Expert Opinion-Micro-Fine Oxygen Bubbles

Toxic Oxygen Bubbles – Thousands of Micro-Fine Oxygen Bubbles in Livewells can poison live bait and tournament fish.

Micro-pore oxygen diffusers and some bait pumps that entrain oxygen or air on the inlet side of a water pump’s impellers can produce thousands of suspended micro-fine gas bubbles in a livewell water column. The size of an oxygen or air bubble can dramatically affect livewell water chemistry, gas transfer rates and dissolved gas concentrations.

We queried university professors and experts. Our concern is the pathophysiology (oxygen toxicity) occurring when micro-fine pure oxygen bubbles physically stick inside fish gills, get into blood, stick in eyes, on scales, fins and skin.


1. When captive fish are forced to breathe in clouds of suspended micro-fine oxygen bubbles so fine the water looks milky, in livewells with relatively small functional water volumes, can these tiny gas bubbles injure fish or bait?

2. Is the stress response increased? Is the probability of delayed mortality increased? And, are we actually causing physiologic harm to tournament fish or live bait when holding and transporting them in clouds of bubbles for hours or even all day? When we transport tournament bass, redfish, snook or live bait for hours or all day, what happens to gill tissue when thousands of tiny oxygen bubbles remain stuck in gills, on scales and fins all day?

3. Images and examples of these problems follow Ph.D. opinions below.

We thank these university professors for offering their time, knowledge, expertise and opinions freely so that catch and release tournament anglers, as well as fishermen worldwide, can take better care of live tournament fish and live bait in livewells and bait tanks during transport. We appreciate their expert opinions in fish cardiovascular physiology, fish biochemistry, fish pathology, fish physiology, and the principles and practices of modern aquaculture techniques.



Professor Joseph J. Cech, Ph.D.

University of California – Davis Campus

Department of Wildlife, Fish, and Conservation Biology

1393 Academic Surge

Davis, CA 95616-8751

(530) 752-3103

Specialty: Physiological adaptations and adjustments of fish to their environments

“Micro-fine gas bubbles sticking to gills could obstruct respiratory gas exchange, by blocking ventilatory water flow between the minute lamellae on the gill filament surfaces.

If the livewell transport water becomes clouded, appearing milky with miniscule bubbles that adhere on gills and scales or to the inside walls of your livewell, consider these conditions potentially toxic and generally unhealthy for the exposed fish.

If the gas/gill exposure is persistent and the partial pressure of the oxygen remains near 1 atmosphere (instead of 0.2 atmospheres, as in air), the exposed fish’s chances of survival will probably decrease.

Compressed oxygen is a good thing when supplied continuously within safe dissolved oxygen concentrations, but exposure to compressed oxygen or delivered at high partial pressures can physically harm your fish. With extremely high oxygen partial pressure in the water, the fish may stop breathing, allowing carbon dioxide to build up in the fish. This may lead to acid-base changes (respiratory acidosis) in the fish and increase delayed mortality after release.

It is important to remember that pure compressed oxygen contains five times the oxygen content as air does. Thus, proportionately less (about 1/5 less) gas flows (bubbling rates) are needed from a pure oxygen supply, compared with an air supply, to adequately oxygenate water for fish.

Very small (micro-size) oxygen bubbles should dissolve faster than larger bubbles because of their greater surface to volume ratio, but all gas bubbles (air or oxygen) need some ‘solubility space’. Without sufficient ‘space’ available for the bubbles to dissolve, tiny micro-fine bubbles may remain suspended within the water column, attach to surfaces, or slowly, rise to the surface. Of course, fish do not breathe (gaseous) oxygen or air bubbles, the oxygen must first be dissolved in water for it to diffuse across their lamellar membranes.

And also, saltwater has a higher density than freshwater does. The higher water density compresses gas bubbles to a smaller size. This characteristic, along with saltwater’s lower gas solubility demands that saltwater livewells should be monitored for signs of oxygen/air bubble-related problems at least as well as freshwater ones.”



Professor Bruce Sidell, Ph.D.

University of Maine

School of Marine Sciences

306 Murry Hall

Orono, Maine 04469

Specialty: Cardiovascular physiology and biochemistry of fish

“If you observe clouds of suspended micro-fine oxygen or even air bubbles in fish transport water, you may be using too much of a good thing. Micro-pore diffusers can generate masses of tiny oxygen bubbles.

This condition may excessively supersaturate the water with oxygen if the mass of gas bubbles cloud the water and remain suspended; and, extreme hyperbaric oxygen can be toxic because of free-radical generation. Clouds of micro-fine air bubbles may also cause problems with nitrogen toxicities, the bends and air emboli. Tiny gas bubbles may affect water quality positively or negatively, either way, avoid transport conditions where clouds of gas bubbles remain in suspension.

There exists a rather rich and extensive literature on oxygen toxicity and gas bubble trauma. Plus, the adherence of the small bubbles to gill surfaces could exacerbate this problem further.

My guess is that the potential oxygen toxicity from adherence of the pure O2 bubbles to the surfaces of delicate epithelia is potentially more of a problem than the possibility of “drying out” the surfaces as you speculate. Both must be considered. These bubbles, after all, are in equilibrium with the water in which the fish swim, a far better source of water than the semi-permeable surfaces of the fish itself.

Arterial gas embolism and tissue emphysema can be a real and present danger when transporting live fish, avoid clouds of suspended gas bubbles in hauling water at all cost.

In my experience of transporting large numbers of capture-stressed fish (although in my case they were striped bass or salmonids that were captured by nets, not tournament hooked fish that were fought and landed), two key ingredients promote well-being of these animals

1. Elevating the partial pressure of O2 above saturation with compressed oxygen and deliver bubbles large enough to escape the surface. A very gentle bubbling with pure O2 is sufficient for preventing coalescence. Problems may arise if gas bubbles stick to gill tissue and remember, with pure oxygen, you need only 1/5 the volume compared to the volume of air needed. Air is composed mostly of nitrogen, micro-fine N2 bubbles can stick to gills too, causing another related set of problems with additional stressors. Any gas bubbles attaching to gills can impair respiration degrading fish health; when transporting fish in foamy water with thousands of suspended bubbles, consider the probability of hypoxia, hypercarbia, respiratory acidosis, disease and possibly death.

2. Elevate the salinity of the water to 3-5 ppt. Something like Instant Ocean or seawater is great, but even just NaCl without iodine would do. Salt will still be very helpful when transporting freshwater fish. Remember that these animals regulate their internal ionic and osmotic composition at much higher levels than freshwater (generally 300-340 mOsm). When under stress, they lose ions and this becomes even more stressful. On top of that, the energetic demand of ion pumping can represent a significant energy expenditure requiring even more oxygen. I am confident that the elevated salinity will help.

Saltwater is denser that freshwater, therefore, micro gas bubbles will be compressed even smaller maximizing coalescence. In other words, this problem is multiplied in saltwater. Stress is multiplied too.”


Professor Kevin M. Fitzsimmons, Ph.D.

University of Arizona

Environmental Research Lab

Tucson, AZ 85712

Phone (520) 626-3324

Specialty: Aquaculture Research Scientist

“Micro-fine gas bubbles that remain suspended in the water column increase the dissolved gas concentration in water more efficiently than larger bubbles in livewell water. Space must be available in the livewell for bubbles to dissolve. Most fish can’t breathe gaseous bubbles made with air or oxygen.

Gas bubble size directly affects water chemistry and when highly concentrated, can negatively affect fish health. Micro-fine gas bubbles may be unhealthy for captive fish being transported in boat livewells and ice chest having relatively small water capacities. Larger gas bubbles may be safer and healthier for captive fish than excessive micro-fine bubble environments.

Water Chemistry and micro-fine gas bubbles

Micro-fine gas bubbles that remain suspended in the water column dissolve quicker and force more gas into solution than larger gas bubbles, a plus for water chemistry when the goal is high dissolved gas concentrations.

Fish Health and micro-fine gas bubbles

Transporting live fish in livewell environments containing clouds of micro-fine gas bubbles with excessive gas supersaturation can be dangerous when transporting live fish, increasing chances of delayed release mortality.

Fish transported in milky looking livewell water containing clouds of suspended tiny micro-fine bubbles can increase stress, cause physical injury, increase susceptibility to infection and disease and may ultimately increase post release delayed mortality.

Micro-fine gas bubbles can stick to gill filaments, scales, fins, skin, and eyes, cause gas bubble trauma and gas embolus. Gill damage and gas embolisms negatively affect fish health and survival, compromise respiratory gas exchange and lead to hypoxia, carbon dioxide retention and respiratory acidosis.

Micro-fine bubbles consisting of pure oxygen can attach to gill filaments, drying, irritating, oxidizing and actually causing chemical burns to delicate epithelial tissue. Pure oxygen gas is a potent oxidizer.

Micro-fine air bubbles consisting primarily of nitrogen can cause gas bubble disease and tissue emphysema in captive fish being transported, a medical condition similar to the bends affecting SCUBA divers.”


Professor Claude E. Boyd, Ph.D.

Auburn University

Department of Fisheries and Allied Aquaculture

Auburn, AL 36849

(334) 844-4078

Specialty: Water Quality and Aeration Systems

“Transporting live fish in livewell environments containing clouds of micro-fine gas bubbles is not healthy for most fish. Continuous exposure to tiny gas bubbles that attach to gill filaments is not normal and unhealthy. Additional transport stress must be avoided as much as possible.

Micro-fine gas bubbles that coalesce and stick to fish’s gills are not healthy and may physically disrupt normal respiratory gas exchange. A few fish specie do breathe gas, but respiration for most fish specie, available gaseous oxygen must be in solution or dissolved in water, commonly known as dissolved oxygen (DO).

When clouds of gas bubbles are visualized in livewell water and the bubbles are suspended within the water column, oxygen bubbles generated with pure compressed oxygen or liquid oxygen can burn gill epithelial cells located within gill filaments. Pure oxygen increases speeds at which oxidative reactions occur. Exposure time and oxygen partial pressures govern oxidative reactions.

Oxidative damage induced by pure gas exposure can harm fish. Upon releasing fish after the transport, provided the fish survives the initial toxic insult with oxygen; gill scar tissue may develop rendering highly stressed fish even more susceptible to pathogens resulting in additional delayed mortality rates occurring within days or even weeks after release.

Clouds of tiny air bubbles trapped and suspended within the water column may create additional fish health problems during transport. Also, the potential for gas bubble disease and arterial air emboli must be considered. Fish transported in shallow livewells cannot dive deeper increasing water pressures that will dissolve fine bubbles trapped within the circulatory system like wild fish released in lakes and swimming to deeper depths.

Excessive aeration with air can harm captive fish being transported in closed livewell systems having limited water volumes. Air entrained on the inlet side of livewell water pump indicates a defective pump and a common cause for high dissolved nitrogen supersaturation. This sort of pump defect may develop dangerously high dissolved nitrogen concentrations when air is sucked into the pump inlet and then pressurized by the pumps’ impellers.

Prolonged exposures to excessive nitrogen supersaturations can cause the bends, create additional stress and gas emboli. The bends, when caused by a defective water pump, is a mechanical problem that is preventable. Understanding what problems to look for and where to look is essential. If you detect an air leak on the inlet side of your livewell pump, repair the air leak.”



You now should be able to better judge and evaluate various livewell oxygenation technologies from a fish health point of view. The health of tournament catch and release fish is dependent upon your understanding of the oxygen technology you choose to use in your livewell. Choosing the wrong livewell oxygen equipment can increase stress during transport and ultimately cause disease and increase delayed mortality. Choosing the right livewell oxygen technology can greatly improve summer livewell water quality improving survival up to 93% in the harshest summer tournament conditions.


Watch for impressive images like these with confusing words (red words alert). Our commentary, (blue words explain).


The slogan for this image may read: Micro-bubble oxygen diffuser produce clouds of extremely fine bubbles. This oxygen diffuser makes bubbles so small they make the water look a milky color. You may not be able to see through clouds of thousands of tiny bubbles suspended in the water column. [This may oxygenate water well, but a set up like this can be very unhealthy for catch and release tournament fish and live bait]

Or, you may see an image of an aerator like this with this kind of information: Millions of micro-fine air bubbles, so small that they remain suspended in the water longer providing more oxygen for your bait and tournament fish. [This is the old “air means oxygen” word trick] Our bait pump sucks in air that mixes with the water at the pumps impeller. [More air does not mean more oxygen, these are two different gases]


In fresh water, the bait pump produces many sizes of bubbles. The larger bubbles, although highly visible, do very little in oxygenating the water. They rise too quickly. Our bait pump produces millions of dust size bubbles that remains suspended in the water longer, virtually invisible to the naked eye. When you place a strong light on the water and observe from the side, like in an aquarium. The dust-sized bubbles are extremely hard to see. [You cannot see these bubbles in the water column in a boat livewell or bait tank.] Put your hand in the water and watch the millions of micro-fine bubbles gathering on your skin. Hold hand in front of the bait pump discharge and watch bubbles collect on the back of your hand. [These are those tiny suspended bubbles that stick inside gills and all over the fish]

You may have seen a picture or display of a unit in salt water producing large numbers of visible bubbles. Bubbles produced when operating in salt water, provides a much more dramatic visual display when well lighted than seen in fresh water. The bubbles are much smaller because of the higher density of saltwater. Put your hand in the water and watch the micro-fine bubbles stick to your hand. [Those tiny, tiny gas bubbles in saltwater mean double trouble for fish, more gas bubbles stick to gills creating even more stress and ill-health]

The bait pump will virtually disappear in a cloud or mass of micro-fine bubbles when used in saltwater. By allowing air to enter the input side of the bait pump, the cavitation effect mixes water with air at the pumps impellers. The output mix is a highly oxygenated [another play on words, this really means highly aerated, not highly oxygenated. Highly aerated water is often supersaturated with nitrogen gas which can cause gas bubble disease along with other serious health problems] stream of water that releases vast amounts of micro-fine bubbles into the live well.

The smaller the bubble size the more efficiently air can be infused into your water supply. Our aeration systems are more than just air pumps they add oxygen. [more play on words implying that air is oxygen] [This interesting play on words, creates the illusion that air is really oxygen.]

Our bait pumps are actually modified boat bilge pumps that are designed to operate in environments where flammable gasoline vapors may be present. See manufacturer comments from Rule, Inc. on our web page titled “Bait Pumps, Electricity”.

Do not be fooled by tricky words: Air is not oxygen, oxygen is not air and pumping air is not injecting oxygen. Interchanging the words air and oxygen often generates confusion for the unknowing fisherman just wanting something to keep his tournament fish or bait alive.

You can’t enrich livewell water with oxygen by entraining air into the inlet side of any water pump or by pumping air with electric air compressors regardless of the volume of air or the volume of water you pump. Air will always be air and oxygen will always be oxygen. The two gases are simply different.