The responses to the query on fish that "duplicate" when randomly recycled are correct. But just for all of you who were wondering, if all 7 fish are set to random, you will be delighted to see 31,824 different combinations of the 18 fish. HOWEVER, on average there will be 2.7 fish that are the same from one randon tank to the next (only 1% of the time no duplication; 10.4% 1 dup; 31% 2 dup; 34% 3 dup; 19% 4 dup; 4% 5 dup; 0.3% 6 dup; hardly ever with all 7 duplicated).

All you statistics fans are welcome to check the numbers; it's a whole lot more tedious than I thought, and I think I dropped a combination or two somewhere. When 99L appears, someone else will have to redo the numbers.