The nose knows...

Let's see what other little tidbit can I tell you about a koi's anatomy? Smell?? In humans taste is waterborne and smell is airborne. In Koi of course it's all waterborne, so the distinction is blurred. Koi have narels on their heads just forward of their eyes. Some koi will display large almost fluffy, tuffs of skin around their nasal receptors. Taste can occur in the mouth, on barbels, or elsewhere on the body. Less appreciated is the role of chemoreception in behavior and orientation. Detection of pheromones is important in breeding and schooling.
Salmon use acute chemoreception in homing in their birth place. When salmon are small in their home stream, they imprint on the subtle unique odors that the watershed gives that particular stream. After migrating downstream and living for years in the ocean, they are able to "sniff" their way home. If the natural stream odors are overwhelmed by a smelly substance, the salmon will imprint on that and later home to wherever the researchers dispense the odoriferous substance. Another experiment showed that blinded salmon could find their way home, but salmon with their nares plugged could not. ( reference to all this can be found in Fundamentals of Ornamental Fish Health, by Helen Roberts)