When considering parasites, one may commonly think of worms and insects. However, the ocean's brutal environment challenges expectations as even sharks face risks.
According to Science Alert, scientific records reveal occasional instances of the snubnosed eel (Simenchelys parasitica) parasitizing the hearts and organs of sharks, highlighting the harshness of underwater life.
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Eels Parasitizing Sharks
In an intriguing case recorded in 1997, a large shortfin mako shark was discovered with two snubnosed eels nestled in its heart, filled with shark blood.
A decade later, in 2007, similar instances occurred with snubnosed eels found in the hearts, body cavities, and muscles of a smalltooth sand tiger. What makes these cases noteworthy is that snubnosed eels, the only species of their genus, are not obligated to be parasites. They can thrive in the ocean, scavenging dead marine animals on the seafloor.
However, snubnosed eels also exhibit a peculiar behavior of burrowing into the flesh of larger fish, including sharks, for their benefit and feasting to their satisfaction. The discovery of eels parasitizing sharks was unexpected, as it was only in 1992 that a male shortfin mako shark was found on the seafloor with two juvenile female snubnosed eels in its heart.
The eels, although dead when recovered, showed signs of previous health and had consumed blood, indicating they had resided within the shark for a considerable period.
Despite the evidence of their presence in the hearts of sharks, the exact mechanism by which the eels entered the hearts remains unknown. Additionally, the sharks with eels exhibited heart damage not found in other eel-free sharks examined.
These findings raise intriguing questions about the dynamics between snubnosed eels and sharks, highlighting the unpredictable nature of the ocean's interactions.
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Parasitic Eels May Contribute to the Death of the Sharks
Limited information is available about the sand tiger shark, but the 2007 paper describes a case where a deceased female shark, found near the Canary Islands, had several snubnosed eels within its heart, body cavity, and muscles.
The shark's ovaries were missing, possibly consumed by the eels, or naturally degenerated. Shark biologist Ian Fergusson wrote in the paper that while no clear cause of death was determined, the presence of the eels may have played a role.
Although only two instances have been observed, the snubnosed eels appear to thrive on non-living food sources. A 2018 paper revealed that the eels were observed in significant numbers feeding on a whale carcass off the coast of Japan.
While the eels currently practice facultative parasitism, not relying on live prey, studying their behavior further could shed light on the potential evolution of obligate parasitism, where organisms depend on another living organism for survival.
As Science Alert reported, the ability of snubnosed eels to temporarily live within another organism holds evolutionary significance. This discovery opens opportunities for phylogenetic and ecological changes that could eventually lead to the development of obligate parasite lineages and true hosts.
Further research into these deep-sea bottom feeders may provide valuable insights into their unique feeding strategies and evolutionary pathways.
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