Shaikh Zayad al-Wasaabi (may Allah preserve him) wrote:
“There is no difference of opinion between the People of Knowledge regarding the permissibility of fish, in all of its types.
The differing is in regards to what is besides that from that which lives in the sea:
The first opinion: everything in the sea is permissible. This is the statement of Mujaahid, Ibn Abi Laylah, al-Awzaai, the Maalikiyyah, and the most correct opinion in the mathhab of the Shaafi’iyyah. It is also reported from Abu Bakr as-Sideeq (may Allah be pleased with him).
Their proof: His statement, the Exalted:
أُحِلَّ لَكُمْ صَيْدُ الْبَحْرِ وَطَعَامُهُ
Lawful to you is (the pursuit of) water-game and its use for food [5:96]
And his (ﷺ) statement:
هُوَ اَلطُّهُورُ مَاؤُهُ, اَلْحِلُّ مَيْتَتُهُ
It’s water is purifying and its dead (animals) are lawful (to eat).
So the verse and the Hadith are both general in the permissibility of all animals in the sea without any exception.
The second opinion: Nothing can be eaten from the sea except the fish. This is the opinion of the Hanafiyyah and an opinion in the mathhab of the Shaafi’yyah
Their proof: His statement the Exalted:
حُرِّمَتْ عَلَيْكُمُ الْمَيْتَةُ وَالدَّمُ وَلَحْمُ الْخِنزِيرِ
Forbidden to you (for food) are: Al-Maytatah (the dead animals – cattle-beast not slaughtered), blood, the flesh of swine [5:3]
It (the verse) does not differentiate between the land and the sea animals. And His statement:
وَيُحَرِّمُ عَلَيْهِمُ الْخَبَائِثَ
And prohibits them as unlawful Al-Khaba’ith (i.e. all evil and unlawful as regards things, deeds, beliefs, persons, foods, etc.) [7:157]
And whatever is besides fish in terms of the animals in the sea are filth, like the frog, the crab, and snake
The third opinion: all the animals in the sea are permissible except the frog and crocodile. It is an opinion of the Haanbilah and an opinion of the Shaafii’yyah. The Hanaabilah also added the snake.
Their proof: is the verse mentioned earlier in the first opinion and they exclude the frog due to the prohibition reported on killing it. And also the crocodile because it eats humans, and the snake because it is filthy.
The fourth opinion: the fish are eaten. As for what is other than the fish, then the animals that are similar to the animals eaten on the the land can be eaten, like the cow, sheep, and other than it. What is not not eaten on the land, then it not allowed to eat [from the sea] like the sea pig, dog, and the likes. Based on that, what ever does not have a comparative [on the land], then it is halal. This is an opinion of the Shaafi’iyyah and an opinion in the mathhab of the Hanaabiliah.
The most correct opinion: is the first opinion and it is the chosen view of Ibn Uthaymeen and Shaikh Fawzan. Ibn Uthaymeen (may Allah have mercy upon him) said: “What is correct is that nothing of that [i.e. animals in the sea] are exempted and that all the animals in the sea, which only live in the sea are lawful, living or dead, due to the generality of the Honorable verse which we mentioned before”
And he said: “Despite the fact that the frog in reality is an animal of the land and the sea. Therefore, it is not from the animals of the sea because the animals of the sea are those that only live in the water.
See: al-Istikhkaar (15/304), al-Mughni (8/607), al-Majmoo’ (9/32), Sharh al-Mumti’ (15/33), and al-‘Atimah (pg. 85)”
Faisal bin Abdul Qaadir bin Hassan