These feisty farmers are the only fish known to engage in agriculture. Damselfish are algae-growers, and they are so protective of their crops that they have been known to attack other creatures that swim too close — even human divers.
The algae they prefer is a species that is competitively weak, compared to other species. If it wasn't for such loyal tillers, the algae would be difficult to find. In fact, it tends to survive only within the protective territories of the damselfish.