Updating Marine Teleost Fish Acclimation Procedures: Part 2

by | Mar 15, 2006 | 0 comments

Quarantine, stress and acclimation were discussed in part one of this two part series. Here we continue covering acclimation, recovery, the role of hyposalinity therapy, factors influencing feeding behaviors and some handy equipment for use during acclimation and quarantine.



The percentage of fish killed directly by poor water quality during transport is small. The largest portions of mortalities that occur post shipment, related to the stress of transport and handling, are due to osmotic dysfunction, impaired immune function and stress mediated disease (Noga, 2000. Stoskopf, 1993). Recently handled and transported fish are susceptible to opportunistic pathogens, especially bacteria that take advantage of stress-weakened hosts (Mazeaud et. al, 1977). Most losses occur in the first week after transport, but the critical period extends to several weeks.

Compromises in the mucus/scale/skin barrier make osmoregulation difficult and cause fish to become more susceptible to opportunistic pathogens, especially bacteria. Products that contain polymers (PVP or polyvinylpyrrolidone) such as Pro Tech Coat Marine™ and StressGuard™ provide a temporary barrier until tissues heal and mucus layer recovers (Carmichael & Tomasso, 1988).

Adding vitamins and highly unsaturated fatty acids (HUFA) to the food can help fish to recover from stress (Kraul et. al, 1993; Ako et al., 1994). Non-specific defense mechanisms of the immune system are vitally important in protecting fish (Secombs & Fletcher,1992). Beta glucan has proven to enhance immune function in fish and other animals as a non-specific immune system booster that can help prevent disease and assist in overcoming infection. Beta glucan is an ingredient in some foods used in aquaculture. You can administer beta glucan to your fish by adding it to their food. For further reading about beta glucan see:

Large, rapid changes in pH and temperature are stressful to fish. However, fish vary in their ability to tolerate changes in temperature and pH. This makes it difficult to suggest recommendations or guidelines as to how much to adjust these parameters in a 24-hour period. Temperature swings influence the metabolic rate, blood pH balance and osmoregulation. Rapid temperature swings can also lead to swim bladder problems. Rapid changes in pH are stressful to fish and affect blood chemistry.

A temperature change of one degree Fahrenheit per hour (1F/hour) with a maximum of just three degrees Fahrenheit to three degrees Celsius (equal 5.4F) a day has been suggested (Noga, 2000). Stephen Spotte suggested that if the temperature is to be raised that the maximum change in a 24-hour period be limited to two degrees Celsius (3.6F) and if the temperature is lowered one degree Celsius (1.8F) (Spotte, 1979). Limiting pH changes to .3pH units in a 24-hour period is a good guideline (Andrews, et. al., 2003). Others suggest that the pH should not change more than .2 to .5pH units a day unless the level is life threatening (Noga, 2000).

Four goals that are crucial to the recovery of fish are:

  • Reducing stress with the subsequent release of stress hormones
  • Regaining normal homeostasis including ion, osmotic, and acid-base balance
  • Recovery of full immune system function
  • Return of feeding behaviors

Quickly reducing stress is critical to recovery. Choose a quiet location for the quarantine tank with dim lighting and plenty of hiding places. Elevated stress hormone levels in the bloodstream inhibit immune function. Minimize the stress factors and the level of stress hormones in the blood will begin to decline. Help the fish regain normal acid-base balance by slowly adjusting the pH and temperature over a few days until these parameters match your display aquarium (provided the water parameters in your display aquarium are at acceptable levels).

Transport stress is diagnosed clinically by a decrease in plasma osmolarity in freshwater fish or an increase in osmolarity in saltwater species (Carmicheal et. al, 1984. Robertson et. al, 1988). Severely stressed fish can lose up to 10% of their body weight in 9 to 49 hours. This weight loss is attributed to osmotic dysfunction leading to dehydration (Sleet & Weber, 1982).

Contrary to the commonly held belief that a salinity lower than natural seawater is stressful to marine teleost fish (bony reef fish), reducing the gradient (difference in salinity) between the internal fluids of fish and the surrounding ambient water alleviates water and ion disturbance (Wedemeyer, 1996. Carneiro &Urbinati, 2001). Fish held in water that is close to isotonic (the salinity of the surrounding ambient water is close to matching the internal fluids of the fish) have increased stress resistance (Lim et. al, 2000). These fish also display a significantly lower mortality rate at 7 days post shipment.

I suggest placing marine teleost fish directly into a hyposaline environment during the acclimation and quarantine period (Lowry, 2004). A salinity of 12ppt (not Specific Gravity) is close to isotonic for bony reef fish. I prefer keeping the salinity at 12 to 14ppt for thirty days or more. The salinity can then be raised a few points a day until it is close to natural seawater, or matches your display aquarium.

Although studies indicate that at least some species of marine teleost fish grow faster in a salinity of 14ppt than at 35ppt (natural seawater) (Lambert, Dutil, and Munro, 1994), I do not suggest maintaining hyposaline conditions indefinitely. Do not subject marine invertebrates, sharks, rayfish, “live rock,” or “live sand” to hyposaline conditions.

Hyposalinity assists marine teleost fish in recovery five ways:

  • Helps control external parasites
  • Helps fish to recover osmotic balance more quickly
  • Helps fish that are injured or have lost mucus protection to maintain osmoregulatory balance.
  • Conserves energy that can be used to recover normal homeostasis and for disease resistance
  • Helps fish to recover feeding behaviors more quickly

The most obvious benefit of hyposalinity therapy to marine fish, while acclimating to captivity, is that it is a proactive approach to dealing with external parasites. However, there are other significant benefits for marine teleost fish.

Osmoregulatory dysfunction is an inherent part of stress in fish. Reducing the salinity gradient between the internal fluids of the fish and the surrounding ambient water helps them to recover osmotic balance more quickly.

Injuries are a common occurrence during transport and handling. Wounds or compromises to the mucus/scale/skin barrier make osmoregulation more difficult and costly energy-wise. In marine fish, osmotic pressure can cause fluids to leak from wounds into the water. Reducing the salinity of the water decreases the osmotic pressure and loss of fluids from wounds or compromises the mucus layer.

Marine teleost fish typically consume 25 to 50% of their metabolic energy in the process of osmoregulation. Conserving metabolic energy makes more available for other processes such as regaining normal homeostasis, diseases resistance, etc.

Since osmoregulatory balance is a factor influencing feeding behaviors, it is reasonable to assume that fish that quickly recover osmotic balance will resume feeding sooner. Fish should regain osmotic balance more quickly in hyposaline conditions.

Factors influencing feeding behaviors

  • Security
  • Overall health
  • Temperature
  • Photo-period
  • Osmoregulatory balance

It is important that fish begin eating within a few days after arrival. You can help the fish feel secure in their environment in several ways. Paint the back, bottom and sides of the quarantine tank. Place the quarantine tank in a quiet location away from activity and noise. Keep the lighting dim over the aquarium and provide plenty of hiding places with PVC pipe of various sizes.

Overall health is also an important factor influencing feeding behaviors. You can add vitamins such as Zoe™ directly to the water in the quarantine tank. Marine fish will absorb the vitamins from the water. Vitamins can help animals to recover overall health and they may stimulate a feeding response. Keep an assortment of medications handy for common infections.

As the water temperature reaches the optimal range for a particular species of fish, they will be more likely to eat. Do not settle for a water temperature that the animal will merely tolerate. Make the goal to provide optimal conditions for the animals, including temperature.

The lighting should be dim most of the time for the first few days. Keep in mind that some species are nocturnal while others only eat during daylight. You may have to experiment with the lighting, as there can be some differences between species as to how they respond to feeding in various lighting intensities.

Osmoregulatory balance is an important factor influencing feeding behaviors. Hyposaline conditions will help fish to regain normal osmotic balance more quickly after transport and handling. With the return of normal homeostasis, fish will be more likely to resume feeding behaviors.

Fish respond to colors, movement, tastes, smells and sounds as feeding stimuli. Live foods make good starter foods although they may not be the most nutritionally complete. Soaking foods in garlic seems to increase feeding responses in some fish. A few drops of cod liver oil on the food may also help. Cod liver oil contains a lot of vitamin A so do not use it on a continual basis, because it is possible to overdose.

Steps to better acclimation:

  1. Prepare a mature biological filter for the quarantine system when possible. Benefits: Provides a stable environment without exposure to toxins such as ammonia.
  2. Adjust the pH and temperature in the quarantine tank to match those at the retailer or the shipping water when possible. Benefits: The fish can be immediately removed from the transport bag and allowed to swim in oxygenated water. This reduces stress and helps fish to remove lactate acid and ammonia from their body. This also allows for slow acclimation to changes in pH and temperature over days rather than minutes or hours.
  3. Employ hyposaline conditions. Benefits: Proactive approach to external parasites, and counteracts osmotic dysfunction due to the stress of transport and handling.
  4. Use dim lighting or red light. Benefits: Prevents photo shock and has a calming effect on fish.
  5. Avoid removing fish from their native environment (water) and the use of nets. Benefits: Water to water transfer with the use of clear plastic bags or specimen containers prevents stress, gill collapse, lactate acid build-up, and reduces injuries.
  6. Get the fish out off shipment water and into clean oxygenated water immediately. Benefits: Allowing fish to swim in oxygenated water away from toxins reduces stress, helps reduce stress hormones in the bloodstream, helps fish remove toxins from their body and provides oxygen essential to osmoregulation and other bodily processes.
  7. Add a polymer such as found in Pro Tech Coat Marine™ or StressGuard™ (polyvinylpyrrolidone) to the quarantine tank. Benefits: Protects wounds and aids in osmoregulation.
  8. Use Beta glucan, vitamins and Omega-3 fatty acids. Benefits: Beta glucan enhances immune function, while vitamins and Omega-3 fatty acids help alleviate stress and speed recovery.
  9. Withhold feeding for 24 hours. Benefits: Metabolic energy is directed toward functions essential to immediate survival such as regaining normal homeostasis.
  10. Slow acclimation to changes in temperature and pH. Benefits: Less stressful on fish than quicker acclimation and should improve survival.

Handy equipment for acclimation and quarantine

  • Poly Filter™ by Poly Bio Marine (Chemical filtration pad).
  • PVC pipe for hiding places
  • Food grade Rubbermaid™ container
  • Refractometer
  • Clear poly bags and specimen containers
  • Beta glucan
  • Highly Unsaturated Fatty Acids (Selcon™)
  • Vitamins
  • Temp Gun™
  • pH test or probe
  • Non-calcareous sand
  • Polymer such as found in StressGuard™ and Pro Tech Coat Marine™
  • Magnifying glass
  • Test kits for ammonia, copper, etc.
  • Medications

Poly Filter™ is a chemical filtration pad that removes toxins such as ammonia, nitrite, copper and other impurities from water. PVC pipe is inert and easy to find at most hardware stores. Rubbermaid containers work well as a quarantine tank. A refractometer is a valuable tool for accurately measuring salinity, especially important when treating fish with hyposalinity. Clear poly bags or specimen containers are difficult for fish to see in water and they work well for catching and transferring fish. Beta glucan enhances immune function. A Temp Gun™ makes a handy tool for quickly checking the temperature in multiple aquariums and shipment bags without opening the bags. A pH tester such as the pH51™ by Milwaukee Instruments can be handy as well. Use non- calcareous sand in quarantine, when necessary, for species such as wrasse and jawfish that sleep or dig homes in the sand. A magnifying glass can make it easier to identify lesions or abnormalities on fish. Having medications handy for common infections can save valuable time.



My recommendations for updating marine teleost fish acclimation procedures are not based upon what is easiest to do, most cost effective, quickest or even what is most practical. My first concern is for the health and longevity of captive fish. I believe that these animals are entitled to benefit from all the knowledge and skill we can provide, giving them the best possible chance of a long and healthy existence in our care.

Acclimation involves more than merely getting fish used to water conditions: It includes helping animals recover from capture, transport and handling. The process of acclimation is not complete until the animals regain their strength, adapt to captivity, become familiar with new foods and grow accustomed to their tankmates and the aquarist that cares for them.

One of the greatest things about marine aquarium keeping is that the hobby is continually evolving. Our willingness to examine new ideas and ways of doing things is one of the hobby’s utmost strengths. As we gain knowledge and grow in our understanding of how to apply it, methods, procedures, equipment and other aspects change. Our skills to maintain, culture and sustain our hobby, along with the animals in our care, grows with each new advance.



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