INTRODUCTION:

The advantages of industrial revolution and extension of industrial growth in the past few decades have added huge loads of pollutants into the environment. One of the most common forms of pollution in developing countries is aquatic pollution. Heavy metals are the most dangerous group of metals and metalloids on the basis of their toxicity and persistence in the environment¹. Hence, heavy metal pollution is considered to be major problem globally². Copper is a widespread heavy metal pollutant in the environment due to atmospheric deposition of metal dust released from anthropogenic activities^3,4,5 such as, mining and smelting processes, leaching from bedrocks, industrial and agricultural discharges, sewage treatment plants and antifouling paints^6,7.

Significant amounts of copper are found near the copper mines⁸. For several years, copper has been used as an effective algaecide and antiparasitic agent in aquatic operations⁹. It is also used as fungicide and herbicide in fish farming as prevention against fungal diseases¹⁰.

Copper is vital trace element essential for the health and proper functioning for the organisms it plays a important role in a extensive range of cellular functions. It acts as a necessary cofactor for antioxidant enzymes, supports cellular respiration and aids in neurotransmitter production. These functions collectively lend support to critical biological processes¹¹. Upon entry from the environment both through intake by water or diet, copper binds to α-globulin and subsequently distributed throughout various body tissues¹². Cu is required in very low (5-20µg/g) amounts^13,14, but it becomes more toxic when it exceeds more than 20µg/g, and can be harmful to fish, shellfish and other aquatic organisms. However, if used beyond limits, the accumulation of copper in an aquatic environment directly impacts man and the aquatic ecosystem, leading to cytotoxic, mutagenic, carcinogenic effects and imbalance to the biological systems¹⁵.

Copper sulphate is often used as an algaecide in commercial and recreational fish ponds to control growth of filamentous algae and copper is more toxic to fish including such cultured species catfish, cyprinids and salmonids¹⁶. Thus, treating plankton with Cu compounds may lead to Cu bioaccumulation and reaching a toxic level in fish. The toxic effect of copper is related to its capacity for catalyzing oxidative reactions and leading to the production of reactive oxygen species^17,18.

Cyprinus carpio, a ubiquitous inhabitant of freshwater bodies, has assumed centrality in such research endeavors¹⁹. The species sensitivity to changes in water quality renders it an invaluable indicator of environmental perturbations. Previous studies have suggested that copper infused waters induce a range of physiological and behavioral modifications in fish, underscoring the multifaceted impact of Cu on aquatic life^20,21. Hence, they are considered as appropriate indicators of aquatic environmental pollution²². In aquatic systems, fishes are good biomarkers for trace metal contamination²³.

Due to its delicious meat and economic reasons Common carp (Cyprinus carpio) is a highly cultured and popular food fish species¹⁹ and plays an important role in polyculture in ponds and reservoirs in all seasons^20,21. It is considered as one of the major food fishes and widely used for histological study. Histological studies of the organs are considered as decisive tools for the assessment of environmental toxicity.

The gills carry out the functions of respiration, osmoregulation and excretion of metabolic water product, remain in contact with external environment and is particularly sensitive to changes in the quality of water are considered to be the primary target of the contamination^24,25. Gill damage can be linked to impaired physiological function in fish and gill histology as a useful early-indicator to monitor fish health in the environment. Histological changes have been widely used as biomarkers in the evaluation of the health of fish, both in the laboratoryand field studies^24,26. Consequently, changes in fish gill morphology are commonly recognized responses to environmental stressors, such as copper²⁷. This study ventures to address these gaps through a meticulously designed investigation centered on the CuSO₄ a popular algaecide, fungicide and herbicide on the histology of gills of Cyprinus carpio.

MATERIAL AND METHODS:

Experimental Animal:

The healthy fresh water common carp Cyprinus carpio used as experimental animals were collected from local fish markets of Raipur (C.G.) and acclimatized in the laboratory for 10 days.

Test Chemical:

Analytical grade copper sulphate (CuSO_4.5H₂O) DJ0D702040 (Anhydrous) with 98% purity was taken from Merck Life Science Private Limited, Mumbai, India and used without purification for the experiment.

Determination of LC₅₀of Copper Sulphate:

The 96 hours Median lethal concentration (LC₅₀) of copper sulphate (4.9mg/L) was calculated by Mazandarani et al. (2015)²⁸ for Cyprinus carpio.

Experimental Design:

To determine toxicities of copper sulphate (CuSO_4.5H₂O), experimental fishes were divided into four groups (01 control + 3 treated) comprising of 10 fishes each. Fishes exposed to normal tap water acted as control while and those exposed to different sublethal concentrations of copper sulphate (1.0mg/L, 2.0mg/L and 2.5mg/L) acted as treated. The experimental duration was 28 days.

Histological Examination:

For histological analysis analysis sacrifices the c. carpio to remove gill. The gill tissues were taken out from both control and exposed fish and washed with saline water to remove blood and impurities. The gills were used for paraffin sectioning and the most widely used method for doing histological analysis. The gill was placed in specific fixatives. After 48-72hour, bouin’s preserve tissue pieces and washed over night in running tap water, dehydrated in ascending grades of alcohol, cleared in benzene and embedded in paraffin wax (60-62℃ melting point), section of 4-6µ thickness were cut though as Spencer’s rotary microtome and stained with hematoxylin and eosin and were examined as well as photographed were captured using a light microscope with 10/40X magnification of its objective lenses, as per the standard protocols²⁹.

RESULTS AND DISCUSSION:

Behavioral observation:

The exposure experiment conducted on C. carpio further elucidated the deleterious consequences of the sub lethal concentration of copper. The observed like erratic swimming, air gulping, schooling, imbalance equilibrium and body posture, increased surface activity, rapid opercular movements and excess amount of mucus secretion over the body are consistent with the recognized behavioral and physiological responses of fish were observed during experiment. The present findings align with previous research indicating that copper contamination can trigger a cascade of adverse effects in aquatic life^{1,30,31,32,33}.

Histology of gill:

In the present study, histological examination of gill of control and copper sulphate exposed Cyprinus carpio were done and comparisons made between the two at weekly intervals (0, 7, 14, 21 and 28 days). The gill tissues of C. carpio in the control group showed normal primary lamella (PL), secondary lamella (SL), mucus cell (MC), epithelial cell (EP), pillar cell (PL) and epithelium without oedema. The histology of gill exposed CuSO₄at the different time interval (0, 7, 14, 21 and 28 days) shows significant alteration from the control group. Most gill lesion types have been reported more frequently after exposure to CuSO₄incomparison to the control group (FIG. F). Experimental group showed histopathological changes, such as, oedema (OE), hyperplasia (HP), epithelium ruptured (ER) at 0 days/12hour of exposure (FIG. A). Hypertrophy (HT), tip ruptured (TR) at 7 days of exposure (FIG. B). curling tip (CT), clubbed off tip (Ct), Epithelium lifting (EL) at 14 days of exposure (FIG. C). swollen mucus cell (SM), curling tip (CT), shaft breakage (SB) and lamellar disorganization (LD) at 21 days of exposure (FIG. D) and curling of tip (CT), necrosis (NC), infiltration (INF) at 28 days of exposure (FIG. E).

Fig. 1: F: Histology of normal (control), Fig. A at 0-day/12hr, Fig. B at 7-day, Fig. C at 14-day, Fig. D at 21-day and Fig. E, at- 28 days gill of C. carpio (10×40 at the normal compound microscope).

The effects were visible as augmented histological abnormalities in the gill epithelia in a dose-dependent manner. Similar observations were seen in common carp (Cyprinus carpio) exposed to copper nanoparticle^34,35,36. Severe damage, such as fusion of lamellae and necrosis, including hyperplasia^37,38 and observed positive correlation between the concentration of copper exposure and the degree of gill damage in Cyprinus carpio. Similarly, adverse effect of copper was observed in the gill of Rutilus rutilus caspicus³⁹. The histology of gills of Oreochromis niloticus showed sever damages such as Edema, epithelial hyperplasia, lifting of lamellar epithelia, curling and clubbed tips of secondary lamella and finally a complete fusion of several secondary lamellae, congestion and necrosis were found when it exposed to copper at higher concentration^40,41. Two types of damages: first, extremely swollen blood vessels, where the blood vessels of primary lamellae got swollen and second, where complete disintegration of secondary gill lamellae were observed in Channa punctatus due to continuous exposure of CuSO₄⁴². Architectural changes in gill morphology can be potentially employed as biomarkers for rapid assessment of metal exposure, such as CuSO₄ received through waters, secondary gill lamellae with loss of shape, clubbing and fusion, shaft breakage, atrophy curvature of tips, thick mucus sheathing, degeneration of rakers and necrosis were observed when fresh water fish Esomus danricus⁴³.

CONCLUSION:

The present study concluded that sub lethal concentrations of copper have profound effect on common carp Cyprinus carpio represented by noticeable changes in histology of gill tissues. Chronic exposure to copper causes devastating impact on gill which may ultimately cause death of the fish consuming toxic contaminated fish can harm organisms including humans. This study highlights the potential negative effects of copper on fish health and thus emphasizes the need for effective measures to prevent such accumulation in aquatic environments.

CONFLICT OF INTEREST:

No conflict of interest exists between the author.

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Received on 15.01.2025 Revised on 21.06.2025

Accepted on 07.09.2025 Published on 10.02.2026

Available online from February 16, 2026

Research J. Pharmacy and Technology. 2026;19(2):638-642.

DOI: 10.52711/0974-360X.2026.00093

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