AsianScientist (Feb. 7, 2013) – Researchers have discovered that fish are able to use chemical cues to find other fish of the same size as themselves.

Forming groups is beneficial for animals because there is strength in numbers and it reduces their individual risk from predators. When animals band together, predators are confronted by numerous prey animals that are almost identical, making it more challenging for the predator to select a target.

Because of this, fish swim together in shoals for protection, preferring shoal mates similar in size and appearance to themselves. However, until now, it was not known how fish can determine if potential shoal mates are of similar size as themselves.

“The key question that motivated our study is this: How on earth does a fish know how big it is?” said Dr Ashley Ward, an author of the study, which was published online in Behavioral Ecology and Sociobiology. “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?”

Knowing that fish have a keen sense of smell, the researchers explored if fish are able to use this to assess the size of other individuals, and also to determine how big they are themselves.

“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,” explained Dr 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.”

In their experiments, the researchers exposed fish from two freshwater shoaling fish species (three-spined stickleback and banded killfish) to a variety of chemical cues emitted by fish of varying sizes from the same species.

They found that fish belonging to both species preferred the chemical cues of same-sized fish over those of larger or smaller fish from their own species.

This suggests that the fish were able to determine their own size relative to other fish of the same species primarily by detecting chemical cues from other fish and comparing against their own emitted chemical cues.

The article can be found at: Ward and Currie (2013) Shoaling Fish Can Size-Assort By Chemical Cues Alone.

——

Source: Springer. Photo: palestrina55/Flickr/CC.

Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.