Well, there are bound to be folks more knowledgable than myself to answer you, but since your question has been posted for so long without response i thought I would pipe up with my 0.02 :

Personally, the small amount that you would get for the trouble wouldn't be worth it to me. A big bottle of fish emulsion is under 10 dollars. And it goes a long way. For what you would get from your filter, even if it is "nutritionally comparable" (and I don't even know if it is), you would have to spend many hours of harvesting the yuk out of the filters....

But sometimes it is just a pleasure to try an experiement, and if that's the case, then cost is of less importance, so if you decide to try it, test your soil before and after the application of the filter contents to see if you made an improvement. And be sure to post again to let us know how it turns out!

Allison