Marine ‘Black Spot’ Disease (Paravortex, Piscinquilinus)
By Aaron Turner
A less common parasite within our home aquarium is the marine ‘black spot’ parasite. Although there could be many parasites which display black spot symptoms upon our aquarium inhabitants the follow article will discuss just a few of those described which are likely to affect our system.
“Turbellarian black spot disease” is the most commonly seen parasite to display these symptoms. ‘Turbellaria’ usually occur as non-parasitic flatworms (Justine et al. 2009) however there are only some species that are known to parasitise marine fish and invertebrate species (Cannon 1986). Paravortex and Piscinquilinus subcutaneous (Syromiatnikova, 1949) are known to produce the marine black spot disease in tropical fish species. (Cannon & Lester 1998). Although both are turbellarians, they each have a unique characteristic. Paravortex sp. burrow into skin leaving a shallow tube open to water, whilst Piscinquilinus are relatively large and lie deep within the dermis. The large Piscinquilinus may result in a pigmented dermis once killed or lost, resulting in a black spot, regardless of a living parasite within the skin. Paravortex Spp. are much smaller turbellarians and appear as grains of black spots rather than lumps.
Both species Paravortex and Piscinquilinus are thought to have a single host lifecycle producing several juveniles (Cannon and Lester 1988). This cycle is completed in 10 days (Kent & Olson 1988) although from research by Justine et al (2009) showed the Piscinquilinus remained on the fish for at least 30 days. Investigations also showed poorly developed reproductive organs indicating maturation once the parasite has left the fish. They then produce a ‘cocoon’ like fibrous structure in the substrate, within which they reproduce and therefore re-infect (Justine et al. 2008).
Paravortex species are known to infect a wide variety of species (Kent and Olson 1986) but Piscinquilinus species maybe more host specific (Justine et al. 2009). Research by Justine et al. found the disease might only be transmitted to fish of the same species and quoted directly “Our observations suggest that the one we found was specific of Naso unicornis (it was not transmitted to the other species in the same tank). Thus, it might be that each fish species, or perhaps each family or each genus, has its own Piscinquilinus species… that would be a lot of cryptic species!”
Use of Quarantine tank
A quarantine tank should be as large as possible. The primary purpose of an isolated system is to prevent the disease from reaching your display tank. However this also doubles as a hospital tank for treating those who suffer from health problems. The tank must contain a mature filter before adding fish; this can be done quickly by adding live rock, or by using filter sponge in an internal filter. Emphasis on bio-security is advised, separate nets, siphons and all other equipment must be used to prevent the spread of disease. A protein skimmer of other form of aeration is advised for those heavily stocked systems.
There has been little report of successful treatment using copper amongst scientific community and is therefore not recommended. As with most parasites, treatments can only kill the free-living stages and therefore careful observation must be taken to ensure re-infection does not occur.
Notably the drug of choice for this parasite. Research by Justine et al. 2009 used a Praziquantel injection (0.2-0.4ml per fish i.e. 17 mg per fish) and another 15 days later leading to diminished spots progressively. Although this method is daunting and not recommended for the average aquarist, it is evidence for its effectiveness. Praziquantel is currently available in many forms notably liquid added to the water column. 0.75-1mg/l single dose for 7 days in a hospital tank or several dips of 6mg/l for one hour is advised and note this is not a general ‘reef safe’ medication and is particularly sensitive to invertebrates such as Echinoderms.
Liquid formaldehyde (37-40%), a very effective treatment but also very toxic. Proper precautions should be taken before administering this treatment. The use of gloves and mask is recommended. Treatment should be in the form of a short bath or with a freshwater dip. The bath should last for 1-2 hours at 200ppm or for 3-5 minutes with a freshwater dip at the same concentration. Long-term treatments can also be used at 25ppm. To reach the concentration of 200ppm you should add 0.5ml per litre
C) Freshwater dips
Please note this is unlikely to work for Piscinquilinus species but will work for Paravortex species. One of the most important things about a freshwater dip is that it will buy you some time to start another treatment or to set up a quarantine tank as even a very badly infected fish can lose most of its parasite in a few minutes and improve quite dramatically.
To carry out a freshwater dip:
- Prepare to some RO water in a small tub (big enough for the fish but small enough to catch again in seconds). Heat the freshwater using a heater or suspend the tub in tank water.
- Adjust the pH using sodium bicarbonate or other buffer.
Catch the required fish and place it in the freshwater, whilst being prepared to end the dip if the fish becomes stressed.
- The dip should least for 3 minutes to remove most parasites and should not last any longer than 5 minutes
- Remove the fish from the freshwater and place back into the main tank.
An alternative method for disrupting the life cycle is the use of Hyposalinity. This is the reduction in salinity down to as low as 1.009 in small units of 0.002-0.003 units per day, killing the infective and free-living stages of the life cycle. This process should last at least 60 days (twice the maximum length of parasitic life expectancy observed by Justine et al 2008). Hyposalinity may also kill Paravortex sp. due to an open shallow tube left in the skin, exposing the parasite.
If you suspect Turbellarian black spot then immediate action is required as this disease progresses rapidly. Any delay can lead to losses however, if prompt action is taken they can be relatively easy parasitic infections to treat and you should be able to avoid further problems. Emphasis on the importance of quarantine for these parasites by preventing this disease entering you reef tank is highly recommended.
Although the above article mentions black spot as a single entity, the aquarist must be aware that many other parasites may display black spots such as the digenean Cryptocotyle. This parasite has a lifecycle including birds and snails; it cannot complete the full cycle within the aquarium. It may require drugs unknown and unavailable to the home hobbyist.
By Aaron Turner
(with guidance from Jean-Lou Justine and Bob Lester, Professors in Parasitology)
Cannon LRG (1986) Turbellaria of the world. Queensland Museum, Brisbane
Cannon LRG, Lester RJG (1988) Two turbellarians parasitic in fish. Dis Aquat Org 5:15–22
Jean-Lou Justine, Philippe Leblanc, Florent Keller & Robert J.G Lester (2009) Turbellarian black spot disease in bluespine unicornfish, Naso unicornis, in New Caledonia, due to the parasitic turbellarian Piscinquilinus sp. Disease of Aquatic Organisms 85:245-249.
Kent ML, Olson AC (1986) Interrelationships of a parasitic turbellarian (Paravortex sp.) (Graffillidae, Rhabdocoela) and its marine fish hosts. Fish Pathol 21:65–72
Syromiatnikova IP (1949) A new turbellarian parasitic in fish and called Ichthyophaga subcutanea. Dokl Akad Nauk SSSR 68: 805–808