Parasitic Snubnosed Eels Found Inside Mako Shark Heart [See Photo]

Two parasitic snubnosed eels were discovered inside the heart of a male mako shark in 1997, but there was no sign of how they got there.

Scientists have occasionally found the snubnosed eel, a parasite that is uncommon but yet possible to be seen in the hearts, cavities, and organs of sharks. The picture has been repeatedly tweeted by many platform users since.

Parasitic Snubnosed Eel in Mako Shark Heart

In one instance from 1997, a huge shortfin mako shark was opened up to show two eels that were swollen with shark blood and nestled inside the heart of the animal.

These situations are intriguing since the eels, the sole species in their genus, are not necessarily parasites. They can live as an eel would on the ocean floor, basically scrounging the dead remnants of marine species.

But Snubnosed eels also enjoy digging into the flesh of bigger fish. In this case, a huge dead shark, 395kg, that was foul-hooked on a longline was the target.

According to Fishing with Rod, the term "foul hooked" refers to a fish that has been hooked somewhere other than its mouth. When a fish gets foul-hooked in British Columbia, it must be released gently. Keeping a fish with a foul hook is prohibited. Snagging, the act of attempting to foul hook or purposefully foul hooking a fish, is also prohibited.

The shark carcass showed it had spent time dead on the seafloor, as indicated by discoloration. The shark was sliced open the following day by researchers Nancy Kohler who works at the Northeast Fisheries Science Center and Janine Caira from the University of Connecticut.

How Eels Got In

Two young female snubnose eels, with lengths of 8.3 and 9.4 inches, were found by Caira in the shark's heart.

They had been taken from the ocean and placed in cold storage, so it was obvious that they were dead. But before that, they seemed to be in good health. There was also proof that the eels had been happily residing in the dead shark's heart for a while.

The guts of both eels were brimming with blood, indicating that they had been inside the shark for at least sufficiently long to feed, according to a 1997 study that was published in the journal Environmental Biology of Fishes. Both eels were completely filled with clotted blood. In neither eel were any digestive contents, food, or parasites discovered.

Other proof of their presence was present. The heart of the shark had damage that was absent from the six other shortfin mako sharks whose hearts had not been damaged by eels. Intriguingly, though, the researchers were unable to locate any evidence indicating how the eels managed to enter the shark's heart from outside.

The research team hypothesizes that the shark may have been damaged or killed by the longline hook when the eels discovered it and decided to feast on it.

According to the authors, at or near the moment of its demise, the shortfin mako was hanging from the capture line after being hooked and compromised.

The two snubnose eels approached the shark and burrowed into its body in the same approximate place somewhere near its gills or throat, either immediately before or right after it died. The eels moved into the heart after entering the circulatory system through an afferent artery or ventral aorta. The eels ingested blood at some point throughout this process.

In another incident ten years later, in 2007, several snubnosed eels were once again discovered in a smalltooth sand tiger's heart, body cavity, and muscles, Science Alert reports.