Clownfish are demersal spawners. Meaning that they lay their nest of eggs on rocks, shells, or other solid objects on or near the bottom. For this reason, their natural instinct is to claim a suitable nesting spot and defend it against all comers. I breed clowns, and this behavior is clearly exhibited among my broodstock pairs. The reason breeders can keep large numbers of juvenile clownfish in a single tank is threefold. 1. Juvenile clowns have not yet experienced the full force of the genetic instict to establish and protect their turf. I stress the importance of noting that I said the "full force" of these instincts, because even in very young clowns, the behaviors associated with their need to carve out their own space is still present. 2. When I raise juvenile clowns, I do so in a tank that is bare bottom, and has as few solid objects in it as possible. Once any structure is introduced, their instinct to take and hold ground becomes very pronounced, even at a young age. Even so, at this young age, the competition is usually only deadly to the weakest specimens. 3. Heavy feedings and frequent water changes. I view it kind of like how I feel after a big meal. I generally want to just chill out on the sofa for a while. Young clowns seem to have a similar response. As long as their bellies are full, they have less motivation to fight.
All of this changes when clowns reach sexual maturity. It is worth noting here that all clowns start of life as males, and will only change sex to female if they are successful in asserting dominance over all the other clowns in the area. Just think about this in human terms. If you took 100 young men, stuck them on an island with no rules, except that only one of them would have the chance to mate, what do you think would happen??? The drive to procreate is every bit as strong...if not stronger... in fish as in humans.
