QUESTION:
I have experienced "gas-bubble disease" in 14 -21 day old sea bream
(Sparus aurata) larvae. However, when the saturation of the gases is
measured, the water is not found to be supersaturated. I can see the
larvae gulping air bubbles and then, upon microscopic examination, air bubbles can be seen in the intestines. This occurs in larvae that have already developed and inflated their swim bladders. Sometimes this phenomenon is seen in older larvae (40 - 50 days old) which are about 40 milligrams in weight. I cannot associate this finding with large mortalities, rather it constantly is seen in our system and causes a continuous low level mortality.
Is anybody familiar with this phenomenon? I would appreciate hearing the experiences of others involved in marine larval rearing.
Glen Pagelson
<pagelson@shani.net>
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COMMENTS 1:
In working with Mysidopsis bahia in a bioassay culture laboratory, we came across a simular situation. In our case it had to do with the external pump sucking air and super saturating the water with nitrogen. In our case it was a simple situation of raising the water level, so that the pump could not create too great of a vortex (first we
saturated the water with air to release the nitrogen, which seems wrong at first glance).
Joseph Myers
<PITTD1.SOMEP1.JMYERS1@itcrp.com>
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COMMENTS 2:
Are you heating your water? I had gas bubble disease, up to and including pop-eye manifestation, when a boiler heated the water. All you need to do in this case is run the water through a packed column before delivering the water to the rearing tank.
Rick Eager
Swimming RockFish and Shrimp Farm
Meggett, South Carolina 29449, USA
email: <dreager@awod.com>
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COMMENTS 3:
I have a question about the relationship between total dissolved gas
pressure and "gas bubble disease". If the total dissolved gas pressure is below 100% could gas bubble disease still occur?
John Hayward
<hambrook@nbnet.nb.ca>
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COMMENTS 4:
The supersaturation can be transient. Should try monitoring over time with probes or repeated testing during the day.
Could the bubbles in the intestine have come from gas bubble disease and not from ingestion? Does your examination of the fish show any gas bubbles elsewhere in the fish?
Jim Brackett, DVM
General Manager, Syndel International Inc.
800 663 2282, 604 321 3900 fax
<brackett@qb.island.net>
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COMMENTS 5:
Gas bubble is primarily caused by nitrogen oversaturation, therefore only nitrogen has to be above 100%. Keep in mind though, that gas bubble can be caused by other means, e.g. bacterial infections.
Mike
<mchris@unix1.sncc.lsu.edu>
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COMMENTS 6:
The question was if gas bubble trauma could develop if the total gas pressure of the water was less that 100%. The answer is that it could if the partial pressure of nitrogen in solution was greater than the partial pressure of nitrogen in the atmosphere.
These circumstances are likely to be quite rare in aquaculture because it would also mean that the dissolved oxygen levels are low. As soon as the water enters the culture tank, nitrogen would try to establish equilibrium with atmospheric pressure by coming out of solution. At the same time oxygen would be going into solution. The total gas pressure of the water would increase sharply and bubbles would form.
In cases where the total gas pressure is greater that 100% and if the gas responsible for causing the condition is nitrogen, the aquatic animals would be susceptible to trauma. However if the gas is oxygen, gas bubble trauma would be less likely because the animals are able to utilize the excess oxygen and thereby prevent bubble formation.
Dr. Howard T. Dryden
Dryden Aqua
Edinburgh
Scotland, UK
e-mail dryden@aqua.ednet.co.uk
web site http://www.ednet.co.uk/~dryden
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COMMENTS 7:
In a previous mail, I said that gas supersaturation with nitrogen was not very common in aquaculture when the total gas pressure was below 100%. However gas supersaturation in aquaculture occurs in approximately 20% of all of the hatcheries in Scotland, and in these farms that total gas pressure is nearly always above 100%.
It is essential that the gas pressures are below 100%. At 101% gas saturation the compensation depth is 100mm below the surface of the water. Therefore any aquatic animal in this top 100mm will be subjected to elevated pressures and will be susceptible to gas bubble trauma. At levels of 102% the compensation depth is 200mm and so on. The compensation depth is the depth at which the hydrostatic pressure head of water is equivalent to the partial pressure exerted
by the dissolved gases.
Water vapour exerts a gas pressure of about 2%, therefore passive degassing columns are not effective in eliminating residual gas pressures. The only way I know of resolving this problem is vacuum degassing of the water. If you would like more information on this subject you may check out our web pages. We are manufacturers of vacuum degassing systems and have been supplying them to many farms in the aquaculture industry for the last 10 years.
Very few fish farms measure the total gas pressure of the water accurately to values less than 105% total gas pressure, therefore some are not aware that a problem actually exists. Details of the problems and sources of gas pressure are given in our web site
http://www.ednet.co.uk/~dryden
Some of the problems are caused by design problems, in other cases elevated gas pressures are natural and transient occurrences. Take for example a situation in which the total gas pressure is 100%, a sudden atmospheric low depression then passes over the farm. Atmospheric pressure drops by 1% making the water 101% gas supersaturated. In a hatchery situation the fish may be kept in shallow tanks or troughs and can not escape below the compensation depth, as a consequence the fish are stressed and mortalities could result.
Howard Dryden
Dryden Aqua
Edinburgh
Scotland, UK
e-mail: dryden@aqua.ednet.co.uk
web site: http://www.ednet.co.uk/(dryden
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COMMENTS 8:
I never knew that atmospheric conditions can cause supersaturation at shallow depths. This may be an additional reason for why survival rates of bivalve larvae in large (deep) containers is much higher than in beakers. (The other reason is that larvae in large containers do not bump into the sides as often.)
Madelon Mottet, Ph.D.
Alaska-Southeast Bio-Research
704 Sawmill Creek Blvd.
Sitka, Alaska 99835 USA
e-mail: madelon@ptialaska.net
Tel/Fax (907) 747 3862
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