Le pregunté a la veterinaria si mi pez necesitaba otro acuario más grande.

Because le is the indirect object pronoun, and a la veterinaria names who that pronoun refers to.

In Spanish, it is very common to use both:

• the pronoun: le
• and the full noun: a la veterinaria

So Le pregunté a la veterinaria... literally has both:

• le = to her
• a la veterinaria = to the vet

This is called clitic doubling, and it sounds natural in Spanish.

So the sentence structure is basically:

• Le pregunté = I asked her
• a la veterinaria = the veterinarian
• si... = whether/if...

You could think of it as:

• I asked the veterinarian... in English
• but in Spanish, very often: I asked her, the veterinarian...

Because with preguntar meaning to ask someone, Spanish uses a before the person.

The pattern is:

• preguntar algo a alguien = to ask someone something
• preguntar a alguien si... = to ask someone whether...

So:

• Le pregunté a la veterinaria si... = I asked the veterinarian whether...

This a is required because the person is the indirect object.

Compare:

• Pregunté la hora = this sounds wrong
• Pregunté la hora al recepcionista = I asked the receptionist the time
• Pregunté al recepcionista si estaba abierto = I asked the receptionist if it was open

Yes. In this sentence, si means if or whether.

After verbs like preguntar, Spanish often uses si to introduce an indirect yes/no question.

So:

• Le pregunté a la veterinaria si mi pez necesitaba otro acuario más grande. means
• I asked the veterinarian if/whether my fish needed another larger aquarium.

Important: this si has no accent.

Do not confuse it with:

• sí = yes

So:

• si = if / whether
• sí = yes

Because pregunté refers to a completed action in the past: you asked the vet, and that action is finished.

The preterite is very common for a single completed event:

• pregunté = I asked
• llamé = I called
• fui = I went

In this sentence, the act of asking is seen as one whole completed event.

If you used the imperfect, preguntaba, it would usually suggest:

• a repeated action,
• an ongoing background action,
• or something habitual.

So here:

• Le pregunté... = I asked her... once, as a finished event.

Because the sentence is reporting what the speaker asked about a situation in the past, not about a completed single action by the fish.

Necesitaba presents the fish’s need as a state or ongoing situation:

• whether my fish needed a bigger aquarium

That is exactly the kind of thing the imperfect is often used for:

• background situations
• ongoing conditions
• states in the past

Using necesitó would sound more like:

• the fish did need it at one specific completed moment

But here the idea is more natural as a condition/state:

• Did my fish need a bigger tank? So Spanish uses:
• necesitaba

This contrast is common:

• Le pregunté si estaba bien. = I asked if he/she was okay.
• Le pregunté si tenía fiebre. = I asked if he/she had a fever.
• Le pregunté si necesitaba otro acuario. = I asked if it needed another aquarium.

It means another bigger aquarium or another aquarium that is bigger.

Break it down:

• otro = another / a different
• acuario = aquarium / fish tank
• más grande = bigger / larger

So the idea is not just a bigger aquarium, but a different aquarium, one that is bigger than the current one.

That is why otro is important. It suggests replacement:

• not the same aquarium
• but a new one, and that new one should be larger

So:

• un acuario más grande = a bigger aquarium
• otro acuario más grande = another aquarium, a bigger one

Because in Spanish, descriptive adjectives usually come after the noun.

So:

• un acuario grande = a big aquarium
• un acuario más grande = a bigger aquarium

This is the normal position.

English usually puts adjectives before the noun:

• a big aquarium
• a bigger aquarium

Spanish usually puts them after:

• un acuario grande
• un acuario más grande

With más + adjective, the same pattern stays:

• una casa más pequeña = a smaller house
• un coche más rápido = a faster car
• otro acuario más grande = another larger aquarium

Yes, you could, but the meaning changes slightly.

• un acuario más grande = a bigger aquarium
• otro acuario más grande = another aquarium, a bigger one

Otro makes it clearer that the fish would need a different aquarium from the one it already has.

Without otro, the sentence still makes sense, but it focuses more simply on size:

• si mi pez necesitaba un acuario más grande = if my fish needed a bigger aquarium

With otro, the idea is:

• it needs a new tank instead of the current one, and that new tank should be bigger

In this sentence, la veterinaria most naturally means the female veterinarian.

That is because the sentence says:

• Le pregunté a la veterinaria... which strongly suggests a person you asked.

Spanish often marks gender in job titles:

• el veterinario = the male veterinarian
• la veterinaria = the female veterinarian

It is true that in some contexts la veterinaria can also refer to the vet’s office / veterinary clinic, especially in everyday speech. But here, because you are asking someone, it clearly means the person.

Because mi pez is the subject of the clause mi pez necesitaba...

In:

• si mi pez necesitaba otro acuario más grande

the fish is the one doing the needing, so it is the subject:

• my fish needed...

Spanish does not use the personal a with subjects.

The personal a is used mainly with direct objects that are people (and sometimes pets or personified beings), not with subjects.

So:

• Mi pez necesitaba otro acuario = My fish needed another aquarium but:
• Vi a mi perro = I saw my dog

Here, mi pez is not an object; it is the subject of necesitaba.

This is a very common question.

In Spanish:

• pez = fish when it is alive, especially as an animal in water
• pescado = fish as food, or fish that has been caught

So in this sentence:

• mi pez is correct, because it means my fish as a living pet

Examples:

• Tengo un pez rojo. = I have a goldfish.
• El pez nada en el acuario. = The fish swims in the aquarium.
• Me gusta comer pescado. = I like eating fish.

You would not normally say mi pescado for a pet fish.

The accent shows the correct stress and also distinguishes the form.

Pregunté is the first-person singular preterite:

• yo pregunté = I asked

Without the accent, pregunte, it would usually be a different form:

• present subjunctive or formal command, depending on context

Compare:

• pregunté = I asked
• pregunte = that I ask / that you ask, or ask! to usted

So the accent is important.

Because Spanish does not choose tense just based on past vs present. It also cares about how the action or situation is viewed.

Both pregunté and necesitaba are in the past, but they are different past tenses:

• pregunté = preterite, a finished action
• necesitaba = imperfect, an ongoing state or background situation

So the sentence mixes two past tenses very naturally:

• I asked = completed event
• whether my fish needed = ongoing condition at that time

This is extremely common in Spanish:

• Le pregunté si estaba cansado.
• Le pregunté si tenía hambre.
• Le pregunté si vivía allí.

The asking is a completed act; the other verb describes the situation being asked about.

Not in this structure.

If you want to say my fish needed another bigger aquarium, Spanish uses:

• mi pez necesitaba otro acuario más grande

You would not say:

• mi pez necesitaba para otro acuario más grande
  or
• necesitaba para mi pez... in this sentence

That is because necesitar directly takes the thing needed:

• necesitar algo = to need something

So:

• mi pez necesitaba otro acuario not
• mi pez necesitaba para otro acuario

If you wanted to restructure the idea, you could say something like:

• Le pregunté a la veterinaria si necesitaba un acuario más grande para mi pez. This would mean:
• I asked the veterinarian if I needed a bigger aquarium for my fish.

That changes the grammar and slightly shifts the point of view.

The given order is very natural:

• Le pregunté a la veterinaria si mi pez necesitaba otro acuario más grande.

Spanish does allow some flexibility, but not all changes sound equally natural.

For example, these are also possible:

• A la veterinaria le pregunté si mi pez necesitaba otro acuario más grande.
  • This puts extra emphasis on a la veterinaria.
• Le pregunté si mi pez necesitaba otro acuario más grande a la veterinaria.
  • Grammatically possible, but less natural in many contexts.

The most neutral order is the original one:

• pronoun first: le
• then the person: a la veterinaria
• then the indirect question: si...

So learners should treat the original sentence as a very good standard model.