Helena Joyce
Pollution has a significant impact on fish and other aquatic organisms. Contaminants such as heavy metals, pesticides, and plastics can directly harm fish, causing deformities, reproductive problems, and even death. Pollution can also indirectly affect fish by damaging their environment and disrupting the delicate balance of marine ecosystems. For example, certain contaminants promote the growth of algae, which can create dead zones where fish suffocate due to a lack of oxygen. Additionally, pollution can lead to behavioural changes in fish, such as altered aggression and learning abilities, and chronic exposure to low levels of pollutants can suppress their immune systems. Overall, pollution has far-reaching consequences for fish health and biodiversity, with potential impacts on human health as well.
| Characteristics | Values |
|---|---|
| Pollutants | Heavy metals, pesticides, hydrocarbons, plastic, oil spills, antidepressants, antibiotics, cadmium, mercury, and other metals |
| Impact on Fish | Deformities, gill damage, fin and tail rot, reproductive problems, suppression of the immune system, reduced metabolism, behavioural changes, neurofunction changes, death |
| Impact on Environment | Lack of oxygen, promotion of fungi, bacteria, and algae growth, impeding the growth of naturally-occurring plants, destruction of habitats |
| Impact on Humans | Decline in certain species, contaminated food sources, microplastics found in bloodstreams |
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What You'll Learn
Behavioural changes
One study found that agricultural contaminants can disrupt the reproductive behaviour of fish, causing a decrease in their overall health and biodiversity. For example, pesticides can lead to immunosuppression, reduced metabolism, and damage to gills and epithelia. Additionally, wastewater and sewage pollution can introduce toxins such as endocrine disruptors, pathogens, heavy metals, and other toxins into aquatic ecosystems, threatening the health of fish populations.
Furthermore, microplastics have been shown to impact the behaviour of planktivorous reef fish. Arsenic exposure has also been found to cause behavioural and neurotoxic effects in zebrafish. Climate change is an emerging stressor in aquatic ecosystems, and the resulting alterations in water temperature and chemistry can affect fish behaviour and physiology.
Pollution-induced behavioural changes in fish can also increase their vulnerability to predation. For instance, a study on brown bullhead fish found that pollution exposure altered their migration behaviour, potentially making them easier targets for predators.
Overall, the effects of pollution on fish behaviour are complex and multifaceted, requiring further multidisciplinary research to fully understand their implications for fish populations and aquatic ecosystems.
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Ingesting plastic
Plastic waste has become a significant environmental problem, with microplastics detected in all aquatic compartments. Laboratory and field studies have confirmed the ingestion of microplastics by aquatic organisms, including fish species of commercial interest to humans. The quantities of microplastics observed in the intestinal contents of these organisms are generally low, but data on their presence in small fish and tissues outside the digestive tract is limited.
Recent studies have shown that the rate of plastic consumption by marine fish is increasing, with plastic turning up in the bellies of wildlife such as mammals, birds, turtles, and fish. The problem is impacting species unevenly, with some more susceptible to consuming plastic than others. For instance, fish in heavily polluted East Asian waters showed the highest levels of plastic ingestion, which is concerning as seafood from this region feeds 2 billion people. Additionally, predatory fish higher up on the food chain are at greater risk, as they are more likely to consume plastic.
The ingestion of microplastics by fish poses a potential risk to humans who consume fishery products. Once ingested, microplastics can reach the gastrointestinal tract, causing oxidative stress, cytotoxicity, and translocation to other tissues. They can also release chemical substances (organic and inorganic) and act as carriers of microorganisms and potentially toxic elements that can be harmful to humans. However, the available data is insufficient to perform a reliable assessment of the risks to human health.
While larger fish may contain a higher total number of microplastics, smaller fish tend to have more microplastics per gram of tissue. This highlights the unique behaviour of microplastics as physical particles, which may differ from chemical contaminants. More research is needed to fully understand the risks and effects of microplastics in food webs and the environment.
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Heavy metal toxicity
Heavy metals are one of the leading causes of environmental contamination globally. The development of industries has resulted in the discharge of toxic substances into the environment. Heavy metals are stable, imperishable compounds that can accumulate in different fish organs when they reach aquatic ecosystems. The most common heavy metals are chromium, arsenic, mercury, cadmium, lead, copper, and nickel, which can contaminate the environment and affect the physiology of fish.
The accumulation of heavy metals in fish organs causes structural lesions and functional disturbances. Heavy metal contamination induces oxidative stress, histopathological manifestations, and altered transcriptional gene regulation in the exposed fish. Heavy metal bioaccumulation leads to various anomalies in non-target species. The gills, liver, and kidney are the major organs susceptible to heavy metal toxicity and are extensively studied for the assessment of histopathological manifestations instigated by heavy metals. These organs respond differently to several metal toxicants and are considered a crucial bio-monitoring tool in analyzing their detrimental outcomes in several fish species.
The degree of heavy metal accumulation is influenced by several factors, including pH, temperature, water hardness, exposure time, species feeding patterns, and habitat complexity. It also depends on the dose and duration of exposure, the species, and the gender of the organism. Aquatic organisms are affected by metal pollution at the cellular level, resulting in an ecological imbalance that weakens the food chain. As top predators in the food pyramid, fish are prime targets for the biomagnification of metals and are likely to act as transfer media to humans.
Fish and other seafood are often a primary source of metal exposure for the general population. Foods containing toxic metals above permitted levels are considered harmful to human health and are banned for trade by many national and international regulations. Some toxic effects of heavy metal consumption include impaired renal and liver function, decreased cognitive function, impaired reproductive capacity, hypertension, neurological changes, teratogenic effects, and cancers.
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Pesticides and hydrocarbons
Pesticides are potent chemical contaminants that enter the aquatic environment through natural and human activities. They are toxic to fish, adversely affecting their growth, physiology, reproduction, immunity, and biochemistry, and induce serious histopathological alterations of several tissues. Fish are sensitive to endocrine disruptors, and sublethal exposure to pesticides has been shown to cause inhibition of important enzymes and growth delay. For example, in 2012, thousands of fish died in Prince Edward Island, Canada, due to pesticide runoff from nearby agricultural fields after heavy rain. This event highlights the lethal consequences of pesticide exposure for fish populations.
Pesticides can also alter the behavior of fish. For instance, carbofuran pesticide alters neurofunction and activity in sea bass, while fluoxetine antidepressant (Prozac) changes aggression, boldness, and learning abilities in the Siamese fighting fish by acting on the serotonin system. Low doses of pesticides have been observed to decrease activity in goldfish, possibly due to increased detoxification costs and physiological defenses. These behavioral changes may be driven by alterations in energetic balance.
Furthermore, pesticides can bioaccumulate in different fish tissues, leading to health concerns for consumers, including humans. For example, a study on Nile tilapia (Oreochromis niloticus) found that prolonged exposure to high doses of the pesticide thiamethoxam resulted in significant negative effects, including potential damage to the kidneys and liver, oxidative stress, and severe degenerative changes in the gills and liver tissues. Thiamethoxam also negatively impacted the fish's antioxidant defense system and left residues in the muscle tissue.
Hydrocarbons, specifically petroleum hydrocarbons, are another type of pollutant that poses a significant threat to aquatic life, including fish. Crude oil spills in aquatic environments can have toxic effects on various organisms, including fish, leading to high mortality rates. The toxicity of crude oil and its constituents has been demonstrated in multiple studies. For example, dispersed oil has been found to reduce growth rates and cause acute toxicity for 1-4 weeks, with toxicity being higher in low-saline environments due to reduced biodegradation.
Polycyclic Aromatic Hydrocarbons (PAHs) are a specific type of hydrocarbon that has been studied for their influence on aquatic species. They can be taken up by fish from sediments and cause toxic effects, including malformations, genetic damage, and mortality in fish embryos and larval stages. PAHs can also affect the behavior of fish, as observed in studies on zebrafish and gilthead seabream. The presence of PAHs in the aquatic environment is a concern due to their toxic effects on multiple species within food chains, including fish.
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Oxygen deprivation
Aquatic life, including fish, relies on sufficient levels of oxygen dissolved in the water to survive. Oxygen depletion can occur for several reasons, including pollution. The primary cause of oxygen depletion in a water body is excessive algae and phytoplankton growth driven by high levels of phosphorus and nitrogen. During the night, these photosynthetic organisms consume oxygen through respiration. Additionally, as algae and phytoplankton die, their decomposition requires significant amounts of oxygen. If these blooms are dense or die off suddenly, the impact on fish can be severe and cause fish kills.
Water temperature also plays a role in oxygen depletion. High water temperatures (86°F or higher) reduce the oxygen-holding capacity of water. Fish are cold-blooded animals, so their body temperature and activities are regulated by the water they inhabit. Warm water increases a fish's consumption of oxygen by accelerating their metabolic rate. Weather conditions can also contribute to oxygen depletion. Cloudy days, for example, slow or halt oxygen production through photosynthesis, and still, windless days limit the circulation of water and the surface diffusion of atmospheric oxygen.
Pollution by biodegradable organic substances, including wastewater from agriculture, the food industry, and public sewage, is the most frequent cause of significant reductions in oxygen concentration in water. In heavily polluted water with coloured organic waste, the increase in organic content alone can lead to an oxygen deficit. Additionally, certain chemicals, such as formalin, directly remove oxygen from the water.
To prevent fish kills caused by low oxygen levels, commercial catfish farms hire night oxygen crews to monitor oxygen concentrations in ponds at two-hour intervals overnight. Aeration systems can be turned on if oxygen levels drop below a certain concentration, typically 2–4 mg/L, depending on the fish species.
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Frequently asked questions
Pollution can cause severe destruction to fish and other aquatic organisms. It can cause direct harm to fish by introducing toxic chemicals such as heavy metals, pesticides, and oil spills, which fish can ingest and cause deformities and even death.
Toxic chemicals are often released into the aquatic environment through industrial and municipal discharges, agricultural practices, and stormwater runoff. These chemicals include PCBs, PBDEs, dioxins, and chlorinated pesticides, which fish absorb from water, sediments, and their food.
Pollution can cause a range of health issues in fish, including immune system suppression, reproductive problems, abnormalities, and developmental issues. It can also lead to specific diseases, such as fin and tail rot, gill disease, and vibriosis.
Pollution can alter the behaviour, personality, and cognition of fish. For example, pesticides can change neurofunction, activity levels, aggression, and learning abilities.
Reducing the release of toxic chemicals into the environment is crucial to mitigate the effects of pollution on fish. Proper waste management and treatment practices can help prevent the contamination of waterways. Additionally, consuming and cooking fish properly can reduce the risk of contaminant exposure, although this does not apply to certain contaminants like mercury.
