River with pill swirls, sea trout silhouette

Do Antidepressants in Our Waterways Affect Fish Behavior? The Troubling Truth

Reese Marlowe in Climate & Environment December 2025 • 4 min read.

"New research reveals how common pharmaceuticals like temazepam and irbesartan are impacting aquatic life, raising questions about water quality and the subtle effects on ecosystems."

For years, scientists have been concerned about the increasing presence of pharmaceuticals in our rivers and streams. These chemicals, which enter the environment through wastewater treatment plants and other sources, can have unintended consequences for wildlife. While it's well-known that certain drugs can affect human behavior, less is understood about how these substances impact animals in their natural habitats.

A recent study published in Aquatic Toxicology sheds light on this issue, focusing on the effects of two common pharmaceuticals—temazepam (an anti-anxiety medication) and irbesartan (a blood pressure medication)—on the behavior of sea trout (Salmo trutta). This research not only highlights the potential risks to aquatic ecosystems but also raises broader questions about water quality and the long-term effects of pharmaceutical pollution.

Researchers from Umeå University and the Swedish University of Agricultural Sciences investigated how exposure to these drugs influences the behavior of sea trout smolts, both in the laboratory and in their natural environment. The results offer surprising insights into how even low concentrations of pharmaceuticals can alter the behavior of fish, with potential implications for their survival and the overall health of aquatic ecosystems.

Pharmaceuticals in Our Waterways: What Are the Risks to Fish?

River with pill swirls, sea trout silhouette

The study focused on temazepam and irbesartan because they are frequently detected in surface waters and have known effects on human physiology. Temazepam, a benzodiazepine, is prescribed to treat anxiety and insomnia, while irbesartan is used to manage high blood pressure. Both drugs have conserved targets in teleost fish (bony fish), suggesting they could exert similar therapeutic effects on these animals.

The researchers conducted a series of experiments to assess how these pharmaceuticals affect sea trout smolts. These experiments included:

Laboratory Exposure: Sea trout smolts were exposed to different concentrations of temazepam and irbesartan in controlled laboratory settings to measure tissue bioconcentration (how much of the drug accumulates in their bodies) and behavioral changes.
Behavioral Assays: The fish underwent behavioral tests, such as the scototaxis assay (measuring anxiety-related behavior) and activity level assessments in specially designed tanks.
Field Migration Study: Tagged fish were released into a small stream with strategically placed antennas to track their downstream migration speed and behavior in a natural environment.

The study aimed to determine whether changes in behavior observed in the lab could predict how fish behave in the wild, and whether exposure to these pharmaceuticals could disrupt their natural migration patterns. The results were both intriguing and concerning.

Why This Matters: Protecting Our Waterways and Wildlife

This research underscores the importance of considering the subtle, yet significant, effects of pharmaceutical pollution on aquatic ecosystems. By demonstrating that common medications can alter fish behavior, even at low concentrations, the study highlights the need for more comprehensive water quality monitoring and improved wastewater treatment processes.

About this Article -

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This article is based on research published under:

DOI-LINK: 10.1016/j.aquatox.2018.11.028, Alternate LINK

Title: Investigating Tissue Bioconcentration And The Behavioural Effects Of Two Pharmaceutical Pollutants On Sea Trout (Salmo Trutta) In The Laboratory And Field

Subject: Health, Toxicology and Mutagenesis

Journal: Aquatic Toxicology

Publisher: Elsevier BV

Authors: Erin S. Mccallum, Anna Sundelin, Jerker Fick, Anders Alanärä, Jonatan Klaminder, Gustav Hellström, Tomas Brodin

Published: 2019-02-01

Everything You Need To Know

What pharmaceuticals were studied and what were their effects on fish?

The study investigated the effects of temazepam, an anti-anxiety medication, and irbesartan, a blood pressure medication, on sea trout. These pharmaceuticals were selected because they are commonly detected in surface waters. The research revealed that even low concentrations of these drugs can alter the behavior of the sea trout, potentially impacting their survival and the health of aquatic ecosystems. This is important because it shows how human medications can have unintended consequences for wildlife.

What were the main experiments conducted in this study?

The study involved several key experiments. In the Laboratory Exposure experiments, sea trout smolts were exposed to different concentrations of temazepam and irbesartan to measure how much of the drug accumulated in their bodies (tissue bioconcentration) and to observe any changes in their behavior. Behavioral Assays involved tests like the scototaxis assay, designed to measure anxiety-related behavior, and activity level assessments in tanks. The Field Migration Study tracked tagged fish released into a stream to observe their downstream migration speed and behavior in their natural environment. These experiments were designed to connect lab findings to real-world impacts.

Why are these findings important for water quality and conservation?

The study's findings have broad implications for water quality and conservation efforts. The fact that pharmaceuticals like temazepam and irbesartan can alter fish behavior, even at low concentrations, underscores the need for enhanced water quality monitoring. Moreover, it highlights the importance of improving wastewater treatment processes to remove these substances before they enter our waterways. This research suggests that the presence of pharmaceuticals in aquatic environments could be disrupting the natural behavior of fish, potentially affecting their ability to survive, reproduce, and maintain healthy populations. It also suggests that these drugs could influence the health and function of the entire aquatic ecosystem.

Why were sea trout chosen for this study?

The study focused on sea trout (*Salmo trutta*) because they are a common species in aquatic environments. Sea trout were used as a model to understand how pharmaceuticals affect fish behavior more broadly. The selection of the species also allowed researchers to study potential effects on migration patterns. The findings regarding temazepam and irbesartan can be extended to understanding potential effects of other pharmaceuticals on other fish and other aquatic species.

Why does the presence of pharmaceuticals in waterways pose a risk to fish?

The presence of pharmaceuticals like temazepam and irbesartan in waterways poses risks to fish because they can alter their behavior. For example, these drugs may affect their anxiety levels, activity levels, and migration patterns. This can impact their ability to find food, avoid predators, and reproduce. The fact that these drugs can affect fish at low concentrations is particularly concerning, as it suggests that even small amounts of pollution can have significant consequences for aquatic life. This highlights the need for a better understanding of the effects of pharmaceutical pollution on aquatic ecosystems.