I'm afraid there aren't many people on this forum that live near Algeria - Fish can ship just about anywhere but they generally have to be shipped overnight in Styrofoam coolers with either a hot pack or cold pack depending on the season. That kind of shipping will cost far more than the fish themselves. Do you have any fish stores in your town? Long before you buy your fish you need to purchase or be given a LOT of things You will want a fish tank of the right size (depends on how many fish you will have), you need a filter, a heater, Then there are little things like fish nets to catch the fish, buckets to help you change/clean the water in the aquarium tank, The fish store can test your water but it's better to have your own test kit. Water conditioner to remove any chlorine your city may be putting in it's water supply. You'll go through a 4-6 week process of cycling your tank which just means growing the good and useful bacteria that will make the water suitable for the fish to live in. By then 4th grade may be over. The fish themselves can be very inexpensive compared to some of these other items.
Sorry I can't be more optimistic for you - but if you at least have a fish store you can visit you can make a list of the things you need and how much they cost. See if you can get some relatives and friends to donate money to your research. Maybe this can be a 5th grade project. I'm impressed that a 4th grader is trying to accomplish something so difficult.