* By Bhavesh Choudhary, Arup Das and Nayan Chouhan
Temperature is a pivotal environmental factor affecting the physiological processes in fish, including reproduction. Fish, being ectothermic organisms, have their body temperature and metabolic rates dictated by the surrounding water temperature. Consequently, fluctuations in temperature can significantly impact their reproductive physiology, including gametogenesis, spawning behavior, and embryonic development.
Introduction
Aquatic habitats are encountering previously unheard-of difficulties as a result of climate charge, which is having an increasingly noticeable effect on global ecosystems. The impacts of climate change on fish reproduction have become a significant area of concern among the many ecological problems. The ongoing changes in global climate patterns pose significant risks to the reproductive success of fish populations. Rising water temperatures can shift the geographical distribution of fish species, alter reproductive timing, and reduce the availability of suitable spawning habitats.
Moreover, increased frequency of temperature extremes threatens the sustainability of fish populations worldwide. Predictive models suggest that many species, particularly those in tropical and temperate regions, may face severe. This article explores the complex interactions between fish reproductive biology and temperature swings, their effect and impacts on aquatic animal reproduction.
Temperature
In aquatic biology, the impact of temperature on fish reproductive, sex determination, and sex change is a complex and important topic. Changes in temperature impact the expression of genes linked to the manufacturing of reproductive hormones, which in turn causes modifications in the hormonal equilibrium and enzyme activity that are essential for fish reproduction.
Higher temperatures can cause both male and female reproductive cycle disruption by timing ovulation and spawning incorrectly, especially in tropical regions. Furthermore, increasing temperatures have the potential to distort sex ratios in species that have either environmental sex determination (ESD) or genetic sex determination impacted by temperature (GSD + TE). Temperature affects the expression of genes involved in aromatase biosynthesis in sequentially hermaphrodite species, which in turn affects the direction and timing of sex change.

1. Physiological changes on fish reproduction
Temperature directly influences metabolic activities at the cellular level, affecting the synthesis, structure, and activity of neurohormones, hormones, and enzymatic complexes involved in steroidogenesis (Nakamura et al., 2003). Fluctuations in temperature affect gene expression controlling the synthesis of reproductive hormones and enzymes crucial for HPG axis functioning (Baroiller et al., 1999).
Fish reproduction is profoundly influenced by environmental temperature, which plays a critical role in determining the reproductive success and population dynamics of various fish species. This paper explores the physiological impacts of temperature on fish reproduction, emphasizing the mechanisms involved and the potential implications of climate change. Temperature is a pivotal environmental factor affecting the physiological processes in fish, including reproduction.
Fish, being ectothermic organisms, have their body temperature and metabolic rates dictated by the surrounding water temperature. Consequently, fluctuations in temperature can significantly impact their reproductive physiology, including gametogenesis, spawning behavior, and embryonic development.
2. Gametogenesis
Gametogenesis, the process of producing eggs and sperm in fish, is highly sensitive to temperature fluctuations. Optimal temperature ranges are essential for the proper development of gonads in both male and female fish. Deviations from these optimal ranges can result in reduced gamete quality and quantity, subsequently affecting fertility rates. For instance, in Atlantic salmon (Salmo salar), elevated temperatures have been associated with impaired spermatogenesis and decreased sperm motility, impacting reproductive success (Wilson and Primack, 2019).
3. Spawning behavior
Temperature also plays a critical role in influencing the external behaviors related to reproduction, such as spawning migrations and site selection. Many fish species rely on specific temperature cues to trigger these behaviors. For example, the spawning migration of sockeye salmon (Oncorhynchus nerka) is initiated by precise temperature thresholds, with deviations potentially disrupting the timing and success of spawning events. Similarly, coral reef fish like the clownfish (Amphiprioninae) show synchronized spawning behaviors closely linked to temperature changes (Wilson and Primack, 2019).
4. Embryonic development
Post-fertilization, temperature remains crucial for embryonic development in fish. The rate of embryogenesis is temperature-dependent, with optimal temperatures promoting healthy development and hatching success. Extreme temperatures can cause developmental abnormalities and increase mortality rates in fish embryos. For instance, in zebrafish (Danio rerio), temperatures above 28°C have been linked to developmental defects and reduced hatchling survival (Wilson and Primack, 2019).
5. Fish reproduction
Slight temperature increases can disrupt the endocrinal activities involved in fish reproduction, particularly in tropical species, leading to mistiming in reproductive cycles (Pankhurst and Munday et al., 2011). High temperatures can advance or truncate the reproduction season in different fish species, potentially affecting ovulation, spawning timing, and gamete quality (Nakamura et al., 2003).
6. Altered spawning timing
Rising temperatures can lead to changes in the timing of spawning events. Many fish species rely on specific temperature cues for reproduction. Warmer waters can cause earlier or extended spawning periods, potentially disrupting the synchronization between spawning and optimal environmental conditions for offspring survival (Pankhurst and Munday et al., 2011).

7. Sex ratio imbalance
Temperature influences sex determination in some fish species, especially those with temperature-dependent sex determination (TSD). Higher temperatures can skew sex ratios towards one gender, often resulting in a higher proportion of males, which can threaten population sustainability (Baroiller et al., 2009).
8. Reduced egg viability
Elevated temperatures can negatively affect egg development, leading to lower hatching success and increased mortality rates of embryos. Thermal stress during the embryonic stage can cause deformities and reduce the overall fitness of larvae (Alderdice and Forrester et al., 1971).
9. Decreased sperm quality
Male fish exposed to higher temperatures may produce less viable sperm. Heat stress can reduce sperm motility and longevity, impairing fertilization success and affecting the reproductive output of populations (Lahnsteiner et al., 1999).
10. Behavioral changes
Temperature rise can alter reproductive behaviors such as courtship and nest building. These behavioral modifications can lead to reduced mating success and affect the reproductive efficiency of fish populations (Kamler et al., 2005).
11. Geographical shifts and migration
Warming waters can drive fish to migrate to cooler regions, which might disrupt local ecosystems and lead to mismatches between fish species and their traditional spawning habitats. This shift can cause changes in the genetic diversity and resilience of fish populations (Perry et al., 2005).
12. Increased disease susceptibility
Higher temperatures can enhance the prevalence and severity of diseases and parasites, which can affect reproductive health and success. Infected fish may have reduced reproductive capacity or transmit pathogens to offspring (Harvell et al., 2002).
13. Metabolic stress
Rising temperatures can increase metabolic rates in fish, leading to higher energy demands. This can divert energy away from reproduction towards maintenance and survival, thereby reducing reproductive investment and success (Pörtner and Farrell et al., 2008)
14. Effect on sexual determination and sex change
Temperature influences sex determination, with thermosensitive genes affecting aromatase biosynthesis, leading to an imbalance in sexual steroids and potential masculinization (Guiguen et al., 2010). Temperature can impede or induce sex change in sequentially hermaphroditic species by influencing the expression of aromatase genes (Nakamura et al., 2003).
In summary, temperature is a crucial factor in the reproduction of fish, affecting different phases of their reproductive cycle. The water temperature is the primary environmental factor that significantly affects the maturity of gonads and the process of breeding. Every aquatic organism has specific temperature and pH requirements for the development of reproductive organs, the process of releasing eggs or sperm, and overall growth. Therefore, fluctuations in water temperature might impact the development and regular behaviour of aquatic organisms.
References and sources consulted by the author on the elaboration of this article are available under previous request to our editorial staff.
Bhavesh Choudhary Ph.D.
Research Scholar, Department of Aquaculture, College of Fisheries, Central Agricultural University (Imphal), Lembucherra, Agartala, 799210 Tripura, India.
Arup Das
College of Fisheries, Central Agricultural University (Imphal), Lembucherra, Agartala, 799210 Tripura, India.
Nayan Chouhan Ph.D.
Research Scholar, Department of Aquatic Health & Environment, College of Fisheries, Central Agricultural University (Imphal), Lembucherra, Agartala, 799210 Tripura, India.