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    Hi all-
    It appears my baby clown and goby has black spot disease. I have a pair of seahorses coming for my aquarium sometime next week. I am treating the fish today. I was wondering that if I treat the fish infected; do I have to remove anything else? Such as live rock, coral, sand, etc. I believe that the source of the disease is from the snails I recently purchased, I believed carried it. Do I have to remove my snails and cleaner shrimp as well? If I treat the fish, can I still keep the seahorses in there? Will it colonize on the live rock and in the tank?

    Pete Giwojna

    Dear Manatee:

    I’m very sorry to hear about the problems you have been experiencing with black spot disease. It will persist in your main tank and reinfect your fish unless it is eradicated from your display tank before you return the fish. This can be accomplished by administering hyposalinity (also known as osmotic shock therapy) to the main tank while the affected fish are being treated in your quarantine tank, as explained in more detail below.

    The live rock, live sand, corals, snails and shrimp should remain in the main tank while you administer a modified form of hyposalinity that is suitable for reef tanks, since they are also infested with the parasites, as long as you are careful to gradually reduce the salinity level so that the more delicate invertebrates can adjust.

    But the first thing you must do is to immediately postpone the delivery of your seahorses until this problem has been resolved once and for all so that your new ponies are not exposed to these parasites. This is how you should proceed, Manatee:

    ‹open quote›

    Give all infested fish a freshwater dip, followed by a formalin bath and continue treatment in a quarantine tank. Praziquantel has been used with some success to treat affected fish in quarantine tanks.

    Preventing Reinfection

    Reinfection will occur no matter how effectively the fish have been treated if these parasitic turbellarian worms are not eradicated from the main aquarium. Unfortunately, because they can survive for several months without a host, this is often not an easy thing to do, but here are some suggestions.

    Leaving the main aquarium devoid of all fish for several months is a cure that some aquarists recommend, however, this is not always possible or desirable. The theory here is that, without a host fish, the life cycle chain will be broken and the turbellaria will not be able to reproduce and you will just be waiting for the turbellaria to die of old age.

    Young worms live in the substrate and feed on detritus and organic debris until such time they go in search of a fish host. Siphoning up the excess organic matter that builds up on the bottom of the aquarium can help to control their numbers.

    For fish-only tanks, or marine aquariums containing no freshwater-sensitive invertebrates, hyposalinity can be applied. When using hyposalinity (osmotic shock), stirring the substrate occasionally will help to release the higher salinity water trapped in the substrate, exposing the flatworms to the lower salinity water in the tank.
    ‹close quote›

    Here are the instructions for administering for performing the freshwater dip and administering hyposalinity in your main tank safely, Manatee:

    Hyposalinity or Osmotic Shock Therapy (OST)

    Fortunately, when problems with protozoan parasites and ectoparasites crop up, we needn’t determine which particular parasite is plaguing our seahorses, since hyposalinity or Osmotic Shock Therapy (OST) is a very safe treatment that is effective against protozoans and ectoparasites in general. OST is totally noninvasive and harmless to seahorses and most other fishes, can be administered safely in the display tank rather than a hospital tank to eradicate the protozoan parasites from your system, and is completely compatible with UV and any medications you may be using (Giwojna, Dec. 2003). OST is therefore the treatment I recommend for problems with external parasites other than Uronema.

    Hyposalinity also helps parasite-ridden fish avoid dehydration and save their strength by reducing osmotic pressure and making it easier for them to osmoregulate. Allow me to explain.

    Because the seawater they live in is far saltier than their blood and internal body fluids (Kollman, 1998), marine fish are constantly losing water by diffusion through their gills and the surface of their skin, as well as in their urine (Kollman, 1998). The mucus layer or slime coat of the fish helps waterproof the skin and reduces the amount of water that can diffuse through its surface (Kollman, 1998). However, when the skin is attacked by parasites such as Costia, Cryptocaryon, Cryptobia, Amyloodinium, Brooklynella, Epistylus and the like, this protective barrier is damaged and water is lost at an increasing rate (Kollman, 1998). The affected fish can easily become dehydrated as a result, further debilitating them.

    Low salinity is an excellent way to treat most such skin infections, since reducing the salinity helps the fish recover in several different ways. It lessens the risk of dehydration by decreasing osmotic pressure (Kollman, 1998), and reduces the amount of energy the fish must expend on osmoregulation, helping the weakened fish to recover (Kollman, 1998).

    And if the salinity is dropped far enough, it prevents reinfection and provides the fish with immediate relief by destroying the parasites in the water and on the surface of the skin (Kollman, 1998). At low salinity, water moves into the parasites’ bodies by passive diffusion until they literally burst (lyse). This method of treatment is known as hyposalinity or Osmotic Shock Therapy.

    At the first sign of parasitic infection, I therefore suggest instituting a two-pronged treatment regimen immediately: (1) first, administer a freshwater dip to your seahorses to reduce the number of embedded parasites, clear the gills and snout as much as possible, and provide the seahorses with some quick relief, and (2) treat your main tank with osmotic shock therapy, dropping the salinity to 15 ppt (1.011-1.012) for several weeks to eliminate the parasites from your system entirely (Giwojna, Dec. 2003). If your seahorses seem too weak to handle the stress of a freshwater dip, then just get them into hyposalinity water ASAP — no acclimation!

    Step 1: Freshwater Dip

    A freshwater dip is simply immersing your seahorse in pure, detoxified freshwater that’s been preadjusted to the same temp and pH as the water the seahorse is accustomed to, for a period of at least 10 minutes (Giwojna, Dec. 2003). It doesn’t harm them — seahorses typically tolerate freshwater dips exceptionally well and a 10-minute dip should be perfectly safe. Freshwater dips are effective because marine fish tolerate the immersion in freshwater far better than the external parasites they play host to; the change in osmotic pressure kills or incapacitates such microorganisms within 7-8 minutes (Giwojna, Dec. 2003). A minimum dip, if the fish seems to be doing fine, is therefore 8 minutes. Include some sort of hitching post in the dipping container and shoot for the full 10 minutes with your seahorses (Giwojna, Dec. 2003).

    If you will be using tap water for the freshwater dip, be sure to dechlorinate it beforehand. This can be accomplished usually one of the commercial dechlorinators, which typically include sodium thiosulfate and perhaps a chloramine remover as well, or by aerating the tap water for at least 24 hours to dissipate the chlorine (Giwojna, Dec. 2003).

    If you dechlorinate the dip water with a sodium thiosulfate product, be sure to use an airstone to aerate it for at least one hour before administering the dip. This is because the sodium thiosulfate depletes the water of oxygen and the dip water must therefore be oxygenated before its suitable for your seahorse(s). Regardless of how you detoxify the freshwater for the dip, it’s important to aerate the water in the dipping container well beforehand to increase the level of dissolved oxygen in the water. Many hobbyists leave the airstone in the dipping container throughout the procedure.

    Adjusting the pH of the water in the dipping container so that it matches the pH of the water in the aquarium is a crucial step. Ordinary baking soda (sodium bicarbonate) will suffice for raising the pH of the water. If there is too much of a difference in the pH, there is a possibility the seahorse could go into shock during the dipping procedure. Preadjusting the pH will prevent that from happening. If you will are unsure about your ability to accurately adjust the pH in the dipping container, avoid this procedure altogether or be prepared to monitor the seahorse very carefully or shorten the duration of the tip to no more than about 4 minutes.

    Observe the horse closely during the dip. You may see some immediate signs of distress or shock. Sometimes the horse will immediately lie on its side on the bottom. That’s a fairly common reaction — normal and to be expected, rather than a cause for concern, so don’t be alarmed if this happens. Just nudge or tap the seahorse gently with your finger if it lies down on its side. Normally, the seahorse will respond to the slight nudge by righting itself again and calm down for the duration of the dip. However, if it does not respond, stop the treatment.

    Most seahorses tolerate the treatment well and experience no problems, but if you see continued signs of distress — twitching, thrashing around etc. — stop the treatment.

    After you have completed the dip and returned the seahorses to the aquarium, save the dip water and examine it closely for any sign of parasites. The change in osmotic pressure from saltwater to freshwater will cause ectoparasites to lyse (i.e., swell and burst) or drop off their host after 7-10 minutes, and they will be left behind in the dipping water. Protozoan parasites are microscopic and won’t be visible to the naked eye, but some of the other ectoparasites can be clearly seen. For example, monogenetic trematodes will appear as opaque sesame seeds drifting in the water (Giwojna, Aug. 2003) and some nematodes may be visible as tiny hairlike worms 1/16-3/16 of an inch long. Other parasites may appear as tiny dots in the water. Freshwater dips can thus often provide affected seahorses with some immediate relief by ridding them of these irritating pests and can also aid their breathing by flushing out gill parasites.

    Step 2: Hyposalinity (Osmotic Shock Therapy)

    Osmotic Shock Therapy (OST) involves maintaining the saltwater in your system at a much lower specific gravity than normal: 1.017 is recommended for reef tanks with live coral and invertebrates, while 1.011 (15 ppt salinity) is appropriate for fish-only tanks (Giwojna, Dec. 2003). Essentially, OST simply places the infectious organisms in an environment in which they cannot hope to survive while the host (or infected fish) is unaffected (Hauter, 2004). It is therefore the parasites that are subjected to the shock, not the fishes, which are normally quite content at the prescribed salinities (Giwojna, Dec. 2003). This low salinity method can be thought of as a continuous freshwater dip, and provides basically the same benefits as a 5-10 minute freshwater dip does, only long term (Giwojna, Dec. 2003).

    When the salinity in the system is lowered initially, it is done as if performing a normal water change, except that the replacement water is simply treated tap or RO water without the salt (Don Carner, pers. com.). (If the replacement water is RO/DI or other softened source, then a buffering agent should be employed to prevent pH and alkalinity drops; Thiel, 2003.) Make sure the freshwater you add is thoroughly mixed with the remaining saltwater in the tank as you proceed. This will assure that your salinity/specific gravity readings are accurate. Monitor the lowering closely so as to not reduce it too fast. Achieving the desired specific gravity (1.010-1.012) over a period of several hours is fine (Don Carner, pers. com.). The bacteria colony in the biofilter will survive, the fish will survive, but the parasites will not (Don Carner, pers. com.).

    By lowering the salinity, we are also lowering the osmotic pressure of the water. The parasites NEED high osmotic pressure externally in order to maintain a normal water balance within their bodies (Don Carner, pers. com.). Reduce the salinity of the surrounding saltwater sufficiently, and water moves via osmosis into the parasites’ bodies until they literally explode (Giwojna, Dec. 2003). As a higher life form, the fish can withstand this treatment very well; invertebrates and parasites cannot (Don Carner, pers. com.).

    For best results, I recommend removing your seahorses to a hospital tank or bucket filled with full strength saltwater (1.022-1.025) while dropping the salinity in the main tank. They can be given their freshwater dips while you are reducing the salinity in the main tank. Once the specific gravity in the display tank has been lowered to the desired level, the seahorses can then be released directly into the main tank without any acclimation whatsoever. They will make the transition from full strength saltwater to hyposalinity wonderful well, without missing a beat, whereas the ectoparasites they are carrying will be subjected to a lethal change in osmotic pressure.

    Do not hesitate to maintain the hyposalinity for the entire treatment period. OST needs to maintained for at least 3 weeks in order to assure that all of the encysted parasites have reached the free-swimming stage of their life cycle and been killed.

    CAUTION! When administering hyposalinity to seahorses, be very careful as you add the freshwater when you approach the target salinity. You do NOT want to overshoot the mark and drop the salinity too far! Seahorses tolerate low salinity very well up to a certain point, but they cannot withstand salinities below 13.3 ppt (specific gravity = 1.010) indefinitely. Salinities below 1.010 may be fatal to seahorses in a matter of days, if not hours.

    In the olden days, many attempts were made to gradually convert seahorses from saltwater to freshwater. Hippocampus erectus tolerated these experiments splendidly all the way down to specific gravity of 1.010, but when the salinity was dropped any further, the seahorses all perished (Bellomy, 1969, p7). These experiments were repeated with several groups of seahorses representing different subspecies of erectus, and the results were always the same: fine as low as 1.010 — defunct at 1.009 (Bellomy, 1969, p7)!

    Keeping that in mind, it is best to make your target salinity 1.011-1.012 to allow a margin for error, and to transfer your seahorses to a hospital tank while you drop the salinity in the main tank. That way no harm will be done if you accidentally take the salinity down too far in your main tank before readjusting it and hitting your target salinity. And when you return the seahorses from normal salinity in the hospital tank to the main tank at 1.011-1.012, the parasites will be subjected to the greatest possible osmotic shock, leaving them no chance at all to adjust to change in osmotic pressure.

    To be safe and effective, administering hyposalinity requires the use of an accurate method for measuring salinity/specific gravity such as a refractometer. If you will be relying on a pet-store hydrometer for your readings, you may wish to consider alternate treatments rather than OST. If you do decide to try hyposalinity using a hydrometer, please observe the following precautions:

    Be aware of the temperature at which your hydrometer was calibrated and make full use of conversion charts to adjust your readings based on the actual temperature of the water aquarium water.

    Make your target salinity 20 ppt (specific gravity = 1.015) to allow for a greater margin for error.

    In addition, when administering OST it is important to monitor your ammonia and nitrite levels closely at first. Hyposalinity may temporarily impact the nitrifying bacteria in your biofilter, so check your readings closely to see if there is a spike once you’ve reached your target salinity. If so, a simple water change will correct the problem and your biofiltration will be back to normal shortly.

    The hobbyist should also bear in mind that hyposalinity can delay gonadal development in immature seahorses and may also prevent mature seahorses from breeding until the salinity is returned to normal. So don’t maintain low salinity for the long term — as soon as the 3-4 week treatment period is over, bring the specific gravity in the main tank back up 1.024-1.025.

    When you are ready to return the system to normal salinity, simply reverse the process, remove some of the low salinity water in the aquarium and replace it with high salinity water. Take your time and raise the salinity slowly and gradually. Fish can become dehydrated if the salinity is increased too rapidly, so be methodical and raise the salinity over a period of several days. Don’t hesitate to take a full week to return the specific gravity to normal levels again in small increments.

    If your tank contains corals or delicate invertebrates, or you just want to be extra cautious with your seahorses as they recuperate, adjust the salinity more slowly. This can be accomplished by making smaller water changes, which will require more steps to raise the salinity back to normal, or by reducing the specific gravity of the high-salinity replacement water somewhat. Make the adjustment back to normal salinity as gradually as necessary in order to be confident that you are not stressing the specimens. The hyposalinity should already have done its job so you can afford to be cautious when readjusting the salinity. Take all the time you want.

    To be absolutely certain that things go smoothly, take advantage of the online Salinity Adjustment Calculator at the following web site:

    This calculator takes the amount of water in your system, your current salinity, the salinity you’d like to achieve, and the maximum change in salinity that you are willing to risk per water change into consideration and performs the necessary calculations. It then returns the number of gallons and salinity of the water for each change (Taylor, 2001b).

    The low salinity system was initially developed at the Instant Ocean Hatcheries in the 1980’s and has since been perfected by other large-scale operations (Giwojna, Dec. 2003). Thomas Frakes at Aquarium Systems recommends this system and Rand Kollman recently conducted a controlled study of the method, as described below (Kollman, 1998):

    During the study, fourteen 40-gallon tanks connected to a common filtration system at Kollman’s dealership were run at 15 ppt salinity (specific gravity = 1.011), while sixteen other 30-gallon tanks, connected to their own separate filtration system, were maintained at normal salinities of 27-30 ppt (specific gravity = 1.020-1.022) and served as the control group for the experiment (Kollman, 1998; Giwojna, Dec. 2003). Both systems had identical filtration and were maintained at the same temperature (between 79-80 degrees F), Kollman, 1998.

    The test period ran continuously from 1994 to 1997, during which time marine fish from the Red Sea, Caribbean and throughout the Indo-Pacific were maintained in both systems (Kollman, 1998). Whenever fish arrived from wholesalers or transshipments, they were divided evenly between the low salinity and the normal salinity (control) system with no acclimation procedures whatsoever (Kollman, 1998; Giwojna, Dec. 2003). No differences in behavior were observed between the fishes in the two systems during the trial period (Giwojna, Dec. 2003).

    The results of the three-year study were dramatic and conclusive (Giwojna, Dec. 2003). Outbreaks of Amyloodinium, Cryptocaryon, turbellarians, and monogenetic trematodes were simply not seen in the low salinity system, and periodic microscopic examinations of skin scrapings and gill clippings confirmed that none of the parasites were present (Kollman, 1998; Giwojna, Dec. 2003). On the other hand, the normal salinity control system continued to have periodic outbreaks of all the above parasites. Furthermore, infected fish from the control system were cleared of their parasites within a few days if transferred to the low salinity system (Kollman, 1998; Giwojna, Dec. 2003).

    Kollman found the low salinity system reduced his previously high mortality rates and that his dealership was able to greatly reduce chemical treatments and subsequent overdoses (Kollman, 1998; Giwojna, Dec. 2003). He concluded that a salinity of 14 to 15 ppt (specific gravity = 1.010-1.011) was an effective treatment level to which fish can be immediately transferred with no special acclimation procedures (Kollman, 1998; Giwojna, Dec. 2003). Although the rapid turnover of specimens at his dealership prevented him from reaching any definitive conclusions about the long-term effects of low salinity on marine fishes, Kollman noted that several fish were maintained in the system for well over a year with no ill effects, and that a Red Sea angelfish (Pomacanthus maculosus) thrived in the low salinity system for three-and-a-half years (Kollman, 1998; Giwojna, Dec. 2003)!

    Kollman’s study and the ongoing program at Instant Ocean hatcheries are not the only reports on utilizing low salinity water to quarantine specimens held under crowded conditions (Giwojna, Dec. 2003). As early as 1985, Colorni published a study in Diseases of Aquatic Organism on the effectiveness of hyposalinity in controlling Cryptocaryon irritans in cultured sea bream (Colorni, 1985). Randolph Goodlett and Lance Ichinotsubo have likewise reported their own low-salinity treatment techniques, recommending at least 3 weeks exposure at 14 ppt (specific gravity = 1.010) for a broad range of marine tropical fish species to control various parasites (Goodlett and Ichinotsubo, 1997). They too reported that fish handled immediate transfer into low salinity water “beautifully (Goodlett and Ichinotsubo, 1997).” Variations of low salinity or OST are also gaining popularity among reefkeepers for curing disease outbreaks in reef tanks where copper and other medications cannot be used (Frakes, 1994; Giwojna, Dec. 2003).

    Low Salinity Pros (Giwojna, Dec. 2003):

    1. Less stressful and longer lasting than freshwater dipping.
    2. More effective than freshwater dipping outside the aquaria, since OST kills the free swimming parasites as they emerge from dormant cysts/spores within the aquaria/system as well as those attached to the fish (i.e., the fish are not reinfected once they are returned from the bath to the main tank).
    3. No special acclimation procedures required for newcomers.
    4. Suitable for all marine teleost (bony) fishes (Red Sea, Indo-Pacific, Florida & Caribbean).
    5. Seahorses tolerate hyposalinity extremely well.
    6. Eliminates outbreaks of Cryptocaryon irritans (White Spot Disease/Marine Ick).
    7. Eliminates turbellarians (Black Spot/Clownfish Disease).
    8. Eliminates most ectoparasites, including trematodes, flukes, leeches and Argulus;
    9. Prevents the spread of protozoal parasites in general.
    10. Reduces the risk of dehydration when the integrity of the fish’ slime coat is disrupted;
    11. Helps weakened fish conserve energy and husband their strength by lowering osmotic pressure and making it easier for them to osmoregulate.
    12. Reduces dependency on chemical treatments such as copper and formalin.
    13. Eliminates the risk of overdoses.
    14. Proven to improve the health of marine teleost fishes kept in crowded containment systems with a heavy biological load.
    15. Can be used safely with protein, skimmers, ozone, UV, and other treatments.
    16. Increases the levels of dissolved oxygen in the aquarium.
    17. Helps prevent gas supersaturation, minimizing problems with gas bubble syndrome.

    Low Salinity Cons (Giwojna, Dec. 2003):

    1. Sharks and rays are unable to adjust to low salinity systems or tolerate OST.
    2. Cannot be used with corals and invertebrates at salinities recommended for fishes.
    3. Can be harmful to seahorses at salinities below 13.3 ppt (specific gravity = 1.010).
    4. May delay gonadal development in seahorses and prevent breeding until the salinity is returned to normal.
    5. Requires an accurate method for measuring salinity/specific gravity such as a refractometer for best results.
    6. May not be helpful in cases of Uronema — the most common protozoan parasite infection in seahorses.
    7. May impact nitrifying bacteria in the biofilter temporarily.
    8. Not recommended for long-term maintenance (this will not be a concern for any fishes that are in the system for 6-8 weeks or less).
    9. The lower salinity makes it difficult to maintain pH at the proper level.
    10. Results vary — many hobbyists report great success with hyposalinity; others have no luck using this technique. Much depends on how OST was administered, how low the salinity was reduced and how quickly it was dropped, the accuracy of the salinity measurements, the particular parasite(s) involved and how early treatment was begun.

    Invertebrates differ in their tolerance for hyposalinity. Kollman notes that he was able to keep several crustaceans at a fairly low salinity of 18-19 ppt (specific gravity = 1.013 to 1.014). These included arrow crabs, peppermint shrimp, and emerald crabs (Kollman, 1998). Hermit crabs are generally perfectly happy undergoing OST, echinoderms (starfish and urchins) typically don’t tolerate it at all, most shrimp are sensitive, snails vary (Giwojna, Dec. 2003). Nerites and periwinkles don’t mind it at all, others are okay at 1.017 but you can kiss them goodbye at 1.010. Most corals are vulnerable to full OST (Giwojna, Dec. 2003). Reefkeepers and hobbyists with sensitive animals usually do a modified version of OST where they lower the salinity to 1.017 rather than 1.010 (Giwojna, Dec. 2003). The delicate animals generally tolerate 1.017 well and although that’s not as effective in eradicating parasites, a specific gravity of 1.017 is still low enough to provide many of the benefits of hyposalinity (Giwojna, Dec. 2003).

    For a standard SHOWLR setup with a clean-up consisting of assorted snails, microhermits, and cleaner shrimp, I recommend relocating the snails and shrimp while treating your seahorse system with full OST at a specific 1.011-1.012 for several weeks. If that’s not practical because it would be too difficult to account for all the snails and/or shrimp and remove them, then I would suggest taking the salinity carefully down to about 1.017 in your main tank, which most of your janitors should tolerate just fine, after moving your seahorses to your hospital tank for treatment at full OST.

    Just set up your hospital tank at a salinity of 15-16 ppt (a specific gravity of 1.011-1.012) and adjust the water to the same temp and pH as the main tank. Then administer a freshwater dip to your seahorses, and transfer them directly into the hyposalinity treatment tank afterwards without any acclimation whatsoever.

    As I mentioned earlier, OST is completely compatible with most medications. (In fact, many medications are more effective at low salinity than they are in full strength saltwater.) Since secondary bacterial or fungal infections often accompany parasite problems, I would also recommend combining hyposalinity in the hospital tank with antibiotic therapy. In that case, simply medicating the hospital tank with the appropriate antibiotics will be easier than administering the antibiotics orally via gut-loaded shrimp. [CAUTION: if administering hyposalinity in your main tank, do not administer antibiotics, which may adversely impact the biofiltration in the aquarium.]

    Nifurpirinol used in conjunction with neomycin will be very effective for medicating the hospital tank during OST, as will the powerful combination drugs that contain both antiprotozoal and wide-spectrum antibacterial agents. Look for a product that includes ingredients such as nitrofurazone and metronidazole, which are very effective against protozoan parasites, as well as antibiotics such as neomycin and kanamycin, which are powerful broad-spectrum medications.

    If you do not see improvement within 4-5 days of administering OST, don’t hesitate to use the alternative treatments discussed for each particular parasite! They can be administered safely in conjunction with hyposalinity, bearing in mind the impact they will have on the biological filtration, or you can carefully return the salinity to normal and then treat with chemotherapeutics. When administering alternate treatments, check your ammonia/nitrite readings closely, and use water changes as needed to keep the levels of ammonia and nitrite at acceptable levels. Also, you are strongly advised to administer daily freshwater dips in addition to treating with chemotherapeutic agents if the alternative treatments are used in the absence of OST. The freshwater dips will provide the same benefits as hyposalinity and enhance the effectiveness of whatever treatment you employ to control the parasites.

    Modified OST for Reef Tanks

    Reefers generally run a modified version of OST in which they maintain a somewhat higher specific gravity, usually around 1.017 (Thiel, 2003), for a longer period of time in order to control protozoal parasites. Most corals are safe at even lower salinities, but 1.017 usually provides adequate protection and provides a margin for error. In any case, as a rule, reef keepers DO NOT take their systems lower than 1.015 for safety’s sake (Thiel, 2003). (This is also a good option for hobbyists who have only a typical pet-store hydrometer for measuring specific gravity, or anyone with many invertebrates in their seahorse setup.)

    Corals typically close slightly immediately after the salinity is lowered, but are open fully again by the next day, and suffer no harmful long-term effects from hyposalinity at 1.017 whatsoever (Thiel, 2003). Reefers who practice OST report that it has no long-term detrimental effects on the growth rate of their corals.

    According to Thiel, corals that are know to be sensitive to hyposalinity, and which are thus not well suited for OST, include Seriotopora hystrix, Montipora digitata, Pocillopora species and other similar hard corals with a fine, dense, polyp structure (Thiel, 2003). Acropora species, however, handle hyposalinity well and soft corals are also generally fine, including such sensitive softies as Xenia, Lemnalia, and the like (Thiel, 2003). As long as the pH and alkalinity are maintained at normal levels, most hard corals are not harmed at a specific gravity as low as 1.017.

    Don’t return any sensitive invertebrates to the main tank until the entire regimen of hyposalinity has been completed and the aquarium has been returned to normal salinity again, Manatee.

    Here are some additional references that you may find helpful if you would like to look into the topic of hyposalinity as a treatment for marine fish in more detail:

    Colorni, A. 1985. “Aspects of biology of Cryptocaryon irritans and hyposalinity as a control measure in captive-raised gilt-bead sea bream Sparus aurata. Dis. Aquat. Org. 1: 19-22.

    Colorni, A. 1987. Biology of Cryptocaryon irritans and strategies for its control. Aquaculture, Vol. 67(1-2): 236-237.

    Frakes, Thomas. 1994. “Treatment of Cryptocaryon irritans in public aquaria.” SeaScope, Editor’s Note, Summer 1994.
    Giwojna, Pete, and Carol Cozzi-Schmarr. 2003. “Horse Forum.” Freshwater and Marine Aquarium, December 2003.

    Goodlett, R. and I. Ichinotsubo. 1997. “Salinity and pH adjustments for quarantine procedures for marine fishes.” Drum and Croaker, Vol. 28: 23-26.

    Hauter, Stan and Debbie. 2004. “Saltwater Ich Diagnosis, Treatment and Prevention — page 7: Other Treatment Methods Continued – O.S.T. (Osmotic Shock Therapy).” (Accessed 28 Mar. 2004) <;
    Kollman, Rand. 1998. “Low Salinity as Quarantine and Treatment of Marine Parasites.” SeaScope. Aquarium Systems: 1,3.

    Lowry, Toby DVM. 2004. “Quarantine of Marine Fish (Teleost) Using Hyposalinity.” Advanced Aquarist, November 2004. <;

    Thiel, Albert J. 2003. Parasites and Low Salinity. Accessed 7 Oct. 2003. <;

    Okay, Manatee, that’s the latest thinking on hyposalinity or OST.

    If you would like to read more about hyposalinity and osmotic shock therapy beforehand, Manatee, you might find the following online article useful:

    Quarantine of Marine Fish (Teleost) Using Hyposalinity (Copyright Advanced Aquarist 2004)

    An Advanced Aquarist Short Take by Toby Lowry DVM

    Just copy the following URL, paste it in your web browser, and press the “Enter” key, and it will take you to the article:

    Best of luck ridding your aquarium systems of the black spot disease, Manatee.

    Pete Giwojna, Ocean Rider Tech Support

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