Assalaamu Alaykum Wa Rahmatullaahi Wa Barakaatuhu
From seafood, only fish is made Halaal for us. Rasulullah (Sallallaahu
Alayhi Wasallam) said, 'Two carions are made Halaal for us; Fish and locust.
' (Mishkaat vol.2 pg.361).
Fish is classified as a Vertebra. Shrimps and lobsters are not vertebras, hence, not permissible.
Some Ulama are of the opinion that shrimps, etc. are fish, therefore,
permissible. Due to the differences of opinion, it is best to adopt Taqwa
and abstain from eating shrimps, etc. but they cannot be regarded as swine
meat which is expressly Haraam.
and Allah Ta'ala Knows Best
Mufti Ebrahim Desai