As-salamu alaykum,
Surah Al-Ma'idah (Chapter 5) Verse 96:
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.
From my understanding it can be derived that almost all sea-food is halal but there are few exceptions to be avoided according to different madhabs
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According to the Hanbaliy and Shafi'ee scholars, all living creatures that live in the sea are halal, whether they are in the form of a fish or not. (Fiqh alal Madhaahib al-Arbaa). Based on this, oyster, oyster extract, shrimp, lobster and shark are all halal and permissible.
According to the Maliki scholars, every living creature of the sea is halal except eel. (Ibid) Hence, oyster, oyster extract, shrimp, lobster and shark are halal and permissible.
According to the Hanafi scholars, the only living creatures of the sea that are permissible are those that are in the form of a fish with an exception of the hagfish and eel. (Ibid). (these 2 even though they are not in the form of a fish they will be permissible to consume).
Hence, according to the Hanafi scholars, it will not be permissible to eat oyster, oyster extract, shrimp and lobsters. It will be permissible to consume shark as it is in the form of a fish.
I hope this clears your doubts.
And Allah (s.w.t.) knows best.
Salam 3laikum