Sayyiduna Abu Huraira (may Allah be pleased with him) reports that a man came to the Messenger of Allah (peace and blessings be upon him) and said: "O Messenger of Allah! We travel by sea and carry only a small amount of fresh water with us. If we use it for ablution, we will be left thirsty. So, can we perform ablution with the water of the sea?" The Messenger of Allah (peace and blessings be upon him) replied: "Its water is pure and its dead (animals) are lawful."
Just as hunting land animals is permissible, similarly, sea animals such as fish are also permissible and lawful. Allah Ta'ala says: «﴿أُحِلَّلَكُمْصَيْدُالْبَحْرِوَطَعَامُهُمَتَاعًالَكُمْوَلِلسَّيَّارَةِ .....﴾ [المائدة : 96]» meaning, "The game of the sea has been made lawful for you and its food (is lawful) for you and for the caravans passing by..."