Questions & Answers about Fiskurinn er gulur.
The suffix changes according to gender, number and case, but here are the nominative forms in the singular and plural:
• Masculine singular: -inn (fiskur → fiskurinn)
• Feminine singular: -in (móðir → móðirin)
• Neuter singular: -ið (hús → húsið)
• Masculine plural: -arnir (fiskar → fiskarnir)
• Feminine plural: -urnar (stúlkur → stúlknar)
• Neuter plural: -in (hús → húsin)