consumer preferences. Different species that were stocked in the range of 500-1200 kg/ha were usually advanced fingerlings, having the following weight ranges: Catla catla,10-25g; Labeo rohita,10-15g; Cirrhinus mrigala, 10-15g; Cyprinus carpio, 5-20g; Labeo bata, 5-10g; Cirrhinus reba, 5-10g; Hypophthalmichthys molitrix, 5-10g; and Oreochromis spp., 5-10g. Polyculture was adopted as a viable method and standardized ratios were obtained through repeated experience: Catla catla 20 percent, Labeo rohita 30 percent, Cirrhinus mrigala 20 percent, Hypophthalmichthys molitrix 20 percent and Oreochromis niloticus 10 percent. However, other cultivable species may have been incorporated on occasion based on consumer preference and market demands. Harvesting of fish took place throughout the year at 2 to 4-day intervals (Figure 5). Harvest weight of Indian major carps ranged from 200 to 500 g and that of exotic carps ranged from 400 to 1000 g (Figures 6a and b). All fish underwent depuration in a nearby freshwater pond immediately after harvest to release any odors resulting from the sewage-fed culture. Three criteria were considered before marketing fish, including: (1) skin luster, (2) health, and (3) activity (Figure 7), all of which consumers preferred when purchasing fish. Conclusions Fish eaters of Kolkata city, mostly the Bengali population, were fond of consuming this major source of protein in daily meals. When supplying a huge amount of fish daily to consumers, sewage-fed fish was the main resource to fill the demand. However, the hygiene of sewage-fed fish was a concern, to keep consumers safe as well as healthy. The Regional Research Centre of ICARCentral Institute of Freshwater Aquaculture, Kolkata, performed a study to determine the level of commonly used agricultural pesticides and heavy metals in fish harvested from EKW. These levels were found to be below detectable levels as per international standards. However, microbial loads were the main concern, with maximum levels found in gills, followed by the liver, intestine and muscle tissues. Dressing eliminated gill, liver and intestine concerns from raw fish, and muscle tissue was reported to be safe for consumption when cooked under high temperature. Evidently, consumers eating sewage-grown fish had not reported any health issues. Given consumers’ health as a priority, regular monitoring was necessary for evaluating chemical and microbial hazards from the sewage-fed system. A substantial number of daily consumers required a low-cost system of fish production. In this case EKW has had no alternatives. Acknowledgments P. K. Sahoo, Director of ICAR-Central Institute of Freshwater Aquaculture, Bhubaneswar, Odisha, India, 7150002 is duly acknowledged for the support of this study. Also, we acknowledge the scientific contribution to this study in East Kolkata Wetland by A. Das, A. Hussan and P. P. Chakrabarti. Notes R. N. Mandal*, S. Adhikari, B. N. Paul, and D. N. Chattopadhyay: Principal Scientists, and Farhana Hoque: Scientist, Regional Research Center, ICAR-CIFA, Rahara, Kolkata, W. B. India, 700118 * Corresponding author: email- rnmandal2003@yahoo.com References Bunting, S.W., J. Pretty, and P. Edwards. 2010. Wastewater-fed aquaculture in the East Kolkata Wetlands, India: anachronism or archetype for resilient aerocultures? Reviews in Aquaculture 2:138–153. Edwards, P. 2008. An increasingly secure future for wastewater-fed aquaculture in Kolkata, India? Aquaculture Asia 13(4):3–9. Ghosh, S. 2018. Waste water fed aquaculture in East Kolkata wetland: state-of-the-art and measures to protect biodiversity. Pages 119-137 In B.B. Jana, R. N. Mandal, and P. Jayasankar, editors. Wastewater Management through Aquaculture, Springer Nature Singapore Pte Ltd. DOI: 10.1007/978-981-10-7248-2 Mandal, R.N., P.P. Chakrabarti, B.N. Paul, D.N. Chattopadhyay, A. Das, A. Hussan and P. Jayasankar. 2018. Recycling of Sewage in Aquaculture: Decadal Technical Advancement. Pages 95-118 In B.B. Jana, R. N. Mandal and P. Jayasankar, editors. Wastewater Management through Aquaculture, Springer Nature Singapore Pte Ltd. DOI: 10.1007/978-981-10-7248-2 Mandal, R. N., P.P. Chakrabarti and P. Jayasankar. 2015. Sewage fed aquaculture: A viable proposition for fish production through nutrients recovery and water conservation, in effect of abating water pollution. Pages 93-113 In R.P. Singh and A. Sarkar, editors. Waste Management, Nova Scientific Publication, USA. Ramsar Convention Secretariat. 2010. Wise Use of Wetlands. Ramsar Handbooks for the Wise Use of Wetlands 4th ed.: Handbook 1. Ramsar Convention Secretariat, Gland, Switzerland.
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