An alga parasiting freshwater shrimps

Hello. This article is translated from my original french one. Please forgive any mistake since english isnt my mother tongue.

To correctly identify the algae that are sent to me, I do a lot of documentary research, and I came across a Japanese paper describing the algae Cladogonium ogishimae, parasitizing the shrimp Neocaridina denticulata. The abstract is in English but the rest of the paper is unfortunately in Japanese, and I do not speak it. Fortunately, another paper entirely in English describes the same parasitic alga on shrimp of the genus Macrobrachium.

Why am I talking to you about this horror? Firstly because it’s my blog so deal with it, but also because this seaweed can threaten our shrimp!

Indeed, in recent years we see pictures of shrimps with strange green growths on the pleopods. Over time, the assumed identity of these parasites has evolved. We first thought it was a mushroom, then it was identified as a protozoa ellobiopsidae. The problem is that ellobiopsids are unicellular and very small and the anatomy does not seem to match. On the other hand it fits well with the algae observed by the Japanese.

Pictures extracted from Kazuyo Matsuyama-Serisawa et al.

Surprisingly, this seaweed does not photosynthesize. Unlike other algae it does not have chlorophyll and has no energy reserves in the form of starch. The rest of its anatomy is typical of filamentous algae of the order of cladophorales. But why is it green if there is no chlorophyll? Because although the filamentous alga itself is not photosynthetic, zoospores are. Those mobile zoospores can infect new shrimps.

I have (fortunately) no case of Cladogonium ogishimae in my stock, but if the opportunity to observe this alga under the microscope appears, I will show it to you.

Knowing that this parasite is a green alga and not a protista ellobiopsidae is important because it will help us to find a targeted treatment, effective and of course, non-toxic for the host shrimp.

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