We've officially moved beyond the eternal "do fish feel pain?" question to discover the unique types of bad vibes that fish can feel. A new study suggests that fish can get the blues, get in a funk, or otherwise feel down after they lose their partner. 

French researchers found that a type of fish known as the Convict Cichlid became more pessimistic and down after losing a mate. 

They figured this out in a study with two parts. In the first, they placed a female fish in a compartmentalized tank with a male fish on either side. When she showed preference for a male, the researchers would either pair the fish with its preferred mate or with the other male. 

In a second test, they trained fish to push the lids off of small clay boxes. A white box contained food, a black box contained nothing. After the fish got the hang of it, they introduced a grey box to the test. Researchers found that fish who had been paired with their preferred beau were more willing to try and open the box, suggesting an optimistic worldview. Those who hadn't, meanwhile, were unlikely to try it.

“Females that were assigned their non-preferred partner exhibited pessimistic bias which indicates a negative affective state,” researchers from the University of Burgundy wrote. 

“Emotional attachment to a partner is not a unique property of our species, since it has also evolved in at least one other species,” François-Xavier Dechaume-Moncharmont, an author on the study, told The Guardian. “It could indicate that these emotional biases are more than biases. Love is maybe not so irrational.”