Fissura literally means "fissure" or "crack," but in Brazilian Portuguese slang, it also means an intense craving or obsession.
In the context of the song, the singer is describing his intense desire and longing to find his love, the "morena," in the streets of Salvador. It's a unique and evocative word that captures the depth of his yearning.
Banda Eva turn a Carnival crush into a whole song. The verses are one man losing someone in the crowd: “Foi difícil te encontrar, morena” (It was hard to find you, brunette), “Nas ruas de Salvador, fissura” (In the streets of Salvador, obsession), until he gives up — “Me cansei de procurar, que pena” (I got tired of looking, what a shame). Then the avenida itself answers him: “Vejo um brilho diferente pintando na avenida” (I see a different glow painting the avenue), “Vem trazendo um colorido de festa pra Bahia” (bringing party colours to Bahia), and in that light he finally spots her.
The chorus is what everyone actually shouts back. “Eu vou, eu vou, eu vou no Eva” (I'm going, I'm going, I'm going with Eva) is a call and “Eu também vou, eu vou no Eva” (I'm going too, I'm going with Eva) is the answer — Eva being the band's own bloco, the moving block of people that pulls a trio elétrico through Salvador. This live Belo Horizonte recording keeps the trade going for the last minute of the track, which is why the song works better as a crowd chant than as a love story.