The endings of the vocative case are the same as the nominative case for all nouns in all genders and number, except for singular masculine 2nd declension nouns, ending in -us/-ius.
If the noun ends in -us, the vocative singular ending is -e.
If the nouns ends in -ius, the vocative singular ending is -ī.
EXAMPLE
Marcus, ī → Marce Fīlius, ī → Fīliī