i heard u could change the fish's prices but how do u do it??? can someone please tell me

Put the fish you want to change the price of into the isolation tank. Then click on species. You can then enter the new price or click on the + or -.

oh! ok thank u i heard people could sell the fish for like thousands and thousands of dollars but i cant even sell it for 50 dollars!

There have been a few reports of bugs, as well corrupt savegame files, that where a fish may sell for $1000. That is far and few between. The most expensive fish will only sell in the mid to upper $400 range, and there are a lot of fish that will only be bought for $7. So don't get discourage.