Caramba! O aquário está vazio.

Portuguese uses definite articles much more often than English. So where English might say The aquarium is empty or even sometimes just Aquarium is empty in a special context, Portuguese normally prefers O aquário está vazio.

In a normal full sentence, leaving out o would usually sound unnatural.

Yes, aquário is masculine, so it takes o:

• o aquário
• um aquário

Many masculine nouns end in -o, and aquário does too, so that helps. But it is still best to learn nouns together with their article, since endings are not a perfect rule in every case.

Portuguese usually uses estar for a condition or state, and ser for identity, essence, or something more permanent.

So:

• O aquário está vazio = the aquarium is empty right now / in this situation
• É vazio would sound odd here, as if emptiness were an essential characteristic

For physical states, location, and temporary conditions, estar is very common.

Because adjectives agree with the noun they describe.

Since aquário is masculine singular, the adjective must also be masculine singular:

• o aquário vazio
• o aquário está vazio

If the noun were feminine, you would use vazia:

• a caixa está vazia

Because vazio is working as a predicate adjective after the verb estar. This is like English is empty.

The structure is:

• subject: O aquário
• verb: está
• adjective: vazio

This is a very common pattern in Portuguese:

• A porta está aberta
• A água está fria
• O quarto está limpo

They mainly show where the stress goes.

• aquário is stressed on quá
• está is stressed on the final tá

So you say roughly:

• a-QUÁ-rio
• es-TÁ

These accents are important in writing because they help with pronunciation and sometimes distinguish words.

A good approximation is ah-KWA-ryoo.

More carefully:

• a as in father
• quá sounds like kwa
• rio here sounds like ree-oo blended together

So: a-QUÁ-rio

For many English speakers, the main thing is to stress the middle syllable: quá.

Yes. In everyday spoken Brazilian Portuguese, está is very often shortened to tá:

• O aquário tá vazio.

This is extremely common in speech and informal writing, but está is more neutral and standard, especially in careful writing.

Yes. Brazilians use many exclamations, and the tone changes slightly depending on the word. For example:

• Nossa! = Wow!
• Uau! = Wow!
• Poxa! = Oh man / gee
• Nossa, o aquário está vazio! = very natural in conversation

Caramba! is natural, but not the only choice.

Yes, it sounds completely natural. A Brazilian might say it exactly this way, especially in a neutral or slightly expressive tone:

• Caramba! O aquário está vazio.

In more casual speech, they might say:

• Caramba! O aquário tá vazio.

Both are natural; the second is more conversational.

It can mean both, depending on context.

• In everyday situations, aquário often means a fish tank.
• It can also mean a public aquarium, like an aquarium building or exhibit.

In this sentence, without more context, most learners would probably imagine a fish tank.