Fish Use Sense of Smell to Find Same-Sized Mates

Written by on February 12, 2013 in Fish, Marine Life
These surgeonfish (Acanthurus leucosternon) are shoaling - notice how they are in a group, but not all facing the same direction.

These surgeonfish (Acanthurus leucosternon) are shoaling – notice how they are in a group, but not all facing the same direction. Photo credit: Uxbona.

According to a new study, fish are able to find other fish of the same size by sense of smell.

Associate Professor Ashley Ward of the School of Biological Sciences at the University of Sydney explained that the formation of groups is a common method of protection from predators. Many animals, including shoaling fish often group with other animals that are all similar in size. Ward said that this adds an additional measure of protection known as the “confusion effect.”

“When animals are matched in size the predator finds it difficult to pick the odd one out and therefore can’t target a victim,” he said.

Shoaling fish are fish that stay together in a loosely-formed group. They differ from schooling fish because in order to be considered a school, the fish must move in the same direction at the same speed in a synchronized manner.

“Fish typically form shoals with fish of the same size. The key question that motivated our study is this: How on earth does a fish know how big it is? For humans this is trivial – we can stand on a flat surface and see whether we’re taller or shorter than someone, or we can look in a mirror. These options don’t exist for fish, so how do they choose to associate with fish of the same size?”

By studying two different species, the three-spined stickleback and banded killifish, Ward and colleague Dr. Suzanne Currie of Mount Allison University in Canada, found that freshwater fish can determine size by using chemical signatures, or cues, emitted by other fish. They found that both species preferred the chemical cues of same-sized fish (of the same species) over those from larger or smaller fish.

“We know the sense of smell is well developed in fish and that they are sensitive to tiny differences in the chemical signature given off by others,” said Ward. “So could they smell how big they are themselves and use this as a template to assess the size of others? It seems they can.”

He notes that their findings are relevant to all shoaling fish, both freshwater and marine, although marine fish generally release fewer chemical cues into the water.

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Copyright © 2013 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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