It is a common question asked by many for sea food for general information about which sea food is halal and which is not. Here you can find complete information that which seafood is halal and which is haram according to Hanfi opinion.

The interpretation of halal sea food is extracted from the following Quranic verses

“Lawful to you is game from the sea and its food as provision for you and the travelers, but forbidden to you is game from the land as long as you are in the state of ihram. And fear Allah to whom you will be gathered.” [Al-Maa’idah 5:96]
 
Interpretation of this verse is taken as following for the sake of understanding purpose about seafood halal or haram precedent.

“Lawful to you is (the pursuit of) water-game and its use for food – for the benefit of yourselves and those who travel". [Al-Maa’idah 5:96]

So from this it is said that all sea food is halal including all plants and all other animals, the general principle of Islam which defines about each product whether it is haram or not is  

"All type of food and drinks are halal except those which are prohibited”

So for calling a thing haram you must have a proof of prohibition given by Islam. Similarly for getting Halal haram information about any action of life the general rule of Islam is

“All the actions are prohibited unless you have a permission of doing it from Islam".

But here we have few things which live is sea water but not halal which include Crocodile, Frogs, here you can read about the ruling from islam about them.

Crocodiles are not considered halal because they have fangs and can live on land despite of the fact that they spend most of time in water, Crocodile is Haram the precedent for this line is “it is a land animal that has fangs”.

While Frog is also Haram because the Hazarat Muhammad (S.A.W) forbade killing frogs, hadith of ‘Abd al-Rahmaan ibn ‘Uthmaan, who said that the Messenger of Allaah (peace and blessings of Allaah be upon him) forbade the killing of frogs. (Narrated by Imaam Ahmad and Ibn Maajah. The rule which is a precedent here is

“Everything which is forbidden to kill is Haram to Eat in Islam; so if it is allowed to kill then it is allowed to eat”.

Here a point which must be consider by you is that all the things which can harmful is not permitted to eat, even if it is coming from sea. Precedent for this is from quran and is as follow,

“And do not kill yourselves (nor kill one another). Surely, Allaah is Most Merciful to you.” [al-Nisa’ 4:29]