Body-Conscious Fish Go On Diets

May 12, 2008

Release from: Jessica Marszalek
Herald-Sun (Australia)

Some fish go on diets to avoid being attacked and shunned by their own species.

The study by the Australian Research Council Centre of Excellence for Coral Reef Studies and James Cook University found some coral reef gobie fish deliberately dieted to avoid posing a treat to their larger rivals.

Dr Philip Munday said the research, published in the journal Current Biology, contradicted previous views that dominant animals retained their positions by terrorising subordinates to take more food for themselves.

Dr Munday said that in gobies, where only the largest male and female had mating rights within the group, all subordinate fish were consistently five to 10 per cent smaller than its next largest rival.

He said all subordinate fish were waiting in line to become the next breeder and reacted violently if another fish threatened its position in the queue.

If a subordinate fish grew close in size to the next largest fish, it was attacked and expelled from the safety of the group to be eaten by a predator, the study found.

"If the second in the queue gets too big then things get nasty and the first in the queue will actually try and boot out the second," he said.

Dr Munday said the research team tried to fatten up some of the subordinate gobies but found the fish refused to eat the extra tidbits.

"We were really surprised," he said.

"We were thrilled when we saw that these things can make a decision, they will stop feeding if it's not in their best interest.

"We usually think of these things as gutses and they'll eat anything that comes by and they'll just grow as much as they possibly can. But this result clearly shows it's more complex than that."

He said researchers would now look into the complex behavioural hierarchies of other species of fish.