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How to Quarantine Marine Fish

Warty Frog Fish (Antennarius maculatus)

By Tony Griffitts

Most saltwater fish we see in the hobby today are still wild caught.  As with a lot of wild caught fish, both fresh and salt water, they often carry external parasites.  In the wild these external parasites rarely if ever become a real problem, because the lifecycle of these parasites in the wild prevents them from reaching plague proportions in the open ocean.  When we bring these fish into our closed systems that have a small amount of water as compared to the ocean, we increase the chance that these parasites can find a host and multiply out of control.  By far the number one cause of a total aquarium fish population being wiped out for marine hobbyist is an external parasite population explosion.

The most common marine external parasite that can be a problem for marine fish in captivity are Marine Ich or Velvet Disease (Amyloodinium ocellatum and Cryptocaryon irritans), and Black Ich (Paravortex).  All of these parasites have similar lifecycles.  Once the parasite matures it falls off the fish where it then breaks open and releases hundreds of new parasites into the water column.  These parasites have a limited amount of time to find a host (your fish) before they die.  In the open ocean these parasites have a couple of factors working against them, first population density of fish in the ocean is very light as compared to the aquarium, so they have a hard time finding a host before they die, and second there are many filter feeding invertebrates, corals, and worms that will feed on them.  In the aquarium we have only a small amount of water, this makes it easy for these parasites to find a host.  Within weeks after introduction these parasites can reach plague proportions and wipeout an entire tank of fish.

Marine Ich, Amyloodinium and Cryptocaryon, appear on the fish as very tiny white dots about the size of a period (.).  While you see the parasites on the fish's body and fins, it also invades the gills, making it very difficult for the fish to get oxygen to the blood.  When fish are heavily infested they die of hypoxia (suffocation).

Black Ich, Paravortex is often found on Yellow Tangs (Zebrasoma flavescens) and appear on the fish as black spots the size of a period (.).  These spots are actually a tubellarian flatworm.  This parasite can kill fish in the same way as Amyloodinium and Cryptocaryon.

To prevent these parasites from invading your display tank, you need to quarantine all new fish for at least 3 weeks in a separate tank.  The quarantine tank needs to be set up for use with copper medication.  I usually use about a 20 gallon (80 l) tank for this process, but the actual size you use can vary depending on the size of your new fish.  To set up this tank I use a hang on the tank power filter that has no carbon in the filter.   Carbon will remove medication so it has no place in a quarantine tank.  A quarantine tank also needs a heater, as you will need to keep the water warm, around 85° F (29.5° C).  The tank should be kept bare bottom (no sand or gravel) as calcium based substrate can pull copper medication out of solution.

It is important to have beneficial bacteria established in the quarantine to keep ammonia and nitrite from accumulating.  You can introduce beneficial bacteria to the quarantine tank by adding filter media or decorations from an established aquarium, and by adding BIO-Spira, a product produced by Marineland.

I prefer to use a chelated copper like Copper Power.  Chelated copper is more stable than non-chelated, staying in solution for a much longer time.  Non-chelated copper quickly falls out of solution and often requires frequent dosing.  Chelated copper is also safer for fish, and is used at a higher concentration than non-chelated copper.  Copper can be a deadly medication for fish if overdosed, so you must not exceed the manufacturers recommended copper concentration.  Before you add a second dose of copper to the tank, you must check the residual copper concentration level in the tank with a copper test kit that can detect the type of copper you use.  Not all copper test kits can detect chelated and/or non-chelated copper, so it is best to check with the manufacturer before you buy.  Once you have tested the copper level, you add only a percentage of a full dose required to increase the concentration to the effective level.  In my experience, copper at the concentrations used to treat fish for external parasites does not adversely affect ammonia and nitrite reducing bacteria.

While on the fish the parasites burrow under the skin of the fish and have this protective layer that helps shield them from the copper in the water.  When the parasites drop off the fish to multiply they are then vulnerable to the killing power of copper.  You can speed up the lifecycle of the parasite by keeping the aquarium water warm (85° F/29.5° C).

If you notice parasites on the fish, you can give the fish a freshwater bath for 3 to 9 minutes.  This will often kill many parasites that are on the fish, but it can not be use as an absolute way of making fish parasite free.  Often some parasites will survive a freshwater bath.  To prepare a freshwater bath, fill a small container with tap water that is about the same temperature that is in the aquarium.  De-chlorinate the water with any commercially available de-chlorinator aquarium product.  Net the fish out and add the fish to the container of freshwater.  Many species of fish will act abnormally when in freshwater, this is normal.  Monitor the fish closely, to make sure the fish is still breathing.  If the fish looks overly stressed you can return the fish to the quarantine tank.  Freshwater bath treatment can be repeated every day if necessary.

Sometimes newly acquired fish (especially Butterflyfish and Angelfish) will come down with a bacterial infection from the stress of transportation within a couple of weeks of being purchased.  If you notice a bacterial infection see Aquaworld Aquarium' s article Treating Marine Fish for Bacterial Diseases.  Bacterial diseases can be treated at the same time you treat with copper, but I only recommend treating with an anti-biotic when necessary.

Some fish like sharks and rays are reported to be very sensitive to copper.  I have not tried treating them with copper, so I can not confirm if this treatment would be safe for these types of fish.  But with all other common marine fish kept in the hobby, I have not seen any adverse affects of long term exposure (one year plus) to chelated copper at levels used to kill external parasites.

Quarantining all new marine fish in a tank with copper should be a standard routine for all marine hobbyist.  Setting up a quarantine tank will save the hobbyist money in the long run and prevent many premature deaths of marine fish in captivity.  Treating a reef tank for a parasite outbreak is very difficult, and often unsuccessful.  The best practice is prevention.

Published - 20060922

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