How long do you keep baby fish seprate from big fish?

It's impossible to give a definitive answer to "how long" without more information! Here's why and what you need to consider:

* Fish Species: Different fish species grow at different rates. A baby guppy might be ready to join a community tank after a few weeks, while a baby oscar could take months.

* Size of the Baby Fish: Once the baby fish is large enough to avoid being eaten, it's usually safe to introduce them. A good rule of thumb is if the baby fish is about 1/3 the size of the adult fish's mouth, they are probably safe.

* Aggression of the Big Fish: Some fish are naturally more aggressive than others. Even if a baby fish is big enough, a very aggressive fish might still try to eat it.

* Tank Size: A larger tank provides more space for the baby fish to avoid the bigger fish.

* Hiding Places: Providing plenty of hiding places for the baby fish will help them feel safe and avoid being eaten.

Here's a general guideline:

* Keep baby fish separate for at least a few weeks to give them time to grow.

* Observe both the baby and adult fish carefully for signs of aggression before introducing them.

It's always best to err on the side of caution and keep baby fish separate for longer if you're unsure. You can often find information on the specific species of fish you have online or from your local pet store.