Sheepshead minnow adapting to fluctuating temperatures in an estuary.

Can Fish Adapt? How Temperature Changes Affect Aquatic Life

Nico Varela in Science & Nature December 2025 • 5 min read.

"Explore how chronic temperature exposure impacts the resilience of sheepshead minnows, offering insights into the broader effects of climate change on aquatic ecosystems."

Estuaries, where rivers meet the sea, are among the most dynamic environments on Earth. Tides bring constant change, drastically altering temperature, salinity, and dissolved oxygen levels. Creatures living in these habitats must be incredibly resilient to survive such rapid and frequent shifts.

Among these hardy inhabitants is the sheepshead minnow (Cyprinodon variegatus), a small fish that thrives in the challenging conditions of estuarine landscapes. Scientists are keen to understand how this species adapts to environmental stressors, especially as climate change intensifies these challenges.

A recent study explored how chronic temperature exposure affects the sheepshead minnow's ability to tolerate hypoxia, a condition of low oxygen. The findings offer valuable insights into the potential impacts of climate change on aquatic ecosystems and the adaptive strategies that allow some species to persist.

How Does Temperature Exposure Affect Fish Resilience?

Sheepshead minnow adapting to fluctuating temperatures in an estuary.

Researchers at Colgate University conducted a study to examine the effects of long-term temperature exposure on sheepshead minnows. The fish were divided into four groups and kept at different temperatures—15°C, 20°C, 25°C, and 30°C—for one month. After this period, the scientists tested how well the fish could tolerate acute hypoxia and measured several indicators of oxidative stress.

Oxidative stress occurs when there is an imbalance between the production of reactive oxygen species (ROS) and the body's ability to neutralize them. ROS can damage cells and tissues, so organisms have antioxidant defenses to counteract their harmful effects. The researchers measured the activity of key antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)—as well as total antioxidant capacity and lipid peroxidation (LPO), a marker of cell damage.

Critical Thermal Maxima (CTmax): The study found that minnows exposed to higher temperatures (25°C and 30°C) for a month had significantly higher CTmax values, indicating an increased tolerance to heat.
Catalase (CAT) Activity: CAT activity increased significantly in the 20°C and 25°C groups, suggesting an enhanced ability to deal with oxidative stress at these temperatures.
Superoxide Dismutase (SOD) Activity: SOD activity was higher in the control groups of the 15°C and 30°C treatments compared to the hypoxia groups, indicating that hypoxia might reduce SOD activity.
Glutathione Peroxidase (GPx) Activity: GPx activity was significantly lower in the 30°C group, regardless of whether they were exposed to hypoxia, suggesting a reduced antioxidant capacity at this higher temperature.
Hydroxyl Scavenging Capacity: This varied across temperature treatments and control/hypoxia groups, indicating complex interactions between temperature and oxygen levels.
Peroxyl Scavenging Capacity and LPO Damage: No significant differences were observed across temperature treatment groups or between control and hypoxia trials for these measures.

These findings suggest that chronic exposure to different temperatures can significantly alter the physiological responses of sheepshead minnows. The increased CTmax at higher temperatures indicates a capacity to acclimate to warmer conditions. However, the changes in antioxidant enzyme activities reveal a more complex picture of how these fish cope with oxidative stress under varying temperature and oxygen conditions.

What Does This Mean for the Future?

The sheepshead minnow's ability to adjust to increasing temperatures and fluctuating oxygen levels offers a glimmer of hope in the face of climate change. By understanding the specific mechanisms that allow these fish to thrive in challenging conditions, scientists can gain insights into the broader adaptive potential of aquatic species. This knowledge is crucial for developing effective conservation strategies and predicting how ecosystems will respond to ongoing environmental changes. Further research is needed to fully understand the long-term implications of these adaptations and to identify other species that may possess similar resilience.

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This article is based on research published under:

DOI-LINK: 10.1007/s10695-018-0583-0, Alternate LINK

Title: How Does Chronic Temperature Exposure Affect Hypoxia Tolerance In Sheepshead Minnows’ (Cyprinodon Variegatus Variegatus) Ability To Tolerate Oxidative Stress?

Subject: Aquatic Science

Journal: Fish Physiology and Biochemistry

Publisher: Springer Science and Business Media LLC

Authors: Ana Gabriela Jimenez, Evan Braun, Kailey Tobin

Published: 2018-11-05

Everything You Need To Know

What is the sheepshead minnow, and why is it significant?

The sheepshead minnow is a small fish, scientifically known as Cyprinodon variegatus. It is particularly well-suited to estuarine environments, which are areas where rivers meet the sea. These areas are characterized by dynamic conditions including fluctuating temperatures, salinity, and dissolved oxygen levels. Its importance lies in its ability to survive in these challenging conditions and its significance to understanding how other aquatic species may adapt to climate change. Understanding its survival mechanisms can offer insight into the broader adaptive potential of aquatic species facing the same environmental stressors.

What were the experimental conditions and methods used in the study?

The study involved exposing sheepshead minnows to different temperatures (15°C, 20°C, 25°C, and 30°C) for a month. After this period, researchers examined the fish's tolerance to hypoxia (low oxygen conditions) and measured indicators of oxidative stress. These indicators included the activity of antioxidant enzymes such as Superoxide dismutase (SOD), Catalase (CAT), and Glutathione peroxidase (GPx), along with total antioxidant capacity and lipid peroxidation (LPO) levels. By measuring these factors, the scientists could assess how the fish's physiology changed in response to varying temperatures and their ability to cope with stress.

What is oxidative stress, and how was it measured in the study?

Oxidative stress occurs when there's an imbalance between the production of reactive oxygen species (ROS) and the body's ability to neutralize them. ROS can damage cells and tissues. The study measured several indicators related to oxidative stress in sheepshead minnows. The measurement of antioxidant enzymes—SOD, CAT, and GPx—provided insight into the fish's ability to counteract the harmful effects of ROS. Lipid peroxidation (LPO) was used as a marker of cell damage caused by oxidative stress. The results showed that different temperature exposures significantly altered the activity of these enzymes, indicating a complex physiological response to temperature and its effect on the fish's overall health.

What specific physiological responses of the sheepshead minnow were measured?

The study measured several key metrics to assess the impact of temperature exposure on sheepshead minnows. The Critical Thermal Maxima (CTmax) represents the highest temperature the fish can tolerate. The higher CTmax values in fish exposed to 25°C and 30°C indicate that they developed a greater tolerance to heat. The activity of antioxidant enzymes like Catalase (CAT), Superoxide Dismutase (SOD), and Glutathione Peroxidase (GPx) was measured. The varying responses of these enzymes to different temperatures revealed how the fish's antioxidant defense mechanisms were affected. The study also measured Hydroxyl Scavenging Capacity and Peroxyl Scavenging Capacity. These data points give information about how the fish's ability to deal with oxidative stress changes.

What are the key takeaways and implications of the study's findings?

The findings suggest that the sheepshead minnow has the capacity to acclimate to warmer conditions. It is shown by the increased CTmax in higher temperatures. The changes in antioxidant enzyme activities like Catalase, Superoxide dismutase, and Glutathione Peroxidase, reveal a complex picture of how the fish manage oxidative stress under different temperature and oxygen conditions. The study implies that understanding these mechanisms could inform conservation strategies. Further research is needed to fully understand the long-term implications and identify other species with similar resilience.