Best Saltwater Fish for a 125 Gallon Tank

If you have acquired, or are at least in the market for a 125-gallon saltwater aquarium, be prepared for a magical experience.

These fish tanks are huge in size which means that they can host an abundance of saltwater fish, ranging vastly in size, appearance, and quantity.

Obviously, owning a tank of this size and stature will require a lot of room and a lot of experience in keeping larger saltwater fish tanks, and complex saltwater fish.

However, if you have the experience, room, and ambition, be prepared to unlock the next level in saltwater fishkeeping!

But first of all, we need to talk about the dimensions, to ensure they are compatible with your home, apartment, or desired place for your new tank.

125 Gallon Fish Tank Dimensions

Typically, 125-gallon tanks come in the same size, or at least very similar dimensions.

The dimensions that you will likely get for your 125-gallon tank are 72" (length) x 19" (width) x 21" (depth), which are the equivalent of 182.9 cm x 45.7 cm x 53.3 cm.

Oh, not to mention that the weight of a 125-gallon aquarium when empty will usually be 206 lbs (93.4 kg), and when full it will be around a whopping 1,405.3 lbs (637.4 kg) - pretty heavy, right?

Below is a graphical representation of the typical 125-gallon tank dimensions.

How to Choose the Best 125 Gallon Saltwater Fish

We understand that the fish featured on our list may not all be exactly what you are looking for, and that is totally fine, it is personal preference.

However, we have hand-picked what we know are the most ideal ones, and you should still look for fish that fit a certain criteria if you want to give them the best and happiest life possible in a 125-gallon tank.

Something else that is important to note is that saltwater fish for a 100-gallon tank or less are more than compatible with a 125-gallon fish tank.

Here are the criteria to be aware of before stocking your 125-gallon tank:

  • You should aim for peaceful/semi-aggressive fish, that for the most part, play well with others. Due to the size of the tank, peaceful fish can hide and swim away from aggressive ones, but you still don't want to cause too much stress.
  • They should also be community fish, and reef-safe, meaning that they thrive in large, reef communities, teaming with life.
  • Thanks to the tank being so big, you can keep small, medium, and large fish, ranging from 5 to 15 inches (12.7 to 38 cm).
  • The fish you add to this 125 gallon aquarium should also be hardy, meaning that they are not prone to disease.
  • And lastly, they should be brightly colored! Who doesn't want a home or office aquarium showcasing incredible patterns and colorations?

Saltwater Fish for a 125 Gallon Aquarium

Down below is our list of the best fish to keep in a 125 gallon saltwater fish tank.

You can safely keep a combination of the fish listed below, but we recommend keeping a sensible amount of each, and for you to look at the sizes of each to work out how many to keep.

To make life easier, we have only featured fish that have the same, or similar temperature requirements to one another, making them more than compatible with each other, and your job a little easier.

It is important, however, that you match the difficulty care level and tank maintenance of each fish to your own experience level, but you should be an experienced hobbyist if you are acquiring a 125-gallon tank.

Now, enjoy the list!

1. Harlequin Tuskfish (1 Fish)

Harlequin Tuskfish are perhaps the most unique member of the wrasse family, not to mention one of the largest! They showcase a blue/green, orange, and silver body, with a lined pattern and display some impressive blue "tusk"-like teeth.

Harlequin tusk requirements:

  • Care level: Moderate
  • Temperament: Peaceful/Semi-Aggressive
  • Maximum Size: 12 inches (30 cm)
  • Temperature: 77 - 80°F (25 - 26.6°C)
  • Maximum Lifespan: 10 years
  • Diet: Carnivore

They tend to do very well when housed with similarly-sized fish, or at least fish that are big enough to hold their own. However, keep them away from other harlequin tusks as they can be territorial and very aggressive towards each other.

Funnily enough, harlequin tusks are actually very shy fish, despite their large size, especially when first introduced to a community tank.

2. Maroon Clownfish (1 - 2 Fish)

Maroon clownfish are the largest subspecies of clownfish, which is certainly required when residing in a large aquarium with big tank mates. They showcase the typical red and white clownfish coloration, except with a darker/maroon-red body.

  • Care level: Easy
  • Temperament: Peaceful/Semi-Aggressive
  • Maximum Size: 6 inches (15 cm)
  • Temperature: 72 - 78°F (22.2 - 25.5°C)
  • Maximum Lifespan: 6-8 years
  • Diet: Omnivore

Keeping a pair of these guys in a 125 gallon tank is a great idea, and who doesn't love clownfish? With the maroon subspecies being comparatively large in size, they can certainly hold their own when it comes to the larger, more aggressive tank mates.

Also, a common misconception when it comes to clownfish is that they need an anemone to survive. Well, they don't. So, that is one less thing you need to worry about with these fish. They are also incredibly hardy fish, making them less likely to catch a disease.

3. Yellow Tang (1 - 3 Fish)

A favorite here at Lionfish Lair are yellow tangs. There is something so beautiful about their simplistic yet bright yellow coloration, and something rather amusing about their body and mouth shape! What we also love about them is their peaceful and playful nature.

  • Care level: Easy
  • Temperament: Peaceful
  • Maximum Size: 8 inches (20 cm)
  • Temperature: 72 - 82°F (22.2 - 28°C)
  • Maximum Lifespan: 15 years
  • Diet: Omnivore

They are hardy fish too, which always helps as it puts less pressure on you as the the hobbyist. Typically, yellow tangs should be kept alone, but due to the larger tank size, you can feasibly keep them in groups of three! We would highly recommend that you purchase from the same family and store at the same time.

If you acquire your yellow tangs separately and at different times you run a serious risk of them being aggressive towards each other and even fighting. So, be careful when housing more than one, and try to introduce them all at the same time.

4. Blue Tang (1 Fish)

Now that you own such a large tank, you can unlock one of the most popular fish in the hobby, the blue tang (Dory). These fish are glorious in appearance, and are so entertaining to watch. They showcase a blue and black patterned body with a yellow tail.

  • Care level: Moderate
  • Temperament: Semi-Aggressive
  • Maximum Size: 12 inches (30 cm)
  • Temperature: 72 - 78°F (22.2 - 25.5°C)
  • Maximum Lifespan: 12 years
  • Diet: Omnivore

Unfortunately, keeping a blue tang happy and healthy is a rather difficult task, and they can be more susceptible than others to disease. So, ensure that you have the experience and the time to dedicate to these awesome fish.

For the most part, they play well with other fish, and keep themselves to themselves, usually swimming around and minding their own business. They have been known to act aggressively towards their own, which is why we recommend only keeping one blue tang per tank, even if you have a 300-gallon tank!

5. Marine Betta (1 Fish)

Unlike their freshwater counterparts, marine bettas are incredibly peaceful and fun-loving fish to look after, perfectly suited to a community-based 125-gallon tank.

They display a darkish brown/black body, with thousands of white spots and some unique yellow coloration at the tip of their fins and body.

  • Care level: Easy
  • Temperament: Peaceful
  • Maximum Size: 8 inches (20.3 cm)
  • Temperature: 72 - 78°F (22.2 - 25.5°C)
  • Maximum Lifespan: 10 years
  • Diet: Carnivore

They are awesome nocturnal fish that will require plenty of dark hiding spaces with lots of shelter during the daytime as they tend to be more active during dusk and night.

Marine bettas can be fussy with their diet upon initially being introduced, so, using live foods to entice them to eat is your best option.

Maine bettas bring a new dynamic to community aquariums, as their behavior is very different to most saltwater fish. They are incredibly fun, however, and are certainly worth giving a try!

Equipment for a 125 Gallon Aquarium

Below is a list of all the equipment and decoration you will need for your 125-gallon saltwater aquarium:

  • A lid or a mesh net to stop your fish from jumping out of the tank.
  • An air pump and airline tubing, or even a powerhead pump to increase/regulate the water flow in your tank.
  • A sponge will help with filtration.
  • You will need a 400-watt heater.
  • An LED light such as a blue filter light is a good choice as it can help mimic the moonlight your fish would typically see when residing in the wild.
  • You should certainly be adding a large live rock or more to a tank of this size. The live rock will act as a home to an abundance of different fish and even invertebrates.
  • Spotted mushroom corals are a good choice for a tank of this size.
  • Introducing some algae for your omnivorous fish is a great idea. We recommend using dragon's tongue algae (Halymenia dilatata).
  • Keeping a few stones and rock formations is always a good idea. This will mimic your fish's natural habitat and provide more hiding spots for them.

Below is a graphical representation of what you should be looking for when it comes to equipment and decor for your 125 gallon saltwater aquarium.

Other Popular Tank Sizes

We completely understand that for most hobbyists, despite wanting a 125-gallon aquarium, it is simply not a realistic size for many. So, here are some smaller tank size fish lists that might be more suitable for you:

40 Gallon Saltwater Fish

55 Gallon Saltwater Fish

65 Gallon Saltwater Fish

75 Gallon Saltwater Fish

90 Gallon Saltwater Fish

Alternatively, if you are interested in an even larger saltwater aquarium, why not check out our 150-gallon salwtater fish list.

Final Thoughts

Thanks for checking out our list of the best saltwater fish for a 125 gallon tank. We are sure you will agree with many of our picks, and even if you do not like all of them, you now have options and ideas of the type of fish to stock in your saltwater fish tank.

Not only that, but you have our criteria as a reference should you wish to choose your own 125 gallon saltwater fish that closely align with the requirements we have noted.