My mother used to get very irate when we called it "fishpaste". "It is trout paté!" she would say, crossly. But needless to say, "fishpaste" persisted.
You could use salmon instead of trout, and I think I fancy trying it with kipper or smoked mackerel, too. This version, I had a slice of smoked salmon that wasn't doing anything, so it went in, too.
The remains of a cooked trout (the sort of amount which isn't enough for another meal, but too much to throw away)
1/2 pack low-fat cream cheese (c 100 g?)
About 75 g butter
Small sloosh tomato puree
Slice smoked salmon (optional)
Seasoning as liked.
Whizz it altogether in the food processor until it's smooth. It freezes well.