Overfishing takes too many fish out of the ocean, so there are not enough to breed and produce the next generation of fish. This causes many problems.
Larger fish in the food chain that need to feed die out from hunger.
Countries that rely on fish for food find that their fishing boats come back empty.
Overfishing also creates large ecological dead zones in the oceans. Although fish will be eventually replaced by jellyfish and shrimp, other species like whales and dolphins will become more and more scarce along with fish.
If one fish is gone then the fish above it in the food chain won't be able to eat that fish and it will mess up the food chain.
