Tag Archives: flounders

Friday Fellow: Flounder Glugea

by Piter Kehoma Boll

While looking for flatfish you may eventually find one with some grotesque growth on the body, like the one in the picture below:


A xenoma caused by Glugea stephani on a flatfish Limanda limanda. Photo by Hans Hillewaert.*

This sort of tumor is called xenoma and, in flatfish, is caused by a microscopical and parasitic fungus named Glugea stephani, or the flounder glugea.

The flounder glugea is part of a group of fungi called Microsporidia that until recently were classified as protists. They are unicellular and parasite other organisms, especially crustaceans and fish.

Once inside a flatfish, the flounder glugea enters an intestinal cell and starts to develop. They induce the host cell to increase in size and may give rise to the xenomas, which are the most extreme stage in the development of the disease. The proliferating and active stage of the glugea are free in the cytoplasm of the host cell, but they may change into a spore-like form called sporoblast that remains inside a vacuole.


Image of electron microscopy of an intestinal cell of winter flounder (Pseudopleuronectes americanus) infected by flounder glugea (Glugea stephani). The S indicates sporoblasts inside the vacuole (SV) and the P the proliferating organisms inside the host cytoplasm (H). Image extracted from Takvorian & Cali (1983).

Fortunately most infections are mild and do not compromise the fish health, at least not very much…

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Takvorian, P. M.; Cali, A. (1983). Appendages associated with Glugea stephani, a microscporidian found in flounder. Journal of Protozoology, 30(2): 251-256.

Wikipedia. Xenoma. Available at: < https://en.wikipedia.org/wiki/Xenoma >. Access on September 17, 2016.

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Filed under Disease, Fish, Friday Fellow, Fungi

Friday Fellow: Winter Flounder

by Piter Kehoma Boll

Can you spot the two fish in the photo bellow?


Perfect camouflage. Two winter flounders, Pseudopleuronectes americanus. Photo by Brent Wilson.*

Belonging to the species Pseudopleuronectes americanus, commonly known as winter flounder or black back, it is a flatfish native to the North Atlantic coast of Canada and the United States. It may reach up to 70 cm in length and 3,6 kg in weight, although in most areas it is smaller.

As with other flatfish, the winter flounder is asymetrical. It lives on the substrate, lying on one of its sides (in this case, on the left side) and its left eye has migrated to the right side, so that both point upwards.


Condemned to lie on its left side.

Living in very cold waters, the winter flounder suffers the risk of freezing during winter. As a result, its blod has a set of proteins that have the ability to reduce the freezing point of water, allowing it to remain liquid below 0°C.

The winter flounder is an important commercial fish in the USA and regarded as having a delicious meat. It has been overfished in the past decades and some populations have been depleted. Despite a recent large reduction in fishing pressure, many populations are recovering very slowly due to other factors, such as habitat degradation and low genetic variability. Furthermore, there are still some areas where overfishing may still be happening.

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Duman, J. G.; DeVries, A. L. (1976) Isolation, characterization, and physical properties of protein antifreezes from the winter flounder, Pseudopleuronectes americanusComparative Biochemistry and Physiology Part B: Comparative Biochemistry, 54(3): 375-380.

Wikipedia. Winter flounder. Available at: < https://en.wikipedia.org/wiki/Winter_flounder >. Access on September 17, 2016.

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic License.

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