| Summary: | Fingerlings of three major carps viz. Catla catla, Labeo rohita and Cirrhina mrigala, were exposed to sub-lethal concentrations of manganese for 30 days. During the exposure period, all three fish species showed negative growth with weight increment values of -0.22, -0.72 and -3.90g, respectively. At the end of stress trial, both treated and control fish were shifted to out-door earthen ponds for semi-intensive culture and monitored for a period of six months. The ponds were fertilized with poultry droppings at the rate of 0.16g nitrogen per 100g net fish weight daily. Moreover, supplementary feed (35% digestible protein) was also dispensed to fish. Analysis of variance on wet weight, fork and total length of three fish species showed that the fortnights, species and treatments exerted significant effects (p<0.01). Among three fish species, Catla catla gained significantly higher weight, followed by Labeo rohita and Cirrhina mrigala. Cirrhina mrigala showed significantly higher value of fork and total lengths, followed by Catla catla and Labeo rohita. However, control fish showed significantly higher weights, fork and total lengths as compared to stressed fish reared under semi-intensive culture system. On the basis of this investigation, it was concluded that stressed major carps under sub-lethal concentrations of manganese showed significantly lower values of weight, fork and total lengths than control fish when reared under semi-intensive culture system.
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