8 June 2010 Growth performance of sex-reversed Nile tilapia (Oreochromis niloticus, Linnaeus) cage cultured in a waste-fed freshwater wetland Adity Sarbajna, 1 Sandipan Gupta, 2 Suman Bhusan Chakraborty, 3 and Samir Banerjee4 Currently, tilapia culture is widely practiced in many tropical and subtropical regions of the world as the cheap source of animal protein (Guerrero 1982, Alvendia-Casauay and Carino 1988) and it is the second largest group of farmed finfish species, only after carp (Popma and Masser 1999). Tilapia has been described as the most important aquaculture species of 21st century (Shelton 2002). Several studies have been conducted to increase tilapia production and it has been observed that androgen treated, all-male tilapia populations grow faster than untreated, mixed-sex tilapia populations (Guerrero and Guerrero 1975, Hanson et.al.1983, Muhaya 1985, Jae-Yoon Jo et.al.1988, Pandian and Varadaraj 1988). Tilapia have been considered as a suitable species for cage culture by many workers (Coche 1982, Rackoy and McGinty 1989, Santiago and Arcilla 1993, Masser 1997, Dikel et. al. 2005) and can be grown to market size in cages without hampering the culture of other fish species in the same pond. In India, the utilization of wastewater for aquaculture purposes has been practiced from a long time (Ghosh 1990, Krishnamoorthi 1990, Jana 1998, Bansal et.al. 2007). The organic load of the discharged wastes provides an excellent source of nutrients for the growing fish and thus reduces the extra costs associated with providing supplemental food (Raychaudhuri et.al.2008). Inasmuch as tilapia are adaptable to poor water quality conditions (Popma and Masser 1999), they are suitable for culture in waste fed freshwater ecosystems. No work has previously been done in India to determine the growth performance of tilapia in cages in waste-fed freshwater wetlands. Therefore, the main aim of our study was to examine the growth potential of sex reversed tilapia in cage culture in a waste fed freshwater ecosystem. Study Methods Collection and Acclimatization of the fish Juveniles of a pure strain of Oreochromis niloticus (Linnaeus) were collected from a fish hatchery, Naihati, West Bengal and were acclimatized to laboratory conditions. They were kept in 5 L glass tanks under similar photoperiod (14 L:10 D), temperature (27 ± 2ºC) and density (10 fish/L). Preparation of Hormone Treated Food A fry feed, crude protein content 30 percent and total digestible energy 3000 ± 400 kcal/kg, was prepared from a mixture of fine fish meal, rice bran and other ingredients and sieved to a size of less than 1 mm. Hormone treated diet was prepared by the alcohol evaporation technique (Shelton et. al. 1978). The synthetic androgen, 17α-methyl testosterone (17α MT; “Sigma” St. Louis, Missouri USA) was dissolved in 95 percent ethanol and then mixed with the pellets (1 L ethanol/kg pellets). The 17α MT containing wet pellets were dried in the open air. Control pellets were prepared similarly without the addition of 17α MT. Fresh food was prepared weekly and stored in a cool place. Hormonal Treatment One group of juveniles was fed the hormone treated diet daily at 10 mg/kg for 30 days (Chakraborty et.al. 2007) and the other group was fed the control diet at the same rate for the same duration. After one month, about 98 percent males was obtained from the hormone treated group and a ratio of Photograph of hormone treated (A) and control (B) tilapia at the time of final harvest.
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