Final answer:
A male swordtail fish with a longer tail fin is more likely to be selected by a female and consume less oxygen while swimming.
Step-by-step explanation:
A male swordtail fish with a tail fin longer than its rivals is more likely to be selected by a female and to consume less oxygen while swimming.
This is because a longer tail fin is considered an attractive secondary sexual characteristic, which may increase the male's chances of mating with a female.
Additionally, a longer tail fin may provide better maneuverability in the water, allowing the male to swim more efficiently and consume less oxygen.