Like other cardinalfish, spotnape cardinalfishes (Ostorhinchus notatus) are paternal mouthbrooders. When a pair of fish are ready to spawn, male and female align side-by-side. As the female pushes out a cluster of eggs, the male fertlizes them, then rapidly moves behind the female to take the eggs into his mouth for brooding. Pictured here is the moment of transfer, with the male below the female, taking the cluster of fertilized eggs into his mouth. At 100% magnification, the eggs that are still inside the female and are just about to emerge are visible. Once the transfer of eggs is accomplished, the male will care for the eggs until maturity. The gestation period varies with water temperature, but hatchout takes place after approimately two weeks. Females in this situation eventually leave the male, but they first exhibit an odd behavior after laying eggs. They appear to harass the male, chasing him and targeting the eggs in his mouth. While avoiding these charges by the female, the male spits out and takes the eggs back into his mouth multiple times. This occurs at blinding speed. The purpose of this post-coital behavior is not clear. It appears almost as if the female is attempting to steal the eggs from the male.
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