Dissolved Oxygen and Shad

Dissolved Oxygen, Temperature (water and air) and salinity affect the dissolved oxygen capacity of water. After dissolving at the surface, oxygen is distributed by current and turbulence.

Dissolved Oxygen (DO) is found in microscopic bubbles of oxygen that are mixed in the water and occur between water molecules.
Dissolved Oxygen is a very important indicator of a water body's ability to support fish.
Fish "breathe" by absorbing dissolved oxygen through their gills.
Oxygen enters the water by absorption directly from the atmosphere or by aquatic plant and algae photosynthesis.
Algae and rooted aquatic plants deliver oxygen to water through photosynthesis.
Oxygen is removed from the water by respiration and decomposition of organic matter.

Water temperature is a key factor in the regulation of water's oxygen levels.

Warm water contains a less oxygen concentration than cold water. When dissolved oxygen levels in water drop below 5.0 mg/l, shad are under stress. The lower the concentration, the greater the stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills. Total dissolved gas concentrations in water should not exceed 110 percent. Concentrations above this level can be harmful to shad. Shad in waters containing excessive dissolved gases may suffer from "gas bubble disease" however, this is a very rare occurrence. Oxygen level in the air is less today than in ancient times (oxygen content was 38% 10,000 years ago, compared to the 21% it is now) and getting worse due to pollution and industrialization.

The main factor contributing to changes in dissolved oxygen levels is the build-up of organic wastes. Decay of organic wastes consumes oxygen and is often concentrated in summer,when aquatic animals require more oxygen to support higher metabolisms. The ratio of the dissolved oxygen content (ppm) to the potential capacity (ppm) gives the percent saturation, which is an indicator of water quality. Dissolved oxygen analysis measures the amount of gaseous oxygen (O2) dissolved in an water solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. Since the air we breathe is composed of nitrogen (approximately 79 percent) and oxygen (roughly 21 percent). An aerator system operating at maximum efficiency can only deliver a maximum of 21-percent oxygen into the live-well water.

When baitfish are first caught and dumped into a live well, their stress level skyrockets causing them to use up the available dissolved oxygen provided by aerators fast. Shad in the live well are subject to stress-inducing factors, such as injury, overcrowding, long runs to the fishing grounds, and warm water temperatures. The oxygen consumption of the bait fish could kill the baits or make them lethargic.

Doubling the amount of air or water flowing through the live well with multiple aerators or pumps
will not significantly increase the dissolved oxygen content much beyond the 21 percent that's available in air.

In some cases, excess water flow will force the baits to swim harder and consume even more oxygen.

When you use pure, dissolved oxygen, high levels of oxygen in the shads blood are the results.
High blood-oxygen levels help produce higher levels of adrenaline, causing the shad to become more active.

Tanks with built-in pumps generate heat which can rob the water of its retention to oxygenate, a factor detrimental to the bait

There are many misconceptions about aeration systems.

Two common fallacies are:

  • Large live wells are required to sustain a large quantity of fish. 

  • Large live well pumps are needed to move large quantities of water through the live well to keep live bait and fish alive.

  • To understand what is really needed for proper aeration, it is best to take a parallel look at ourselves and fish.

    • If we were enclosed in a large airtight room we would be able to breathe for many hours before we would consume all the oxygen.

      If we were in an airtight closet, the oxygen would be consumed a lot quicker.

      If we were swimming underwater without a snorkel, the oxygen in our lungs would be consumed very quickly.

      In all cases, without additional oxygen we would eventually expire!

      However, we could stay alive indefinitely, if we could use a breathing tube or snorkel that was in contact with outside fresh air or oxygen. It would not matter about the size of the container or the quality or air that surrounded us.

      If we enclosed a shad in a sealed, 1,000 gallon tank, it would survive for a long time before consuming all the oxygen.

      If we enclosed the same shad in a sealed 10 gallon tank, the oxygen would be consumed more quickly.

      If we removed the same shad from the tank and placed it on a table, the shad could live for an extremely short time.

      In all cases, without additional oxygen the shad would eventually die.

      However, our shad could stay alive indefinitely if we could put oxygenated water through its gills and keep it wet. It would not matter about the size of the tank.

      If an aerator can provide enough oxygen in the water for the fish to breathe, it doesn't matter how much water surrounds the fish! The only reason that water must be changed occasionally in live wells is to remove ammonia. The smaller the container of water, the more frequent the changing.


A human breathes in oxygen and gives off carbon dioxide (CO2). The carbon dioxide is then dissipated into the atmosphere. A fish breathes in oxygen from the water and gives off carbon dioxide. The carbon dioxide is absorbed into the surrounding water.

The carbon dioxide is then dissipated into the atmosphere through the process of aeration.

An air bubble as it passes through water has the ability to put oxygen into the water and also absorb carbon dioxide as it passes slowly to the surface.

The bubble then pops at the surface and the carbon dioxide is dissipated into the atmosphere.
The smaller the bubble, the longer it remains in the water to exchange oxygen and carbon dioxide.

Oxygen in the water

An oxygen bubble will insert a higher percentage of oxygen into water than a normal air bubble.
This allows for higher quantities of fish in a given size of container, or it will make bait fish lively.

However, an oxygen bubble does not have the ability to absorb CO2.
 As the fish eliminates CO2 in it�s body, there will be a build-up of CO2 in the water.
When the percentage of CO2 equals that of the fish, the fish will be unable to expel the CO2
and absorb the enriched oxygenated water.

If a closed livewell does not have the ability to aerate and remove the CO2, the fish will suffocate.

Too Much pure Oxygen can Kill Your Fish!


Spray bar aerators add oxygen to the water by jetting small streams of water into the surface.
Some air is absorbed into the spray as it passes from the spray bar to the water surface,
and when the spray strikes the water surface, air bubbles are injected into the water.
For the most part, these bubbles are rather large.

Jets of water from spray bars are generally harsh to delicate bait. Their protective coating and scales are easily removed, and their survival is drastically reduced in small tanks or bait buckets.
Spray bars for the most part are an inefficient aeration system, and should be used only on the hardiest bait.

Air Stones

Air stone aerators are an inexpensive way to keep bait alive in small containers.
They are quiet and gentle, but because their bubbles are typically larger, they need a greater amount of bubbles for a large amount of bait.
Air stone aerators do provide gentle aeration, but they sustain less bait per unit of air than aerators that produce smaller bubbles


This is the much copied, old aeration technology. They can be purchased as a floating aerator or a bottom aerator with suction cups.
The fast-moving water at the output of the pump creates a vacuum, which suck air into the pump output.
This system typically provides larger amounts of smaller air bubbles than previously discussed aerators.
Some models damage bait due to the high speed of water from the pump output

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