Assuming you are referring to aquarium fish equipment, there a few different ways you can sterilize it.
One way is to soak the equipment in a 3% hydrogen peroxide solution for 30 minutes. After that, rinse everything off with clean water.
Another way is to use a UV sterilizer. You can either purchase one or build your own. This method is effective, but can be expensive.
A third way is to boil the equipment for 10 minutes. This will kill any bacteria and parasites that may be present. Just make sure that everything is dry before using it again.
No matter which method you choose, it's important to regularly clean and sterilize your fish equipment to help prevent the spread of disease.