How Fish Brain and Gills React to Acidic Seawater

Jenn Hoskins
23rd March, 2024

How Fish Brain and Gills React to Acidic Seawater

Image Source: Natural Science News, 2024

Key Findings

  • In a Shanghai study, fish gills quickly respond to ocean acidification by producing stress hormones
  • The fish brain's stress response is slower, taking days to react to acidification
  • These findings help understand how marine life adapts to environmental changes like increased CO2
Understanding how marine life copes with environmental stressors is crucial for conservation and fisheries management. A recent study by researchers at Shanghai Ocean University[1] has shed light on the response of marine medaka fish to one such stressor: ocean acidification. Ocean acidification occurs when CO2 from the atmosphere dissolves in seawater, lowering the pH and altering the chemical balance. This change can affect marine organisms, particularly their stress response systems. The study focused on the corticotropin-releasing hormone (CRH) system, which is pivotal in managing stress. CRH is a hormone primarily produced in the brain's hypothalamus but is also found in other body parts, like the gills, which are in direct contact with water. The researchers exposed marine medaka to different levels of CO2-acidified seawater (440 ppm, 1000 ppm, and 1800 ppm CO2) and observed the effects over various time frames (2 hours, 4 hours, 24 hours, and 7 days). They discovered that the gills' response to acidification was rapid. Within 2 to 4 hours, the expression of crh mRNA in the gills increased with the CO2 concentration, indicating an acute local response to the environmental change. This suggests that the gills may secrete CRH to help regulate the local environment within the fish, possibly to maintain the balance of acids and bases in its body. Interestingly, during the same early time frame, the brain did not show significant changes in CRH gene or protein expression. It was only after 7 days of exposure that researchers observed an increase in CRH-positive cells in the hypothalamus and an overall rise in Crh protein in the brain. This delay suggests that the brain's stress response system might be more involved in long-term adaptation to environmental changes, rather than in immediate reactions. The study also found that two other genes related to the CRH system, crhbp and crhr1, were significantly increased in expression in the gills. These genes are part of the pathway that controls the synthesis and release of CRH, indicating a complex local response to acidification. These findings align with previous research on various fish species. For example, earlier studies on the large yellow croaker showed that ocean acidification impacts the fish's auditory system, potentially affecting their balance and survival[2]. This suggests that environmental stressors like acidification can have widespread effects on different physiological systems in marine organisms. Another study on chickens highlighted the importance of the CRH system, which is conserved across vertebrates, in regulating stress responses, further underscoring the relevance of the CRH system in managing environmental challenges[3]. Moreover, research into the evolution of CRH genes in vertebrates, including their loss or duplication in certain groups, points towards the adaptive significance of these genes in responding to environmental pressures[4]. The rapid acid-base regulatory responses observed in European sea bass when exposed to high CO2 levels also demonstrate the importance of efficient stress response mechanisms in marine fish[5]. The insights from the Shanghai Ocean University study suggest that local CRH secretion in the gills plays a crucial role in the immediate response to short-term acidification stress, potentially mitigating the damage caused by this environmental challenge. This autocrine secretion (where a cell produces a signal to induce changes in itself) in the gills contrasts with the systemic response involving the brain, which seems to be more gradual. Understanding these mechanisms is essential for predicting how marine life will cope with ongoing environmental changes. As ocean acidification is a result of increasing atmospheric CO2 levels, this research is timely and critical for the development of strategies to manage and protect marine species in a rapidly changing world.

EnvironmentBiotechMarine Biology

References

Main Study

1) Response of CRH system in brain and gill of marine medaka to seawater acidification.

Published 21st March, 2024

https://doi.org/10.1007/s10695-024-01332-7

Related Studies

2) Balance dysfunction in large yellow croaker in response to ocean acidification.

https://doi.org/10.1016/j.scitotenv.2023.162444

3) Characterization of CRH-Binding Protein (CRHBP) in Chickens: Molecular Cloning, Tissue Distribution and Investigation of Its Role as a Negative Feedback Regulator within the Hypothalamus-Pituitary-Adrenal Axis.

https://doi.org/10.3390/genes13101680

4) New Insights Into the Evolution of Corticotropin-Releasing Hormone Family With a Special Focus on Teleosts.

https://doi.org/10.3389/fendo.2022.937218

5) Rapid blood acid-base regulation by European sea bass (Dicentrarchus labrax) in response to sudden exposure to high environmental CO2.

https://doi.org/10.1242/jeb.242735


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