One of the greatest joys of owning a marine aquarium is choosing the fish that will bring your reef to life. From the brilliant colours of a Mandarin Dragonet to the bold personality of a Clownfish or the graceful movement of a Tang, saltwater fish are among the most spectacular animals you can keep at home.
However, selecting marine fish isn’t simply about choosing your favourites. Every species has unique care requirements, dietary needs, temperament, and space requirements. Choosing compatible fish that suit your aquarium is one of the biggest factors in creating a healthy, peaceful, and thriving marine ecosystem.
In this guide, we’ll explore everything you need to know when selecting saltwater fish, from understanding compatibility and tank size to discovering some of the most popular species available to hobbyists.
Why Fish Selection Matters
Unlike freshwater aquariums, many marine fish have specialised requirements and territorial behaviours.
Choosing the wrong combination of fish can lead to:
- Aggression
- Competition for food
- Stress
- Disease outbreaks
- Poor water quality
- Coral damage
Careful planning helps create a stable aquarium where every fish can thrive.
Consider Your Aquarium Size First
Before choosing any fish, consider the size of your aquarium.
Many marine species grow far larger than people expect.
For example:
- A juvenile Yellow Tang may only be a few centimetres long when purchased but can grow to over 20cm as an adult.
- Large Angelfish can exceed 35cm.
- Some Wrasses require long swimming distances.
Always research the adult size, not the size at purchase.
Think About Swimming Space
Marine fish use aquarium space differently.
Some species spend their time:
- Swimming continuously in open water
- Weaving through rockwork
- Hovering near coral
- Resting on the substrate
Species like Tangs require long tanks with plenty of swimming room, whereas Gobies may spend most of their lives close to the sand bed.
Design your aquarium around the needs of the fish you wish to keep.
Reef Safe vs Non-Reef Safe
If you keep corals, always check whether a fish is considered reef safe.
Reef-Safe Fish
Generally leave corals and invertebrates alone.
Examples include:
- Clownfish
- Gobies
- Blennies
- Firefish
- Dartfish
- Chromis
- Cardinalfish
- Most Wrasses
Fish That May Damage Corals
Some species may nip:
- LPS corals
- Soft corals
- Zoanthids
- Clams
These include many:
- Angelfish
- Butterflyfish
- Triggerfish
- Pufferfish
Always research individual species before purchase.
Understanding Fish Temperament
Every marine fish has its own personality.
Some are peaceful.
Others become highly territorial.
Common temperament categories include:
Peaceful
Suitable for community aquariums.
Examples:
- Firefish
- Gobies
- Clownfish
- Banggai Cardinalfish
Semi-Aggressive
Require more careful stocking.
Examples:
- Dottybacks
- Some Wrasses
- Dwarf Angelfish
- Hawkfish
Aggressive
Usually best kept with similarly robust species.
Examples:
- Triggerfish
- Large Groupers
- Lionfish
- Some Damselfish
Introducing peaceful fish before territorial species often reduces aggression.
The Most Popular Saltwater Fish
Clownfish
Arguably the world’s most popular marine fish.
Why people love them:
- Hardy
- Colourful
- Beginner friendly
- Full of personality
- Available in many captive-bred varieties
Perfect for both reef and fish-only aquariums.
Yellow Tang
One of the most iconic reef fish.
Benefits:
- Bright yellow colour
- Excellent algae grazer
- Active swimmer
- Reef safe
Requires a generously sized aquarium due to its active lifestyle.
Kole Tang
A fantastic algae eater that specialises in grazing film algae from rocks and glass.
Suitable for mature reef aquariums with plenty of grazing opportunities.
Tomini Tang
A smaller Bristletooth Tang ideal for medium-sized reef aquariums.
Known for:
- Attractive orange highlights
- Excellent algae control
- Peaceful temperament
Foxface Rabbitfish
Highly regarded for controlling nuisance algae.
Benefits include:
- Eats many algae types
- Generally peaceful
- Reef compatible with caution
- Beautiful yellow colouration
Remember that Rabbitfish possess venomous dorsal spines and should be handled carefully.
Banggai Cardinalfish
A calm, elegant fish that adapts well to reef aquariums.
Advantages:
- Peaceful
- Easy to feed
- Slow swimmer
- Excellent for community reefs
Often kept singly or as bonded pairs.
Royal Gramma
One of the most colourful reef fish available.
Recognisable by its striking:
- Purple front half
- Bright yellow rear half
Generally peaceful and reef safe.
Firefish
A favourite among beginner reef keepers.
Known for:
- Graceful swimming
- Peaceful temperament
- Bright colours
- Small adult size
Provide plenty of hiding places as they may jump if startled.
Gobies
Gobies are available in many fascinating species.
Popular examples include:
- Watchman Goby
- Neon Goby
- Clown Goby
- Yasha Goby
Many develop fascinating relationships with pistol shrimp.
Blennies
Blennies combine personality with practicality.
Popular species include:
- Lawnmower Blenny
- Starry Blenny
- Tailspot Blenny
Many species help control nuisance algae while entertaining owners with their curious behaviour.
Wrasses
Wrasses offer incredible diversity.
Popular reef-safe species include:
- Six Line Wrasse
- Melanurus Wrasse
- Yellow Coris Wrasse
- Pink-Streaked Wrasse
Many help control unwanted pests such as flatworms and pyramid snails.
Mandarin Dragonet
One of the most beautiful marine fish available.
However, Mandarins require:
- Mature aquariums
- Large copepod populations
- Stable reef conditions
Best suited to experienced reef keepers unless captive-bred individuals have been trained onto prepared foods.
Chromis
Blue-Green Chromis add constant movement to reef aquariums.
Advantages:
- Peaceful
- Schooling behaviour
- Easy to keep
- Attractive blue-green colouration
Ideal for larger reef systems.
Dwarf Angelfish
Popular species include:
- Coral Beauty
- Flame Angel
- Lemonpeel Angel
Although stunning, some individuals may nip corals, making them reef-safe with caution.
Butterflyfish
Butterflyfish are among the most elegant marine fish.
However, many species consume coral polyps and are therefore unsuitable for reef aquariums.
Research individual species carefully.
Compatibility Matters
Even reef-safe fish may not always be compatible with one another.
Consider:
- Territory
- Feeding behaviour
- Adult size
- Swimming style
- Aggression levels
Adding fish slowly gives each new arrival time to establish itself before introducing additional livestock.
Quarantine New Fish
Quarantining new fish before introducing them into your display aquarium helps prevent diseases such as:
- Marine White Spot (Ich)
- Velvet
- Brooklynella
- Flukes
A simple quarantine tank allows you to observe and treat new arrivals if necessary.
Many experienced reef keepers consider quarantine one of the best investments they can make.
Feeding Marine Fish
Different species have different dietary needs.
Some are:
Herbivores
Examples:
- Tangs
- Rabbitfish
Require:
- Marine algae
- Nori
- Herbivore pellets
Carnivores
Examples:
- Hawkfish
- Lionfish
Require:
- Frozen seafood
- Meaty foods
Omnivores
Most community reef fish enjoy a varied diet consisting of:
- Marine pellets
- Frozen mysis shrimp
- Brine shrimp
- Krill
- Copepods
- Marine flakes
Providing a varied diet promotes colour, health and longevity.
Avoid Overstocking
One of the most common beginner mistakes is adding too many fish.
Overstocking leads to:
- Higher nitrate
- Increased phosphate
- Aggression
- Reduced oxygen
- More maintenance
Adding fish gradually allows both your filtration system and existing livestock to adjust.
Choosing Healthy Fish
Before purchasing any marine fish, look for:
- Bright colours
- Clear eyes
- Full fins
- Healthy breathing
- Active swimming
- Good appetite
Avoid fish showing:
- White spots
- Torn fins
- Heavy breathing
- Cloudy eyes
- Weight loss
Buying healthy livestock greatly increases long-term success.
Creating a Balanced Community
A successful reef aquarium usually contains a mixture of species occupying different areas of the tank.
For example:
- Clownfish near their host coral or anemone
- Gobies on the substrate
- Wrasses swimming throughout the rockwork
- Tangs grazing algae
- Cardinalfish hovering in open water
- Blennies perched on rocks
This creates natural behaviour while reducing competition.
Common Mistakes
Buying on Appearance Alone
A beautiful fish isn’t always suitable for your aquarium.
Always research:
- Adult size
- Diet
- Temperament
- Compatibility
Adding Aggressive Fish First
Territorial species introduced first often dominate the aquarium.
Generally add peaceful fish before aggressive ones.
Ignoring Tank Size
Many marine fish require significantly more swimming space than beginners expect.
Plan for the fish’s adult size.
Forgetting to Cover the Aquarium
Many marine fish, including Wrasses and Firefish, are excellent jumpers.
A mesh lid can prevent expensive and heartbreaking losses.
Final Thoughts
Choosing the right saltwater fish is one of the most rewarding parts of building a marine aquarium. By selecting species that are compatible with one another, suited to your aquarium’s size, and appropriate for your level of experience, you’ll create a vibrant and harmonious underwater community that can thrive for many years.
Take your time, research every species thoroughly, and introduce livestock gradually. With careful planning and good husbandry, your marine aquarium will become a beautiful, healthy ecosystem filled with fascinating fish displaying natural behaviours and stunning colours.
At Charterhouse Aquatics, we stock a wide selection of marine fish, reef-safe livestock, aquarium foods, water testing equipment, and aquarium accessories to help you build the perfect saltwater aquarium. Whether you’re setting up your very first marine tank or adding the finishing touches to an established reef, our experienced team is always on hand to offer expert advice and support.
