Carp swimming in water with hormone symbols.

The Curious Case of Carp: How Climate Change is Shifting Fish Sex Hormones

Beau Callahan in Climate & Environment August 2025 • 4 min read.

"Uncover the surprising link between rising temperatures, fish reproduction, and the future of aquaculture in Khuzestan, Iran."

Reproduction is key to the survival of any species, and for fish, it's a delicate dance choreographed by hormones and environmental cues. Understanding this process is particularly important for aquaculture, where consistent and predictable breeding cycles are essential for reliable food production.

In the world of fish, sex steroid hormones like testosterone, estradiol, and progesterone play starring roles in regulating everything from sexual differentiation to reproductive behavior. These hormones are not just internal drivers; they're also highly responsive to external factors, especially temperature.

New research from Khuzestan, Iran, sheds light on how seasonal temperature changes are affecting the sex hormone levels of Indian major carp (Catla catla), a vital species for aquaculture. This study offers valuable insights into the potential impacts of climate change on fish reproduction and the broader implications for food security.

What Happens to Fish Hormones When the Seasons Change?

Carp swimming in water with hormone symbols.

Researchers studied 40 female and male Catla broodstocks over a year, tracking their sex hormone levels (testosterone, estradiol, and progesterone) across different seasons. The results revealed significant seasonal variations in all sex steroids.

Here's a breakdown of the key findings:

Testosterone: Both female and male carp showed high testosterone levels during the winter, coinciding with sexual maturation.
Estradiol: Female carp displayed the highest estradiol levels in the fall.
Progesterone: Progesterone levels in female carp peaked in the winter.
Temperature Matters: The study highlighted a strong correlation between water temperature and hormone levels, suggesting that climate conditions significantly influence gonad development.

These findings suggest that temperature plays a crucial role in regulating the reproductive cycles of Catla catla by influencing the production and activity of key sex hormones. This is consistent with previous research showing that external cues like water temperature and photoperiod can profoundly affect circulating hormone levels in fish.

Why Does This Matter?

Understanding the intricate relationship between temperature and fish sex hormones is crucial for several reasons. First, it allows us to better predict how climate change may disrupt fish reproductive cycles, potentially impacting aquaculture yields. Second, this knowledge can inform the development of strategies to mitigate these effects, such as adjusting breeding seasons or implementing temperature control measures in aquaculture facilities. Finally, studying fish endocrinology provides valuable insights into the broader impacts of environmental change on wildlife and ecosystems.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.4172/2161-0525.1000227, Alternate LINK

Title: Seasonal Fluctuations Of Sex Steroid Hormones In Indian Major Carp Catla Catla In Khouzestan, Iran

Subject: General Earth and Planetary Sciences

Journal: Journal of Environmental & Analytical Toxicology

Publisher: OMICS Publishing Group

Authors: Homayoun Hosseinzadeh Sehafii, Mozhgan Khodadadi

Published: 2014-01-01

Everything You Need To Know

What specific sex hormones are affected by seasonal changes in Indian major carp?

The study focused on three key sex steroid hormones: testosterone, estradiol, and progesterone. These hormones were tracked in both male and female Catla catla (Indian major carp) to understand how their levels fluctuated throughout the different seasons. The research revealed significant variations in these hormone levels, directly correlating with the changing seasons and, consequently, the water temperature in Khuzestan, Iran.

How does temperature influence the reproductive cycles of Indian major carp?

The research conducted on Catla catla in Khuzestan, Iran, showed a strong correlation between water temperature and the levels of sex hormones. During winter, when temperatures are lower, both male and female carp exhibited hormonal shifts linked to sexual maturation. The study revealed that as the water temperature changes with the seasons, the production and activity of testosterone, estradiol, and progesterone in the carp are significantly influenced. This direct impact of temperature on hormone levels suggests that climate conditions play a pivotal role in the gonad development and, therefore, the reproductive cycles of the fish.

What were the key findings regarding testosterone, estradiol, and progesterone levels in the carp?

The study found that both male and female Catla catla showed high testosterone levels during winter, which corresponded with the onset of sexual maturation. Female carp exhibited their highest estradiol levels in the fall, while progesterone levels in females peaked in the winter. The research highlighted that these hormone level changes are directly related to seasonal water temperature fluctuations, emphasizing temperature's critical role in the reproductive cycles of these fish.

Why is it important to understand the link between temperature and fish sex hormones in the context of aquaculture?

Understanding the intricate relationship between temperature and fish sex hormones is crucial for several reasons within aquaculture. It helps in predicting how climate change might disrupt fish reproductive cycles. Such knowledge informs the development of strategies to mitigate these effects, such as adjusting breeding seasons or implementing temperature control measures in aquaculture facilities. Consistent and predictable breeding cycles are essential for reliable food production in aquaculture. Climate change may influence the levels of key hormones: testosterone, estradiol and progesterone. The changes in these hormone levels could lead to decreased yields in aquaculture.

Can you explain the broader implications of the research on Indian major carp beyond aquaculture?

Beyond the realm of aquaculture, studying the relationship between temperature and sex hormones in Catla catla offers valuable insights into the broader impacts of climate change on wildlife and ecosystems. These insights highlight how environmental factors influence the reproductive success of various species and provide a foundation for understanding and mitigating the effects of climate change on fish populations. The research contributes to the broader field of fish endocrinology, which enhances our understanding of how environmental changes influence wildlife and ecosystems.