When you've got all those fish schooled up shoulder to shoulder....their agression/dominance levels are maxing out. You see all those mouth flashes and body flashes...agression/dominance communication. They will bite eggs or egg like looking baits because they don't want someone elses progeny to survive. They also bite at each other...thats where black yarn comes into play. Two colors are dominant in this communication and agression...Black and white. Black pisses them off and they bite at it.

gooose laugh