NEED OF GUIDANCE AT SECONDARY SCHOOL LEVEL

Abstract

Laboratory tests were conducted to determine the acute toxicity of Al, As, Ba, Cr and HMM, in terms of 96-hr LC50 and lethal concentrations, to three age groups viz. 60-, 120- and 240-day of Catla catla, Labeo rohita and Cirrhina mrigala at constant water temperature (30oC), pH (7.50) and total hardness (300 mgL-1). The growth performance, condition factor, feed intake and feed conversion efficiency of 240-day three fish species viz. Catla catla, Labeo rohita and Cirrhina mrigala under chronic (1/3 of LC50)exposures of Al, As, Ba, Cr and their mixture for 90 days were also determined. The fish were fed with feed (34% DP and 3.00 Kcalg-1 DE) to satiation daily. At termination of each trial, the fish were dissected and their organs viz. bones, gills, gut, intestine, kidney, liver, scales, skin, muscle and fats isolated for the determination of metal concentrations. The toxicity of aluminium, arsenic, barium and chromium to the three fish species viz. Catla catla, Labeo rohita and Cirrhina mrigala fluctuated significantly as a function of their diverse physico-chemical characteristics. The 60-day all the three fish species showed significantly higher sensitivity to all metals and their mixture while 240-day fish were significantly least sensitive. Catla catla were significantly more sensitivity to arsenic, followed by the sensitivity caused by metal mixture, chromium, aluminium and barium with the mean 96-hr LC50 values of 7.96 ± 1.40, 27.35 ± 9.17, 77.01 ± 22.47, 81.68 ± 28.54 and 112.45 ± 31.35 mgL-1, respectively. Labeo rohita were significantly least sensitive against barium (126.12 ± 22.76 mgL-1) while Cirrhina mrigala to aluminium with the mean concentration of 118.36 ± 28.91 mgL-1. Significant variations in the sensitivity of Catla catla, Labeo rohita and Cirrhina mrigala to various metals appeared species specific depending upon the nature of metals, exposure concentration and properties of water viz. water temperature, dissolved oxygen contents and pH. Exposure of aluminium to the fish caused significantly higher mean metal in the fish body, followed by that of barium, chromium and arsenic with statistically significant differences. Fish organs showed significantly variable ability to concentrate metals and therefore liver and kidney exhibited relatively high potentials for metals accumulation during short term (96-hr) acute exposures. All the three control (un-stressed) fish species exhibited significantly better growth due to significantly higher feed intakes than those grown under sub-lethal toxicity of either individual metals or metal mixture. Cirrhina mrigala gained significantly higher weight gains, followed by that of Catla catla and Labeo rohita under metal stress. All the three fish species showed significantly variable responses, in terms of increase in wet weights, fork and total lengths, feed intake and feed conversion ratios, due to chronic sub-lethal exposure to either individual metals viz. Al, As, Ba, Cr and mixture. However, all the three control (un-stressed) fish species exhibited significantly better growth due to significantly higher feed intakes than those grown under sub-lethal toxicity of either individual metals or metal mixture. The exposure of metal mixture (Al + As + Ba + Cr) caused significantly least growth, in terms of mean wet weights, in all the three fish species indicating a metal combination (Al + As + Ba + Cr) to be additive or synergistic in their mode of action in fish body. Among the three fish species, Cirrhina mrigala gained significantly higher weight gains, followed by that of Catla catla and Labeo rohita under metal stress. However, the difference between Catla catla and Labeo rohita for their growth rates was statistically non-significant. Therefore, lesser growth as a result of low feed utilization and feed conversion efficiency in fish, during sub-lethal exposure of metals and metal mixture, exhibited impaired normal 1 physiological functions in fish. Among the individual metals, chromium exposure caused significantly minimal effects on feed conversion efficiency of all the three fish species. The exposure of fish to individual metals viz. aluminium, arsenic, barium and chromium, during 90-day growth trials, caused significantly variable accumulation of these metals in the body organs of three fish species. However, fish liver, kidney and gills accumulated significant amounts of heavy metals. Three fish species also showed significantly variable responses for their tendencies to accumulate metals in their body organs. The exposure of metal mixture (Al + As + Ba + Cr) to all the three fish species caused significant accumulation of all metals in the fish liver, except arsenic in Labeo rohita. However, metal mixture exposure to all the three fish species caused significantly least accumulation of all metals in body fats. Among the three fish species, Cirrhina mrigala showed significantly higher ability to concentrate all the metals in their body organs.