Monday, May 4, 2015


  The key to keeping your marine fishes healthy, like this Limbaugh's angelfish (Holacanthus limbaughi), is to keep stress at a minimum. Photo by Scott W. Michael 
Reducing stress to our fish is indeed one of the biggest challenges we face as marine fish keepers. Your marine fishes are exposed to stress from the moment the diver begins the process of trying to catch them. The fish is then transported, in an unfamiliar environment (e.g., a bucket or live well), to tanks on shore. In some cases the fish are handled carefully and provided with proper care, but not always. In most collection stations where the fish are caught and at wholesalers here in the states, the fish are held in bare tanks. This makes it easier for staff or customers to observe the fish. But, think about this for a moment. You have a fish that was living in a coral labyrinth, where hiding places abound, that is now in a little Plexiglas box without any shelter. Even if other environmental parameters (e.g., water quality) are optimal, this fish is more than likely going to experience some degree of stress.


  • Select the species you keep carefully – not all species deal with stress in the same way.
  • Feed your fish a nutritious diet.
  • Select tankmates carefully to help avoid aggression problems.
  • Provide lots of behavioral substrate (places to hide).   
  • Maintain optimal environmental conditions (e.g., water quality).
  • Reduce the likelihood of sudden changes in environmental conditions.
  • Capturing, moving or handling your fish should be done as infrequently as possible. 

On a side note: I would recommend that collectors/wholesalers add behavioral substrate to the aquarium to help reduce some of this stress. The best thing to use for hiding places is PVC of varying diameters to form holes and caves.

The fishes also experience varying degrees of exercise stress when their captured in the wild, when caught in the collector or wholesalers tanks and when captured at your local aquarium store. The more the fish is chased about the tank the more exercise stress it is likely to experience. In some cases fish have been reported to suffer from post exercise mortality after having engaged in strenuous exercise for only a few minutes! When a fish is caught it is also exposed to handling stress.

Then there is the long plane flight from the Red Sea, the Philippines, Indonesia, etc. to the Untied States. The fish are shipped in a plastic bags that are partially filled with water and topped off with oxygen. The fish can be in this plastic bag for a day or more. The chemistry of the bag water changes – toxic compounds build up, oxygen levels drop, pH drops. This causes stress. The fish arrives at the US wholesaler and is then introduced to its new, temporary holding tank. No place to hide. Lots of people moving about. Stress. In most cases, the collectors and wholesalers do not feed the fish because they are best shipped on a empty stomach. If the fish is fed and placed in a shipping bag, it may defecate which will pollute the shipping water and could increase the likelihood the fish will die in transit. As a result, the fish may have to fast for a week or more. More stress.

At the wholesaler, some fish are purchased by local retail stores, while others are sent to retailers across the country in relatively small shipping bags. If the retailer is lucky, the shipment is on time and the boxes of fish are treated with care while in transit. But in many cases, the airlines leave them in areas where the temperature can cause the temperature in the shipping bags to rise or fall (depending on the time of year). Fish shipped in the wintertime are often left in the cold for great lengths of time. I have had fish arrive in shipping bags where the water temperature was less than 70 degrees Fahrenheit and on several occasions where the bags were under 60 degrees! Of course, this is a temperature much lower than these fishes are exposed to in their natural habitat. If the low temperatures do not kill the fish outright, the low temperatures cause more stress.

Studies have shown that stress can cause short and long-term physiological changes. It can cause hormonal changes, upset respiration, cause osmoregulatory and metabolic disturbances, elevate blood sugar levels, etc. Some fish rebound from these stressful encounters, while others may die days or even weeks after the initial stress was induced. Stress factors also cause immune suppression, which can lead to parasitic and bacterial infections.

After reading this you are probably amazed that any fish live at all! That is why it is so important to try and provide the fish with a stress free environment once they arrive in our home aquariums. At Reef Tectonics we condition and quarantine all our fishes before we take them to our customers. This ensures that the fish that we place in your tank are in better condition and more likely to survive the acclimation period.

There is no doubt that different species of reef fishes can withstand different levels of stress. This may be one of the more important determining factors when considering how well a species does in your home aquarium. There are some species that do not do well for most aquarists in Nebraska, that will do well when kept by hobbyists that live where they are collected. For example, I have had Hawaiian aquarists tell me they have had good success with the Hawaiian longfinned anthias (Pseudanthias hawaiiensis). I have found that those P. hawaiiensis shipped to me here in Nebraska usually do poorly. In many cases, they never seem to recover from the stress induced during the shipping process.

Not only is there species specific differences in their ability to withstand stress, there can be a difference between size classes. For example, Pomacanthus angelfishes between 2 and 4 inches tend to ship better and acclimate more readily to captivity than tiny juveniles and large adults.  When purchasing angelfishes I would suggest that you keep this in mind. I am not sure how your tank décor is arranged, but also make sure that your angelfish have suitable bolt holes, that is, caves and holes that they can dash into when they are startled or feel threatened.

  ©  Scott W. Michael- Reef Tectonics

 Reef Tectonics Aquarium Maintenance and Design - Lincoln, Omaha, Des Moines, Kansas City

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