Fish in jelly, 25% off (3)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A GAR (a jelly prepared from seaweeds of various kinds used in bacteria-culture, medicine, glue-making, silk-dressing, and cooking) excluding (off) the first A , one of 4 [25%] l etters in the word, to leave GAR