Gas Bubble Disease

Overview

What is Gas Bubble Disease (GBD)?

Gas Bubble Disease (GBD), also termed Gas Bubble Trauma (GBT), is a non-infectious, physically induced condition arising from supersaturated water. It can affect any fish species, including farmed species such as Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), gilthead seabream (Sparus aurata), European sea bass (Dicentrarchus labrax), and Atlantic cod (Gadus morhua). It happens when water holds more dissolved gas than the surrounding pressure can keep in solution, so the excess gas — mainly nitrogen and oxygen — comes out as bubbles inside a fish's blood and tissues. 1 3 14.

The underlying physics follow Henry's Law: gas solubility in water is proportional to its partial pressure at the gas–water interface. When dissolved gas pressure within fish tissues exceeds the sum of hydrostatic and atmospheric pressure, gases transition from solution to bubbles, a process mechanistically similar to decompression sickness in human divers 14. Nitrogen and oxygen differ in their hazard profile. Nitrogen, being metabolically inert, produces GBD at supersaturation levels as low as 103–118% TGP, whereas oxygen is consumed by fish tissues and requires approximately 200–285% saturation to cause equivalent harm 1 3. Total dissolved gas pressure, not any individual gas fraction, determines pathological risk.

GBD can manifest as a chronic form at around 103% TGP, characterised by slow, symptom-free mortality particularly in larvae and fry, or as an acute form when TGP exceeds 110–115%, producing rapid onset of clinical signs and heavy mortality 3. Recent experimental work demonstrated that Atlantic salmon and brown trout parr develop acute GBD with median lethal times of 4–15 hours at 120% TGP, while rainbow trout parr are more tolerant (LT50 = 25 hours at equivalent levels) 11. GBD results in significant economic losses through direct mortality, impaired growth, and elevated susceptibility to secondary infections 1 13.

Clinical Signs of Gas Bubble Disease

Common Signs

• Physical Signs:

  • Gas Bubbles: Visible gas bubbles under the skin, in the eyes, gills, fins, lateral line, and buccal cavity. In larvae and fry, bubbles may appear between the yolk sac membrane and the perivitelline space, causing buoyancy disruption and forced surface gathering 1 11.
  • Exophthalmia: Protruding or bulging eyes, often unilateral, due to gas accumulation in periorbital tissues. This is one of the most diagnostically recognisable external signs of GBD 1.
  • Haemorrhages: Reddened areas on the skin, fin bases, gills, and internal organs caused by vascular gas emboli rupturing capillaries. Petechial haemorrhages on gill lamellae are a consistent histopathological finding 1 3.
  • Fin Erosion: Gas emboli in fin capillaries cause progressive erosion and whitening of fin tips, particularly in the pectoral and caudal fins, and are often the first grossly visible sign in parr 1.
  • Abdominal Distension: Swollen abdomen due to gas accumulation in internal organs, particularly the swim bladder and gastrointestinal tract. Hyperinflation of the swim bladder produces permanent buoyancy dysfunction and is a critical cause of larval mortality in sea bream and sea bass larviculture 1.

• Behavioural Changes:

  • Abnormal Buoyancy and Surface Gathering: Fish float at the water surface, unable to swim down. In acute episodes, fish may jump repeatedly from the water, a response attributed to activation of nociceptors in the gill vasculature 14.
  • Loss of Appetite: Decreased feeding behaviour and significant weight loss. Even sublethal supersaturation impairs nutrient digestibility and reduces growth rates in rainbow trout 11.
  • Abnormal Swimming Patterns: Erratic swimming, loss of equilibrium, convulsions, and violent head-shaking in acute cases. Flared opercula, gaping mouth, and darkened skin are common terminal signs 1 11.
  • Lethargy: In chronic presentations at lower supersaturation levels, reduced activity and sluggish swimming predominate without accompanying acute external signs 1.

Progression of Symptoms

GBD progresses through three characteristic stages 14:

• Early Stages: Microscopic bubbles will appear on the gills 5 Gas pressure equilibration in tissues with nonlethal cavitation; subtle signs including mild lethargy, slightly reduced feed intake, and early fin-tip whitening. Morbidity increases but mortality remains low 3 14.
• Advanced Stages: Rapid and heavy mortality with pronounced physical symptoms including visible gas bubbles, exophthalmia, and haemorrhages. Without correction of the supersaturation source, mass die-offs occur within hours at TGP ≥ 120% 1 3 11.
• Impact on Fish Health: GBD severely compromises normal fish function, causing stress, reduced growth rates, swim bladder dysfunction, impaired osmoregulation, and elevated susceptibility to secondary bacterial, viral, and parasitic infections. Fish that survive acute exposure are more vulnerable to GBD upon any subsequent supersaturation event, as tissue damage from prior episodes accelerates re-development of lesions 1 3 9.

Causes of Gas Bubble Disease

Etiology

• Non-infectious Condition: GBD is not caused by a pathogen but by environmental supersaturation of water with dissolved gases, governed by Henry's Law 1 3. When water dissolved gas pressure exceeds atmospheric pressure plus local hydrostatic head, dissolved gases transition from solution to bubbles within fish blood and tissues.

• Contributing Factors:

  • Supersaturated Water: High levels of dissolved gases (nitrogen, oxygen) arise from multiple aquaculture-relevant sources including groundwater, pressurised water systems, oxygen injection, rapid water heating, algal photosynthesis in ponds (especially in combination with still water), and hydropower spillway discharge 1 2 3, .
  • Groundwater and Borehole Sources: Well water is the most common cause of nitrogen supersaturation in land-based hatcheries, routinely measuring 109–111% TGP when pumped to atmospheric pressure. This is the single most prevalent GBD risk in freshwater salmonid production 1 3.
  • Pump Cavitation and Air Entrainment: Air leaks on the suction side of water supply pumps, or vortex formation in collection sumps, can cause gas to be forced into solution (by the pressure of the pump) 6, 20.
  • Oxygen Supplementation in RAS: Pure oxygen injection in recirculating aquaculture systems (RAS), submerged aerators, oxygen cones, and pressurised columns dissolve O₂ under elevated pressure. When this water returns to atmospheric conditions in rearing tanks, total gas pressure may reach hazardous levels. Atlantic salmon pre-smolts developed GBD after 14–16 days of exposure to 160–220% dissolved oxygen in controlled trials 2.
  • Water Heating: Gas solubility decreases as temperature rises. Rapid heating of cold, near-saturated groundwater without downstream degassing creates supersaturation proportional to the temperature increase 1. GBD has been shown to develop when water temperature only increased by 3-5 Celsius 6
  • Algal Photosynthesis: Most common in pond and outdoor aquaculture systems, phytoplankton photosynthesis drives dissolved oxygen to 200–300% saturation during afternoon periods, creating daily GBD risk windows. Still water exacerbates this problem by limiting the ways excess gas can escape 1, 20
  • Hydropower Spillways: Water plunging over dam spillways forces air into deep plunge pools under pressure, generating TGP of 120–140% in the downstream river reach, a well-documented cause of salmonid GBD mortality in regulated river systems 8 4.
  • Lice Treatment and Transport Boats Salmonids can develop GBD when loaded at 0.4ata into a wellboat for lice treatment or transport 24

Risk Factors

• Environmental Factors: Supersaturation risk is highest in land-based hatcheries and RAS facilities using groundwater, oxygen injection, or water heating. Shallow tank depths (20–30 cm) offer negligible hydrostatic compensation, as depth compensates for supersaturation at approximately 10% TGP per metre; a fish in a 20 cm tank cannot compensate for even 103% TGP 8. Sea cage environments are lower risk due to open water exchange and fish access to depth.
• Farm Management Practices: Inadequate TGP monitoring, absence of continuous sensors, over-reliance on pure oxygen without downstream degassing, and insufficient equipment inspection all significantly increase GBD risk 1 2.
• Life Stage: Larvae and fry are most vulnerable, with harmful effects documented at TGP as low as 102% 22.
• Species: Some species can tolerate supersaturation better than others, for example rainbow trout can tolerate the same conditions 2-5x longer than Atlantic salmon or Brown trout 11

Diagnosis

Diagnostic Methods

• Clinical Examination: Observation of physical symptoms remains the primary field diagnostic method. Key indicators include subcutaneous emphysema over fin bases, unilateral or bilateral exophthalmia, gas bubbles visible in the buccal cavity and gill arches, and fin erosion with whitened tips. Fish floating at the surface or crowding near water inlets in an acute episode are a strong behavioural indicator 1.

• Laboratory Tests:

  • TGP Measurement: Confirmation of gas supersaturation in the water using calibrated saturometers (e.g., Point Four TGP Tracker, OxyGuard TGP Probe, Weiss Saturometer GhPa-400) can directly assess gas supersaturation 20. Continuous inline sensors with automated alarms at all critical water handling points represent industry best practice 20.
  • Histopathology: Microscopic examination of gill lamellae, fin tissue, and internal organs reveals intravascular gas emboli, endothelial cell degeneration and exfoliation, exposed subendothelial connective tissue with fibrin strands, and tissue necrosis, findings pathognomonic for GBD 1 3.
  • Ultrasound Imaging: Two-dimensional ultrasound has been validated as an emerging diagnostic tool capable of semi-quantitatively detecting intravascular gas bubbles in Atlantic salmon in vivo, enabling quantification of gas bubble burden without sacrificing fish. This approach offers advantages over visual observation, which cannot quantify internal gas load 21.

Differential Diagnosis

• Distinguishing GBD from Other Conditions: Exophthalmia is also a presenting sign in bacterial infections such as furunculosis (Aeromonas salmonicida), enteric redmouth disease (Yersinia ruckeri), and viral conditions. Key differentiators for GBD are: (1) gross gas bubbles visible in multiple external locations simultaneously, (2) concurrent water supersaturation confirmed by TGP measurement, (3) rapid temporal onset associated with an identifiable supersaturation event, and (4) absence of pathogen isolation on bacteriology or PCR 1 3.

Treatment and Prevention

Prevention Monitoring TGP for species limits helps prevent chronic and acute cases of GBD from occurring 7.

Treatment Options

• Current Treatments: There are no specific pharmaceutical treatments for GBD. Management centres entirely on correcting the environmental conditions causing gas supersaturation and supporting affected fish through the recovery period 1 3.

  • Source Identification and Correction: The immediate priority in an acute GBD event is identifying and eliminating the supersaturation source: inspection of pump seals, oxygen injection settings, heating systems, and water supply lines for air entrainment. Do not attempt to burst gas bubbles on fish, as this causes additional tissue damage and creates portals for secondary infection 1.
  • Water Aeration: Increasing surface splash aeration and turbulent water flow promotes passive gas release. Transfer of fish to confirmed degassed water (TGP ≤ 103%) is the most effective immediate intervention 20.
  • Water Flow Management: Increasing water exchange rate through affected tanks dilutes supersaturated water and promotes gas equilibration with the atmosphere 1 3.
  • Depth Access: In sea cage environments, fish should be permitted to access compensatory depth. Research confirms that approximately 47% of steelhead displaying active GBD signs recovered within hours when given access to adequate depth 9.

• Supportive Care:

  • Monitoring Health: Fish that survive acute GBD exposure are immunocompromised and at elevated risk of secondary bacterial and viral infections. Regular health monitoring, reduced stocking density, and high water quality in the post-event period are critical. Continuous TGP monitoring should be maintained until the supersaturation source is fully resolved 1 3.

Preventive Measures

• Biosecurity Protocols:

  • Implementing strict water quality management with continuous TGP monitoring and automated alarms at all critical points: post-pump, post-heating, post-oxygenation, and at tank inlets. Target thresholds: ΔP ≤ 20 mmHg (≤ 103% TGP for larvae; ≤ 110% TGP for all other life stages) 1 3 20.
  • Regular inspection of pump seals, pipe flanges, and oxygenation equipment to prevent air entrainment and cavitation 1 3.

• Farm Management Practices:

  • Adjusting water aeration and flow systems to maintain optimal dissolved gas conditions, with degassing infrastructure installed on all water streams sourced from groundwater, heated supply, or oxygen supplementation 1 2 3.
  • Implementing packed column degassers (1–3 metre counter-current columns with high-surface-area packing media) as the standard engineering control for hatcheries using groundwater or oxygenated water. These reduce ΔP to ≤ 20 mmHg with no moving parts in gravity-fed configurations 20 22.
  • Implementing vacuum degassers for higher-supersaturation well water, achieving reductions from 120% to 90% TGP or below, to avoid GBD in all life stages 20.

Case Studies

Real-World Examples

• Notable Outbreaks:

  • United States — Klamath River (2024): Hundreds of thousands of newly hatched Chinook salmon fry died from GBD during the largest dam removal project in U.S. history. Rapid changes in river hydrodynamics caused acute gas supersaturation that overwhelmed the newly hatched fry before they could access compensatory depth, illustrating the particular vulnerability of early life stages to rapid TGP changes 4

  • United States — Columbia/Snake River System (ongoing): Downstream supersaturation from hydroelectric dam spillways has caused recurring GBD mortality in migrating juvenile salmonids since the 1960s. During high-spill years, TDG below Snake River dams has approached 140%, well above the 120% state limit. In a NOAA field experiment, about 47% of hatchery steelhead released with external GBD signs no longer showed them after migrating to the next dam and passing through its turbine intake and bypass system, consistent with depth compensation during passage. The authors note that this loss of signs means monitoring at dams can underestimate exposure 9 8.

  • Norway — Hydropower-Associated Supersaturation (1980s–present): Gas supersaturation linked to hydropower operations has been documented across Norwegian river systems since the late 1980s, notably contributing to Atlantic salmon population decline in the Vosso watercourse 10. Caged-smolt field studies in two Norwegian rivers recorded the onset of mortality and GBD signs in Atlantic salmon smolts at an average of 108.3% TDG (maximum 111.0%, measured at 0.55 m depth) over two days, with mortality differing significantly from controls from 110.2% TDG, suggesting Atlantic salmon may be more sensitive than Pacific salmonids 16. A controlled study exposing landlocked "bleke" Atlantic salmon to 111% TGP found that 90% developed clinical GBD signs within six days despite zero mortality over the study period, suggesting that sublethal field exposures may carry welfare costs not reflected in mortality statistics 12.

  • Norway — RAS Oxygen Supplementation, Nofima Marin (2010): Controlled experiments at a Norwegian research hatchery demonstrated GBD development in juvenile Atlantic salmon pre-smolts under progressive dissolved oxygen supersaturation. Subcutaneous gas bubbles appeared after 14 days at 160% O₂, with 10% of fish developing confirmed GBD at the 130–160% O₂ exposure level and approximately 50% affected at 190% O₂ after 16 days, confirming that oxygen-specific GBD represents a quantifiable risk in intensive salmon RAS production 2.

  • Czech Republic: A newly installed tank for a local trout farm resulted in repeated deaths, where fish skin and gills were pale and microscopically gas bubbles could be seen on the gill surface and filaments. Oxygen saturation was measured at 136%. Oxygen was then reduced to 100% and the problem was resolved 23

Data Insights

Disease Impact by Country

Norway

• Gas Bubble Disease Incidence in Norway:
  • The earliest documented incidences of Gas Bubble Disease (GBD) or gas bubble trauma in Norway are associated with hydropower activities, particularly in the late 1980s. These events were linked to gas supersaturation in rivers downstream of hydroelectric installations, which affected Atlantic salmon populations, such as the decline observed in the Vosso watercourse 10. Norwegian researchers have since identified over 800 hydropower stations as potential TGP risk sites, with 28% classified as high risk, and confirmed acute GBD mortality at a minimum of 8 stations 16.
  • In aquaculture, non-infectious causes, including gas supersaturation, are recognised contributors to hatchery-phase mortality. Norway's annual Fish Health Reports (Fiskehelserapporten), produced by the Norwegian Veterinary Institute, document total mortality figures but do not disaggregate GBD as a separate category. The 2024 report recorded 45.8 million salmon and 3.4 million rainbow trout hatchery deaths, the highest level ever recorded, with water quality identified among the primary challenges 17.
  • No binding regulatory TGP thresholds currently exist in Norway. A national committee in the 1980s concluded that TGP above 110% is harmful, but this was never codified. New consolidated animal welfare regulations expected in 2027 may address TGP monitoring requirements for the first time 12.
• Economic Impact:
  • The economic impact of Gas Bubble Disease (GBD) in Norway is not documented in specific terms. The disease contributes to broader environmental mortality losses in freshwater production whose full scale remains unquantified at the disease level. Costs associated with mitigating GBD, including degassing towers, vacuum systems, and continuous TGP monitoring infrastructure, represent both a preventable loss and an ongoing capital burden for farms relying on groundwater or intensive oxygenation systems.

Scotland

• Gas Bubble Disease Incidence in Scotland:
  • Scotland's Fish Health Inspectorate (FHI), operating under the Aquatic Animal Health (Scotland) Regulations 2009, does not classify GBD as a notifiable disease. GBD incidents are subsumed within general environmental mortality categories, preventing systematic disease-level tracking. Scotland's environmental regulator (SEPA) focuses on nutrient loading, chemical treatments, and benthic impact, not TGP.
  • Historic research at the Seafish Ardtoe hatchery identified gas supersaturation as a critical management challenge in Scottish salmon and flatfish hatcheries, noting that larval stages are particularly vulnerable to TGP as low as 102% 22. No specific numerical TGP thresholds are prescribed in Scottish or UK aquaculture regulations. The RSPCA Assured standard, covering approximately 70% of UK salmon farms, requires water quality monitoring programmes but does not define TGP limits.
  • Total salmon mortality in Scottish sea farms reached approximately 15 million between January and November 2022, compared to 8.58 million in 2021. The contribution of GBD to this rising trend is unknown due to the absence of disease-specific reporting.

Iceland

• Gas Bubble Disease Incidence in Iceland:
  • Iceland's aquaculture sector presents a unique geothermal GBD risk profile not found in other major producing nations. Subsurface geothermal water frequently contains dissolved volcanic gases, including CO₂, N₂, H₂S, and CH₄, held under high subterranean pressure. When pumped to atmospheric pressure, this water arrives supersaturated with multiple gas species simultaneously, creating compound GBD risk that differs mechanistically from the single-species nitrogen or oxygen supersaturation typical in other countries 3.
  • Iceland's aquaculture regulator (MAST, Matvælastofnun) oversees fish health, but no geothermal-adapted TGP monitoring guidance has been published. Monitoring remains operator-driven. No specific GBD outbreak records for Icelandic aquaculture have been identified in the published literature, though the geothermal water profile warrants targeted research and sector-specific regulatory guidance.

Chile

• Gas Bubble Disease Incidence in Chile:
  • Chile is the world's second-largest Atlantic salmon producer, with over 700,000 tonnes of annual production. The country's regulatory focus following the 2007–2008 ISA outbreak has centred on infectious disease control, antimicrobial stewardship, and sea lice management, with comparatively less attention to physical water quality parameters such as TGP. Chile's regulator Sernapesca operates the RAMA benthic monitoring programme but has established no specific TGP standards or mandatory gas supersaturation monitoring requirements.

Mediterranean

• Gas Bubble Disease in Sea Bream and Sea Bass Aquaculture:
  • Mediterranean aquaculture, centred on gilthead seabream (Sparus aurata) and European sea bass (Dicentrarchus labrax), faces distinct GBD challenges compared to northern salmonid industries. Warmer water temperatures (summer highs of 26–30°C in the eastern Mediterranean) reduce gas solubility, meaning the same dissolved gas concentration represents higher percentage saturation than in colder northern waters. Intense diurnal algal photosynthesis in coastal net pens routinely drives dissolved oxygen to 200–300% saturation during afternoon periods 1.
  • Experimental exposure of European sea bass (82 g) to 220% dissolved oxygen (ΔP = +167 mmHg) for 84 days caused significant mortality, reduced growth, and gas bubble formation in and around the eyes and fins. Medium hyperoxia (135% O₂) at negative ΔP (ΔP = −160 mmHg) improved growth by 5.8% with no GBD signs, confirming that total gas pressure differential, not dissolved oxygen concentration alone, drives pathology in this species 15. A fish model study achieved severe GBD lesions at TGP levels as low as 108–109% over 18 hours, demonstrating high susceptibility at comparatively modest supersaturation 18.
  • GBD in sea bream and sea bass larvae is documented but underreported. A pan-Mediterranean survey across 50 facilities in 10 countries found that Mediterranean farms generally do not maintain or report sufficient health data quality for systematic disease impact analysis 19. No species-specific TGP thresholds have been published for either gilthead seabream or European sea bass, representing the most significant knowledge gap in Mediterranean aquaculture fish health management. Precautionary application of salmonid guidelines (≤ 103% for larvae, ≤ 110% for grow-out) is the current recommended approach pending dedicated threshold research.

Research and References

Latest Research Findings

Recent studies on Gas Bubble Disease in farmed fish have substantially advanced understanding of species-specific thresholds, diagnostic capabilities, and the global regulatory landscape. Notable findings include:

1. "Tolerance to total dissolved gas supersaturation in Atlantic salmon, brown trout, rainbow trout, and European minnow" Authors: Isaksen, T. E., et al. Reference: Isaksen, T. E., et al. (2026). Tolerance to total dissolved gas supersaturation in Atlantic salmon, brown trout, rainbow trout, and European minnow. PLOS ONE, 21(2), e0342556. Link to study

2. "No additional stress of sublethal gas supersaturation in a landlocked population of Atlantic salmon exposed to environmental acidification" Authors: Höglund, E., et al. Reference: Höglund, E., et al. (2024). No additional stress of sublethal gas supersaturation in a landlocked population of Atlantic salmon (Salmo salar) exposed to environmental acidification. Scientific Reports, 14, 3482. Link to study

3. "A meta-analysis of gas bubble trauma in fish" Authors: Pleizier, N. K., Algera, D., Cooke, S. J., & Brauner, C. J. Reference: Pleizier, N. K., Algera, D., Cooke, S. J., & Brauner, C. J. (2020). A meta-analysis of gas bubble trauma in fish. Fish and Fisheries, 21(6), 1175–1194. Link to study

4. "Documentation of welfare and quality effects on farmed salmon during crowding, loading and transport directly from the deep (Bottom-Up)" Project leader: Silje Stensby-Skjærvik Reference: Ongoing. Forskningsfondet for fiskeri og akvakultur. Link to study

5. "Assessment of diagnostic tools to detect acute gas bubble disease in Atlantic salmon (Salmo salar L.)" Authors: Stensby-Skjærvik, O., et al. Reference: Stensby-Skjærvik, O., et al. (2025). Assessment of diagnostic tools to detect acute gas bubble disease in Atlantic salmon (Salmo salar L.). Journal of Fish Diseases, 48(5), e14142. Link to study

6. "Acute effects of gas supersaturation on Atlantic salmon smolt in two Norwegian rivers" Authors: Stenberg, S. K., Velle, G., Pulg, U., & Skoglund, H. Reference: Stenberg, S. K., Velle, G., Pulg, U., & Skoglund, H. (2022). Acute effects of gas supersaturation on Atlantic salmon smolt in two Norwegian rivers. Hydrobiologia, 849(2), 527–538. Link to study

7. "Effects of hyperoxic water conditions under different total gas pressures in European sea bass (Dicentrarchus labrax)" Authors: Lemarié, G., Hosfeld, C. D., Breuil, G., & Fivelstad, S. Reference: Lemarié, G., Hosfeld, C. D., Breuil, G., & Fivelstad, S. (2011). Effects of hyperoxic water conditions under different total gas pressures in European sea bass (Dicentrarchus labrax). Aquaculture, 318(1–2), 191–198. Link to study

8. "Establishment of a fish model to study gas-bubble lesions" Authors: Velázquez-Wallraf, A., et al. Reference: Velázquez-Wallraf, A., et al. (2022). Establishment of a fish model to study gas-bubble lesions. Scientific Reports, 12, 6592. Link to study

9. "Understanding gas bubble trauma in an era of hydropower expansion: How do fish compensate at depth?" Authors: Pleizier, N. K., Nelson, C., Cooke, S. J., & Brauner, C. J. Reference: Pleizier, N. K., Nelson, C., Cooke, S. J., & Brauner, C. J. (2020). Understanding gas bubble trauma in an era of hydropower expansion: How do fish compensate at depth? Canadian Journal of Fisheries and Aquatic Sciences, 77(3), 556–563. Link to study

These studies represent advancements in understanding the prevention, control, and economic impact of Gas Bubble Disease in various regions, particularly in Norway and other European countries with significant salmon farming industries.

Additional Resources

• Podcast (in Norwegian): Gassboblesyke - små bobler, store konsekvenser ("Gas bubble disease: small bubbles, big consequences"). Listen on Spotify

Conclusion

Gas Bubble Disease (GBD) is a non-infectious, physically induced condition affecting commercially important aquaculture species including Atlantic salmon, rainbow trout, gilthead seabream, and European sea bass. The pathophysiology is well established, threshold data exist for key salmonid life stages, and effective engineering controls are commercially available. GBD is not classified as a notifiable disease in any major producing nation, is absent from binding regulatory frameworks outside North America, and is not systematically recorded in standard fish health surveillance programmes. Its true incidence and economic impact therefore remain incompletely quantified.

Current guidance recommends maintaining TGP below 103% for larval and early juvenile stages and below 110% for all other life stages, with engineered degassing applied to all water streams passing through pumps, heating systems, or oxygen injection equipment. GBD should be included in the differential diagnosis for any episode of surface-gathering, buoyancy loss, and unexplained mass mortality, requiring immediate TGP measurement. Species-specific thresholds have not been published for Mediterranean species; precautionary application of salmonid guidelines is the current recommended approach pending dedicated experimental data. Continuous TGP monitoring, appropriate degassing infrastructure, and routine equipment inspection represent the primary controls for reducing GBD incidence and associated welfare impacts in commercial aquaculture.

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Last Modified: 2026-11-03

Tags: #GasBubbleDisease, #Salmonids, #Salmon, #AtlanticSalmon, #Trout, #RainbowTrout, #Norway, #Canada, #Chile, #Scotland, #Iceland, #Mediterranean, #SeaBream, #SeaBass, #environmentalconditions

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[2] Espmark, Å. M., Hjelde, K., & Baeverfjord, G. (2010). Development of gas bubble disease in juvenile Atlantic salmon exposed to water supersaturated with oxygen. Aquaculture, 306(1-4), 198-204. https://www.sciencedirect.com/science/article/pii/S0044848610002875

[3] Bohl M. (1997). Gasblasenkrankheit der Fische [Gas bubble disease of fish]. Tierarztliche Praxis, 25(3), 284–288. https://pubmed.ncbi.nlm.nih.gov/9289892/

[4] M.Singh (5th March, 2024) "Hundreds of thousands of salmon dead from ‘gas bubble disease’ in US river" The Guardian. https://www.theguardian.com/environment/2024/mar/05/salmon-klamath-river-dam-removal-project Accessed June, 2026.

[5] Veterinary Vision Center. June 1st, 2022. "There’s Something In The Water: Gas Bubble Disease In Fish" Veterinary Vision Centerhttps://veterinaryvisioncenter.com/theres-something-in-the-water-gas-bubble-disease-in-fish/ Accessed August, 2026

[6] Marking, L. L. (1987). Gas supersaturation in fisheries: causes, concerns, and cures (Vol. 9). US Department of the Interior, Fish and Wildlife Service. https://books.google.no/books?hl=en&lr=&id=3iVBRZ-NeswC&oi=fnd&pg=PA1&dq=Gas+Supersaturation+in+Fisheries:+Causes,+Concerns,+and+Cures.&ots=HVoidpQ8UX&sig=z3a2zGvlsggKydBV6dgaqI7xBe4&redir_esc=y#v=onepage&q&f=false (Accessed August, 2026)

[7] Noble, C., Gismervik, K., Iversen, M. H., Kolarevic, J., Nilsson, J., Stien, L. H., ... & Nofima, A. S. (2020). Welfare indicators for farmed rainbow trout: tools for assessing fish welfare. https://www.storre.stir.ac.uk/bitstream/1893/31242/1/Welfare%20Indicators%20for%20farmed%20rainbow%20trout-Noble%20et%20al.-May%202020.pdf

[8] Pleizier, N. K., Nelson, C., Cooke, S. J., & Brauner, C. J. (2021). Correction: Understanding gas bubble trauma in an era of hydropower expansion: how do fish compensate at depth?. Canadian Journal of Fisheries and Aquatic Sciences, 78(10), 1563-1563. https://cdnsciencepub.com/doi/full/10.1139/cjfas-2021-0207

[9] Monk, B. H., Absolon, R. F., & Dawley, E. M. (1997). Changes in Gas Bubble Disease Signs and Survival of Migrating Juvenile Salmonids Experimentally Exposed to Supersaturated Gasses: Annual Report 1996. Bonneville Power Administration. https://www.webapps.nwfsc.noaa.gov/assets/26/6581_07202010_120759_Monk.et.al.1997-rev.pdf

[10] Sondre Kvalsvik Stenberg (2016). Effects of gas supersaturation on migrating Atlantic salmon smolt (Salmo salar) in Evangervatnet. https://link.springer.com/article/10.1007/s10750-020-04439-z

[11] Isaksen, T. E., Pulg, U., Lennox, R. J., Stranzl, S. F., Bye-Ingebrigtsen, E., Handegård, R., & Velle, G. (2026). Tolerance to total dissolved gas supersaturation in Atlantic salmon, brown trout, rainbow trout, and European minnow. Plos one, 21(2), e0342556. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0342556

[12] Höglund, E., Loland, L.Z., Høgberget, R. et al. No additional stress of sublethal gas supersaturation in a landlocked population of Atlantic salmon (Salmo salar) exposed to environmental acidification. Sci Rep 14, 3482 (2024). https://doi.org/10.1038/s41598-024-53637-5 https://www.nature.com/articles/s41598-024-53637-5

[13] Pleizier NK, Algera D, Cooke SJ, Brauner CJ. A meta-analysis of gas bubble trauma in fish. Fish Fish. 2020; 21: 1175–1194. https://onlinelibrary.wiley.com/doi/10.1111/faf.12496

[14] Bouck, G. R. (1980). Etiology of Gas Bubble Disease. Transactions of the American Fisheries Society, 109(6), 703–707. https://doi.org/10.1577/1548-8659(1980)109<703:EOGBD>2.0.CO;2 https://www.tandfonline.com/doi/abs/10.1577/1548-8659(1980)109%3C703:EOGBD%3E2.0.CO%3B2

[15] Lemarié, G., Hosfeld, C. D., Breuil, G., & Fivelstad, S. (2011). Effects of hyperoxic water conditions under different total gas pressures in European sea bass (Dicentrarchus labrax). Aquaculture, 318(1-2), 191-198. https://www.sciencedirect.com/science/article/abs/pii/S0044848611002511

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