The blackspot angelfish and the sex change...

Angelfish are one of the most commonly kept freshwater aquarium fish, as well as prized for its unique shape, color and behavior. Angelfish pairs form long-term relationships where each individual will protect the other from threats and potential suitors. Upon the death or removal of one of the mated pair, breeders have experienced both the total refusal of the remaining mate to pair up with any other angelfish and successful breeding with subsequent mates.

The blackspot angelfish can change from a female to male but this happens for a specific reason....

The angelfish live in groups with a single male, which is blue in color and four female fish which are yellow in color. The male is stronger and largest member in the group protecting the others acting as a "security guard".

When the male dies, the group needs a "security guard". This is when the largest female fish in the group begins to change its appearance. She starts growing larger in size and changing its color to blue. Slowly her behavior changes and begins to behave like a male. Two weeks later, the black strips appear on her body. This indicates the completeness of the sex change.

Now she is completely a male~~~