The popular and (sometimes) pugnacious six line wrasse

Pseudocheilinus hexataenia, commonly known as Six Line Wrasse or Six Stripe Wrasse, is one of the most popular saltwater fish you can find in stores and online. One look at them and it isn’t hard to see why they are so popular. This article will cover some of what makes this fish so interesting and answer a few of the most common questions about keeping them in a reef tank.

What is the minimum six line wrasse tank size?

The six line wrasse, Pseudocheilinus hexataenia, requires a minimum tank size of 55-gallons (~208 liters), for maximum health. Adults will grow to about 3-inches in total length, but they require open space for swimming. 

Feel free to jump ahead to review some of the most frequently asked questions:

• How big do they get?
• Are they reef safe?
• Do they eat corals?
• Do these fish eat flatworms?
• Are they jumpers?

Whether they are blue with orange stripes or orange with blue stripes, I’m not quite sure, but the bottom line (did you like that pun?) is that they are very attractive fish.

My favorite aspect about these fascinating fish is to watch their eyes as they hunt. Their eyes dart around and remind me of a chameleon that way. They are generally inexpensive and widely available and are perpetual motion machines zooming around the tank without a care in the world.

How big does a six line wrasse get?

The typical size to see a six line wrasse at a local fish store is in the 1-2 inch range, but they will grow to between 3 and 4 inches in total length when fully grown.

Ideal habitat

Pseudocheilinus hexataenia originates in the Central and Indo-West Pacific Ocean, and the Red Sea as well. These fish can also be found in the northern part of New South Wales, the northern part of the Great Barrier Reef, and areas around northwestern Australia.

They are hardy fish that are relatively easy to keep in a saltwater aquarium. A relatively small fish, they tend to stay under 3 inches long, but they need a lot of open water in which to swim, so they are best kept in a tank that is at least 55-gallons in volume.

According to a 2021 survey, the most common aquarium size was between 55 and 90 gallons.

Six stripes are boldly-mannered fish, naturally, but they also tend to do best when kept with a moderate amount of live rock. They will dart in and out of the aquascape for protection and will scour the rock looking for a tasty morsel to eat.

Is the Six Line Wrasse reef safe?

The Six Line Wrasse is reef safe. In a 2021 survey, 81.7% of respondents indicated that they were completely reef safe. The other 18.2% observed compatibility issues with either anemones, corals, clams, crabs, or starfish. Of all the invertebrate issues, 47% were between the Six Line Wrasse and crabs.

Source: Saltwater Aquarium Blog survey data October 2021.

Survey answers	Percentage
Completely reef safe	81.7%
Not reef safe (observed compatibility issues)	18.2%

Among the 18.2% of reports that the Six Line Wrasse was not reef safe in their tank, the following issues were reported:

Anemones	7%
Corals	13%
Clams	13%
Crabs	47%
Starfish	20%

Do six line wrasses eat coral?

Six line wrasses do not eat coral. Their natural behavior is to hunt for tiny invertebrates like worms, copepods, snails, or other meaty foods that are living among the coral tissue. Even though the fish is not eating the coral, damage and stress to the coral could still be a result.

In the 2021 study, 13% of reef safety and compatibility issues with the Six Line Wrasse involved challenges keeping them with corals.

Feeding and nutrition

Pseudocheilinus hexataenia is a carnivorous fish, spending most of its time picking at live rocks in search of small worms (like bristle worms), parasites, and crustaceans.

Most individuals will accept standard saltwater fish food, like flakes, pellets, or tablets, but what they would appreciate most is frozen food and even small live food.

These are very active fish. If possible, try to feed them 2-3 times a day.

Do six line wrasses eat flatworms?

Six line wrasses will eat some flatworms and segmented worms, like the bristle worm. However, one should not expect that a single individual will be sufficient to rid your aquarium of these pests completely. There also appears to be variability in how eager an individual fish is to eat them.

Some eat them voraciously, others seem to ignore them.

How many per tank?

The vast majority of aquarium owners keep a maximum of 1 Six Line Wrasse per tank. 51 of 57, or 89% reported keeping just 1 individual in their tank, 9% kept 2, and 2% had 3.

Behavior and tank mates for the 6 line wrasse

Compatibility is one of the biggest issues with keeping the six-line wrasse because they can be semi-aggressive and pester other fish, especially other members of the wrasse family, including:

• Yellow coris wrasse
• Fairy wrasses
• Melanurus wrasse
• Leopard wrasse
• Cleaner wrasse

They can stress out shy fish so much they may succumb to parasites or even die.

This isn’t just speculation, take a look at these data:

The chart above shows the number of times a fish type was indicated as compatible with the six line wrasse, in blue, and the number of times it was indicated incompatible, in red.

At a glance, that means, the longer the blue line, the more times an actual aquarium owner observed the peaceful coexistence of the two fish.

The longer the red line, the more times a different aquarium owner (most time) observed significant compatibility issues between the two types of fish.

Key compatibility takeaways from this survey:

1. There were compatibility issues with each of the top 10 most popular saltwater fish types
2. The most issues were with other wrasses, tangs and blennies

The chart above shows the magnitude of the potential problems, at a glance. But if we focus now on the incompatibility rate of the fish pairings with the highest number of reported issues, we start to see some actionable data emerge:

Fish type	Probability of an issue
Wrasses	1 in 3
Dottybacks	1 in 5
Basslets/Grammas	1 in 8
Blennies	1 in 8
Tangs	1 in 10
Gobies	1 in 11
Angelfish	1 in 11
Cardinalfish	1 in 12
Chromis	1 in 12
Clownfish	1 in 25

The data above indicate the magnitude of the issues reported among the most commonly reported fish types, but those were not the only compatibility issues that were reported. The six line wrasse was indicated as incompatible, at least once, 26 out of the 32 possible saltwater fish types surveyed.

Fish type	Compatible	Incompatible	% Incompatible
Wrasses	18	11	38%
Tangs	45	5	10%
Blennies	38	5	12%
Gobies	43	4	9%
Angelfish	41	4	9%
Dottybacks	17	4	19%
Clownfish	65	3	4%
Cardinalfish	36	3	8%
Chromis	34	3	8%
Basslets/Grammas	22	3	12%
Dartfish	11	3	21%
Filefish	6	3	33%
Damselfish	28	2	7%
Butterflyfish	13	2	13%
Boxfish	1	2	67%
Groupers	1	2	67%
Grunts/Sweetlips	0	2	100%
Anthias	18	1	5%
Rabbitfish	13	1	7%
Dragonets	8	1	11%
Hawkfish	4	1	20%
Jawfish	3	1	25%
Lionfish	3	1	25%
Eeels	2	1	33%
Pufferfish	2	1	33%
Hogfish	1	1	50%
Triggerfish	8	0	0%
Assessors or Marine Bettas	5	0	0%
Pipefish	2	0	0%
Tilefish	2	0	0%
Seahorses	1	0	0%
Squirrelfish	1	0	0%

Tank size is correlated with aggression and incompatibility, but not the way you may expect

The most surprising conclusion from the survey data is that tank size matters when it comes to aggression and compatibility issues with the Six-line wrasse, and there were fewer issues in the smaller tanks. Wait, what? See for yourself:

Size of the tank does appear to be correlated with compatibility issues, but why? Piecing each of the individual conclusions from the survey together, a pattern is starting to emerge. While it appears that certain types of fish are more likely to cause problems than others, the fact that someone proactively indicated they were incompatible in a serious way at least 1 time with nearly every fish type possible, it suggests that there is more at play here.

Perhaps it’s a variable not captured in the survey, like the order in which the wrasse was added--but what about the shots on goal theory--would we expect to have more issues with aggression and incompatibility with a higher number of fish interactions?

It’s likely no surprise that larger fish tanks have more fish in them.

But owners of larger tanks not only have more fish, they also reported more incompatible types, on average, than smaller tank owners.

Check out the data:

It was already established that there were not many people in the survey who had a tank < 20 gallons, but when we divide the total number of fish types listed as incompatible by the total number of aquarium owners with a specific tank size in the survey, another clear trend emerges.

Those people with larger tanks experienced a higher average number of incompatible fish types, giving more weight to the ‘shots on goal’ strategy.

That conclusion runs a bit contrary to some traditional advice in this hobby that larger tank sizes result in more territory to split up, and therefore less expected issues.

who took the survey It turns out, that people who reported compatibility issues in larger tanks, also listed a larger # of fish types that were incompatible with their 6 lines. So, perhaps it’s less about the size of the territory and more about the number of potential fish combinations and the order of those combination.

Conclusions about compatibility

When we look at the full body of data on the 6 line, a s

Smaller and shy fish like the marine betta, fairy wrasses, firefish, Royal gramma fish, or leopard wrasses won’t make good tank mates, as they run the risk of constantly being harassed by the six-line wrasse.

Also, while not a significant finding from the research conducted here, I still do advise against keeping this fish with slow swimmers like mandarin gobies, seahorses, and pipefish. The docile nature of these great fish make them likely to starve in their presence of an aggressive-eater like this, regardless of whether or not there are specific aggression/incompatibility issues..

Another aspect not explored in this research was whether or not the order in which the wrasse was introduced into the tank had an impact on compatibility.

In other studies, it has already been established that the order in which a fish is added to the tank does impact the relative aggression. The incumbent fish in a territory is more likely to fight to defend its territory from an interloper than the interloper is likely to challenge the incumbent to take away their territory or resources.

As such, if you are inclined to add a six stripe to your tank, consider adding it to a tank without a lot of other fish, and add them last.

Are six line wrasses jumpers?

There is some risk that a six-line wrasse will jump out of the tank when startled if you do not have a tight-fitting lid or another way to prevent the jump.

Pros and cons to consider before adding a 6 line wrasse to your tank

These fish are extremely popular, but like any good decision, there are some pros and cons you should consider before adding them to your tank.

5 reasons to keep them

• Beautiful
• Inexpensive
• Hardy
• Will eat parasitic pyramid snails, flatworms, and bristle worms
• Can be kept in reasonably small tanks (about 20-30 gallons or so)

2 reasons not to keep them

• Can be aggressive fish
• May out-compete shy fish for food

Six-Line Wrasse recommendations

There is no doubt, this is a gorgeous, hardy, and inexpensive fish--but the big question is whether or not you should add one to your reef tank. In a survey of 89 Six-Line Wrasse owners, 66% recommended them (as indicated by a score of 4 or 5 out of 5), while 11% did not (a score of 1 or 2 out of 5).

For more information

Check out this short video to learn more about the six line wrasse:

Here are a few other articles about semi-aggressive saltwater fish similar to the six line wrasse:

• Blue devil damselfish
• Domino damsel

Or perhaps you would rather check out these other peaceful, hardy fish instead:

• Royal gramma
• Pajama cardinalfish
• Flame angelfish

Conclusions

A lot of data were revealed here about the true intereactions between the semi-aggressive Six Line Wrasse and its fellow aquarium tankmates. Until now, it was unclear whether to trust the people who cursed the name due to compatibility issues they suffered or the people who raved about the brilliance of these fish.

As is often the case in life, both situations were likely true and accurate. It turns out that the is fish has a record of being a fine, trustworthy reef tank companion the majority of the time. About 4 in 5 reports indicate they were completely reef safe.

However, only 3 in 5 recommend the fish to others.

The next time you see this fish at your favorite local or online fish store, the data in this study should help you make an informed decision about what you can expect if you add one to your tank.

References:

Saltwater Aquarium Blog Survey Data, October 2021