Yes, crayfish is halal. In Islamic law, eating locusts (which can be likened to crayfish in terms of dietary rules) is permissible even if they are dead, as mentioned in the Hadith. The Prophet Muhammad (peace be upon him) said: “Two types of dead meat are permissible for us: fish and locusts.” (Ahmad, Ibn Majah). No specific method of slaughter is required for locusts as their dead bodies are considered pure.

Source: Islamweb