Should it be "Issa, kodra iēdri mōzun." because "iēdri" is plural?
iēdar is an embar-type aquatic noun, which means the nominative plural and the accusative singular forms are identical (iēdri). Since the noun in this case is "I", it is pretty clear that it's the accusative singular, not the nominative plural.
Right, I forgot that "ieedri" is accusative singular as well.