Chronic effects of nickel and cobalt on fish growth

Chronic exposure impacts of waterborne and dietary nickel (Ni) and cobalt (Co) on the growth performance of juvenile major carps viz. Catla catla, Labeo rohita and Cirrhina mrigala were studied under static water bioassay. Fish growth was monitored in terms of wet weight and fork length increments, condition factor, feed intake and feed conversion efficiency (FCE). All the three treated fish species showed exploratory behavior during first few hours of both waterborne and dietary exposure of metals. However, these responses were more pronounced in the fish exposed to waterborne than that of dietary metals. The exposure of both Ni and Co caused significant effects on weight and fork length increments, feed intake and FCE of all the three fish species. Exposure of waterborne metals caused significantly lower weight and fork length gains to all the three fish species, while feed intake, FCE and condition factor were significantly better due to dietary treatments. All the three control fish species exhibited significantly higher feed intakes that resulted into significantly better FCE than the fish either exposed to waterborne or dietary metals. Dietary exposure of both Ni and Co increased the feed intake by the fish that showed positive relationship with its growth, while waterborne exposure of both metals resulted into significant loss of apatite to cause significant reduction in growth of all the three fish species. L. rohita showed significantly higher sensitivity to metallic toxicity as evident from its lower weight increment than C. mrigala, while the difference between C. catla and L. rohita was non-significant. The condition factor and feed intake of all the three fish species did not change significantly due to the toxicity of both waterborne and dietary exposure of metals. The response of three fish species towards FCE fluctuated significantly that followed the order: C. mrigala greater than L. rohita greater than C. catla.