As the title said, I have finished the entire questline up to the final quest, as shown in the attached screenshot.

However, it says that I need 4 iridescent shellfish in order to get the fish tank. I am not sure what happened but I only have 1 iridescent shellfish in my entire account. My fishing level is at Master 12. 

I submitted a ticket too to seek help, but didn't get any reply after 5 days. So I'm here trying out my luck in the forum.