well, if you demand deep-frying...that's one idea.  I've got used to just "frying" the fillet....a small bottle now lasts a whole trip, fish nightly.  No more submerging....just a 1/4" in the bottom of the pan, turn the heat down lower....and wait a few minutes longer...same great taste and minimal oil useage.  But IMO...if I demanded submergence of my fillets, or signifigant oil useage...I'd find bringing another bottle easier than the recycling hassle.

One trip, turned down the temp even further as no oil left, put some fake butter in the pan...low enough to not "burn" it....fish did get done and was indeed good.