Hmmm, I posted Chan eil eun coltach ri t-iasg as I thought Gaelic vowels did not like each other and should be separated, but I guess my sentence is A bird is not similar to the fish?
Yeah. Your logic is correct. Gaelic tries to avoid that contact where it can.
The t-hyphen is actually a part of the definite article. It's an t-, not t-iasg.