Wow, that looks like a big’un, fish. Definitely the crysalis of a caterpillar 
Actually, it looks to me like a moth pupa, but I have no idea what species. Keep an eye on it an see what crawls out – stick it in a jam jar with the lid on (holed for ventilation of course) then you’d be able to take a piccy of the emerged beasty and post it up._________________
*Boudicca – Gets REALLY stroppy after a pint!*