Effects Of Pollution On Aquatic Biota

Immediately following exposure of water bodies to organic pollution there is a decrease of algae due to de-oxygenation and a small amount of light. Further, this is followed by a gradual increase in algae abundance once conditions improve. This gradual increase is fueled by the heavy concentrations of nutrients that are likely to be present (Mason, 1991). Plankton (phytoplankton and zooplankton), macrobenthos, fish species, and macrophytes are badly affected by biodegradable organic pollution (Hines, 1960; Malik et al., 2018; Kumar et al., 2018). Generally, de-oxygenation reduces light levels, increases TSS and settling of material thus leading to a decrease or loss of aquatic species that are most sensitive to pollution (Hawkes, 1962; Haslam, 1987). There is a potential of a problematic DO mainly from biodegradable organic pollution in the downstream areas of rivers (Mason, 1991).

It causes some glitches for migratory fish species with high DO requirements i.e. in case of Salmo salar and Salmo trutta. In some cases, the levels of DO and organic pollutants may prompt escape behavior and act as a barrier that prevents them from reaching highly oxygenated breeding and spawning grounds (Richardson et al., 2001).

Effect of water pollution on algae and macrophytes

Macrophytes are types of aquatic plants that grow in water and are classified as either emergent, f loating, or submerged. Macrophytes act as bioindicators because they quickly respond to the rate and variability of multiple environmental characteristics i.e. water flow, alkalinity, substrate, shading, and nutrient concentrations (Barendregt and Bio, 2003; Lacol and Friedman, 2006). Total suspended sediment adversely affects algae and aquatic macrophytes by limiting the amount of light reaching the water column, which subsequently limits the frequency of photosynthesis. A high amount of suspended solids is usually transported by fast flowing rates, wherein algae and aquatic macrophytes are also carried off the bed substrate, resulting in damage to their photosynthetic structures (Steinman and McIntyre, 1990).

The process of sedimentation can reduce submerged vegetation which reduces the rate of photosynthesis. Some plants do particularly well in water low in dissolved nutrients and high in saturated water while other plants do fine in water rich in nutrients. This made it possible to rank and score aquatic macrophytes according to their preference for different chemical and physical conditions (Hauri et al., 2002). Moreover, macrophytes are reasonably tolerant of irregular pollution and are inclined by geology and soil type (Mason, 1991). Moreover, macrophyte community structure is often determined by certain interconnected aspects that can make assigning the absence/presence of species to specific pollutants difficult (Pentecost et al., 2009). Macrophytes play an important role as bioindicators of chronic pollution problems in any water bodies.

Effects on Macrobenthos

Macrobenthos are aquatic animals that lack an internal skeleton, visible to the naked eye and inhabit the bed substrate of bodies of water. Bottom-dwelling organisms mostly include larvae, insects, crustaceans, annelids, worms and pupae of molluscs. Macrobenthos are excellent indicators of water quality and pollution load due to some factors (Malik et al., 2020) including: • Macrobenthos are widespread, abundant and can be found in all types of habitats but most numerous in polluted or disturbed habitats. • Due to their short life cycles (usually about one year) fluctuations in water quality are reflected in the populations. • Mainly they are quite immobile and cannot survive pollution. • Spend most of their lives in water. • Easily sampled and also easy to identify. Estimating the abundance and diversity of benthic macrobenthos in an aquatic ecosystem provides a clear indication of biological conditions. It is well known that unpolluted water bodies support a wide variability of macrobenthos taxa, including many pollution intolerant species, while any polluted water bodies gave sustenance to only pollution-sensitive species and small species diversity. Total suspended solids can subject macrobenthos to abrasion as sediments move and push them into the water column. This causes damage to exposed breathing organs or makes the organism more vulnerable to predation upon dislodgement (Langer, 1980). A high amount of suspended solids can choke feeding structures and decline the feeding efficacy of filter-feeding macrobenthos leading to reduced growth rates, amplified stress levels and even mortality (Hines, 1970). A wide variety of many research has shown that increased suspended solids levels directly affect the downstream migration of macrobenthos. Sedimentation results in contamination of the interstitial habitat of macrobenthos, which is important for crevice-occupying macrobenthos as well as suffocating benthic organisms by covering their respiratory surfaces, which are likely to result in death.

Effect of pollutants on survival of fish species

A high amount of suspended water pollutants can disrupt the normal behavior of fish populations. Various fish species rely on vision to quickly capture their prey. Perch, brown trout, etc. are susceptible to high amounts of suspended solids and show very strong avoidance behavior. In some cases where fish species survive in turbid water habitats, suspended solids can clog/damage apertures and reduce resistance to various disease and parasites (EPA, 2012). Fish species may also consume these suspended solids, causing disease by exposing them to potential toxins or pathogens on the sediment. If the fish species does not die by consuming suspended solids, it may alter the blood profile and also harm its development (EPA, 2012). Water pollutants can reduce the eggs, embryos by reducing their survival. Pollutants interfere with various physiological processes without causing any death. The lethal components and suspended dregs cover all the mucous membranes of the gills of the fish which affects the respiratory process. Mainly, mercury and lead interfere with the activities of digestive enzymes.

Pollutants impact a given fish population without being lethal to the adult organisms in several ways (i.e. Subhendu, 2000). • Nutrition and food chain • Physiological progress • Life cycle • Behavior • Occurrence of diseases • Migration. • Genetic effects • Reproduction and spawning • Changes in morphology

Morphological deformities in fish body due to pollutants
Various types of morphological abnormalities formed on all parts of fishes were reported several times by researchers (Abel, 2007; 2009; Adams, 2004; Kaklu, 1987; Kumar et al., 2018: Kamboj et al., 2020; Shama et al., 2018; 2019). These are: • Scale disorientation • Split fins • Fin deformity • Opercular deformity • Hyperplasia of mouth surface • Depression of mouth or nasal part.

Effects of pollutants on fish behavior

Pollutants directly and indirectly impact the behavior of aquatic organisms (Zala and Penn, 2004; Saaristo et al., 2018), especially in fish species (Robinson, 2009; Sloman and McNeill, 2012). Inorganic and organic pollutants also impact various behavioral activities i.e. feeding, sexual and socializing aggression behavior (Table 3). Some pollutants can cause alterations of neurotransmitters, hormone levels and cholinesterase activity of fish species (Brodin et al., 2014; Vincas et al., 2017). Pollution-induced variations in fish behavior can potentially further increase the level of exposure to pollutants and result in positive feedback loops that reflect the negative effects of pollution on fish health.

Several types of spatial behaviors i.e. activity, exploration and avoidance are the main behavioral characters that are habitually affected by water pollution. Aquatic organisms that spend most of their lives in metal-polluted areas (e.g. lead and cadmium) with higher levels of metal in their blood profile show a slower exploration tendency (Grunst et al., 2019). Such a reduced exploration tendency has affected the ability of fish to assess habitat quality as exploration is the main trait that enables the individual to collect information and cues about the ecosystem around them (Pathak, 2015), also, interactions within the community are often altered by these contaminants (Ward et al., 2008) due to the social learning and information gain benefits for them. Spatial memory strength and learning ability are profoundly affected by pollutants in the case of Atlantic salmon where aluminum contamination decreased learning performance in a maze task and reduced their ability to process information and manage with novel environments (Grassi et al., 2013). Pesticides also impaired some activities and spatial memory in Danio rerio and Gobiocypris rarus (Hong and Jha, 2019).

Water pollution induced histopathological changes in fish organs/tissues

Histopathology deals with the structure of body tissue. Any abnormal change of cells can specify the effect of toxins and the presence of various diseases. Abdullah et al. (2008) reported various histological changes in the liver of Tilapia nilotica reared in water polluted with heavy metals showing cloudy swelling, vacuole and hydropic variations of hepatocytes and also prominent coagulative necrosis. Velcheva et al. (2010) studied the pathological fluctuations in both gills and liver of Alburnus alburnus and perch from polluted Dam Lake showing deterioration of cytoplasm in hepatocytes which eventually became necrotic and infiltrated with inflammatory cells. Similar lesions were also recorded in Tilapia nilotica fish by Abdullah et al., 2008). Recently Ebrahimi and Taherianfard (2011) reported histopathological variations in liver, kidney and muscle of cyprinids f ish species from polluted river core where hemosiderosis, melanophage hyperactivation, bile canaliculi dilatation, and perivascular edema occurred in the fish organ and tissue. Moreover, the skin of tilapia species was adversely affected by heavy metals pollution showing hyperactivation of goblet cells and dermal melanosis and dermal granuloma. Similarly, the kidney of carp fish from polluted water showed interstitial nephritis, renal necrosis, and mononuclear cell infiltration, the brain also showed dermal granuloma symptoms of meningitis and gliosis.

Effect of Pollutants on Fish Liver

El-Nagar et al. (2009) reported that the liver plays an important role in digestive activity during f iltration and for storage of glucose in all fish species. T yal et al. (2008) reported that bile is also produced by the liver which is later stored in the gall bladder. So, the liver of fish is a good indicator of aquatic pollution, as one of the main functions of the liver is to clear any toxins or pollutants from the bloodstream (El-Nagar et al., 2009). Because the liver is mostly associated with detoxification and biotransformation progress, it is one of the most affected organs by contaminants in water (Mohamed, 2009). Various types of changes include necrosis, fibrosis, pyknosis, fatty degeneration, and hemocidin degeneration in fish mainly caused by heavy metal pollution. The liver of both Mugil cephalus and Mugil capito fish showed similar histopathological changes to the kidney from Manzalah (Kadri et al, 2003). Mohammed, (2001) reported cellular deterioration in the liver due to oxygen deficiency leading to vascular dilatation and intravascular hemolysis with gradual stagnation of blood. Hepatocyte degeneration and necrosis may be due to the combination effect of nutrients and salts (Othman and Abbas, 2007). In addition, accumulation of hemosiderin in liver cells may be due to accelerated and continuous destruction of erythrocytes (Ibrahim and Mahmood, 2005).

Effect of pollutants on kidney of fishes

Kidneys are vital organ of fish body and perform important functions like maintaining homeostasis. Removal of wastes from bloodstream, selective reabsorption activities, maintaining volume and pH of blood and body fluids are performed by kidneys (Iqbal et al., 2004). Thofon et al. (2003) reported in their research, that kidney was one of the first organs to be affected by contaminants in polluted water. Kidneys of Mugil cephalus and Mugil capito of Lake Manzalah showed histopathological changes with varied degrees of severity (Kadri et al., 2003). Mahmood et al. (2008) reported that industrial, agricultural and sewage wastes caused renal injury in kidneys of fish species living in different areas of the Nile River. Similar results were observed in C. carpio species exposed to sewage wastes (Kakatta and Murachi, 1997). Several scattered necrotic lesions in the hematopoietic tissue and renal tubules of rainbow trout were observed by (Kapkin et al., 2006) due to changes in water quality such as increases in pH level, temperature, hardness, etc. (2003) reported some injuries in the renal tissues of Liza Ramada fish obtained from polluted water in Manzalah Lake. These injured kidneys showed degeneration of renal tubules and pathology of glomerular capillaries.

Effect of pollutants on fish eggs, spawn, fry and fingerlings

Generally, eggs of fish species are much more resistant than adult fish species. Generally, eggs are developed between pH 6 to 9. The eggs displayed exocytosis and even collapsed in the water body where the acid pH is more than 4.0, similarly in other conditions where the water is more alkaline than pH 9.0 it showed endocytosis with swollen eggs and the yolk also turned white. The critical value of oxygen tension for newly fertilized eggs is about 40 mmHg and increases during the development of the embryo to about 100 mgHg (60% saturation) at the time of hatching. Salmon and trout fish species usually lay their eggs in gravel-beds through which water must infiltrate while the eggs and fry live the yolk of the eggs (Adams and Onorato, 2005).

Conclusion

Various types of impurities and toxic substances enter the aquatic ecosystem and affect the water quality and disturb the life cycle of aquatic organisms. Some of the pollutants are very active to harm the aquatic organisms both morphologically and metabolically. Nevertheless, there is only insufficient evidence that water impurities and pollutants are indeed accountable for the spread of disease in aquatic animals. Exposure of aquatic animals to pollutants for long periods resulted in continuous health risk. Therefore, directly and indirectly, aquatic animals are at greater risk due to various anthropogenic activities. For these problems, it is very evident that everyone should take necessary pre-emptive measures to protect aquatic communities. The diverse effects of pollutants on the population of different fish species have been reported from time to time by many researchers and a chronic level of exposure has been predicted to cause diverse effects on aquatic life i.e. histopathological, physiological damages, migration, embryonic and developmental changes especially in fish species. Many pollutants in the atmosphere formed various toxic compounds i.e. organophosphate compounds bring lethal effects in fish species. Thus, to overcome these problems it is important to develop some approaches using molecular biology techniques that will modernize toxicological tests that are low priced and do not demand aquatic animals to detect ecological stresses. More research struggles should be done to establish the concentration levels and exposure time of all pollutants and it is very important to persuade the significant lethal and sub-lethal effects on aquatic organism.

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