I too have a bad fish smell coming from inside my bosch 300 series dishwasher. The smell was there from the very first wash. I tried all the remedies and so far the smell persists. to make a long story short here is what I think is happening. It could be that bosch has coated its stainless with a fish oil to help prevent corrosion. under normal washing temperatures, there is no smell relesed from the coating. This dishwasher has no drying element. what it does is it supper heats its final rinse so hot that it drys quicker. I think its this final rinse that releases the smell from the coating. Some units have less of this fish oil than others.
Anyways I wish I lower the temperature of the final rinse.