Should I feed fish first day?

First day first fish in the aquarium.
Molly fish
2 males 4 females

I have one Sailfin and he keeps hanging out at the top of the tank and I think he's hungry, don't know if I should feed them though? Just got them in the tank around 3 hours ago

 

I'd give it a go. Some fish will be happy to eat day one, some won't. I usually will drop a few flakes, pellets, whatnot in, and if they go for them, great, and if not, then not a big deal. Even my betta who took a while to adjust to his tank was happy to eat once he went into the tank.

 

I would let them settle in for the first day before feeding them.

However, I see in your profile that you don't know about the nitrogen cycle. This is very important in an aquarium. Basically, fish produce toxic waste and bacteria is needed to make it less toxic however the bacteria needs time to grow. I would recommend returning the fish and start your cycle before getting fish again.

https://www.fishlore.com/NitrogenCycle.htm

Also, how large is the tank? Do you have a heater and filter?

 

I have a 20 gallon tank with the filter and heater set up and i've been letting it sit for almost a week, the girl at the store told me the mollies are pretty hardy fish to start the tank and they seem pretty happy in their new home.. most of them seem to be swimming around exploring, don't seem stressed at all. I added conditioner to the water about 6 days ago and let it filter since. Just the Sailfin seems to be hanging out mostly at the top, looks hungry.

Also the water has been 78 F for a few days, not sure if that's the best temp for mollies? I'm planning on making a community tank eventually.

 

Good job on having a heater and filter

Letting the filter sit doesn't do anything. When you cycle the tank you need to feed the bacteria and let them grow. They're probably relatively fine at the moment, but the toxic waste (ammonia) will accumulate. So while it's true mollies are pretty hardy, they can and do get sick if kept in a poor environment.

You have a few options:
1. Return fish and do a fishless cycle. This is the recommended method since it causes the least stress for you and the fish. Methods are outlined on page 2 of the Nitrogen Cycle link.

2. Do a fish-in cycle. You'll need to do 50% daily water changes. So that's 10 gallons every day with temperature matched, conditioned water. If you use a water conditioner like Prime or Amquel, you can do this every other day. The water changes removes and dilutes the build up of ammonia.

3. Fish-in cycle with bottled bacteria.
A. Tetra SafeStart (TSS) is a popular bacterial additive, however, I think you have too much fish for it to work properly. If you choose to use this you'll need to return 4 of the fish and read these carefully.
https://www.fishlore.com/aquariumfishforum/threads/q-a-with-tetra-about-tetra-safestart.58116/


B. You could also use Seachem Stability. You'll still need to do water changes daily or every other day (depending on whether you use Prime or Amquel), but this will cycle your tank faster. If you want, you could also use this or TSS in a fishless cycle.

Whichever method you choose to use, you'll need a test kit to monitor your cycle. However, a test kit is especially important if you do a fish-in cycle.

As for the temperature, 78F is fine.
You're also pretty close to being fully stocked. What else are you thinking of getting?

 

Some people say to just let them chill and not worry about it the first day. Which makes sense... But I feed mine the first day, usually at least 6 hours after putting them in!

 

Welcome to FishLore!

As mentioned above, I highly recommend you you read up on and fully understand the nitrogen cycle. It is the most important thing to understand when keeping fish. The second most important thing to understand is that 99 out of 100 times the advice you get from the fish store is wrong. (Yeah, I was surprised to learn this also).

BTW, mollies reproduce like rabbits, so prepare for a lot of fry in the not too distant future.

 

I feed on the first day. I don't necessarily know when the lfs fed last. I usually shut the lights out too, because it seems to help the fish settle in.