A recent study has revealed that long-term exposure to fluoxetine (Prozac), a common antidepressant medication, can significantly disrupt the behaviour and reproductive traits of the male guppy fish.

The study, led by a group of biologists from Australia’s Monash University and Italy’s University of Tuscia, was published in the Journal of Animal Ecology on August 26 and highlights the far-reaching effects of pharmaceutical pollution on aquatic ecosystems.

“Our results reveal that chronic exposure to global pollutants can affect phenotypic traits at both population and individual levels, and even alter individual-level correlations among such traits in a dose-specific manner,” the study mentioned.

The researchers exposed wild caught guppies to low (31.5 ng/L) and high (316 ng/L [Nanograms per litre]) concentrations of fluoxetine over multiple generations to simulate the chronic pollution found in water bodies.

Only male guppies were used for the experiment since they are particularly sensitive to environmental changes.

They observed several concerning impacts on the fish.

Effects on fish with low concentrations of fluoxetine

At low concentrations, fluoxetine reduced activity levels and increased refuge-seeking behaviour in male guppies. Refuge seeking behaviour refers specifically to how much time the fish spend in hiding or protected areas, as opposed to open, potentially more dangerous spaces in their habitat.

It also altered their body condition, increased the size of their reproductive organs, and reduced sperm velocity. These effects could have significant implications for mating success and reproductive fitness in polluted waters.

Interestingly, the study found that fluoxetine exposure reduced behavioural plasticity in the fish, suppressing within-individual variation in both activity and refuge.

Individual fishes are behaving more rigidly, potentially limiting their ability to respond flexibly to their environment.

This could have significant ecological implications, especially in dynamic or changing environments where behavioural flexibility is important for survival.

The findings suggest that the pollutant may have a stabilising effect on behaviour over time, potentially favouring more consistent behavioural profiles. While this could improve mating success in some contexts, it may also limit the fish’s ability to adapt to changing environmental conditions

Effects of high concentration of fluoxetine

The researchers also observed dose-specific effects on body condition and sperm production.

High fluoxetine concentrations increased variation in body condition between individuals, while low concentrations increased variation in sperm numbers.

This shows why it’s important to look at individual level responses to pollution, as group-levels (population-levels) might vary.

The researchers also discovered that fluoxetine changed ‘pace of life syndromes’, which are an organism’s biological and behavioural traits using which they interconnect and evolve together.

For instance, in polluted water, fish that were more active tended to be less healthy, insinuating that high activity might be a waste of energy that could have kept the fish healthier.

Also, fish with larger reproductive organs usually had lower quality sperm, hinting at altering reproductive behaviour when faced with pollution.

Upama Aich, the study’s lead author, emphasised on the broader implications of these findings: “Our research shows that the effects of pharmaceutical pollutants go far beyond simple average responses. They can fundamentally alter the relationships between different traits, potentially constraining the adaptive capacity of wildlife facing environmental challenges .”

These findings show that pollution can have complex effects on fish, influencing not just single traits, but how different aspects of fish biology work in tandem.

While their study focused on guppies, the findings likely have relevance for many other aquatic species exposed to pharmaceutical pollution.

As pharmaceutical use continues to increase globally, this study underscores the urgent need for improved wastewater treatment and management strategies to mitigate the long-term impacts of these pollutants on aquatic life.

Simply Put: Fishing and evolution