Updating Marine Fish Acclimation Procedures: Part 1

When I set up my first saltwater aquarium, in 1973, the
hobby was still in its infancy. Over the years, we have seen
many changes and improvements in the way that we care for
aquarium inhabitants. We know more about water chemistry,
filtration methods have improved and we have learned more about
the specific needs of various species. The quality and variety
of the foods available now are better than ever. Our hobby
continues to evolve and grow as new information is presented on
husbandry, breeding, lighting and other aspects of marine
aquarium keeping. This knowledge has helped the hobby advance
to the point that many species of fish and invertebrates once
considered difficult or impossible to keep now thrive, grow and
reproduce in captivity.

In our hobby, there will always be room for improvement and
new ideas. Some of these new ideas or ways of doing things may
meet with resistance. Nevertheless, any idea based on knowledge
and sound reasoning is worth investigating.

One aspect of aquarium keeping that warrants a closer look
is fish acclimation procedures. We now have a better
understanding of the physiological, biochemical and behavioral
effects of stress in fish. Armed with this knowledge, we can
implement changes in the way we acclimate and care for our
stock. These changes will help animals recover more quickly
from stress and improve survival.

In our hobby, there will always be room for improvement and new ideas.
Some of these new ideas or ways of doing things may meet with resistance.
Nevertheless, any idea based on knowledge and sound reasoning is worth investigating.


Some of the effects of transport, handling, confinement,
capture and air exposure on fish include:

  • The release of stress hormones such as catecholamines and
  • Impaired immune function related to elevated stress
    hormone levels
  • Elevated levels of plasma and muscle lactate acid
  • Muscle fatigue as the result of exhaustive exercise
    leading up to capture
  • Gill collapse from air exposure
  • Reductions in energy fuels such as phosphocreatine (PCr),
    adenosine triphosphate (ATP) and muscle glycogen
  • Elevated hematocrit, red blood cell swelling, spleen
    transfusion, and fluid shifts
  • Osmotic, electrolyte and acid base disturbances caused by
    fluid shifts and the accumulation of metabolic wastes.


We can eliminate or reduce exposure to some stress factors
and help alleviate the consequences of others by preparing
ahead of time. Ready the holding tank or quarantine system
prior to bringing your new fish home. A ten-gallon aquarium can
serve as a quarantine tank for small specimens, but a larger
tank with more swimming room is preferable. Paint the back,
bottom and sides of the quarantine tank to reduce the fishs
awareness of the outside surroundings. A matured biological
filter will ensure that your new acquisitions are not exposed
to ammonia poisoning and other toxins. A sponge filter powered
by an airpump, or outside filter with a biowheel can work well
for this purpose. These filters will also provide water
movement and gas exchange. You can seed your sponge filter or
biowheel with the bacteria that perform biological filtration
easily. Just leave them in a matured aquarium or in the sump
for a few weeks. Place several pieces of PVC pipe, of various
sizes, in the quarantine tank for hiding places. You will also
need a heater. Acclimating in dim lighting or under red light
has a calming effect on fish and reduces stress. Keep a batch
of well-aged and aerated saltwater ready at all times for a
quick water change.

The quarantine aquarium should not contain invertebrates,
substrate, or rock. Invertebrates do not tolerate many of the
disease treatments used on fish. Rock and substrate in the
aquarium complicate treatment with copper and antibiotics.

Consider the needs of each particular species as you may
need to make exceptions to accommodate them. Examples: certain
species of wrasse sleep buried in the sand and jawfish
construct a home using sand and rubble from the substrate.

Quarantine each new specimen in isolation from other animals
with the possible exception of mated pairs and schooling fish.
In isolation, your new fish will not have to deal with
aggression from tankmates or competition for food. Practicing
proper quarantine procedures also reduces the risk of exposing
your established stock to contagious disease and


Chasing fish to catch them for transport can cause lactic
acid to accumulate in their blood plasma and muscle tissues.
Lactic acid build up is toxic to fish. The amount of time that
is takes to recover from lactacidosis (lactate acid build up
and depressed blood pH) appears to be related to the cortisol
(stress hormone) blood level. The cortisol level typically
recovers two to six hours after the stress factors are
resolved. It appears that fish recover from stress and lactic
acid build up more quickly when allowed to swim in oxygenated
water. Recovery time for blood and muscle metabolite and
acid-base balance can be reduced to about two hours if the fish
are allowed to swim (Hooke & Milligan, unpublished). Full
recovery of normal metabolism in fish takes up to twelve hours
(Milligan & Wood, 1986).


During shipment, ammonia and carbon dioxide build up in the
bag, the pH and oxygen level of the water declines and the
temperature will rise or fall with the influence of the
surrounding air. It is crucial to minimize exposure to free
ammonia and high carbon dioxide concentrations by immediately
removing the animal from the bag upon arrival. The fish also
need sufficient oxygen to help them remove ammonia, carbon
dioxide and lactic acid from their body. Immediately after
transfer to a holding tank, provide the animals with aeration
and water surface movement for good gas exchange.

Oxygen is the most crucial element. Oxygen provides the
cellular energy necessary for osmoregulation and other
processes. Without a sufficient supply of oxygen vital
functions shut down and the fish will eventually die from
stress and oxygen deprivation.

The degree of deterioration in the water quality and stress
level of the fish due to handling and transport depends,
largely, on how long the animals are confined to the shipment
bag. Animals held in a bag for several hours or more than one
day are exposed to a reduction in the oxygen level, carbon
dioxide build up, increasing ammonia toxicity and a decline in
pH. These factors are less severe when the animals are making a
short trip from the local fish store to your home and only in
the bag for a brief time.

Oxygen is the most crucial element. Oxygen provides the cellular energy
necessary for osmoregulation and other processes. Without a sufficient supply
of oxygen vital functions shut down and the fish will eventually die from
stress and oxygen deprivation.

When fish are removed from their native environment (water)
it causes the gills to collapse so they do not function
properly in respiration or in the removal of toxic substances.
Exposure to air after exercise increases blood lactate
concentration. Avoid removing fish from water whenever
possible. Water to water transfer is possible by catching and
moving the fish in a clear plastic bag or specimen container
rather than a net. If the fish must be exposed to the air, then
minimize the time that they are out of the water to seconds.
Exposure to the air for as little as thirty seconds
significantly increases mortalities (Ferguson & Tufts


If you are purchasing a fish locally then ask the manager or
employee to test the pH and temperature of their aquarium. Then
adjust the temperature and pH of your holding tank to match
closely before bringing your new acquisition home. You can use
phosphoric acid packaged by Aquarium Pharmaceuticals as pH
Down to reduce the pH. Muriatic acid , used in pool supplies,
will also reduce the pH of water. Numerous products are
available to buffer water and bring the pH up including
Seachems Marine Buffer. Sodium bicarbonate (baking soda) will
also raise the pH. When adjusting the pH be careful not to
change it too much at one time or too quickly.

Matching the pH and temperature of the water in the
transport bag becomes more complicated when delivered directly
to your home, or when shipped from great distances. The water
parameters in these circumstances can vary widely. When the bag
is opened, test the pH immediately because this parameter will
rise quickly as the carbon dioxide escapes from the bag. If
your local fish store has received animals from the same source
before and tested the water conditions of other shipments on
arrival then they can better anticipate what the pH and
temperature may be.


Although fish do need time to adjust to changes in pH and
temperature, this is not true for all water parameters. Do not
delay in providing animals with plenty of oxygen just because
the oxygen level in the shipment bag was low. You certainly
should not take your time getting fish away from exposure to
ammonia or other toxins. Marine teleost fish (bony reef fish)
readily adjust to a rapid drop in salinity without any apparent
ill effects. Place fish directly into a salinity of 12-14ppt.
Monitor the pH daily as this parameter has a tendency to fall
in dilute saltwater.

It is a common practice to float fish in the bag to adjust
the water temperature to match the aquarium. The toxicity of
ammonia and other toxins increases as the water temperature
rises. This includes problems with a high carbon dioxide level
and acidosis (low blood pH). Acclimating fish to changes in pH
and temperature over days rather than minutes or hours will
also reduce losses and help to speed recovery. Removing fish
from exposure to toxic ammonia, carbon dioxide and lactic acid
levels is an important part of these processes.

An adequate oxygen level to provide energy is the top
priority crucial to survival and recovery. A sufficient oxygen
supply and allowing the fish to swim will reduce stress and
help them to remove toxins from the body. Osmoregulation
consumes a great deal of metabolic energy. This energy is
provided via aerobic metabolism that requires oxygen. Without a
sufficient supply of oxygen, the osmoregulatory processes shut

It is important to work quickly once the bag is opened,
because the ammonia inside can damage the fins, skin and
delicate gill tissues. As carbon dioxide escapes the bag, the
pH of the water will elevate. Ammonia becomes more toxic as the
pH rises. Check the temperature and pH immediately to get
accurate readings. Then without delay move the fish to a
holding tank with a temperature and pH that matches the water
in the shipment bag as closely as possible.

A swing in pH from 7.0 or so (maybe lower) to the pH of
natural sea water (about 8.3) in just a few hours is highly
stressful. Even a small change in pH, if it is rapid, can cause
severe acidosis in fish leading to death. Rapid temperature
swings are also stressful contributing to blood chemistry
changes and inhibited immune function. It is better to adjust
the quarantine aquarium to match the temperature and pH of the
shipment water. After the fish is in a holding tank with a
similar pH and temperature, you can then immediately begin to
adjust these parameters. Slowly adjust the pH no more than .3
per day (example: pH of 7.7 adjusted to 8.0) and the water
temperature a couple degrees Fahrenheit each day until these
parameters match the conditions in your display aquarium.

I use an instrument called a Temp Gun to check the water
temperature without opening the bag. Check the aquarium
temperature at the same time. This handy little device fits in
the palm of your hand and the PE-1 model retails for around
twenty-five dollars. For more information go to:
The pH51 by Milwaukee Instruments is another handy tool. This
probe can quickly check the pH of the water in shipment bags
and retails for around fifty-five dollars. For more information
go to:

Do not feed the fish for the first twenty-four hours in the
quarantine tank. Digestive processes require energy and consume
oxygen. It is important that the fish expend their energy for
activities that are crucial to their immediate survival such as
regaining normal homeostasis before they begin to eat. Once
they have regained normal homeostasis and stress hormone levels
have fallen, they will be more likely to begin eating again.
Stop feeding during short periods of high water temperature as
the oxygen demand necessary for digestion may exceed the supply
(Stevenson, 1987).

Fish should remain in hyposaline conditions for several
weeks. Marine teleost fish need more time to adjust to an
increase in salinity than a decrease. Raise the salinity a few
points a day until it matches your display aquarium before
moving the fish to its final destination.


Part two of Updating Marine Fish Acclimation Procedures
will continue in the next installment. I will discuss recovery,
the role of hyposalinity therapy, factors influencing feeding
and some handy equipment for acclimation and quarantine.


  1. Bartelme, T.D., Reducing Losses Associated with
    Transport & Handling in Marine Teleost Fish
    . Advanced
    Aquarist Online Magazine, May, 2004.(also available from http://www.marineaquariumadvice.com/reducing_losses_with_transport.html)
  2. Bartelme, T.D., Beta Glucan as a Biological Defense
    Modulator: Helping Fish to Help Themselves
    . Advanced
    Aquarist Online Magazine, September, 2003c.(also available from
  3. Bartelme, T.D. No Nets Please: Better Health Through
    Better Handling
    . Reefkeeping, September, 2003b.(also available from http://www.marineaquariumadvice.com/no_nets_please.html)
  4. Ferguson, R.A. & Tufts, B.L. “Psychological Effects of Brief Exposure in
    Exhaustively Exercised Rainbow Trout: Implications for
    “Catch and Release” Fisheries
    ,” Canadian
    Journal of Fisheries and Aquatic Sciences. 49, 1157-62,
  5. Maule, A.G. Tripp, R.A. Kaattari, S.L. & Schreck, C.B. Stress Alters Immune Function and Disease Resistance in
    Chinook Salmon.
    Journal of Endocrinology, 120, 135-142,
  6. Milligan, C.L. & Wood, C.M. Intracellular and
    extracellular acid-base status and H+ exchange with the
    environment after exhaustive exercise in the rainbow
    Journal of Experimental Biology, 123, 93-121,
  7. Noga, E.J. Fish Disease: Diagnosis and Treatment.
    Ames, IA: Iowa State University Press, 2000.
  8. Pickering, A.D. Stress Responses and Disease Resistance
    in Farmed Fish.
    In Aqua Nor 87, Conference 3: Fish
    Diseases – a Threat to the International Fish Farming Industry.
    Pp. 35-49. Norske Fiskeoppdretteres Forening, Trondheim ,
  9. Stevenson, J.P. Trout Farming Manual. Ed 2,
    Fishing News Books, pp 259, Oxford, England, 1987.
  10. Stoskopf, M.K. Fish Medicine. W.B. Saunders
    Company. Philadelphia, Pennsylvania, 1993.
  Advanced Aquarist

 Terry D. Bartelme

  (16 articles)

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