Flowerhorns locking lips and butting heads
The owner of these flowerhorns claims both are alive and well despite the initial aggressive he captured on video. Flowerhorns are known as very aggressive fish, so it's generally not advisable to keep more than one per tank, and certainly not the best idea in a tank this small. There are a scary number of videos showing flowerhorns fighting with other flowerhorns, arrowanas, jack dempseys, oscars, red devils, etc.
A curious red blood parrot cichlid might be the best part of the whole video. When it's not photobombing with its cute puffy face, it watches the whole awkward Flowerhorn kiss with keen interest. Blood parrots are another man-made hybrid but with a much more docile personality.
A quick genealogical rundown for Flowerhorns (and for those who have a bone to pick with fancy goldfish and designer clownfish, you may want to skip the next two paragraphs): They are a relatively new hybridized cichlid that does not occur in the wild. Originating in the early 1990s, it is believed Asian breeders crossed trimac cichlids (Amphilophus trimaculatus) with red devil cichlids (e.g. Amphilophus labiatus) with who-knows-what-other-cichlids. The truth is no good documentation exists on the origins of Flowerhorns so their genealogy is murky at best. They are a mish-mash Frankenstein of whichever cichlid could yield desirable traits.
Breeders in Malaysia and Taiwan coveted fish with protruding heads. Through selective breeding, they were able to create Flowerhorns with highly exaggerated forehead humps. These protrusions are fat stores called "koks" and were first developed in males, although lesser koks are developing in females of certain strains as well. The bigger a male's kok, the more desirable the fish. <snicker> Spectacular specimens can command prices in the thousands of dollars. Successive generations have created bigger and bigger koks.