Take a look at the passage again:
Marina, the beautiful mermaid, wanted some tuna salad.
But had a small problem since she was allergic
to celery. At Sammy’s Sub Shop, Marina hoped to find tuna salad free of this
dangerous vegetable. Flopping across the tiled floor to the counter. Marina
placed her order and then checked her sandwich for celery. Not noticing, however,
the spoiled mayonnaise. At five o'clock that evening, Marina became violently
ill with food poisoning. When a lifeguard at the beach discovered the problem,
he called 911. Even though the mermaid had fishy breath. A handsome paramedic
gave her mouth-to-mouth resuscitation. Wailing like a sick dog, the ambulance
sped off to the hospital. Where the doctor on call refused to treat a sea creature
with a scaly tail. A kind nurse, however, had more sympathy. After she found
some Pepto-Bismol. Marina drank the entire bottle of pink liquid, feeling an
immediate improvement. The mermaid told the rude doctor never to swim in the
ocean. For she would order hungry sharks to bite off the doctor's legs. While
sharp-clawed crabs plucked out his eyes. Tossing her long hair, Marina thanked
the nurse for the Pepto-Bismol. And took a mint from David, the handsome paramedic.
A fragment will not contain a main clause. A main clause follows this pattern:
Subject + verb = complete thought.
In the highlighted item, Marina is the subject, and wanted is the verb. This pair makes a complete thought, so you do indeed have a main clause here. This item is a sentence, not a fragment.