BASIC INFO
Cryptocaryon irritans is an external parasite belonging to a group of organisms known as protozoans. These organisms were long thought of as belonging to the kingdom of Animalia, but as the classification of living things has become more detailed, they have now been moved to a separate kingdom called Protoctista. This new kingdom
encompasses single celled organisms such as amoebas, dinoflagellates (responsible for causing toxic red tides), slime moulds, ciliates, and certain algae.
C. irritans is also referred to as marine white spot disease, or marine ich from its external similarities to the freshwater white spot parasite lchthyophthirius multifiliis. These two similar parasites are however not related. They are both ciliates (characterized by being covered by cilium, or fine 'hair-like' processes that beat in unison to give movement), both have similar life cycles and pathology (development and nature of disease), but have reached these similarities from convergent evolution (Noga, 2000).
C. irritans is one of the most important 'diseases' in warm water marine aquarium fish. It has been described as being opportunistic, waiting until the defense mechanism of the fish host is weakened before infestation occurs. This statement, however, fails to reflect the natural relationship the parasite has with the host. Within natural populations, the parasite and host exists in a symbiotic relationship, with most wild fish only having a light infection which has very little impact. Aquarium fish, however, are susceptible to critical outbreaks of the parasite, as the closed aquarium system benefits the parasites high reproduction rate, and allows the parasite to overwhelm the host. There are also reported to be several different 'strains' of the parasite and possibly even more than one species of Cryptocaryon (David Vaughan, pers corn, Diamant et al., 1991), which may prove to be increasingly immune to various common treatments and controls utilized in the marine industry today.
DIAGNOSIS
Individual fish behavior is the best method for determining problems with disease as this is usually the first sign of upcoming problems. A lack of appetite, increase in respiration, scratching or rubbing on rocks or other equipment, a loss of colour or hiding may lead to closer examination and therefore picking up disease related problems before they are serious.
Even fish with heavy infestations of C. irritans may not show the characteristic white spots of this parasite, as infection sites may differ between individual outbreaks. Gills are usually the preferred site of attachment, increasing the respiratory due to clogging with the parasite, mucus and tissue debris, driving most fish to the surface where the
dissolved oxygen levels are usually higher.
Using a torch to 'backlight' the fish in a darkened aquarium is the best method to visually inspect whether the fish has an outbreak of C. irritans. Depending on the severity of infection, the fish can either have a few white nodules over its body, or can look like it has a dusting of salt. A loss of colour can occur in the areas surrounding the infection as the parasite destroys the pigment cells of the fish's epithelium.
As a few different parasites cause similar external characteristics on the host, the most definitive method of diagnosis is by use of a microscope. A scraping of the host's epithelium showing the ciliated parasite is pathognomonic (characteristic). The ciliate will appear to be spherical to oval shaped, covered with fine 'hair-like' cilium, and either moving quite rapidly (infective tomite stage), or slowly rotating in place (mature trophont stage). The mature trophont also has a four lobed nucleus, which is characteristic of C. irritans (Noga, 2000).
TREATMENT
Once the fish has been definitively diagnosed with Cryptocaryon there are a few different methods that can be utilized to eradicate the parasite Treatment should occur as soon as detected as the parasite can reproduce very quickly, infecting other fish within the aquarium.
The infective "theront" stage of the Cryptocaryon lifecycle is quite susceptible to reduced salinity allowing euryhaline (wide salinity range) fish to be treated easily. Decreasing the aquarium salinity to 16 parts per thousand (ppt) or below can halt the spread of the parasite. Keeping the salinity at this level for at least 3 full lifecycles of the parasite (each life cycle being anywhere from 6 - 15 days at 24 degrees Celsius) will help in the removal of most trophonts from the host. Once the salinity is increased to above 20ppt, any remaining trophonts on the fish are able to then resume the lifecycle if conditions within the aquaria favor another outbreak. Many stenohaline (narrow salinity range) fish will tolerate an indefinite salinity of 16ppt. but some may become aggressive or hyperactive. Most invertebrates will not tolerate a significant lowering of salinity for any duration.
Dipping in freshwater to remove the trophont stage from the fish is only usually partially successful. Smaller trophonts can be protected from the osmotic shock of the reduced salinity by being under the epithelium layer and mucus of the fish, therefore only larger trophonts which have grown through the epithelium are lysed by the freshwater. Freshwater dips are also very stressful on the fish and therefore can be counterproductive to treatment.
As Cryptocaryon is pathogenic at temperatures between 20°C and 30°C, lowering the temperature below 19°C will stop reproduction. This method is very unpractical however, and most tropical fish will not tolerate the drop in temperature. If dealing with temperate species, maintaining the aquarium at less than 19°C is a method of control that is least stressful for the inhabitants.
Chemical treatments work by killing one or more stages of a disease's lifecycle. Many parasites such as Cryptocaryon are very resistant to most chemicals while attached to the host (trophont stage), or undergoing cell division on the aquarium substrate (tomont stage). Luckily the infective theronts (free swimming stage that hunts down the fish host) are susceptible to a number of chemicals (see below) and can be killed quite easily.
Copper has been used historically to treat Cryptocaryon outbreaks, but is not advisable in the author's opinion for many reasons. Firstly it is an immuno-suppressant and toxic to gill tissue, causing the fish's usually already decreased immune system to become further reduced. This most likely leads to secondary infections from opportunistic bacteria and viruses that may be living within the aquarium. Secondly copper has a very low therapeutic level, allowing very easy overdosing of the animals. Thirdly, there are a lot of fish that cannot tolerate the levels of copper in the water that is needed to kill the theronts. Species such as sygnathids (seahorses and pipefish), mandarin fish, elasmobranches (sharks and rays), various wrasse, butterfly, and clownfish species, banggai cardinals, and firefish to name a few are considered to be sensitive. All invertebrates (corals, anemones, crabs, snails, sponges etc.) are also considered to be copper sensitive, and will not tolerate any addition of copper to the system. Fourthly, copper can come out of suspension and 'plate' objects such as piping, aquarium glass, and pumps. Even once all the copper has been removed, the 'plated' object can 'leach' copper back into the aquarium, causing mortalities in invertebrates that have been newly added.
Quinine based medication (Chloroquine phosphate and Quinine hydrochloride) have been used with great success to treat Cryptocaryon outbreaks. Quinine is an anti-protozoal drug used mainly in the human treatment of malaria (also a protozoan). The quinine kills the theronts stage of the parasite on excystment from the tomont thus stopping re-infection of new fish. It is non-toxic to most fish at the correct dose rate (5-10mg/l) but it is highly toxic to micro- and macroalgae, and to some invertebrates (anemones, corals etc.). It is also non-toxic to bacteria, therefore not affecting the beneficial aerobic and anaerobic bacteria within the aquariums biological filter. Being a human medication, quinine is relatively expensive, and needs to be purchased through a qualified medical practitioner within Australia (either doctor or vet).
Formalin (which is an aqueous solution of 37 to 40% formaldehyde gas) has been used to treat a variety of fish diseases including protozoal ectoparasites, monogenean worms, and water moulds on eggs with mixed success. It is, however, both volatile and irritating, and has caused cancer in lab rodents. Formalin works by interrupting tomont division and is also lethal to theronts. It also has moderate antibacterial properties thus it inhibits biological filtration. As well as being irritating to the gills, it has algaecidal properties (Schnick, 1973) therefore having the potential to further reduce oxygen levels. Because of this, if formalin treatment is going to be used, it is strongly recommended to heavily aerate the water. Some fish are also susceptible to formalin so levels should be increased slowly and fish behavior observed.
Using herbal remedies such as garlic and onion to treat diseases has become increasingly common. Unfortunately there is no evidence that suggests that these are effective in the treatment of Cryptocaryon and may be even detrimental to the fish's health if overdosed. Garlic extract - allium satiyum - has however been proven to kill freshwater white spot lchthyophthirius rnultifiliis at the theront stage after 15 hours, as well as controlling monogenean flatworm infestations, while onion is useful for treating parasitic copepods.
CONCLUSION
Ideally the best method of treatment of any disease is by quarantining and probiotic measures. By quarantining any new fish in a separate aquarium for a minimum of 21 days at 24 degrees (some reports recommend even a 6 week quarantine period) and treating as if they were infected by a suitable proven method of control is the only way to be sure that the fish is free from the parasite. Once they have been introduced into the main aquarium, using probiotics such as spirulina to promote the fishes own immune system is advised. It is also beneficial to enrich foods with essential compounds such as omega 3 oils, lipids, protein and pigments, ensuring that you are providing your fish with the highest nutrition and therefore best possible means of fighting off any infection.
