ASSESSMENT OF GROWTH AND GENOTOXICITY IN PERIPHERAL BLOOD ERYTHROCYTES OF FISH EXPOSED TO METALS TOXICITY

Abstract

The assessment of growth and genotoxicity in peripheral blood erythrocytes of fish exposed to metals toxicity was conducted in three phases i.e. (i) toxicity of metals to the fish, (ii) chronic effects of metals on fish growth and (iii) genotoxic effects of metals in fish. Acute toxicity of aluminum, arsenic, copper, nickel, zinc and Al+As+Cu+Ni+Zn mixture (MM) was determined, in-terms of 96-hr LC 50 and lethal concentrations, for three age groups of four fish species viz. Labeo rohita, Cirrhina mrigala, Catla catla and Ctenopharyngodon idella under controlled laboratory conditions. Accumulation of metals in fish organs at 96-hr LC 50 and lethal concentrations were also determined. Fish growth performances in-terms of increase in wet weights, fork and total lengths, condition factor, feed intake, feed conversion efficiency and specific growth rate of 150-day old Labeo rohita, Cirrhina mrigala, Catla catla and Ctenopharyngodon idella, were monitored under sub-lethal chronic exposure of aluminum, arsenic, copper, nickel, zinc and MM, separately. After 150-day growth trials, fish organs viz. liver, kidney, gills, gut, muscles, bones, skin, fins and scales were analyzed for their respective exposure metals and MM. During 3 rd phase, all the four fish species were exposed, separately, to four sub-lethal concentrations viz. 17, 25, 33 and 50% of aluminum, arsenic, copper, nickel, zinc and MM LC 50 for 30 days. Fish blood samples were analyzed through Comet assay and Micronucleus test to determine genotoxic effects of individual metals and MM on fish. The extent of DNA damage was measured in-terms of mean percentage of damaged cells, genetic damage index (GDI) and cumulative tail length (μm) of comets, frequency of micronuclei and other nuclear abnormalities viz. bi-nucleated, dumble, blebbed, notched and de-shaped nuclei. Among the four fish species, Catla catla were significantly more sensitive to individual metals and MM while Labeo rohita showed significantly least sensitivity. The 150-day age groups of all fish species were found significantly (p<0.05) least sensitive to all metals, followed by that of 120- and 90-day fish. However, sensitivity of all age groups of fish, in-terms of 96-hr LC 50 , towards individual metals and MM followed the order: MM > copper > arsenic > nickel > aluminum > zinc while for lethal concentrations it was: MM > copper > arsenic > nickel > zinc > aluminum. All the fish species were significantly more sensitive to MM than all the individual metals. Therefore, metals in a mixture form exhibited additive effects towards sensitivity of all the four fish species under study. All the four fish species showed significantly variable ability to bio- accumulate metals in their bodies, during acute exposures. Overall accumulation of aluminum, arsenic and copper in all the four fish species followed the order: Ctenopharyngodon idella > Cirrhina mrigala > Labeo rohita > Catla catla. However, the accumulations of both nickel and zinc were significantly maximum in Cirrhina mrigala. Accumulations of aluminum, nickel and zinc were significantly maximum in fish liver while kidney showed significantly higher tendency to concentrate arsenic and copper. However, fish scales and fins showed significantly lower ability to amass all these metals. The chronic exposure of individual metals (aluminum, arsenic, copper, nickel, zinc) and MM exerted significant impacts on the growth performance of all the four fish species. All control fish species exhibited significantly better growth than the treated fish. However, exposure of MM caused significantly lowest increments in wet weights and lengths of fish. Both MM and arsenic exposures caused significant impacts on fish growth, followed by that of copper, nickel, aluminum and zinc. Among metals exposed fish, Labeo rohita showed significantly higher growth, followed by that of Catla catla, XXICirrhina mrigala and Ctenopharyngodon idella. The overall ability of four fish species to convert feed into mass was significantly higher for Catla catla with the mean FCE of 90.15±10.65 %. However, Cirrhina mrigala showed significantly minimum FCE of 88.22±12.82 %. Therefore, fish growth has appeared a reliable end point of chronic stress of metals in order to predict the physiological course of action in estimating their impacts related with feed intake, metabolism and assimilation by the four fish species under study. The fish body organs showed significant variability in their tendency to accumulate metals. Fish liver, kidney, gills and gut accumulated significantly higher amounts of aluminum, arsenic, copper, nickel and zinc while minimum accumulation of all these metals were observed in fish fins and scales. All the four fish species showed significant differences in their ability to concentrate metals under chronic exposure of MM. However, Ctenopharyngodon idella and Cirrhina mrigala showed significantly higher ability to bio-accumulate metals than Labeo rohita and Catla catla. The DNA damage determined in-terms of percentage of damaged cells, GDI and cumulative tail length of comets, micronuclei frequency and frequency of other nuclear abnormalities varied significantly due to exposure of various concentrations of individual metals (aluminum, arsenic, copper, nickel and zinc) and MM. Among the four fish species, Cirrhina mrigala were significantly more susceptible to metal’s toxicity as it had significantly higher percentage of DNA damaged cells, GDI, cumulative tail length of comets, frequency of micronuclei and other nuclear abnormalities while Catla catla appeared significantly least sensitive. The toxic potential of metals to induce DNA damage in the peripheral erythrocytes of four fish species in-terms of percentage of damaged cells, GDI and micronuclei frequency followed the order: arsenic > MM ≥ zinc > aluminum > copper > nickel while cumulative tail length of comets was affected significantly due to arsenic > MM > aluminum > copper > nickel > zinc. Labeo rohita, Cirrhina mrigala, Catla catla and Ctenopharyngodon idella, of 90-, 120- and 150-day age groups, showed variable responses towards aluminum, arsenic, copper, nickel, zinc and MM toxicity due to their physiological differences and species-specificity to interact against various metals. Moreover, the genotoxic potentials of aluminum, arsenic, copper, nickel, zinc and MM suggested a serious concern towards their potential danger to the survival and growth of fish, under study, in the natural aquatic habitats. Therefore, it is concluded that by using Comet assay and micronucleus test, Labeo rohita, Cirrhina mrigala, Catla catla and Ctenopharyngodon idella can suitably be used as bio- indicators of metallic ion pollution in the natural aquatic habitats.