Cladogonium ogishimae, commonly known as 'green fungus', in Neocaridina davidi shrimp (cherry shrimp)

Introduction

Although commonly known as 'green fungus', Cladogonium ogishimae is actually an ectoparasitic algae that grows on and in the muscle tissue along the underside of fresh-water shrimp (Hirose & Akiyama, 1971). Shrimp-keepers typically confuse Cladogonium ogishimae with the parasite, Thalassomyces marsupii, and often refer to this as Ellobiopsidae. However, Cladogonium ogishimae and Thalassomyces marsupii are distinctly different for a number of reasons. According to shrimp-keepers, 'green fungus' is largely incurable, and current suggested treatments including Malachite green, hydrogen peroxide (H202) and almond leaves, are apparently limited in their success. Whilst methylene blue does not appear to have been suggested as a treatment for Cladogonium ogishimae anywhere else on the internet, we have found that it produced a curative effect in one mild-moderately infected, mature female cherry shrimp.

About Cladogonium ogishimae

Cladogonium ogishimae has a clear filamentous body of approximately 1-2mm from which grow several branches that terminate in (usually) four club-shaped sporangia (Hirose & Akiyama, 1971). Whilst its vegetative cells are colourless, the zoosporangia and the zoospores are furnished with bright green chloroplasts. These green chloroplasts are normally the first visible sign of infection, by which time the zoospores are mobile and can infect other shrimp. Cladogonium ogishimae obtains nutrients from the muscle of the shrimp, and left untreated, will result in the death of the shrimp.

Comparison of Cladogonium ogishimae with Thalassomyces marsupii

Cladogonium ogishimae:

• Infects fresh-water shrimp (Hirose & Akiyama, 1971).
• Remains on the underside of the shrimp and occurs along the entire length of the abdomen (Hirose & Akiyama, 1971).
• Turns green (Hirose & Akiyama, 1971).

 Thalassomyces marsupii:

• Infects marine crustaceans (Galt & Whisler, 1970).
• Occurs on the underside but in the region of the brood pouch only of amphipods (Kane, 1964). Neocaridina davidi shrimp are decapods, not amphipods. Neocaridina davidi shrimp do not have a marsupium; they carry their eggs on their pleopden (swimerettes).
• May develop a yellowy-brown tinge when mature, but remains transparent (Galt & Whisler, 1970). Does not turn green.

Thalassomyces racemosus, another marine species, may also attach ventrally to the abdomen of particular species of Oplophoridae shrimp (Wasmer, 1986). However, Neocaridina davidi are Atyidae shrimp, not Oplophoridae shrimp. Another Thalassomyces, Thalassomyces fagei, which is found infrequently on various marine euphosids (krill), remains white in colour, and typically attaches to the topside of the animal near the heart (Hoffman & Yancey, 1966). However, Neocaridina davidi shrimp are fresh-water decapods, not salt-water euphosids.

An exhaustive search of host records contained in peer-reviewed, academic literature indicates that no species of Ellobiopsis have ever been observed in Neocaridina davidi shrimp. Therefore, we believe conclusively that 'green fungus' in Neocaridina davidi shrimp is Cladogonium ogishimae, not a species of Ellobiopsis, whether Thalassomyces marsupii, Thalassomyces racemosus, Thalassomyces fagei, or any other Thalassomyces.

Methylene blue treatment

We treated our Cladogonium ogishimae infected shrimp with methylene blue. Methylene blue is traditionally used in aquariums as a disinfectant, and to treat nitrite and ammonia poisoning, and fungal and parasitic infections in fish. We could not find any reference of methylene blue being used to treat shrimp. However, having nothing to lose, we decided to try it. Having set up a hospital tank for the infected shrimp using water from the main tank treated with H202 at 1.5ml per 4.5litres, we first treated her with methylene blue at 0.5ml in 350ml of tank water, leaving her in this solution for 24 hours. We then transferred her to the hospital tank. Although the treatment appeared to considerably reduce the infection, she remained relatively inactive and uninterested in feeding. However she successfully molted a week later, and so we treated her again with methylene blue as before, and changed the water in the hospital tank before returning her. After a further seven days, as the following photos illustrate, she appears infection-free, and currently is continuing to behave and eat normally:

 

Conclusion

'Green fungus' in Neocaridina davidi shrimp is the ectoparasitic algae, Cladogonium ogishimae. Treatment with methylene blue as described above appears to produce a cure for mild-moderate infection within two weeks.

List of References

Galt, J. & Whisler, H. (1970) Differentiation of flagellated spores in Thalassomyces ellobiopsid parasite of marine crustaceae. Archiv für Mikrobiologie, 71 (4): 295-303.

Hirose, H. & Akiyama, M. (1971) A Colorless, Filamentous Chlorophyceous Alga, Cladogonium ogishimae Gen. et Sp. Nov., Parasitic on Fresh-water Shrimps. Botanical Magazine, 84: 137-140.

Hoffman, E. & Yancey, R. (1966) Ellobiopsidae of Alaskan Coastal Waters. Pacific Science, XX: 70-78.

Kane, J. (1964) Thalassomyces marsupii, a new species of ellobiopsid parasite on the hyperiid amphipod Parathemisto gaudichaudii (Guer.). New Zealand Journal of Science. 7: 289-303.

Wasmer, R. (1986) New Records of Parasitic Thalassomyces Species (Ellobiopsidae) from Oplophorid Shrimps in the South Pacific. Crustaceana, 50 (3): 312-318.