Panama's position between two oceans and with coastline on both means seafood is a constant and generally excellent. The Pacific brings corvina, red snapper, and shellfish; the Caribbean brings lobster and coconut-based preparations. Ceviche is the defining street food: corvina (white sea bass) cut into small pieces and dressed with lime juice, thinly sliced white onion, and ají chombo — a Panamanian Scotch bonnet variety that adds real heat. It is served cold, eaten with saltines, and found everywhere from street stalls to fine restaurants.
The Mercado de Mariscos near the Casco Viejo is the best place in the city for fresh ceviche at market prices. The ground floor is a functioning fish market; the upper floor is a dozen small stalls where you can eat a bowl of ceviche or a plate of seafood with cold beer for a few dollars. It is popular with locals and with visitors who know about it, lively on weekend lunchtimes, and one of the more honest eating experiences in the city.
Beyond ceviche: arroz con mariscos (rice cooked with mixed seafood, closer to a Caribbean-style preparation than a Spanish paella), patacones con ceviche (fried green plantain used as a scoop or base), and camarones al ajillo (garlic prawns) are the reliable orders.