Marine Fish Acclimation Procedures: Part 1

by | Jan 15, 2006 | 0 comments

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 corticosteroids
  • 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 fish’s 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 parasites.



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 1992).



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 down.

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
  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
  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, 1992.
  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, 1989.
  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 trout. Journal of Experimental Biology, 123, 93-121, 1986
  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, 1987.
  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.


Submit a Comment

Your email address will not be published. Required fields are marked *