I came accross this questionand answer in “The Majlis”:
Q. A senior Mufti says that prawns/shrimps can not be labelled haraam because there is no Qati Daleel to substantiate the prohibition. At most it will be Makrooh Tahrimi.
A.(1) Makrooh Tahrimi is also called haraam. If the honourable Mufti does not know this fact, then ask him to check the kutub of the Fuqaha and he will find innumerable prohibitions for which there is no Qati Daleel, but which the Fuqaha proclaimed Haraam. This is such a simple issue that it will be a waste of time for us to cite examples. The honourable senior Mufti will have access to the kutub. He only needs to expand his mutaa-la -ah (research) a bit. For Hanafis, prawns, shrimps, lobsters, crayfish and all sea animals besides fish are Haraam. Please can Mufti comment on this as I am quite confused and do not know whether to regard prawns as halaal or not. The Mufti of “The Majlis” is quite honourable and I respect His views too.