O aquário precisa de oxigenação.

In Portuguese, it is very common to use a definite article with a noun when talking about a specific thing or when the context makes it clear which thing you mean.

So:

• O aquário precisa de oxigenação. = The aquarium needs oxygenation.

If you just say Aquário precisa de oxigenação, it can sound more like a general statement headline, label, or note rather than a normal full sentence in everyday speech.

Because the verb precisar normally takes de before a noun.

• precisar de algo = to need something

So:

• O aquário precisa de oxigenação.
• Eu preciso de ajuda.
• Eles precisam de água.

This is one of the most important patterns to remember:

• precisar de + noun

But when precisar is followed by another verb, Portuguese usually does not use de:

• O aquário precisa funcionar bem.
• Eu preciso estudar.

So in your sentence, oxigenação is a noun, which is why de is required.

Oxigenação means oxygenation or, in a more natural aquarium context, aeration / oxygen supply.

It is a noun formed from oxigênio (oxygen). In practical use, this sentence means the aquarium needs better oxygen in the water or a process/system that oxygenates it.

Depending on context, Brazilian Portuguese speakers might also say:

• O aquário precisa de mais oxigênio.
• O aquário precisa de aeração.

All of these are possible, but oxigenação sounds a bit more technical or formal.

Because grammatical gender in Portuguese does not always depend only on the final letter, although -o often does suggest masculine.

Here the noun is:

• o aquário = masculine singular

So the article must match:

• o aquário
• os aquários

You generally just learn the noun together with its article.

Because abstract or general nouns often appear without an article in Portuguese, especially after expressions like precisar de.

So:

• precisa de oxigenação = needs oxygenation

This sounds natural and general.

If you added an article, it would usually make the meaning more specific:

• precisa da oxigenação adequada = needs the proper oxygenation
• precisa de uma oxigenação melhor = needs better oxygenation / a better level of oxygenation

Without an article, the sentence sounds broad and natural.

A good approximation is:

• aquário → ah-KWA-ryoo

The stress is on QUÁ.

A few pronunciation notes for Brazilian Portuguese:

• aquá sounds like ah-KWA
• the r in the middle is softer than English r
• the final -io sounds like yoo

A good approximation is:

• oxigenação → oh-shee-jeh-nah-SOWN in many Brazilian accents

The stress is on the last syllable: ÇÃO.

A few helpful notes:

• xi often sounds like shee in Brazilian Portuguese
• ge sounds like zheh or jeh, depending on how you approximate it
• ção is a very common ending, sounding roughly like sown but nasalized

They show the stressed syllable.

• aquário → stress on QUÁ
• oxigenação → stress on ÇÃO

This is very helpful because Portuguese stress is not always predictable from spelling alone.

The accent mark does not just decorate the word; it tells you where the voice should naturally fall.

Yes. That is correct.

• precisar de = to need
• necessitar de = to need

So:

• O aquário precisa de oxigenação.
• O aquário necessita de oxigenação.

Both are grammatical, but precisar is more common and more everyday.

Yes, and that may even sound more natural in some everyday contexts.

Compare:

• precisa de oxigenação = needs oxygenation / aeration
• precisa de oxigênio = needs oxygen

The first focuses more on the process or condition. The second focuses more directly on the oxygen itself.

In aquarium talk, both can work depending on what exactly you mean.

It can mean both.

In Brazilian Portuguese, aquário can refer to:

• a home aquarium / fish tank
• a public aquarium

Context tells you which one is meant.

In your sentence, most people would probably understand it as a fish tank unless the context suggests a large public aquarium.

It would be:

• Os aquários precisam de oxigenação.

Changes:

• o → os
• aquário → aquários
• precisa → precisam

So the pattern is:

• singular: O aquário precisa de oxigenação.
• plural: Os aquários precisam de oxigenação.

Portuguese does allow some flexibility, but the normal, neutral order is:

• O aquário precisa de oxigenação.

That is the most natural version.

Other word orders are possible in special contexts, but they may sound poetic, emphatic, or unnatural for a beginner. So this is the best order to learn and use first:

• subject + verb + complement