One of the diseases that occur in tuna that traders often worry about is caused by a parasite called Myxosporidean protozoan, especially the Kudoa variety. This parasite causes disease in many different host species.

This kudoa has a rather complex life cycle consisting of 2 hosts: fish and worms. Spores of protozoan released from these hosts randomly enter the tuna’s body through their skin. First, they invade muscle tissue, forming small bumps or pseudo-cocoons. These small white spots can appear all over the loin, sometimes up to an inch in length.

When the tuna is alive, it can fight these parasites. But when the fish dies, the enzymes continue to work to soften the flesh. This phenomenon is called “Sashi”. Sashi reduces the economic value of tuna because they cause liquefaction of the muscle after the tuna dies, making the fish meat soft and can’t be sold. The process of muscle breakdown takes a long time and is not noticeable within a few days. Often, they are discovered after the fish is sold or cut into loin pieces. Fortunately, this disease does not affect humans.

Another parasite commonly found in tuna of the species Copepod

Copepods are small crustaceans, only a few millimeters long. Some Copepod species are usually parasitic on specific hosts, but some species are more parasitic on any host. Depending on the species, these tiny insect-like creatures are often found on body surfaces such as the host’s fins, gills, and nose. This tiny parasite is not highly pathogenic. The degree of influence of this species depends on its density. Large copepods can cause significant damage. Copepod parasites in the gills of fish can weaken the breathing ability of fish.

Bluefin tuna is sometimes host to a parasite called Pennella filosa.

This parasite can be easily seen. Their head is plugged into the fish muscle, their body is long, and shaped like a worm, and they hang their body in suspension. Samples of this species are several inches long. Although this parasite is not dangerous to humans, it will reduce the quality of fish.


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