Are crabs (sea, land, river, blue, mangrove, etc.) permissible?
In the Name of Allah, the Most Gracious, the Most Merciful.
According to the Hanafi Madhab, only fish from the creatures of the water is permissible. All other sea creatures are prohibited except what the scholars have defined as a fish (samak) or categorized as a fish. The prohibition of all sea creatures besides the fish is deduced from the Quran and Ahaadith of The Prophet ﷺ.
Allah mentions in The Quran;
And made lawful for you is the prey of the sea and eating thereof. (5:96)
The Hanafi jurists restricts the meaning of “prey of the sea” to specifically meaning the fish. The Prophet ﷺ specifically mentions fish when permitting carrion of the sea.
Messenger of Allah (ﷺ) said: “Two kinds of dead meat have been permitted to us: fish and locusts.” (Ibn Majah 3218)
Crab therefore is impermissible according to the Hanafi Madhab as it is not considered a fish. The same will apply for all types of crabs: sea, land, river, blue, mangrove, etc.
For details on the ruling of shrimp see http://fatwa-tt.com/is-it-permissible-to-consume-shrimp-according-to-the-hanafi-madhab/
And Allah Ta’āla Knows Best
Mufti Arshad Ali
Darul Iftaa, Jaamia Madinatul Uloom (Trinidad)