When they spawn, the male wraps himself around the female and squeezes out the tiny eggs, which he fertilizes and puts into the bubble nest. The eggs are almost invisible, so any that looked large may have been infertile and fungused over. The way things usually work is the female gets put into another aquarium as soon as they're done spawning. The male then tends the eggs and nest until the fry are free swimming, at which time he gets removed before he eats all the babies. Aquarium raised fish, especially ones that are inbred to achieve certain features, lose some of their instincts and other natural equipment, so they don't always respond correctly to the procreation urge.
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