The word roach has two main meanings:

1. A cockroach, one of the world's oldest and most resilient insects. Roaches have been around for over 300 million years, surviving since before the dinosaurs. They can live almost anywhere, eating nearly anything, and famously can survive for weeks without food. While they make terrible houseguests (they spread germs and can trigger allergies), scientists actually admire their incredible toughness. Some species can even survive for days without their heads because their nervous system is spread throughout their bodies. When someone says a place is “infested with roaches,” they mean it's overrun with these unwelcome insects.
2. A small freshwater fish common in European rivers and lakes. It has a silvery body and reddish fins, and anglers often catch them while fishing. Unlike the insect, these roaches are harmless and actually quite pleasant to look at.