Bizarre deep-sea fish found with blood-sucking parasite 'pigtails'; watch video here

This fish was spotted with parasitic copepod hitchhikers during the #SouthSandwichIslands expedition, where an international team of scientists is documenting biodiversity and examining the seafloor for evidence of geohazards. (Image: Schmidt Ocean Institute)

Watching the deep sea can often feel like sci-fi. But a recent video from the ocean’s depths has stunned even seasoned scientists — showing two parasites firmly attached to a fish’s head, looking oddly like pig tails.

Creepy duo spotted clinging to rattail fish
The footage was shared by Schmidt Ocean Institute on Facebook. It captured two Lophoura szidati copepods latched onto a rattail fish's head. Long egg sacs behind them gave the parasites a pigtailed look. These copepods, part of the Sphyriidae family, feed on the fish’s muscle and fluids.

James Bernot, a biologist at the Smithsonian, confirmed this. "They use their scraping mouthparts buried in the muscle," he told Live Science. The video was recorded at 1,604 feet underwater. The team was exploring the seafloor near the South Sandwich Islands, a group of volcanic islets in the South Atlantic.

Copepods drill into hosts and stay for months
The copepods, part inside and part outside the host, are mesoparasites. The back of their bodies and egg sacs hang outside, while their heads remain embedded in the fish’s tissue.

Scientists identified the fish as from the genus Macrourus, known as grenadiers or rattails. These fish are common in deep, cold Atlantic and Southern Ocean waters, often found from 1,312 to 10,450 feet deep.

Bernot added that L. szidati is one of the most common parasites in this region. However, little is known about deep-sea parasites in Antarctic waters.

Copepods carry eggs and leave marks for years
Copepods begin their life attached to hosts as larvae. They bury into the skin, then grow and form anchor-like holdfasts. In the video, each parasite holds two sacs filled with hundreds of eggs. “They’re surprisingly caring for invertebrates,” Bernot said.

Once hatched, the larvae — called nauplii — go through several stages. They eventually seek out new hosts. These parasites stay with their fish hosts for months. Even after dying, their embedded heads remain in the fish's tissue for years.

The video not only startled the public but also highlighted just how little is known about life in the ocean's depths.