Every animal which is stipulated by the Shariah to be from those that have to be slaughtered, will only become Halal (permissible to eat) by slaughtered in accordance with Islamic teachings. Fish and locusts are the only expections which are Halal without being slaughtered. Allah swt says in the the Holy Quran.
Expect those which you salughter. (Surah Al Maidah, 5:3)
The Holy Prophet of Allah (pbuh) said,
“two dead animals are Halal for us – fish and locusts.” (Musnad Al Imam Ahmad and other works narrate this from Ibn’Umar (ra).