Category Archives: Fish

Friday Fellow: Ocean Sunfish

by Piter Kehoma Boll

Let’s swim to the world of fishes once more. And today we are meeting the heaviest of the bony ones, the ocean sunfish!

mola_mola

The ocean sunfish looks like a giant piece of mushroom, don’t you think? Photo by Per-Ola Norman.

Scientifically known as Mola mola, the ocean sunfish is found in tropical and temperate oceanic waters throughout the world and has a very strange look. And this is not the only strange thing about it. More than being the heaviest bony fish in the world, weighing up to 1,000 kg, it feeds almost exclusively on jellyfish, eating a huge amount of them to become that big. Also, the female ocean sunfish is known to produce up to 300 million eggs at a time, more than any other vertebrate!

The weird lump on their rear end is not a caudal fin. Actually, sunfish have no tail at all. This structure, called clavus, is formed by projections of the dorsal and anal fins.

Despite their huge size, sunfishes are not a direct threat to humans. People can swim among them without any problem. The most common forms of accidents with these fish are caused when boats collide with them or when a sunfish jumps out of the water and ends up inside a boat. Imagine a 500-kg fish landing on your head!

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References:

McGrouther, Mark (2011).”Ocean Sunfish, Mola mola“. Australian Museum Online. Available at <http://australianmuseum.net.au/ocean-sunfish-mola-mola&gt;. Access on December 8, 2016.

Wikipedia. Ocean sunfish. Available at <https://en.wikipedia.org/wiki/Ocean_sunfish&gt;. Access on December 8, 2016.

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Filed under Fish, Friday Fellow, Zoology

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:

glugea_stephani_xenoma

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.

glugea_stephani

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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References:

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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*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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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?

pseudopleuronectes_americanus

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.

pseudopleuronectes_americanus_2

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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References:

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

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Friday Fellow: Porkfish

by Piter Kehoma Boll

Let’s dive into the tropical sea waters filled with coral reefs at the Atlantic coast of America to know this handsome Friday Fellow: the porkfish (Anisotremus virginicus).

Found from Florida to Southeast Brazil, the porkfish is a beautiful reef fish popular in public aquariums. In its natural environment, it occurs in a depth ranging from 2 to 20 meters and may reach 40 cm in length and 930 in weight, although most individuals are around 25 cm long.

A porkfish from a school in Mexico. Credits to Simões et al. (2014).

A porkfish from a school in Mexico. Credits to Simões et al. (2014).

The food of the porkfish consists mainly of invertebrates, such as mollusks, echinoderms, annelids and crustaceans, that it captures at night. Young specimens usually pick parasites from the bodies of larger fish. Adults may also feed on epibionts growing on sea turtles, such as the hawksbill turtle (Eretmochelys imbricata), though it does not seem to constitute a widespread habit.

Despite sometimes being consumed as food by humans, the porkfish may be contaminated by ciguatoxins, a group of toxins that cause ciguatera, a kind of food poisoning.

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References:

Froese, R. Anisotremus virginicus. In.: Froese, R.; Pauly, D. (Eds.) FishBase. Available at: <http://www.fishbase.org/summary/1124&gt;. Access on February 27, 2016.

Sazima, C.; Grossman, A.; Sazima, I. 2010. Turtle cleaners: reef fishes foraging on epibionts of sea turtles in the tropical Southwestern Atlantic, with a summary of this association type. Neotropical Ichthyology, 8(1). Doi: 10.1590/S1679-62252010005000003

Simões, N.; Zarco Perello, S.; Moreno Mendoza, R. 2014. Checklist of fishes from Madagascar Reef, Campeche Bank, México. Biodiversity Data Journal 2: e1100. Doi: 10.3897/BDJ.2.e1100

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