O peixe ornamental está no aquário desde janeiro.

O is the masculine singular definite article, meaning the.

So o peixe ornamental = the ornamental fish.

In Portuguese, articles are used more often than in English, so a sentence like this normally includes o before the noun.

In Portuguese, adjectives often come after the noun.

So:

• peixe ornamental = ornamental fish
• literally, fish ornamental

Some adjectives can go before the noun, but with a descriptive adjective like ornamental, the most natural position is after the noun.

Portuguese has two main verbs for to be: ser and estar.

Here, está is used because the sentence talks about the fish’s location:

• estar = used for location, condition, and temporary states
• ser = used for identity, permanent characteristics, origin, etc.

So:

• O peixe está no aquário. = The fish is in the aquarium.
• Using é here would sound wrong for location.

Está is the third person singular form of estar in the present tense.

It can mean:

• is
• is being in some contexts

In this sentence, it means is:

• O peixe ornamental está no aquário = The ornamental fish is in the aquarium

Because o peixe is singular, the verb is singular too: está.

No is a contraction:

• em
  • o = no

So:

• no aquário = in the aquarium

Portuguese commonly contracts em with definite articles:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

So em o aquário is not the normal form. The correct form is no aquário.

Because Portuguese usually uses an article with nouns in cases where English often does too, and sometimes even where English does not.

Here, o aquário means the aquarium, and after the contraction with em, it becomes no aquário.

So the structure is:

• estar em o aquário → estar no aquário

Desde janeiro means since January or from January onward.

It tells you the starting point of a situation that began in the past and continues into the present.

So the sentence implies:

• the fish has been in the aquarium since January
• and it is still there now

That continuing idea is very important.

This is a very common difference between English and Portuguese.

Portuguese often uses the present tense with desde to express a situation that started in the past and still continues now.

So:

• O peixe ornamental está no aquário desde janeiro.

is literally The ornamental fish is in the aquarium since January, but in natural English we usually say:

• The ornamental fish has been in the aquarium since January.

So the Portuguese present tense can correspond to the English present perfect in this kind of sentence.

In Portuguese, the names of months are normally written with a lowercase letter.

So:

• janeiro = January
• fevereiro = February
• março = March

This is different from English, where month names are capitalized.

The accents mostly help show stress and pronunciation.

• está: the accent shows the stress falls on the last syllable: es-TÁ
• aquário: the accent shows the stress falls on QUÁ: a-QUÁ-rio

Accent marks in Portuguese are important because they can change pronunciation and sometimes distinguish words.

In Brazilian Portuguese, peixe is pronounced approximately like PAY-shi.

A rough guide:

• pei sounds like pay
• xe sounds like shee or shi

So peixe ornamental sounds roughly like:

• PAY-shi or-na-men-TAW

The exact sound depends a little on accent and region, but that approximation is helpful for learners.

Yes, sometimes, but the original order is the most neutral and natural:

• O peixe ornamental está no aquário desde janeiro.

You might hear a variation like:

• Desde janeiro, o peixe ornamental está no aquário.

That puts extra focus on since January.

But for a normal statement, the original order is the best choice.

You would usually change no aquário to em um aquário:

• O peixe ornamental está em um aquário desde janeiro.

Why?

• no aquário = in the aquarium / in the fish tank
• em um aquário = in an aquarium / in a fish tank

So the difference is definite vs. indefinite:

• o / no = the
• um / em um = a / an

It can mean both, depending on context.

Aquário can refer to:

• a home fish tank
• a larger aquarium, such as a public aquarium

In this sentence, many learners will understand it as fish tank, because that is the most everyday interpretation. Context would tell you which meaning is intended.