Abstract
Effects of exposure of common carp juveniles (Cyprinus carpio L.) to dietary copper and its recovery rate were investigated with the aim of determining the growth and physiological impact. The fish were fed elevated copper diets (1000 mgCukg-1 and 2000 mgCukg-1 as diet 2 and diet 3 respectively) and control diet (5 mgCukg-1, as diet 1) for 42days and were then fed the control diet for a further 21days. After 42days of exposure to elevated copper diets, growth performance examined showed that there was significant increase at (p 0.05). Hepatosomatic index increased significantly in fish fed both elevated diets compared to control diet (p 0.05), but, fish fed diet 2 showed a significant reduction in condition factor compared to other diets (p<0.05). Tissue Na+, Ca2+ K+ were disturbed throughout the experiment with sodium increasing from 257.82 ± 2.50 μmol/g to 388.14 ± 1.32μmol/g and calcium increasing from 499.54 ± 6.81 μmolg-1 to 1025.94 ± 9.16 μmolg-1 reducing gill copper from 11.63 ± 0.37 mgCukg-1to 0.00 ± 0.00mgCukg-1. Intestinal copper decreased from 14.93 ± 0.1 mgCukg-1 to 0.00 ± 0.00 mgCukg-1 as a result of sodium increasing from 130.30 ± 5.12 μmolg-1 to 438.72 ± 2.44 μmolg-1. The reduction in intestinal calcium was sodium dependent as increasing sodium decreased calcium absorption. Increased gill copper of the 1000 mgCukg-1 diet exposed fish during exposure compared to the control was due to copper induced decrease in plasma ion regulatory sodium (Na ATPase activity), which protected fish from direct toxicity effect and could also suggest another pathway other than the common Na/Cu apical channel shared between sodium and copper through which copper binds to fish gill; diet 2 fish showing significant increase at (p<0.05) in haematocrit, red blood cell, white blood cell and neutrophils, and a significant reduction in lymphocyte and mean cell hemoglobin compared to diet 1 and diet 3, (p<0.05). This increase in blood indices is indicative of stress onset to which fish fed diet 2 is subjected. Fish fed diet 3 showed significant reduction in haematocrit, red blood cell, white blood cell and increased lymphocyte (p<0.05) and became anaemic with severe skin discoloration, indicative of a worsening effect of excess dietary copper exposure on the fish. There were not significant differences in moisture content of all tissues during and after copper exposure (p<0.05), although, gills of fish fed diet 2 showed reduction in moisture compared to diet 1 and diet 3-fed fish for both exposure and recovery phases, increasing from 75.3 ± 3.20% to 79.5 ± 6.44% after recovery for 21 days. Gills of fish fed diet 3 also increased post-exposure, indicative of protection of the structural integrity of the gill to prevent hypoxia through oxygen supply from water.
Highlights
Copper is an essential trace element that plays a vital role in the physiology of animals for fetal growth and early post – natal development, for hemoglobin synthesis, connective tissue maturation especially in the cardiovascular system and in bones for proper nerve function and bone development, and inflammatory process
Histology, hematology as well as tissue ion and moisture were investigated during the two phase of the experiment water quality was monitored throughout the exposure phase and result showed that all parameters were within the range required and tolerated by common carp
This study is a first report of chronic dietary copper exposure/ toxicity in common carp; and overall, fish, in this research, accumulated excess copper in the liver and intestine
Summary
Copper is an essential trace element that plays a vital role in the physiology of animals for fetal growth and early post – natal development, for hemoglobin synthesis, connective tissue maturation especially in the cardiovascular system and in bones for proper nerve function and bone development, and inflammatory process It is involved in different biochemical process of animal metabolism such as: enzyme – co enzyme catalytic reactions. It is associated with the function of a number of enzymes such as oxygenases including cytochrome C oxidase and copper- zinc super oxide dismutase [1,2] and; ion transport for instance with ceruloplasmin (ferroxidase1), a putative copper transport protein required for the incorporation of iron into transferring for it is transport in plasma [3]. Symptoms include depression of growth, anaemia, bowing of legs, spontaneous fractures, ataxia of new borns, Cardiac and vascular disorders and a depigmentation, decrease in some organs weight, depressed reproductive performance including egg production.Copper, though essential in fish diet, can be harmful when large single or daily intake occurs
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