In most species the motto is the bigger the better. The biggest and strongest animal becomes the leader of the group. This is not the case for the little goby. It goes on a diet to not become bigger than the leader and here is why.

In the goby colony, the largest fish is the dominant leader. This is usually the only breeding male. All other members are smaller. If a smaller fish grows too quickly and becomes larger than the fish immediately above it in the hierarchy—or approaches the size of the dominant leader—the leader will likely attack or expel them.

Expulsion from the coral usually means death due to predators. Therefore, smaller gobies will consciously reduce their food intake, go on a diet or simply get less food, to remain smaller than the dominant fish, keeping the peace.

These colonies act as a “queue” for breeding. The smaller fish are waiting for the leader to die so they can move up in rank. Subordinates stay intentionally smaller to maintain the stability of the group. As soon as a superior fish dies, the next in line will start eating more to grow into the new, larger position.

The “trouble” is not that they are necessarily fighting, but that the subordinate is out-competing the leader, forcing the leader to defend its position.

Gobies live in strict, size-based, hierarchical colonies within corals. This behaviour is a survival strategy to avoid being evicted by the dominant leader.

On the subject of behaviour here is a fact on the Yellow Watchman Goby. They are known for symbiotic, peaceful relationships like living with pistol shrimp. We wrote about this in our blog some time back.