People fly with their animals often, which is why one student was upset when Southwest Airlines wouldn’t allow her pet fish on her flight.Lanice Powless, a student at the University of Colorado, was trying to fly with her pink betta fish, Cassie, from California to Denver. After arriving at the airport with Cassie in tow, she discovered that Southwest Airlines wouldn’t let her board the plane with her pet fish.MORE Airlines & Airports Powless tried to leave her pet fish at the Southwest counter for a friend to pick up within 30 minutes, but the airline wouldn't allow it. She asked a stranger, a passenger on another airline, to hold the fish until her friend arrived. Powless never got the person’s name and it's unclear where the fish is now.Powless claims she’s brought her fish onto planes before without any issue.It’s true that some airlines allow pet fish to board planes. Even the Transportation Security Administration says live fish can travel in carry-on bags in clear containers. They cannot be placed in checked luggage.However, Southwest Airlines’ website states that only small cats or dogs are allowed to travel on their aircrafts.In a statement to USA TODAY, a Southwest representative said, "A Customer attempted to bring a pet fish onboard their flight from Denver to San Diego. Our Customer Service Agents informed the Customer about Southwest’s pets policy which does not allow for live fish to travel in the passenger cabin.”“Our Team offered to re-book the Customer for a later flight to allow them to make arrangements for their pet but the Customer refused that option. The Customer eventually traveled on their originally scheduled flight."