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Fish in groups decide quicker, better
It may not always work for humans, but making decisions by committee can be a life saver for fish.

Research from the University of Sydney shows for the first time that the larger a shoal of fish, the quicker and more accurately they can make decisions. The research also throws new light on the benefits of social networking.

In the study, published this week in Proceedings of the National Academy of Sciences, Associate Professor Ashley Ward and James Herbert-Read presented mosquito fish (Gambusia holbrooki ) with a choice to swim down one of two arms in a Y-shaped channel. One arm contained a replica predator, the other was empty.

The researchers found that the larger groups of mosquito fish made the correct decision to swim down the predator-free arm more rapidly than smaller groups or individuals.

"All the things we understood had suggested that as group size increased, the time taken to make a decision should also increase. You see that in human committees - the larger the committee, the longer it takes to make a decision," says Ward.
Quick decision-making

"We expected that fish in groups would make more accurate decisions, but not necessarily at any greater speed.

"So we were really surprised when the larger groups not only made better, more accurate decisions, but they also made them much, much faster."

Fish in groups of eight and more showed almost 90 per cent accuracy, whereas single fish only managed 56 per cent accuracy.

Ward says the actual time fish spent in the decision making zone (at the start of the channel) was between 1.5 and 2 seconds.

"But chances are they are deciding a lot quicker than that," he says.

"The incredible thing is, these animals can make decisions without talking to each other," says co-author James Herbert-Read, also from the University of Sydney.

The researchers wondered if the group might contain fish with a particular ability to make decisions, who might influence the others.

Herbert-Read tested 44 individual fish in the same Y-shaped channel, to see if some excelled at avoiding the predator.

"But the trials showed that they all have a similar ability: we didn't find either idiots or experts."
More than the sum of the parts

Given that fish don't appear to have charismatic leaders, the researchers speculate they must be communicating some other way.

"We don't know how they do it, but if somebody was to act in an obvious way, people would take notice of them," says Ward.

"In the same way, if a fish makes a sudden major turn, the others might take that as being an important thing to copy perhaps."

Herbert-Read says he hopes the study will get people interested in the benefits of grouping.

"We have this new and upcoming field where you have these individuals coming together and their collective response is more than the sum of the parts. We see this in our stockmarket and also how Google works," he says.

"It might go some way to explain why we see so many animals species living in these large groups - because they're more accurate at making decisions."

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