Mrs. Puff

A common problem

Lamp-murders are a serious problem in Bikini Bottom

In the episode, they show a pufferfish made into a lamp (like how they sell dead sea creature knick knacks in beach giftshops), so the theory is that Mrs. Puff killed her husband and made him into a lamp.

I always thought that he had gotten caught at the "carnival" and Mrs. Puff never saw him again...