Hazardous Effects of Arsenic Contaminated Water on the Biological Characteristics of Fishes: A Review

The aim of the current review is to deliberate on arsenic chemistry, its existence in aquatic ecosystem and its effects on the biological systems of fishes which are regarded as potential indicators for any change in water quality. Water is a major storehouse of arsenic which is present in the form of arsenate and arsenite. Anthropogenic activities including unlimited application of arsenic pesticides, industrial activities and mining operations have increased the universal incidence of soluble arsenic above tolerable levels of 0.010 mg/L. Variations in fish behaviour, growth rate, haematological and biological parameters and organ systems have been observed in arsenic contaminated water. Data regarding these parameters indicate that the fish shows aggressive behaviour and its weight increases due to a high arsenic uptake. The production rate of biochemical compounds like carbohydrates, proteins and lipids is reduced due to arsenic bonding with their precursors. Among organ systems, skin is a highly affected organ, while muscles are the least affected due to high arsenic concentration. Low concentration of arsenic results in bioaccumulation, conspicuously in liver and kidney, upon incessant exposure to freshwater ﬁsh. This bioaccumulation turns into biomagnification and becomes the cause of lethal diseases in human beings, such as hyperglycaemia, diminution of enzymatic activities and immune system abnormalities. Keeping in view all of these above mentioned facts, it is imperative to take action against excessive arsenic usage and to develop its eco-friendly management ways.


Introduction
Arsenic (As) is a mobile, toxic, and carcinogenic element that is widely dispersed in aquatic environment, mostly in the form of sulphide and oxide complexes. It has three modes of existence, that is, arsine gas, organic and inorganic existence which are normal, moderately and highly toxic, respectively [1]. Due to its toxicity, it poses serious threats to the environment [2]. Anthropogenic activities including industrial processes, preservation of timber and burning of fossil fuels have led to its increased concentration in our environment that causes haematological and biochemical damage to organisms and has also resulted in worldwide health issues, such as food poisoning. Arsenic contamination has badly affected the aquatic fauna with fishes being the highly disturbed organisms in this ecosystem. So, it is being used as a model while studying environmental pollution caused by arsenic [3] because they are greatly affected by the BioScientific Review Volume 1 Issue 3, 2019 presence of arsenic in water. It results in bioaccumulation and biomagnification which act as risks for higher trophic levels [4]. This review mainly emphasizes arsenic's chemical nature, occurrence in the environment, contamination, estimation of the adverse effects of changes in physiology, biochemistry, haematology, behaviour and metabolism of fishes in arsenic contaminated water.

Chemical Forms of Arsenic
Arsenic is a brittle metal belonging to VA group with the atomic weight of 74.92 and melting and sublimation points at 817 ºC and 613 ºC, respectively. It has three allotropic forms, yellow, black, grey. It belongs to VA group with four oxidation states, that is, -3, 0, +3, and +5. It has two trivalent forms, arsenide and arsenic trichloride. Its pentavalent forms are arsenic pentoxide, arsenic acid and arsenates [5]. Its chemical forms are described in Table 1.
It is known that toxicity caused by arsenic is due to the creation of imbalances between pro-oxidant and antioxidant homeostasis which leads to oxidative stress.

Effects on Fishes
Fishes are highly developed aquatic organisms and any change in water qualities can have adverse effects on them, including variations in haematology, biochemistry and various organ systems. Potential indicators used to detect toxicity in fishes are alanine aminotransferase and aspartate aminotransferase enzymes. The effects of arsenic can be determined by arsenic exposure to these enzymes and it was concluded that arsenic exposure for 96 hours to Indian Major Carp caused increased activity of these enzymes that resulted in hepatic damage [6].

Behavioural and Growth Changes in Fishes
When a change occurs in the surroundings of fishes, they respond to it by changing their behaviour as in the case of arsenic contamination. An experiment was conducted on the invasive mosquito fish in laboratory by providing a natural environment in which certain algae were also present to check their effect on low arsenic level [7]. As the arsenic level increased, it lead to a significant increase in the aggression level of fishes and decreased operculum movement. Arsenic accumulation in the body of fish increases its weight and algae acts as nature defence mechanism to control weight gain [7]. Another laboratory experiment was conducted on rainbow trout and feathered minnows upon exposure to diet borne and water borne arsenic for 28 hours. Trout growth is affected when >10 µg As/L is given while 16 mg As/L quantity of arsenic leads to growth reduction and high mortality. Mortality rate in feathered Department of Life Sciences Volume 1 Issue 3, 2019 minnows is high even with little concentration of arsenic; however, trout is more sensitive than minnows in this regard as far as growth rate is concerned. When growth effects are based on accumulation in the fish, waterborne and diet borne exposures show similar dosimetry and are roughly additive [8].

Effects on Organ Systems of Fishes
Fishes are ideal organisms to work with in toxicogenomic studies due to the strong power of fish models to establish the biomarkers of exposure. Arsenic affects fishes in the same way as it affects human, that's why fishes are widely taken as the study model. Various organ systems of fishes such as liver, kidney, brain, skin, lungs and muscles are affected by arsenic exposure (Table 2).

Effects on liver.
Liver plays a major role in the uptake, accumulation, biotransformation and excretion of arsenic and liver damage is greater at high concentrations of arsenic as was observed in Channa punctuata. Its maximum mortality rate was observed at 100ppm, within 18-20h of exposure [9].
A toxic form of arsenic, that is, sodium arsenate leads to the fragmentation of the chromosomal DNA of fish liver. In case of accumulated in a large concentration in the liver and but when arsenic exposure is long, it causes complete degradation of the liver. Upon exposure to low dose sodium sublethal concentration of arsenic in Indian catfish leads to the induction of significant changes in liver cells. It causes reduction in total protein contents in liver cells [11]. Many other degenerative changes, such as apoptosis and pyknosis in hepatocytes of fishes are observed when they are exposed to different sublethal arsenic concentrations [12].

Effects on muscles:
Fishes usually comprise up to 80% muscle tissues which play a major role in swimming activities. They are somewhat resistant to arsenic contents and least affected due to the absence of any direct connection between them. However, as the age of fish increases, the accumulation of arsenic in muscles also increases. While arsenic exposure during the early stages of fish growth may lead to muscle dysfunction. Several types of malfunctioning including necrosis, atrophy and molecular degeneration are detected when H. fossilis is exposed to between 7 and 20 mg/L of arsenic [18].

Biochemical Changes in Fishes
Biochemical parameters are affected by change at molecular level upon exposure to arsenic contaminated water. Among these parameters, blood glucose level is a majorly affected parameter [11].

Blood carbohydrate level.
is highly suppressed by arsenic in water. Arsenic induced hyperglycaemic effects in three major Indian carps at the level of sublethal dosage.
It resulted in similar hyperglycaemic effects on Tilapia zillii and Mugil capito. It was observed that hyperglycaemic effects were due to extensive glycogenolysis [13]. Another cause found was that the beta cells of pancreas altered their insulin secreting capacity due to mutation in gene expression of insulin related genes that resulted in less insulin production.

Proteins.
are also affected by arsenic and its metabolites because arsenic reacts with phosphates and the thiol group of proteins leading to its impairment. Arsenic metabolism releases free radicals that also cause damage to protein structure. Inorganic forms of arsenic such as arsenite and arsenate bind with sulfhydryl and phosphate groups, respectively. Usually, upon exposure to arsenite, heat shock proteins get activated and their expression patterns depend on the specific dose and tissue. These proteins are involved in cell protection by ensuring cell survival [19]. Labeo rohita was exposed to sublethal concentrations of arsenic for 28 days and a significant reduction in protein contents was observed [20]. It was observed that fish liver proteome is altered in Zebra fish on exposure to 50 g/L sodium arsenide for seven days [21]. These findings illustrate that arsenic contaminated water results in transmuted protein expression along with the activation of heat shock proteins.

Lipids.
are also an important physiological component and after arsenic exposure lipolysis is enhanced. It was shown that 1.0 mg As/L exposure of arsenic to rainbow trout resulted in decreased dry weight of fish although the wet weight remained the same [22]; however, an increased concentration of arsenic leads to a decrease in wet weight also. This decreased weight is due to kidney damage on arsenic exposure [23]. For lipid contents, the duration and route of arsenic exposure also matters. In this context, a study was conducted on Anabas testudineus [10]. After the fish was exposed to arsenic at the rate of 1.5 mg/L level, significant changes in lipid level were observed. contaminated water may cause changes in carbohydrates, proteins and lipids levels in fishes [24].

Haematological Changes in Fishes
Changes in haematological parameters are also observed in fishes living in arsenic contaminated water. They act as indicators for environmental disturbances. It helps in the diagnoses of the functional status of fishes [25]. Haematological parameters are affected by oxidative stress in fish liver. The duration of arsenic exposure includes acute and chronic exposure. Acute and chronic exposure cause reduction in the number of erythrocytes and leukocytes, respectively. Haematological parameters were determined by taking Catla catla as model organism. 43.78 mg/L arsenic was provided to the fish for 96 hours. It declined the normal values of haemoglobin, plasma, RBC, and WBC count, while the mean cell volume, mean cell haemoglobin and mean cell haemoglobin concentration were increased [24]. A decreased level of haemoglobin was observed in C. batrachus exposed to waterborne arsenic [26].

Conclusion
Arsenic is a heavy metal and its concentration is increasing in the aquatic environment day by day due to both natural and anthropogenic activities. Fishes are taken as an indicator of arsenic contamination. Many research works have unveiled that arsenic contamination has hazardous effect on liver and kidney. It disturbs the normal body functioning that results in onset of diseases. Understanding the noxious effects of arsenic in the aquatic ecosystem is helpful to reduce its effects on fishes and other organisms, such as human beings who eat fish. Consistent observations of arsenic levels assist us to monitor health hazards associated with arsenic contamination in fishes. These fishes do not provide a complete insight into the overall conditions of the ecosystem; still, it is helpful to reveal the potential effects of arsenic contamination on food chain.

Recommendations
Arsenic contamination is hazardous for fish health and its major sources are natural and anthropogenic activities, so it is recommended here to make laws against the release of arsenic wastes. People should be made aware about the harmful effects of arsenic through seminars and conferences and they should be charged in case of rules' violation. It is also recommended that biological control as well as phytoremediation should be applied to treat contaminated water. A lot of research should be conducted on the cleaning of water through phytoremediation due to the absence of any side effects. [17] Palaniappan PL, Vijayasundaram V.
The bioaccumulation of arsenic and the efficacy of Meso-2, 3-dimercaptosuccinic acid in the selected organ tissues of Labeo rohita fingerlings using inductively coupled plasma-optical emission spectrome-