Fish Larvae Use Olfactory Cues to Sniff Their Way Back Home

A team of researchers have solved the mystery of how tiny fish larvae travel away from the reef and then successfully navigate their way back home.

The latest collaborative study conducted by a team of international researchers at One Tree Island in the Great Barrier Reef, established that the reef fish larvae can sense the presence of coral reef even at a great distance and can navigate their way back home using that odor.

Prior to this study, shore-based laboratory experiments were done under controlled measures, which revealed that the reef fish larvae have the ability to differentiate between odors of different reefs surrounding them. But the fish larvae preferred the odor of the reef where they were staying.

According to Dr. Jelle Atema, Boston University Professor of Biology, odor cues can be detected even in field conditions.

In the latest study led by Dr. Claire Paris, Professor at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science, the researchers used an outflow plume from the island to examine the larvae's response in a natural open ocean setting. They gathered settlement-stage larvae from two reef fish families namely cardinalfish and damselfish.

The researchers used a unique device called o-DISC (Ocean Drifting In Situ Chamber) to measure their movements and placed it in the north and south of the One Tree Island. The device consisted of a circular behavioral arena that was transparent to light, sound and small scale turbulence. The researchers recorded the swimming and bearing activity of the cardinalfish and damefish larvae with the help of underwater motion sensing and imaging system. They tracked the larval movement using odor cues.

They noticed that the cardinalfish and damselfish reacted differently to the olfactory stimulus. The cardinalfish speeded up their movement in response to the odors but their orientation toward the reef was not evident.  Their zigzag movements within the o-DISC chamber led the researchers to assume that they were using random odor cues to orient whereas the damselfish lowered their swimming speed and their orientation was limited along the west shorelines. 

"Ocean currents do not appear to influence the orientation of fish larvae," Paris said in a news release. "They do not provide a frame of reference since larvae are transported within. Instead, we find that fish larvae navigate by detecting turbulent odor signals transported kilometers away from the reef. Subsequently they switch to a directional cue, perhaps magnetic or acoustic, which allows them to find the reef."

Other fishes that navigate using olfactory signals include freshwater juvenile salmon and mature sharks. But this is the first study that proves fish larvae also use olfactory signals to navigate.

Paris concluded stating, "The implications of this study are tremendous, because we have to take into account the impact that human activities might have on the smells contained within the ocean. If these larvae cannot get their 'wake up' cues to orient back toward the reef they may stay out at sea and become easy prey before finding home."

The study also included researchers from Boston University, Laboratoire Oceanographique de Villefranche, James Cook University and Oldenburg University.

The researchers documented their finding in the journal PLOS One.