Histopathological changes in
M. cephalus and
S. sihama of the study site Ennore and relatively unpolluted reference site were observed under the microscope were given in (Fig 3-6). The histology of various organs of two species collected from selected site, Ennore and Arambakkam. The results were compared with respective organs of the same species collected from two different sites, Ennore and Arambakkam and the histological changes were marked.
Gills, are considered as a primary target of the contaminants as they participate in many important functions in fish, such as respiration, osmoregulation and excretion, remain in close contact with the external environmentand particularly sensitive to changes in the quality of the water (
Poleksic and Mitrovic, 1994;
Fernandes and Mazon, 2003). The fish gill is a multi-function organ that is directly exposed to its environment and is an excellent model for the study of fish diseases and toxicology, which focus on gill alterations and responses
(Samanta et al., 2018). Histology of control gill showed normal filaments and well-shaped lamella separated by large interlamellar space with well-differentiated primary lamella and secondary lamella, normal pillar cells
(Badroo et al., 2020). Marked variations like primary lamellae, secondary lamellae, primary lamellar epithelium, blood vessel, interlamellar region, cartilaginous core were noticed in gill tissues of
M. cephalus and
S. sihama collected from the polluted site Ennore.
The histological alterations were found in
M. cephalus and
S. sihama collected from the polluted site (Fig 3 and 5) exhibited abnormalities like erosion of secondary gill lamellae, shortening of secondary gill lamellae, lifting up of epithelium, blood congestion in the secondary lamellae, curling of secondary lamellae, hyperplasia, excessive mucus secretion, hemorrhage at secondary lamellae and cartilage tissue hypertrophy.
Similar histopathological observations were made in
Terapon jarbua and
Arius maculatus inhabited in a sewage polluted site along Thoothukudi Coast of Gulf of Mannar, South India (
Kalaiarasi,et al.,2017). The present study agreed with findings of
Rajeshkumar et al., (2015) the histopathological damage in
Mugil cephalus collected from heavy metal polluted Berbice-Corentyne coast of Guyana. Through the gills, as the main site of xenobiotic transfer, the toxins are distributed through their bodies accumulating in tissues and organs and may have deleterious effects (
Vasanthi etal.,2013). According to
Karan et al., (1998), gill histopathology changes are the fastest and easiest adaptations to low water qualityand have the purpose of decreasing the respiratory surface and increasing diffusionand result from exposure to a number of inorganic and organic pollutants
(Viana et al., 2013).
In their study,
Anabas testudineus groups exposed to paraquat herbicide exhibited lamellar epithelial lifting, hyperplasia and fusion in their gills. The lamellar epithelial lifting is the separation between epithelial cells and lacuna in the secondary lamella. This separation increases oxygen diffusion distances between the epithelial cell and lacuna
(Maharajan et al., 2016). Mallatt (1985) reviewed that most common gill lesions found under several stressful conditions and reported the common changes like epithelial lifting, necrosis, hyperplasia, hypertrophy and hemorrhage as a of lethal conditions. A typical chronology of damage from acute exposure to the test chemical is first a lifting of outer layer of lamellar epithelium usually starting in the area of chloride cells. Edematous spaces are formed between the layers of epithelium and these may become infiltrated with leukocytes. Eventually, the whole epithelium sloughs off and the lamellar loses rigidity on the blood side of the lamellar, the central space collapse, but the marginal channel often remains normal until the rest of the lamella is essentially destroyed (
Heath, 1987). The proliferation of chloride cells are thought to be a compensatory response to iron loss. And therefore, chloride cells hyperplasia may therefore be a good biomarker of adaptation. Hyperplasia of undifferentiated epithelial cells, which results in clubbing and lamellar fusion is a much less specific lesion associated with a wide variety of unrelated insults (
Hinton and Lauren, 1990).
Histology of liver tissue of both fish species collected from a reference site (Arambakkam) (Fig 3 and 5) showed normal histoarchitecture. The liver tissue of fish species collected from Ennore site showed several abnormal changes in the organs due to pollution. The liver is a detoxification organ that is serves as a biomarker for environmental quality
(Gartner et al., 2014). Moreover, liver plays a major role in complex enzymatic process that are responsible for vital functions, such as accumulation and biotransformation of xenobiotics in the fish. Some distinct changes like rupture of hepatocytes, melanomacrophages, cytoplasmatic vacuolization, blood congestion, degeneration of hepatocytes, cellular necrosis, increased pycnotic nucleus, nuclear degeneration were observed in the liver of fish of polluted Ennore creek (Fig 5).Since liver is involved in detoxification of pollutants
(Afifi, et al., 2014), it is susceptible to a greater degree of disruption in its structural organization due to toxic stress. Macrophage aggregates have been suggested as potentially sensitive histological biomarkers and or immunological biomarker of contaminant exposure.
Histopathological alterations in the form of irregular shape, vacuolation, pycnotic nuclei and focal necrosis of hepatocytes, ruptured sinusoids with hemorrhages, perivascular fibrosis of liver cells, disposition of yellow-brown grains on hepatic tissues were found in cypermethrin treated
O. niloticus (
Majumder and Kaviraj, 2022). The liver tissues of
Mugil cephalus collected from polluted Ennore creek showed histological alterations like vacuolization in the hepatocytes, fibro blast proliferation vacuole formation granula degenerationand necrosis
(Vasanthi et al., 2013). Afifi et al., (2014) studied the histological alterations in liver tissue of
Siganus canaliculatus and
Epinephalus morio caught from oil polluted Jeddah coast and reported that lipid aggregation, hydrophic degeneration, necrosis, pyknosis and karyorrhexis with cholangitis of proliferated bile duct epithelium, spongiosis hepatis, Hepatocyte with enlarged nuclei with prominent nucleoli (megalocytes). Congestion of hepatoportal blood vessels, intravascular hemolysis, hemorrhage and intravascular vacuolated leukocytes are seen in the liver tissue histology. A study conducted by (
Javid and Usmani 2013), in
Mastacembelus armatus for the assessment of heavy metal (Cu, Ni, Fe, Co, Mn, Cr, Zn) pollution in effluent dominated water. The result showed severe lamellar fusion, hyperplasia, hypertrophy and epithelial lifting, swelling and deformed lamella, in some parts sloughing off and curving of lamellae.
Rajesh kumar et al (2015) assessed the heavy metal pollution in east Barbic-Correntyne, Guyana by using histology of
Mugil cephalus liver tissue. The result showed the alterations like vacuolization in the hepatocytes, fibroblast proliferation, vacuole formation, granular degeneration and necrosis.
Bakhiet (2015) reported that fishes collected from sewage contaminated Nile river stretch showed histological changes in liver tissues due to bioaccumulation of heavy metal. The result revealed degeneration of the hepatocytes, congestion of central vein and nuclear pyknosis in the majority of hepaticcells. Similar results were observed by
Van Dyk (2003). The fish’s liver is sensitive to environmental contaminants because many contaminants tend to accumulate in the liverand exposing it to a much higher levels than in the environment, other organs (
Heath, 1987). These findings were apparent as the liver considered the organ of detoxification, excretion and binding proteins such as metal lothionein. The metal-binding proteins present in the nuclei of hepatocytes suggested that the increase in the cell damages.
In the present study, kidney of both the fish species suffered damages due to the exposure to the pollutants. Some distinct changes like hypertrophied epithelial cells, melanomacrophages aggregation, narrowing lumen, dilated lumen, shrunken glomerulus, degenerated tubule, degenerated glomerulus, blood congestion were observed from both the fish species from the study area. Histology of kidney tissue of both the fish species from a reference site (Arambakkam) showed normal histoarchitecture (Fig 3 and 5). The kidney tissue of fish species collected from the polluted site Ennore showed several abnormal changes due to pollution. The kidney of fish receive the vast majority of post branchial bloodand because of that, renal lesions can be expected in the fish when toxicant agents exist in the environment.
Majumder and Kaviraj (2022) reported that the cypermethrin treated
O. niloticus also exhibited glomerular shrinkage and expansion of the space between glomerulus and Bowman’s capsule. Moreover, intracytoplasmic vacuolation in the renal tubular epithelium, hyaline degeneration of tubular epithelium and dilation of tubular lumen were also noted due to cypermethrin exposure.
Coulibaly (2012), noted the histological changes in kidney of black finned tilapia from heavy metals contaminated Bay Bietri and reported vacuolization, dilation in renal cells, severe dilation with renal cells degeneration, hemorrhage, parasitic cyst, vacuolar degeneration in the epithelium of renal tubules, parasites, dilation in renal blood vessels and cyst were observed.
Gusma et al., (2012) reported that the larvae of Marine Pejerrey
Odontesthes argentinensis exposed to water-soluble fraction of petroleum resulted in histological alterations, like enlargement of glomerulus, intercellular spaces and abnormal nucleus of epithelial cells and hypertrophy were noticed. Non-specific kidney histopathological lesions e.g. degenerative changes in tubular epithelium, dilation of tubular lumina, proteinaceous or cellular casts within tubular lumina, tubular necrosis and/or epithelial desquamationand necrosis of interstitial hematopoietic tissues were observed following exposure of fish to organochlorines, petroleumc ompounds organo phosphate, herbicides and heavy metals (
Gartner and Hiatt 2014). Kidney histopathology in some feral fish shows promise as an indicator of organic contaminant exposure
(Myers et al., 1992).
In more severe cases, the degenerative process can lead to tissue necrosis (
Takashima and Hibiya, 1995). The presence of tubule degeneration, coupled with the absence of necrosis in the kidney in the present study indicates that the kidney suffered damage after exposure to pollutants. Some distinct changes like blood congestion, increased periglomerular space, increased peritubular space, glomerulus, degenerated tubules, shrunken glomerulus, necrosis, vacuolation, melanomacrophage, degenerated glomerulus, loss of cytoplasm were observed in the kidney of fish.
