pH Stress Responses in Aquatic Organisms

Aquatic organisms inhabit environments in which the hydrogen ion concentration (pH) can fluctuate due to natural processes and anthropogenic influences. Deviations from the optimal pH range disrupt acid–base balance, impair ionoregulation and generate oxidative stress. Acidic conditions may lead to acidosis, characterised by lowered blood and tissue pH, while alkaline conditions provoke alkalosis. Both imbalances challenge vital physiological systems, including gill ion transporters, renal excretion mechanisms and cellular buffering capacity. To counteract pH perturbations, fish, crustaceans and molluscs deploy an array of acclimatory responses: modulation of ion‐transport proteins such as H⁺‐ATPases and Na⁺/H⁺ exchangers; upregulation of antioxidant enzymes that detoxify reactive oxygen species; and activation of stress‐response pathways involving heat shock proteins and inflammatory mediators. Chronic pH stress can impair growth, reproduction and immune competence, with cascading effects on population dynamics and ecosystem health. Emerging evidence highlights species‐specific thresholds and the role of local adaptation in determining resilience. Understanding these mechanisms is crucial for predicting the impact of ocean acidification, freshwater acid rain and aquaculture water quality on global aquatic biodiversity and food security.

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pH Stress Responses in Aquatic Organisms publication trend

The graph below shows the total number of articles in ph stress responses in aquatic organisms across all publications each year (not limited to Nature Index journals).

Technical terms

Acid–base balance: The physiological regulation of internal pH through buffering systems and ion transport to maintain homeostasis.

Oxidative stress: Cellular damage caused by an excess of reactive oxygen species overwhelming antioxidant defences.

H⁺‐ATPase: A proton pump enzyme in cell membranes that transports hydrogen ions to regulate intracellular and extracellular pH.

Na⁺/H⁺ exchanger (NHE): A membrane transporter that extrudes H⁺ in exchange for Na⁺ to stabilise intracellular pH.

Single‐cell RNA sequencing (scRNA‐seq): A technique to profile gene expression in individual cells, revealing cell‐type‐specific stress responses.

Iono­regulation: The process by which organisms control the uptake and excretion of ions to preserve fluid and electrolyte balance under varying pH.

References

1. Changes in pH and Nitrite Nitrogen Induces an Imbalance in the Oxidative Defenses of the Spotted Babylon (Babylonia areolata). Antioxidants (2023).
2. Growth and health responses to a long-term pH stress in Pacific white shrimp Litopenaeus vannamei. Aquaculture Reports (2020).
3. Water pH and hardness alter ATPases and oxidative stress in the gills and kidney of pacu ( Piaractus mesopotamicus ). Neotropical Ichthyology (2019).
4. Na+/H+ exchanger (NHE) in Pacific white shrimp (Litopenaeus vannamei): Molecular cloning, transcriptional response to acidity stress, and physiological roles in pH homeostasis. PLOS ONE (2019).
5. Highly sensitive and specific responses of shrimp gill cells to high pH stress based on single cell RNA-seq analysis. Frontiers in Cell and Developmental Biology (2022).
6. Primary, secondary, and tertiary stress responses of juvenile seahorse Hippocampus reidi exposed to acute acid stress in brackish and seawater. Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology (2021).