Why do Trout get Hooked Jaws?

hook jawTrout have one main purpose in life, and that purpose is to spawn so other little trout can enter the world. Spawning in its simplest definition, is to lay eggs.

When do Trout spawn?

Not all species of trout spawn at the same time of year. Rainbow trout, for example, spawn late spring into early summer. Lake trout spawn in the fall months at night.

Physical changes preparing for spawn.

As an adult trout nears maturity it goes through physical changes to prepare for spawning. Trout are generally silver in color, but as the time for spawning approaches, they turn red, pink, and green in places. Females become stouter in preparation for carrying eggs. Males develop something called a kype, or as more popularly known, a hooked jaw. In comparison, the females mouth area becomes shorter and more rounded.

How does the spawn work?

When a female trout is ready to lay her eggs, she will look for a place in clear water that is near or in the shade. The looser the silt or gravel on the bottom the better. She will take her fin and dig a shallow depression. The male will swim along beside her and drop his milt onto the eggs to fertilize them. The female then covers the eggs and moves on to the next prime laying spot and fertile male. Don’t think the male has it that easy! Before he can fertilize the eggs, he must entice the female with an impressive mating dance, while fending off other males.

So why does the male trout need a hooked jaw?

The hooked jaw is in the lower jaw and where there are strong teeth. The male uses the hooked jaw to bite other males that are trying to fertilize eggs. It really is as simple as that. Some trout seem to have longer hooked jaws than others. That is from the hooked jaws not entirely disappearing from the fish after the spawning season. The surviving fish will grow the hooked jaw again, thus just adding to the length of what didn’t entirely disappear to begin with.

Photo credit: nilsrinaldi / Foter.com / CC BY