Fish larvae sniff their way back home

Reef fish larvae can smell the presence of coral reefs from as far as several kilometres offshore and use this odour to find home, according to a new study.
The research led by Dr Claire Paris, Professor at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science was conducted at One Tree Island in the Great Barrier Reef.
Members of the research team had established earlier that reef fish larvae could discriminate between the odours of different nearby reefs while preferring the odour of the reef where they were settling. However, these experiments were done under controlled conditions in a shore-based laboratory.

"In this collaborative study we expanded our work to demonstrate that the odour responses can also be detected under the field conditions," said Dr Jelle Atema, Boston University Professor of Biology.
"This establishes for the first time that reef fish larvae discriminate odour in situ," Atema said.
Working with colleagues from Laboratoire Oceanographique de Villefranche, James Cook University and Oldenburg University, researchers tested the response of larvae in a natural open ocean setting using an outflow plume from One Tree Island.

Using light traps, the team collected settlement-stage larvae from cardinalfish and damselfish.
In deployments to the north and south of One Tree Island, single larvae were observed in the central chamber of an o-DISC (ocean Drifting In Situ Chamber), a device created in Paris' laboratory.

The light-weight piece of equipment was set adrift in the water column and the swimming activity and bearing of the larva was recorded using an underwater motion sensing and imaging system. The o-DISC tracked larval movement and orientation using odour cues from the environment.
Species from the two reef-fish families reacted very differently to the olfactory stimulus. Cardinalfish tended to speed up their movement in response to odours in the plume, but their orientation toward the reef was not apparent.
They zigzag within the o-DISC chamber, which led the researchers to believe they were using infotaxis, or sporadic odour cues, in their attempt to orient.

In contrast, damselfish slowed their swim speeds, and there was orientation along the shoreline and toward the west. They seemed to be moving with a compass, triggered by the odour stimulus.
Other fish, including mature sharks and freshwater juvenile salmon navigate using olfactory signals, but this is the first study to report that fish larvae use similar odour cues.
The study was published in the journal PLOS ONE.