What can fish eat besides food?

Fish primarily eat food, but they can also accidentally ingest a few things that aren't traditionally considered food:

1. Gravel and Sand: Some fish, especially bottom feeders, accidentally ingest small amounts of gravel and sand while foraging. This is usually harmless and passes through their system.

2. Small Rocks and Pebbles: Similar to gravel and sand, small rocks and pebbles can be accidentally ingested, particularly by fish that explore rocky areas.

3. Plants: While not all fish are herbivores, some species will nibble on aquatic plants, algae, and even terrestrial plants that fall into the water.

4. Algae: Many fish graze on algae, which can be a significant part of their diet.

5. Other Fish (for predatory fish): Carnivorous fish will eat smaller fish, insects, worms, and crustaceans. Some fish may even eat other fish of the same species, especially if they are stressed or hungry.

6. Debris and Waste: Unfortunately, fish can sometimes ingest debris and waste that accumulate in their environment. This can be harmful and lead to health problems.

7. Air (for some species): Some fish, like lungfish, have lungs and need to come to the surface to breathe air.

It's important to remember that fish should not be given anything besides their intended food. Their digestive systems are designed to process specific types of food, and anything else can cause health problems.