Is the word mariscos the same in Brazilian and European Portuguese?

No.

The difference lies in typical usage and semantic scope. In Brazil, "mariscos" (plural) is often used to refer to specific types of mollusks or shellfish, while the broader category of all seafood (including fish and cephalopods like squid) is typically called "frutos do mar." In Portugal, "marisco" (singular/collective) is the standard term used to represent the entire category of shellfish, encompassing both crustaceans and mollusks. Additionally, a Portuguese speaker is much more likely to use the singular form "marisco" to describe the category as a whole.

Brazilian Portuguese

1. Eu adoro comer mariscos na praia. (I love eating shellfish at the beach.)
2. Esse restaurante tem os melhores mariscos da cidade. (This restaurant has the best shellfish in town.)
3. Vamos pedir uma porção de mariscos para dividir? (Shall we order a portion of shellfish to share?)
4. O preço dos mariscos subiu muito este mês. (The price of shellfish has gone up a lot this month.)
5. Eu não gosto de mariscos, prefiro peixe. (I don't like shellfish, I prefer fish.)

European Portuguese

1. Adoro comer marisco à beira-mar. (I love eating shellfish by the seaside.)
2. Este restaurante serve um marisco fresquíssimo. (This restaurant serves very fresh shellfish.)
3. Vamos pedir um prato de marisco para partilhar? (Shall we order a shellfish dish to share?)
4. O preço do marisco está muito caro ultimamente. (The price of shellfish is very expensive lately.)
5. Não gosto de marisco, prefiro peixe. (I don't like shellfish, I prefer fish.)