Fish Nest-Building and the Competition to Breed

This is a survival strategy for weaker individuals: by moving in groups they gain safety and find more food.

The male weaves these materials tightly together, as if sewing, and fixes the nest firmly in place by gluing it with his bodily fluids. To block predators, he adjusts the size of the nest's entrance, showing a craftsmanship similar to bird nest-building.

Once the spawning bed is complete, the pair twist their bodies around each other to stimulate the female's belly so she lays her eggs; the laid eggs are covered with sand to hide them from predators.

As the dance grows more intense and the male fully wraps the female's body, the eggs burst out; this has been recorded as a rare spawning scene never before observed or reported.

In response, the male spotted-fin catfish shows its fierce temperament, driving off the intruders with strong threats and protecting its own eggs.

To improve the survival rate of the eggs, the female moves between several locations and spawns in multiple rounds; after spawning, the sweetfish weakens and dies, returning to nature.

Male salmon display sharp snouts and fangs in a fierce competition to claim females, and weaker males sometimes use a 'sneaker' strategy, releasing their sperm during another pair's spawning moment.