author(s)
Safina Kousar, Muhammad Javed, Muazzma Akhter and Sajid Nadeem

abstract
During this investigation, the growth performance (wet weight and length) of three fish types was studied under the sub-lethal nickel (Ni²⁺) concentrations of 70.40g, 71.99g and 79.11g for Catla catla, Labeo rohita and Cirrhina mrigala, respectively. The increase in fish weight was monitored in glass aquaria for eight weeks. During these metal-stress trials, fish were kept under constant temperature (30 °C), pH (7.0) and total hardness (200 mg·L‾¹). Physio-chemical variables, e.g. dissolved O₂, Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₂, total NH₃ and electrical conductivity of the test mediums used for each growth trial were recorded on a daily basis. An increase/decrease in wet weight, fork and total length of fish were monitored on the Fortifying basis for eight weeks of growth trial. Statistical analysis of the research data showed significant effects of metal stress on wet weights. Among the three treated fish species, Catla catla gained significantly maximum weight of 18.28 ± 0.95g, followed by Labeo rohita (16.18 ± 0.89) and Cirrhina mrigala (15.25 ± 1.15g). Fork and total length increments were observed significantly higher in Catla catla, followed by Labeo rohita and Cirrhina mrigala. However, under the exposure of nickel, all the fish species showed considerably lower weights than the control fish. It was concluded that sub-lethal metal (nickel) exposure to the fish significantly affected the growth performance (weights, fork and total length gains) and feed conversion ratios (FCR) of all the three fish species.