An Overview on the Potential Hazards of Pyrethroid Insecticides in Fish, with Special Emphasis on Cypermethrin Toxicity

Simple Summary Pyrethroid insecticides are extensively used in controlling agricultural insects and treatment of ectoparasitic infestation in farm animals. However, the unhygienic disposable and seepage of pyrethroids from the agricultural runoff will lead to contamination of the aquatic ecosystems, which will, in turn, induce harmful toxic effects in the exposed living aquatic organisms, including fish. Cypermethrin (CYP) is a commonly and widely used type II pyrethroid insecticide with known dangerous toxic effects on the exposed organisms. Serious hazardous effects of these toxicants have been reported in several fish species leading to high mortalities and economic losses of the exposed fish. Abstract Pesticides are chemicals used to control pests, such as aquatic weeds, insects, aquatic snails, and plant diseases. They are extensively used in forestry, agriculture, veterinary practices, and of great public health importance. Pesticides can be categorized according to their use into three major types (namely insecticides, herbicides, and fungicides). Water contamination by pesticides is known to induce harmful impacts on the production, reproduction, and survivability of living aquatic organisms, such as algae, aquatic plants, and fish (shellfish and finfish species). The literature and information present in this review article facilitate evaluating the toxic effects from exposure to various fish species to different concentrations of pesticides. Moreover, a brief overview of sources, classification, mechanisms of action, and toxicity signs of pyrethroid insecticides in several fish species will be illustrated with special emphasis on Cypermethrin toxicity.


Introduction
The present era of the green revolution, witnessing a swift increase in human populations across the globe, depicts the dependency of human beings on available natural resources. The current scenario has led to efforts for technological advancements to cope with the need of societies. This, in turn, is ensured by evolving ever-increasing dissolution of different synthesized chemicals in the environment, which induce pollution, specifically in aquatic bodies used as dumping sites in most parts of the world [1][2][3]. Pollution is the critical universal off-putting factor, which is worsened by the hasty growth of human Therefore, this review discusses the most toxic impacts of pesticides on fish, specifically pyrethroids, emphasizing CYP-induced toxicity.

Detrimental and Toxic Effects of Pesticides in Fish: A General Overview
Exposure to pesticides in sub-lethal and lethal doses produces toxic effects in aquatic organisms, including fish [33,36,37], which can be categorized into the following.

Behavioral Changes
Pesticides may induce behavioral responses, such as schooling behavior, higher mucus production from the goblet cells of the skin (sliminess), jumping, motionlessness, modification in the migration behavior, vertical (upside down) positions, sinking to the bottom, non-responsiveness with hyperexcitability, rapid, jerky movements, higher opercular rate (increased respiration rate), and changes in the body color of several fish species, such as Tor putitora, C. carpio, Mozambique tilapia (Oreochromis mossambicus), L. rohita, C. catla, Cirrhinus mrigala, Clarias batrachus, and Channa punctatus [38][39][40][41]. Moreover, they could modify and disturb the swimming behavior in aquatic vertebrates, such as fish and amphibians, and depress their growth rates [4,25]. Reports showed that exposure to pyrethroids downregulated the dopamine active transporter activity, leading to irregular behavior characteristics [42].

Reproductive Disorders and Malformations
Pesticides may also induce some reproductive disorders in brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) [43]. Moreover, some studies reported several developmental alterations in fish exposed to the pesticide [31]. Several studies have proved the toxic effects of pyrethroids in fish reproduction and during early developmental stages. For instance, the bifenthrin and permethrin pyrethroids can delay synthesizing egg proteins (vitellogenin, choriogenin) in juvenile fish [44]. At the same trend, Wu et al. [45] stated that DLM at concentrations of 20 or 40 µg/L showed toxic effects on swim bladder development in zebrafish embryos.

Histopathological Alterations
Pesticides, such as malathion, carbofuran, diazinon, and dichlorvos, caused several histopathological alterations, and affected the biological functions of some vital organs such as the kidney, liver, gills, testis, and ovaries of different fish species, in the form of necrotic changes, loss of the granularity of cytoplasm, shrinkage of cells in various tissues, nuclear pycnotic alterations, vacuolation in the cytoplasm (in gill lamellae, kidneys, and filaments), degeneration of glomerulus, shrinkage of nuclear materials, ruptured epithelial lining, cytoplasm clumping, altered tubular line size, degeneration of follicular cells, collecting duct damage, and changes in ovigerous lamellae in many fish species, including L. rohita, Heteropneustes fossilis, C. carpio, Channa punctatus, O. mossambicus, Nile tilapia (O. niloticus), and Cirrhinus mrigala [33,[46][47][48].

Endocrine Disruption
Pesticides also have an endocrine-disrupting effect on fish [56]. When used in higher concentrations, these chemical compounds may induce molecular toxicity in various types of fish, such as goldfish (Carassius auratus), L. rohita and, Cirrhinus mrigala [2,40,57]. In addition, histopathological studies revealed that pesticides might negatively influence the endocrine system of L. rohita and O. mykiss [58,59]. Moreover, bifenthrin has been revealed to reduce the 17-β estradiol levels in the bloodstream, consequently decreasing the ovarian follicle diameter in O. mykiss [60]. Moreover, bifenthrin showed higher binding capacity with thyroid hormones through the downregulation of hypothalamus-pituitarythyroid (HPT) axis-related genes in zebrafish embryos [61].

Effects on Proximate Body Composition
Results of Lakshmanan et al. [62], Muthukumaravel et al. [63], and Bibi et al. [54] revealed that pesticides negatively influenced the values of proximate body composition of fish (such as crude protein, crude lipids, ash, moisture, etc.), including O. niloticus, H. fossilis, C. batrachus, L. rohita, Colisa fasciatus, C. carpio, and African catfish (C. gariepinus). Furthermore, a notable rise in the concentration of ascorbic acid and cholesterol in the kidney, liver, and muscles and depression in the level of glycogen, albumin, and protein contents were also recorded.

Genotoxicity
Pesticides usage exhibit carcinogenic and genotoxic effects, which cause different forms of nuclear abnormalities, such as chromosome and chromatid breaks, centromeric attenuation, extra fragments of DNA (DNA fragmentations), pyknosis, stubbed arms besides changing the DNA replication, which leads to different kinds of mutations and cell proliferation [64]. Moreover, it was reported that increased DNA fragmentation of hepatocytes and gill cells was found in C. carpio exposed to sub-lethal CYP levels [33].

Immunotoxicity
It was reported that pesticides negatively impact the immune status of various fish species. They pose immune deficiency responses by a low level of granulocytes and lymphocytes, by inhibition of B and T cell proliferation, a decrease in phagocytic cell functions, and lower leucocytes number, which lead to reducing the resistance of fish to combat infections and diseases [65,66]. For instance, Soltanian and Fereidouni [32] clarified that chronic CYP toxicity in common carp induced immunotoxic effects, which manifested by increased mortalities after experimental challenges with pathogenic Aeromonas hydrophila.
The experiential changes in the above-stated factors have been found in various fish classes, including their body parts. Moreover, observations recorded in the light of the above parameters suggest the occurrence of different levels of harmful impacts for different kinds of pesticides on various tissues of exposed fish species [67].

Pyrethroid Insecticides
Pyrethroid insecticides are synthetic derivatives from pyrethrins, which some plants naturally produce, such as Tanacetum cinerarieafolium or Chrysanthemum cinerariifolium [68,69]. Chemically, the pyrethroid derives from acids and alcohols of chrysanthemum acid (ethyl 2,2-dimethyl-3-(1-isobutenyl) cyclopropane-1-carboxylate) [70,71]. Pyrethroids have been widely used for controlling insects in the agriculture and ectoparasitic infections in humans and animals [69,72,73]. Both pyrethroids and pyrethrins are highly toxic and rapidly degrade in the environment under proper temperature, light, and moisture levels [74]. The degradation process usually occurs in one or two days in sunlight and proper atmosphere. Pyrethroids are considered promising alternatives to conventional pesticides because they do not contaminate groundwater [75].

Classification and Types of Pyrethroids
Pyrethroids are synthetic organic insecticides divided into two distinct groups (type I and type II). Type I pyrethroids lack a cyano moiety and type II pyrethroids are with an alpha-cyano group [76]. Permethrin pesticides include bioremethrin, resmethrin, allethrin (Allyl analog), and tetramethrin, as examples of type I pyrethroids, whilst type II pyrethroids include CYP, cyphenothrin, deltamethrin (DLM), cyfluthrin, and fenvalerate. Both types of pyrethroids inhibit spontaneous activity in the neurons of target organisms [77]. Type I pyrethroids produce reflex hyperexcitation and fine tremors, while type II involves more complex syndromes, such as higher gill mucus secretions and clonic seizures. In addition, type I alters the sodium channel actions in different ways, while type II modifies transitions to the sodium channel in inactivated and open states [78].
DLM, CYP, and lambda-cyhalothrin are commonly used synthetic forms of pyrethroid insecticides worldwide. Kumar et al. [79] reported that DLM is highly effective against malaria vectors, making it efficient in the manufacture of mosquito evictor nets. It is categorized as a type II pyrethroid and is soluble in organic solvents (acetone and alcohol), but insoluble in water [80]. Besides, it is created from natural pyrethrins compounds, which quickly affect the nervous system of insects, inducing a fast knockdown influence [81]. Furthermore, DLM is linked with the prolonged opening of voltage-gated sodium channels, which causes depolarization in neuron membranes, repetitive discharges, and produced synaptic disorders [71,80]. It also diminishes the ion exchange process between chloride and calcium channels of the neurons [75,80].
CYP is an active synthetic pesticide expansively applied to households, industrial, and agricultural fields to control many insect pests. It is also categorized as a type II pyrethroid that displays stability in neutral and acidic solutions. It could prohibit the transportation process of sodium ions through the cell membrane [82].
Lambda-cyhalothrin is a synthetic acaricide pyrethroid insecticide that is used to prevent a broad spectrum of crop pests [83]. It is synthesized from a mixture of cyhalothrin isomers, which altered the nervous system functions [84]. It was restricted due to its higher toxicity to fish [85].

Modes of Action of Pyrethroids
Pyrethroids are categorized as neurotoxins targeting the peripheral and central nervous system axons by intermitting with sodium channels in insects [83]. In this concern, Bradberry et al. [75] reported that the selective toxin activity of pyrethroids towards insects is 2250 times higher than animals. This may be attributed to the presence of more active sodium channels and lower body temperature in insects. The toxic effects of pyrethroids in fish species, e.g., shellfish, and finfishes have been reported in several studies, and that related to the disturbing action of pyrethroids on the ion exchange process neuronal and mitochondrial membranes [86][87][88][89].
In mammals, sodium channels are the major proteins of the nervous system concerned with electrical signaling and the supporting of essential functions such as osmoregulation, heart pulse, and the activity of the brain. Some fish species, such as zebrafish, showed ex-pression patterns of voltage-gated sodium channel genes similar to those in mammals [90]. All pyrethroid compounds caused prolonged sodium outflow with delaying in sodium activation gate closure resulting in decreased and extended sodium tail discharge [91]. Some pyrethroids increased the neurotransmitter release in the postsynaptic gap by prohibiting the calmodulin proteins responsible for connecting calcium ions and the intracellular membrane, and limiting the calcium removal process from the nerve endings, leading to reduced spontaneous neurotransmitter release [92]. The toxic effects of pyrethroids may depend on the sequences of the amino acid in sodium channels, specifically at position 918 (methionine), thereby making a difference in sensitivity [93]. Moreover, it has been shown that the toxicity of pyrethroids, such as bifenthrin, depends on the relative proportion of negative and positive pairs, with the negative pairs being more active than the positive and the neutral ones [94].
The long-term exposure to pesticides excites the outer cell membrane and the nervous system. Furthermore, some pyrethroids have an adverse effect on the γ-aminobutyric acid (GABA) receptors in the nervous filaments [27,95,96]. Moreover, they could prevent chloride ions from transportation into the nerve cells and modulate the activity of voltagegated calcium channels [97]. There were minor preventing effects of pyrethroids towards the Ca-ATPase, Ca-Mg ATPase neurotransmitters, and the peripheral benzodiazepine receptors [98].
Pyrethroids could penetrate the epidermis and be combined directly with a carrier protein in blood or lymph. Consequently, the diffused pyrethroids and the epidermis cells directly affect the central nervous system via the connection with sensory organs of the peripheral nervous system [99]. Moreover, the pyrethroids may enter the body in a small portion through the breathing process in a vapor phase. Besides, they could penetrate the blood or hemolymph through the digestive tract during the digestion process [100].

Biotransformation and Acute Lethality of Pyrethroids to Fish
Several studies have documented the sensitivity of fish towards pyrethroids pesticides [95,[101][102][103]. Unlike most mammals, fish are not able to produce the enzymes that hydrolysis the insecticides. The lipophilicity properties of pyrethroid compounds make them susceptible to the non-water-soluble components of the cells. They can also be quickly absorbed by the gills, even though water containing a small portion of these compounds [101]. The lethal effects of pyrethroids in fish may be due to their biotransformation properties.
Pyrethroid compounds are partly broken down in the gut by non-specific esterase, reducing their absorption rate. While in fish, many toxin levels are absorbed by gills, then rapidly enter the circulatory system [104]. In the hepatocytes, the hydrolysis of pyrethroids depends on oxidation by cytochrome P450 or carboxylesterase. It produces a high level of non-bioactive metabolites secreted via the urine and the bile [105].
Pyrethroids pesticides induce different types of toxicity in fish. Some of these toxic impacts in the form of alterations in various physiological, behavioral, anatomical, biochemical, hematological, enzymatic, molecular, and hormonal aspects, are briefly illustrated in Table 1.

Cypermethrin as a Pyrethroid Model
Cypermethrin (CYP) [(RS)-cyano-(3-phenoxyphenyl) methyl-(IRS)-cis -Trans-3-(2, 2 dichloroethenyl)-2, 2-dimethyl-cyclopropane carboxylate], is one of extensively used and highly effective synthetic pyrethroids. It is lipophilic and synthetically obtained from a natural source known as pyrethrin. CYP is broadly engaged mainly in commercial agriculture, forestry, gardens, buildings, and farmyards to prevent and control insects [2]. CYP is used as an insecticide in a broader range of crops, such as wheat, sugarcane, brinjal, okra, cabbage, onion, lettuce, cotton, and sunflower [2,111]. Interestingly, it is thought that CYP is immobile and does not be expected to be biomagnified through the food chain.
Furthermore, CYP is commercially registered to kill soybean and cotton pests successfully [112,113]. The report of Bekele [114] suggests that proper application of this unique insecticide may effectively repel and control mosquitos, whilst the most effective results were found in preventing many kinds of malarial parasites. Moreover, globally, aquaculturists apply this insecticide to control parasitic infections, such as planktonic marine copepods [115]. Furthermore, the possible negative impacts of CYP on natural aquatic ecosystems were also reported [33,116]. CYP is the most broadly used pesticide during the past two decades in various parts of the world [117]. CYP readily enters the nervous system of the animal body and elicits cellular oxidative damage by inducing the production of free radicals and reducing the antioxidant effects of the body [118].

Menidia beryllina
Hinder with metabolic processes and endocrine signals ↓ reproductive performance [138]     ↑ plasma GLU level ↓ in the level of liver glycogen ↓ ACP and ALP activities of liver ↓ ascorbic acid levels of blood, liver, and kidney Saha and Kaviraj [120] 0.4, 0.8 and 1.2 µg/L 48 and 72 h Channa punctata Oxidative stress and genotoxicity in fish erythrocytes Ansari et al. [130] 0.08 and 0.265 ppm 2, 4 or 8 d

Clarias batrachus
Inhibition in the activities of total Mg+2, and Na+-K+ATPase enzyme and glycogen content A significant induction in the levels of glycogen phosphorylase Begum [127] 0. 3

Conclusions
Our rapidly growing population requires intensification of crop production. Thus, it is essential to control pests and insects that cause economic losses in crop production. Pesticides have become a necessary part of the production cycle for eliminating plant diseases and killing pests that can drastically reduce harvestable products. Moreover, a polluted environment with a high concentration of synesthetic pyrethroids has caused several adverse effects in living aquatic organisms. This literature explained the biological modes of action of some pyrethroids in fish species and the underlying biological impacts of pyrethroid-contaminated water on reared fish. Furthermore, toxicological experiments showed individual responses against pyrethroid lethality. This review article provides insight for future research studies to evaluate the toxic effects of pyrethroid insecticides and sheds light on CYP toxicity mechanisms in fish.