Muraena et mugil prope saxa natant.

Because the subject is actually two nouns joined by et: muraena et mugil = the moray eel and the mullet.

In Latin, just as in English, two singular subjects joined by and usually take a plural verb:

• muraena natat = the moray eel swims
• mugil natat = the mullet swims
• muraena et mugil natant = the moray eel and the mullet swim

So natant is the correct 3rd person plural form.

They are both in the nominative singular, because they are the subject of the sentence.

• muraena = nominative singular
• mugil = nominative singular

Even though the two words together make a compound subject, each noun itself is singular.

Because prope is a preposition that takes the accusative case when it means near or close to.

So:

• prope saxa = near the rocks

The noun saxum means rock or stone. Its accusative plural is saxa.

This is a very common thing to notice in Latin: prepositions often require a specific case, and prope takes the accusative.

Saxa is the neuter plural form of saxum.

The pattern is:

• saxum = rock, stone
• saxa = rocks, stones

This is a standard 2nd-declension neuter pattern:

• singular nominative/accusative: -um
• plural nominative/accusative: -a

So prope saxa means near the rocks, not near the rock.

Because Latin has no definite article and no indefinite article.

So Latin does not have separate words for:

• the
• a
• an

That means a sentence like Muraena et mugil prope saxa natant can be translated depending on context as:

• The moray eel and the mullet swim near the rocks
• A moray eel and a mullet swim near rocks

In most teaching contexts, the English translation uses the because it sounds more natural.

Yes. Latin word order is much more flexible than English word order because the grammar is shown largely by endings, not just by position.

So all of these could mean basically the same thing:

• Muraena et mugil prope saxa natant.
• Prope saxa muraena et mugil natant.
• Natant prope saxa muraena et mugil.

The original order is straightforward and natural, but Latin often moves words around for emphasis, style, or rhythm.

Et means and. It joins muraena and mugil into one compound subject:

• muraena et mugil = the moray eel and the mullet

It is one of the most common Latin conjunctions.

Not always, but in this sentence it is clearly a preposition.

Here it introduces a noun phrase:

• prope saxa = near the rocks

So in this sentence, prope functions just like an English preposition such as near.

Natant is:

• present tense
• active voice
• indicative mood
• 3rd person plural

Its basic meaning is they swim.

The singular form would be natat = he/she/it swims.

So:

• muraena natat = the moray eel swims
• muraena et mugil natant = the moray eel and the mullet swim

Because they belong to different declensions.

• muraena is a 1st-declension noun
• mugil is a 3rd-declension noun

Latin nouns do not all follow the same pattern. English speakers often expect nouns to behave more uniformly, but in Latin the ending depends on which declension the noun belongs to.

That is why two singular subject nouns can look quite different even though they are doing the same job in the sentence.

You learn it from the noun’s dictionary form and declension pattern.

With 3rd-declension nouns, the nominative singular often has a less predictable ending. So mugil is simply the nominative singular form of that noun.

This is normal in Latin. Not every nominative singular will have a very transparent ending. Over time, learners get used to recognizing common 3rd-declension patterns.

Yes. In Latin, neuter nouns have a very important pattern:

• nominative and accusative are always the same
• in the plural, those forms usually end in -a

So for saxum:

• nominative singular: saxum
• accusative singular: saxum
• nominative plural: saxa
• accusative plural: saxa

That is why saxa could be either nominative plural or accusative plural in form. In this sentence, it must be accusative plural because prope requires the accusative.

Yes. For example:

• Natant muraena et mugil prope saxa

would still be understandable. Latin often places the verb at the end, but that is a tendency, not a strict rule.

In your sentence, putting natant last is a very common and beginner-friendly arrangement.