Top level view:
You get a import license to bring stuff into the country. Then you pay and schedule someone to inspect the shipment on arrival. This can be very expensive if it lands outside of normal business hours which is fairly common, or let the fish sit till the next day. From there, you need to know what is legal to import. You'd need to know that you can only import from the countries you applied for. Koi and Goldfish need health certificates to come into the country. Aka more fees.
Importing fish probably starts at $750 for 1 box of fish between the fees, flight cost, inspection etc. Where it makes sense is when you add more boxes. 2 boxes might only be $1000, and 3 boxes is 1200, etc. This doesn't include the cost of the fish.
So it's one of those things that is doable, a license is like $100 a year to maintain. But the cost/hassle shouldn't be overlooked. When you are trying to schedule someone to look at the import, flight gets delayed, or rebooked etc. It's a stressful time each time we do it.