I just had an idea. I don't know if this would help or not, but lemon juice is supposed to kill the smell of fish on your hands after working with it, right? At least that's what I thought I had heard. Could you try soaking one item in a bucket with water and lemon juice? Maybe it would remove the fish smell. Might be worth a try anyway.
Ok, I just googled getting the smell of fish out of clothes and wound up on the Thriftyfun web site for a thread about the smell of fish in clothes. There were two responses I thought might be helpful to you.
One said they worked in a Salmon processing plant and that hanging the clothes in the sun for a prolonged period, up to three days, helped to rid the clothes of much of the odor, which made it easier for the detergents to do their job. This person had good luck with it.
The next response was using a product called Right Stuff citrus cleaner. about a cup to the laundry, but I am not sure if it was a full load.