Fish Survival In Polluted Waters: Is It Possible?

Fish are incredibly vulnerable to the effects of water pollution, which can directly kill or harm them, or change the makeup of their surroundings, killing off sources of food or causing plant or algae overgrowth that starves them of oxygen. Water pollution can also cause deformities, reproductive problems, and even death. With pollution affecting every corner of the world, fish are now facing an additional threat to their survival, on top of the daily struggle to escape predators and find food.

Pharmaceuticals in wastewater

A range of pharmaceuticals, including antidepressants, opioids, muscle relaxants, and sleep aids, have been detected in treated wastewater released into streams. These drugs can affect both juvenile and adult fish, with varying impacts on different species. For example, juvenile fathead minnows exposed to pharmaceuticals experienced reduced growth and altered escape behaviour, making them more susceptible to predation. Adult male fish exposed to certain pharmaceuticals exhibited reduced nest defence behaviours, while adult female fish showed increased relative liver size, indicating a reaction to the influx of pharmaceuticals.

The presence of pharmaceuticals in wastewater can also lead to gender-bending effects in fish, with elevated oestrogen levels in rivers causing a transformation in the gender of fish. Additionally, antidepressants have been found to reduce territorial aggression in some fish species and alter feeding rates.

The accumulation of pharmaceuticals in fish tissues has been studied extensively, with detection rates varying depending on the compound and fish species. Psychoactive drugs, such as antidepressants and antiepileptics, are often the most prevalent, with venlafaxine, carbamazepine, and sotalol being commonly detected. These drugs are highly prescribed and relatively resistant to degradation during conventional wastewater treatment.

The bioaccumulation of pharmaceuticals in fish can have ecological implications, with potential effects on food-web properties and ecosystem functioning. However, the scarcity of standardised behavioural studies and the complexity of real-world conditions make it challenging to draw general conclusions about the ecological impact of pharmaceuticals in aquatic systems.

Pesticides and heavy metals

Fish can be exposed to pesticides and heavy metals in several ways. They can absorb them from the water they live in, the food they eat, and the sediment at the bottom of the body of water. Fish can also be exposed to these pollutants through their gills, skin, and muscles.

Heavy metals, in particular, can bioaccumulate in fish tissues, meaning that larger, older fish tend to have higher concentrations of these contaminants. This makes them a serious health risk to humans who consume them.

Some of the heavy metals commonly found in fish include lead, chromium, copper, zinc, cadmium, mercury, and arsenic. These metals can cause DNA damage and cancer, as well as damage to the central nervous system and possible adverse effects on the cardiovascular system.

To reduce exposure to pesticides and heavy metals, it is recommended to consume smaller, wild-caught fish from less polluted waters. Farmed fish, especially those that are not organic, tend to have higher levels of contaminants. When choosing fish to eat, it is important to consider the species, origin, and farming method to minimize the risk of consuming high levels of pesticides and heavy metals.

Plastic pollution

The Impact of Plastic Pollution on Fish

The Problem of Microplastics

Microplastics, plastics smaller than 5mm, are of particular concern. Due to their microscopic size, they are easily consumed by fish and other marine organisms. These microplastics have the ability to adsorb toxins, which then transfer to the fatty tissues of the organisms that ingest them. The long-term impacts of microplastics are still being studied, but their presence in the food chain is undeniable. A study found traces of microplastics in the guts of all seven species of sea turtles from the Atlantic, Pacific, and Mediterranean Seas. Additionally, hundreds of fish species, including those consumed by humans, have been found with microplastics in their bodies.

Addressing the Issue

The most effective way to tackle marine plastic pollution is to prevent plastic from entering our oceans in the first place. This includes minimizing plastic leakage, reducing plastic toxicity, and promoting plastic reuse, repurposing, and recycling. It is crucial to shift our perspective on plastic and treat it as a valuable resource rather than waste. By doing so, we can reduce the amount of plastic pollution in our oceans and mitigate its harmful effects on fish and other marine life.

Oil spills

The immediate health effects of oil exposure for marine and coastal wildlife include skin irritation, immune system alterations, reproductive or developmental damage, and liver disease. In high doses, oil ingestion can cause gastrointestinal irritation, ulcers, bleeding, diarrhea, and digestive complications, ultimately impairing the animal's ability to absorb nutrients. Oil absorption through the skin can damage the liver and kidneys, cause anemia, suppress the immune system, and induce reproductive failure. Inhalation of volatile organic compounds released by oil can cause respiratory inflammation, irritation, emphysema, or pneumonia.

The effects of oil exposure are particularly detrimental to fish in their embryo or larval stage, as this is when they are most vulnerable to toxins. Exposure during this critical period can cause deformities in the heart, spine, and brain, as well as behavioural defects that make it harder for fish to survive. Confronted with predators, oil-exposed fish are less likely to seek shelter or flee, and they are more likely to take risks that endanger their lives.

The vulnerability of fish to oil spills also depends on their mobility and feeding habits. Many shellfish species, for instance, are relatively immobile and indiscriminate filter feeders, making them more susceptible to oil exposure compared to more mobile finfish that can be selective about their food sources.

Fertilizer nutrients

Impact on Oxygen Levels

The excessive growth of algae and aquatic plants due to nutrient pollution has a significant impact on oxygen levels in water. As these organisms grow and eventually die off, they undergo decay, a process that consumes oxygen in the water. This leads to a decrease in dissolved oxygen levels, creating "dead zones" where fish and other aquatic organisms cannot survive due to suffocation.

Harmful Algal Blooms

Long-term Effects

The presence of excess fertilizer nutrients in water can have long-term effects on fish populations. The depletion of oxygen and the accumulation of toxins can lead to fish kills, disrupting the natural balance of the ecosystem. Additionally, the toxins can bioaccumulate in the tissues of fish, making them unsafe for human consumption. This can have economic implications for fisheries and fishing communities.

Preventative Measures

To mitigate the negative impacts of fertilizer nutrients on fish and aquatic ecosystems, proper nutrient management practices are essential. Farmers can adopt techniques such as applying the right amount of fertilizer at the appropriate time of year and using methods that minimize runoff. Implementing conservation practices, such as cover crops, field buffers, and conservation tillage, can also help reduce nutrient losses and prevent excess nutrients from reaching water bodies.

By addressing the issue of fertilizer nutrient pollution, we can protect fish populations and maintain the health and sustainability of aquatic ecosystems, ensuring their survival for future generations.

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