Greta Jimenez
Water pollution is caused by any element, whether chemical or natural, that upsets the balance of a fish's environment. Water pollutants are wide-ranging and depend on the region of the world the fish live in, but there are some that are common across the globe, such as pesticides, heavy metals, hydrocarbons, and oils. These pollutants can directly kill fish or change the makeup of their surroundings, killing off sources of food or causing plant or algae overgrowth that starves the fish of oxygen. For example, pesticides are toxic to waterborne insects that fish feed on, and if the insects are not killed, the pesticide is transferred to the fish when they eat the insects. Over time, the pesticide builds up in the fish until it reaches a fatal level. Similarly, oils discharged into rivers or ponds reduce the transfer of oxygen from the air to the water, contaminating the gills of fish and reducing their respiratory capacity.
| Characteristics | Values |
|---|---|
| Pollution Type | Heavy metals, pesticides, hydrocarbons, oils, inorganic compounds, pharmaceuticals, sediment, sewage, nitrogen, phosphorus |
| Impact on Fish | Immunosuppression, reduced metabolism, damage to gills and epithelia, gill disease, liver damage, neoplasia, ulceration, abnormalities, reproductive problems, reduced biodiversity, oxygen deficiency, contamination, starvation, behavioural changes |
| Specific Diseases | Epidermal papilloma, fin/tail rot, vibriosis, enteric redmouth |
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What You'll Learn
Pesticides and heavy metals
Pesticides are biological pollutants used to kill pests and increase crop yields. They can contaminate water, ground, grass, and other vegetation. While pesticides are designed to kill pests and insects, they can also be toxic to other creatures such as birds, fish, and beneficial insects.
Fish can be directly or indirectly impacted by pesticides. For example, pesticides can cause metabolic and reproductive disorders in fish, as well as histopathological changes in their gills, liver, and other organs. They can also result in genetic defects and behavioural disorders.
The economic cost of the impacts of pesticides on fish is significant. One estimate assumes that the economic value of fish killed by pesticides each year is $10-25 million. This is likely an underestimate, as fish kills due to pesticides are hard to trace. As fish kills due to pesticides increase, there will be less fish available for recreational fishing, which will increase costs for citizens who participate in this activity.
Heavy metals are another type of pollutant that can accumulate in fish bodies. Heavy metals are non-biodegradable and can cause toxicity in fish and other aquatic organisms. They can be deposited into water and sediments, where they can be taken up by fish. Certain heavy metals, such as zinc, cadmium, chromium, arsenic, lead, and nickel, have been found in high concentrations in some fish species.
The accumulation of heavy metals in fish can pose a serious threat to human health. For example, a single gram of mercury can contaminate a 20-acre lake to the extent that fish become unsafe for human consumption. Heavy metal pollution in aquatic environments is a worldwide concern, and it is essential to address this issue through awareness and action.
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Oil discharge
Oil spills have devastating effects on fish, from hatching to maturity, and can even cause death. While most oils float, and therefore do not affect organisms living in the water column or on the ocean floor, non-floating oils can smother fish that dwell on the bottom of oceans and lakes, or damage aquatic vegetation, leading to starvation.
In shallow waters and confined areas, such as lakes, lagoons, and some nearshore areas, oil spills can have more harmful consequences. For example, in 1994, territorial reef fishes in nearshore areas off Puerto Rico were greatly affected by an oil spill. Similarly, fish were killed in the polluted waters following Hurricane Rita in the Gulf of Mexico in 2005.
Oil spills can also affect fish eggs and larvae, causing lethal and sublethal impacts. Salmon eggs in a streambed, for instance, can be wiped out by an oil spill. Fish embryos exposed to the Deepwater Horizon oil spill developed heart defects and other deformities, shortening the lives of some and killing others.
Additionally, oil spills can indirectly harm fish by poisoning their food sources. Phytoplankton, a vital food source for many marine animals, can be poisoned by oil, which then affects any fish that eat the compromised food. This can quickly become a problem as oil travels up the food chain to larger predatory animals and, eventually, humans.
Furthermore, oil spills have been found to affect the behaviour of juvenile fish, making them less likely to seek shelter from predators and more likely to engage in risky behaviour, which can jeopardize their survival. These behavioural defects occur even with low concentrations of oil and can have consequences for the larger ecosystem as well.
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Lack of oxygen
Aquatic life, including fish, requires oxygen to survive. A lack of oxygen in water bodies, also known as hypoxia, poses a grave threat to these ecosystems. Low oxygen levels in water bodies can be caused by a variety of factors, including natural causes and human activities.
One natural cause of hypoxia is stratification in the water column. This occurs when less dense freshwater from an estuary mixes with heavier seawater, restricting the supply of oxygen from the surface to the bottom waters. Another natural cause is the overgrowth of certain species of algae, which can lead to oxygen depletion when they die, sink, and decompose. This process of decomposition requires a significant amount of oxygen, and if the algae blooms are dense or die off suddenly, it can have severe impacts on fish populations.
Human activities can also contribute to hypoxia and low oxygen levels in water bodies. Nutrient pollution, specifically the excess of nitrogen and phosphorus nutrients, is a significant factor. This can be a result of agricultural runoff, fossil fuel burning, and wastewater treatment effluent. Municipal wastewater treatment systems, urban stormwater runoff, and vegetation decay add to the loadings of pollutants when they discharge into rivers and other waterways, reducing dissolved oxygen levels.
Additionally, temperature plays a crucial role in oxygen levels. High water temperatures reduce the oxygen-holding capacity of water. As fish are cold-blooded, their metabolic rate increases in warmer water, leading to higher oxygen consumption. Weather conditions also influence oxygen levels; cloudy days can slow or halt oxygen production through photosynthesis due to reduced light penetration. Still, windless days limit the circulation of water and the diffusion of atmospheric oxygen.
The impacts of low oxygen levels on fish are significant. Fish may exhibit gasping behaviour, indicating insufficient oxygen levels. Prolonged exposure to low oxygen can lead to increased stress, diseases, and even death. Lethal oxygen levels for fish are typically between 1 and 3 mg/L. While some aquatic organisms have adapted to tolerate lower oxygen levels, many fish and invertebrates are highly susceptible to oxygen depletion.
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Pharmaceutical drugs
Pharmaceutical pollution in waterways is a growing concern, with over 900 different pharmaceutical ingredients detected in rivers and streams globally. While the impact on humans is currently unknown, research shows that pharmaceuticals can accumulate in fish and other aquatic organisms, leading to adverse health and behavioural effects.
Laboratory and field studies have found that exposure to pharmaceuticals can lead to reduced growth and altered escape behaviour in juvenile fish, while adult males exhibited reduced nest defence behaviour and produced plasma vitellogenin, a protein associated with female egg production, indicating feminisation.
Additionally, antidepressants, psychiatric drugs, and antihistamines have been shown to induce behavioural changes in fish, with varying effects on different species. For example, perch became more active while damselfly behaviour remained unaffected. Furthermore, Arabian killifish exhibited increased sociality after exposure to fluoxetine, and fathead minnows showed increased boldness after exposure to sertraline.
The presence of pharmaceuticals in fish has been extensively studied, with psychoactive drugs, antihistamines, β-blockers, antibiotics, anti-inflammatories, and synthetic hormones detected in fish tissues. These compounds can bioaccumulate in freshwater and marine fish, leading to potential multigenerational effects and impacts on higher members of the food web.
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Fish waste and litter
When fish waste decomposes through bacterial action, it can deplete the water of dissolved oxygen, leading to oxygen depletion, which is harmful to fish and other aquatic life. This process can also create unpleasant odours, especially during warmer temperatures, and attract scavengers such as stingrays, pelicans, and seals. While this provides a food source for these animals, it alters their normal behaviour and could potentially affect their health and fitness.
The increase in global fisheries and aquaculture production, driven by advancements in fishing technologies and aquaculture development, has resulted in a remarkable increase in fish waste worldwide. It is estimated that about two-thirds of the total amount of fish is discarded as waste, creating economic and environmental concerns. The improper disposal of fish waste can lead to water contamination and negatively impact water quality, aquatic life, and even human health.
To reduce the impact of fish waste on the environment, it is essential to practise responsible waste management. This includes disposing of fish waste in designated bins or taking it home instead of tossing it into nearby waterways. Additionally, familiarizing oneself with fishing techniques that minimize gear loss and marine litter, such as using a tackle box to keep gear tidy and packaging-free, can help prevent litter from entering waterways.
Litter, including fishing litter and lost gear, can also contribute to water pollution and harm fish and other aquatic organisms. It is important to properly dispose of rubbish, bait, and unwanted tackle, and to leave no trace by cleaning up any litter, even if it is not yours. Leaving a fishing spot cleaner than you found it helps reduce the impact of litter on the environment and ensures the health and safety of aquatic life.
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Frequently asked questions
Fish require untainted food, a suitable habitat, and adequate oxygen to survive. Pollutants can directly kill or harm fish, or change the makeup of their surroundings, killing off their food sources or causing plant or algae overgrowth that starves the fish of oxygen.
Pesticides are toxic to waterborne insects that fish feed on, even in low concentrations. If the pesticide does not kill the insect, it is transferred when a fish eats it. Over time, pesticides build up in the fish until they reach a fatal level.
Heavy metals are particularly toxic in the early stages of a fish's development. They can also accumulate in the sediments and in aquatic flora and fauna (bioaccumulation). Mercury, selenium, and cadmium have a particularly high bioaccumulation capacity.
When oils are discharged into rivers or ponds, they spread on the surface, reducing the transfer of oxygen from the air to the water. The gills of fish can become mechanically contaminated and their respiratory capacity reduced. Oil products may contain toxic substances such as benzene, toluene, and xylene, which can have a direct toxic effect on fish.
