A 2026 study of 207 Eastern Hellbenders at the Indianapolis Zoo found that raising water temperature from 16°C to 21°C had no effect on growth rates, challenging the assumption that warmer conditions help these endangered salamanders grow faster. According to Gram Research analysis, this suggests zoos can maintain cooler, less expensive tank conditions without harming hellbender development, and should instead focus on optimizing diet and tank conditions.
Scientists at the Indianapolis Zoo studied whether raising the temperature in tanks helps Eastern Hellbenders—an endangered salamander-like creature—grow bigger and faster. They kept 207 young hellbenders in two different temperature settings for over a year and measured their growth every 8 weeks. Surprisingly, the hellbenders in warmer water (21°C) didn’t grow any better than those in cooler water (16°C). This finding challenges what many zoos thought about raising these rare animals and suggests that other factors like food and tank crowding might matter more for helping them thrive in captivity.
Key Statistics
A 2026 study of 207 Eastern Hellbenders conducted at the Indianapolis Zoo found no significant difference in growth between animals raised at 16°C (61°F) and those raised at 21°C (70°F) over an 18-month period.
Research published in Zoo Biology in 2026 tracked 207 young hellbenders every 8 weeks and found that warmer water temperatures did not increase mass or body length compared to cooler conditions, suggesting temperature may not be a limiting factor in captive rearing.
A 2026 controlled experiment with 207 Eastern Hellbenders showed that despite predictions based on general amphibian biology, this endangered species grew equally well in cool water (16°C) as in warmer water (21°C), challenging conventional captive breeding assumptions.
The Quick Take
- What they studied: Whether raising the water temperature helps Eastern Hellbenders grow larger in captive breeding programs
- Who participated: 207 young Eastern Hellbenders raised at the Indianapolis Zoo from February 2023 to July 2024
- Key finding: Hellbenders raised at 21°C (70°F) grew at the same rate as those raised at 16°C (61°F), showing no significant difference in size or weight gain
- What it means for you: If you work with endangered amphibians or support conservation efforts, this suggests zoos don’t need to invest heavily in heating systems to help hellbenders grow—they should focus on other factors like better food and proper tank conditions instead
The Research Details
Researchers divided 207 young Eastern Hellbenders into two groups at the Indianapolis Zoo. One group lived in water kept at 16°C (about 61°F), which is the typical temperature used at most zoos. The other group lived in warmer water at 21°C (about 70°F). Every 8 weeks for 18 months, scientists carefully measured how much each hellbender weighed and how long it was from head to tail. They tracked these measurements over time to see if the warmer group grew faster or bigger than the cooler group.
This type of study is called a controlled experiment because the scientists kept everything the same except for one thing—the water temperature. This makes it easier to see if temperature alone affects growth. The researchers collected data regularly and carefully, which helps make their results reliable.
Many zoos and breeding facilities have assumed that warmer water helps amphibians grow faster, based on what scientists know about other cold-blooded animals. However, hellbenders are unusual creatures that live in cool, fast-moving streams in nature. This study tests whether that general rule actually applies to hellbenders specifically. Understanding what conditions hellbenders really need is crucial for saving the species, since their wild populations are disappearing rapidly.
This study is reliable because it tracked a large number of animals (207) over a long period (18 months), used consistent measurement methods, and compared two clearly different conditions. The research was conducted at a professional zoo with proper animal care standards. The main limitation is that this study only tested two temperature levels, so we don’t know if other temperatures might work better. Also, the study only looked at one factor (temperature) and didn’t test whether other conditions like food quality or tank crowding might be more important.
What the Results Show
The most important finding was that Eastern Hellbenders grew at nearly identical rates in both temperature groups. Hellbenders in the cooler 16°C water gained weight and length just as well as those in the warmer 21°C water. This was surprising to the researchers because most cold-blooded animals grow faster when it’s warmer.
The study measured growth over 18 months with regular check-ins every 8 weeks, so the researchers had plenty of data to be confident in their conclusion. The lack of difference between the two groups was consistent throughout the entire study period—it wasn’t just a temporary pattern.
This finding suggests that Eastern Hellbenders may be different from many other amphibians. They might have adapted to thrive in cool water, which makes sense since they naturally live in cold mountain streams. Their bodies may not need warmth to grow well, unlike frogs or other salamanders that benefit from higher temperatures.
While the main finding was about temperature, the study also provided useful information about how hellbenders grow in general. The researchers documented normal growth patterns and rates for this species in captivity, which hadn’t been well-studied before. This baseline information helps other zoos understand what healthy growth looks like for hellbenders.
According to Gram Research analysis, this study challenges a common assumption in the amphibian conservation field. Many scientists and zoos believed that because temperature affects growth in most cold-blooded animals, it would also help hellbenders. However, this research shows that hellbenders may be an exception. The findings suggest that conservation programs should reconsider their heating strategies and instead focus on other factors that might be more important for this specific species.
The study only tested two temperature levels (16°C and 21°C), so we don’t know if other temperatures might produce different results. The research was conducted only at one zoo, so results might differ in other facilities with different conditions. The study focused only on temperature and didn’t test how other factors—like the type of food, how crowded the tanks were, or water quality—might affect growth. Additionally, all the hellbenders were young animals, so we don’t know if temperature affects adult hellbenders differently.
The Bottom Line
Zoos and conservation programs can confidently continue using cooler water temperatures (around 16°C) for captive Eastern Hellbenders without worrying that they’re slowing growth. This can actually save money on heating costs. However, facilities should still maintain consistent, stable temperatures and focus their efforts on improving other aspects of care, such as diet quality, tank design, and population density. The evidence for these temperature findings is strong based on this well-designed study.
Zoo professionals, amphibian conservation programs, and anyone involved in breeding endangered hellbenders should pay attention to these findings. Wildlife managers planning new breeding facilities can use this information to design more cost-effective systems. General nature lovers should care because this research helps save a species that’s disappearing from the wild. However, this study is specifically about captive breeding and doesn’t change anything about protecting wild hellbenders in their natural habitats.
If a zoo implements these findings by reducing heating costs and reinvesting in other improvements, they might see benefits within a few months as they improve other aspects of care. However, growth changes in hellbenders would take weeks to months to observe, similar to the 8-week measurement intervals used in this study.
Frequently Asked Questions
Do Eastern Hellbenders need warm water to grow in captivity?
No. A 2026 study of 207 hellbenders found they grew equally well at 16°C (61°F) and 21°C (70°F), suggesting temperature doesn’t significantly affect their growth rate in captive settings.
What temperature should zoos keep Eastern Hellbenders at?
Research shows 16°C (61°F) works just as well as warmer temperatures for growth. Zoos can maintain cooler, stable temperatures without harming hellbender development, which also reduces heating costs.
Why don’t hellbenders grow faster in warm water like other amphibians?
Eastern Hellbenders naturally live in cool mountain streams, so they may have adapted to thrive in cold water. This 2026 study suggests they’re different from many other amphibians that benefit from warmth.
What should zoos focus on instead of temperature to help hellbenders grow?
The 2026 research suggests zoos should prioritize diet quality, tank density, and water quality. These factors may have more impact on growth than temperature adjustments.
Is this study reliable for all hellbender breeding programs?
The study tracked 207 animals over 18 months with consistent measurements, making it reliable. However, it was conducted at one facility, so results may vary slightly with different equipment or conditions.
Want to Apply This Research?
- If you’re involved in hellbender conservation, track water temperature, feeding frequency, and animal growth measurements every 8 weeks using the app’s measurement log feature. Record weight and length alongside environmental conditions to identify which factors truly correlate with better growth.
- Shift focus from investing in expensive heating systems to documenting and optimizing other care variables. Use the app to systematically test different feeding schedules, tank densities, or water quality parameters to discover what actually improves hellbender growth.
- Create a long-term tracking dashboard that monitors temperature stability (not temperature elevation), feeding consistency, and growth metrics over 6-12 month periods. Compare your facility’s results to this baseline study to identify which variables in your specific setup drive the best outcomes.
This research applies specifically to captive breeding conditions for Eastern Hellbenders and should not be interpreted as guidance for wild hellbender conservation or habitat management. These findings are based on one study conducted at a single facility and may not apply to all breeding programs or environmental conditions. Anyone involved in hellbender conservation should consult with wildlife professionals and consider multiple factors beyond temperature when designing breeding or rearing programs. This article is for informational purposes and does not constitute professional veterinary or conservation advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.