Aquariums set up purely for marine fish are in decline, with many hobbyists opting for the more challenging reef environment. But this means you miss out on some of the best fish, says Jeremy Gay.
As a new marine keeper you are bombarded not only by livestock choice, but also by people displaying fish, yet telling you they aren’t suitable for your tank. Most people these days opt for a reef system – but some of the best fish can’t be kept in such a set-up. I’ll take the opportunity here to highlight some of the best marine fish — and those with the most character.
Ease of keeping
Lionfish, puffers, triggers, moray eels; they are all big, colourful fish with interesting shapes and loads of character and they are archetypal tropical marine fish. Yet increasingly we give them a miss in favour of reef-safe specimens that don’t have as much character, but won’t munch corals either.
However, if you think about it, a fish-only tank is the most suitable choice for some new fishkeepers. They only have to concentrate on the fish and don’t need to consider other factors like watts per litre of lighting, calcium, magnesium and alkalinity and corals. And one of the most common problems facing new marine keepers is stocking a tank with live rock, fish and corals too quickly, whitespot developing and trying to tackle it with a weak, coral-friendly parasite treatment.
Keep only fish, quarantine them and keep an eye on pollutants. It is a lot less hectic way into the hobby — and less expensive! Despite what we think, some marine fish are actually as tough as hardy tropicals!
With no inverts to worry about you’ll find that marines tolerate a wide range of temperatures and salinity, and some species will tolerate surprisingly high levels of nitrate too. In fact, keep marine fish in a lower salinity and they will be far less likely to develop whitespot in the first place.
A fish-only marine tank can be just like keeping tropicals: use filtration to deal with waste, change the water, keep an eye on health, and add salt. You can even buy ready mixed seawater!
I’ve included butterflies not because of their character, but because if you are going to own a large fish-only tank you have to take advantage of the fish you weren’t allowed when you had a reef. If butterflies were reef safe they would be as popular as Yellow tangs but, seeing as most aren’t and some are very specialised coral polyp eaters, they remain exclusive.
The trophy fish has to be the Golden butterfly, Chaetodon semilarvatus (pictured above). It’s one of the most outstanding marines you are likely to see and are sometimes available in pairs which is even better. It’s not massive on personality maybe, but if going for the fish-only marine tank you have to include a butterfly species!
These are a group high on entertainment, colour, shape and character. The Picasso trigger (above) is one of my favourites and is hardy, colourful and doesn’t get too big. PFK contributor Scott Michael says that it is “a species for modern art lovers or anyone who desires a fish that thinks it’s a dog.“ I couldn’t have put it any better!
Picassos will eat any meaty foods and large triggers as a whole can demolish live rock and eagerly crunch their way through purple, coralline algae. Similar looking and behaving triggers include the Arabian Picasso, Bursa and the Rectangular — Hawaii’s unofficial state fish. Known by the locals as Humuhumukununukuapua'a, this brilliant name means ‘fish with a pig's nose’ in Hawaiian.
The Undulate trigger is perhaps even more boisterous yet equally easy to keep, though it won’t mix with as many other species as the Picasso. The Clown trigger still demands a high price even at small sizes, grows large, and lives for a long time. These can be mixed with some really big companions as they will easily hold their own, but again won’t be fond of any other triggers in the same tank.
Queen triggers are hardy, but grow huge and can be very aggressive.
These have been in the marine hobby for as long as the hobby itself and few fish are as recognisable, even by non-fishkeepers. Most familiar is the large Volitans lionfish, (like the one shown here) which is also one of the easiest to keep. Lionfish are always quite reasonably priced and, with their lavish fins, you get quite a lot of fish for your money.
In terms of character, they do have it, but like to give the impression that they will never be tamed. Because of their venomous spines you always need to treat this fish with respect. Make sure they are either at the other end of the tank, partitioned off, or, better still, moved to another tank when undertaking tank maintenance.
I kept a Volitans for some time in a reef tank with all the small fish and shrimp removed.
As they glide over the reef they look superb and adopt a head-down posture to hunt. Mine adopted a head-up posture to take cockles as soon as they hit the surface and one day its lunge made a jet of water shoot from its mouth and straight into the workings on my metal halide suspended above.
There was a loud bang and the house was instantly dark as the electrics tripped out. Great fish though and one day I would like to keep a group of them.
With a massive freshwater following as well, puffers have got to be some of the best character fish. They’ve got it all — weird shape, weird swimming style, big eyes that look comical when they face forwards and focus on prey, and some have great colour too.
If you had to choose the ultimate marine fish pet, this would be it. Interaction with owners is second to none and I have even seen them backswim, spit water and do tricks while begging for food.
The larger, fish-only pufferfish from the genus Arothron, like the A. hispidus pictured above, are easier to keep than the smaller Canthigaster species and have much more character too. Perhaps the best known of the large marine puffers is the Porcupine or Spiny, Diodon holocanthus.
I love Spiny puffers as they are cute, colourful and entertaining, and would dearly love to keep one — but they do grow large. The books state a maximum aquarium size of around 30cm/12”, but in the wild and, exceptionally in captivity, these fish can reach 91cm/36”, making them only suitable, ultimately, for public aquaria.
Other well-known puffers are the Spotted dogface and Panda, though newly imported fish can go on hunger strike. Once acclimated they are fine, but make sure they are feeding if you fancy buying one. A. hispidus has all the familiar marine puffer traits — including sulking, begging for food, spitting, and, occasionally if you put your hand in, biting — but they are hardy and remain a great fish, if large at a maximum 45cm/18”.
One my favourites is the Guinea Fowl puffer, Arothron meleagris. Confusingly. It may appear in the shops in two colour phases; either bright yellow with the odd patch of grey, or jet black with tiny white spots all over. Both look stunning and large specimens command a price tag into hundreds of pounds.
They have character and are boisterous, though I find that specimens of 15cm/6” and under are more prone to starving and whitespot than large ones.
Guinea fowl puffers get really excited at feeding time and press their teeth against the glass before trying to swim at full thrust. This can generate quite a wave and, with teeth like that scraping the front glass, I wouldn’t want to risk keeping one in acrylic. These are stunning display fish for the very large marine fish-only tank.
There are loads available and lots are suitable for a large tank of character fish. The Harlequin tuskfish is a highly-prized member of the wrasse family and looks stunning. The Birdmouth wrasse (above) is a bizarre-looking species with large, green males that are very active, flapping around the tank with their pectoral fins.
Dragon wrasse are often seen in shops as juveniles, but would be an interesting addition to the larger fish-only tank as they can change pattern completely when mature.
Wrasses from the genus Thalassoma make great fish-only additions and are active and hardy.
l used to practically collect the dwarf species in my marine tanks as I loved them so much, but the larger species can be even better. The flagship large angel must be the iconic Emperor angel (juvenile form pictured above) and possibly the Queen angel, but my list of favourites include the Blue face, with cheeks so blue they look painted, the Regal, which borders on being reef safe, the Blue ring, even the subtly coloured Six-banded. I love them all.
They may be aggressive and territorial towards other angels and if they decide to start picking on each other the loser may die. I had the misfortune of watching an adult Emperor thumping a smaller species in a shop tank and it wasn’t nice.
In terms of body shape and character I find the large angels quite cichlid like and they definitely help to make a stunning fish-only display. Most average 25-30cm/10-12” in the aquarium, but the French angel is one to avoid as it gets massive. Standard 183 x 61 x 61cm/6 x 2 x 2’ tanks just aren’t big enough for a French angel.
I don’t think I am alone in having a healthy fear of Moray eels, as I have had the good fortune to keep and feed a few of them, and seen on many occasions how they take their prey apart. The most suitable species has to be the Snowflake as it is colourful, doesn’t grow too large and can be kept with other fish.
Their iconic shape and behaviour endears them to me as much as their character. They move at speed around the tank — unless feeling secure with most of their body tucked away in a cave with their heads stuck out observing everybody and everything else.
What drives this fish’s character though must be its feeding behaviour.
I always feed Morays using tongs as their dentition could really damage you. I lowered a set of these tools once into a deep display tank with some whitebait on the end. The fish took a second to observe the food before stretching beyond to try and take my hand instead! Caution is advised, as when they grab prey they can also go into a death roll.
But again, it’s a great fish that deserves its place in the large fish-only tank, and one that will make a great conversation piece.
On the subject of Moray eels, I reckon I have found one exceptionally hardy specimen. On a Merseyside shoptour in October 2006 we visited Wavertree Nook Aquarium, a great shop recently refitted after a fire. Owner Hugh Thomas took showed me the one survivor from that incident — a Yellow head moray eel, Gymnothorax fimbriatus.
This amazing fish survived extreme heat, cracked tanks, toxic fumes, no power and even an extended dose of fresh water from the fire hoses. And who said marines were difficult to keep?
Leave them out!
Some fish-only species are circulated in the shops but make bad additions because of their eventual size. These include batfish, sharks, panther groupers, lyretail groupers, pilotfish, Harlequin sweetlips and even boxfish. Always research the size and requirements of all potential purchases before you buy and use a good reference book like A Pocket Expert Guide to Marine Fishes, by Scott W. Michael.
Setting up a tank for big marine fish
Some big marines can be hardy and easy to keep, but it isn’t fair to keep them in too small or polluted accommodation.
I like to keep tropicals and marines in a tank six times the length of the fish and at least twice as wide. This means that a 30cm/12” angelfish or lionfish really deserves a 180 x 60 x 60cm/71 x 24 x 24” tank or larger.
If you feed large meaty foods like cockles, mussels, prawns and whitebait, be prepared for when it comes out of the other end of the fish.
A Berlin system can be used with live rock, strong flow and a protein skimmer — or simply an external filter and protein skimmer in combination, with no live rock. For sump systems, either go for lots of biological media and a skimmer, or live rock and a skimmer, though lots of biological media will result in lots of nitrate, which must be eliminated.
The standard, old-fashioned way to control nitrate is with water changes, and plenty of them, or you can fit it, denitrifying equipment. The natural denitrifying way is to install either a deep sand bed, a mud bed or one in combination with an algal refugium. With big angels in the tank above, you could also feed the spare macro algae to them, forming a nice cycle.
Phosphate control is up to you. Low levels of phosphate are not harmful to fish, as they are to corals. But you can also be plagued with nuisance algae and phosphate-removing resins may help.
Fish-only systems will also benefit from ultra-violet sterilisation. It will keep disease pathogen numbers down, which is good for whitespot-prone puffers. With no live rock in the system you could even run copper — meaning that you add a non-reef safe, parasite treatment that contains copper. This works as a preventative treatment, stopping ailments like marine whitespot before they happen.
Copper is not safe for any marine invertebrate, be it sessile or mobile, and some fish species like Harlequin tusks are copper intolerant too. Always follow manufacturers’ instructions.
Above all, if keeping big marine fish you must have a big tank and big equipment to cope with their waste. In a fish-only system you cannot over mechanically and over biologically filter, and you cannot over skim.
Big marine fish have few décor requirements other than plenty of swimming space or, if an eel, a cave to hide in. You could decorate with coral sand, coral gravel and ocean rock, barnacle clusters, lava rock, tufa rock (though some sources believe tufa holds nitrate,) or even replica rock and fake corals.
If you include any grazers like angels, tangs and butterflies they will do a lot better with good quality live rock to pick from. If you have large triggers or puffers they may demolish your live rock, so keep it in a sump or don’t use it all.
So to aquascaping. You rarely see a great looking, aquascaped fish-only tank, which is a real shame. You just need to treat it like any other aquascaping venture and use lots of décor to create atolls and overhangs.
Lighting can be as little as one fluorescent tube and you could even have light just as a spotlight, or just down one side, so that your big fish seem to swim into view from the gloom.
Blue light is popular in fish-only displays and LED light casts eyecatching beams of light and ripples across the tank floor. The fish are the main focus in any fish-only marine tank, though they will look much better against a well aquascaped backdrop.
The highlight of the day is going to be feeding time. These clever fish will need some environmental enrichment in the form of feeding challenges and nothing is more natural for a large wrasse, trigger or puffer than breaking into something still in its shell.
Cockles are available in shell and I noticed live mussels in shell at my supermarket the other day. Also look at crabs, prawns — anything with a bit of crunch — and you just can’t beat the awesome spectacle of a large puffer or trigger crunching through crab claws with ease (dead crabs of course!) and it’s good for them too.
For more omnivorous fish like large angels offer a whole range of foods — from dry pellets and flake to meaty foods, to vegetable-based foods. Enrich large frozen foods by stuffing them with foodsticks and pellets, or soaking them in vitamin supplements. Wild butterflies and angels get their fantastic colours from diets that we simply can’t provide, so we must offer them as much variety as we can to try and keep the colours vibrant.
Here’s your shopping list
What you need for a fish-only marine set-up:
Tank and cabinet
Filter (either sump, external or live rock)
Hydrometer (or refractometer)
Substrate (coral sand or coral gravel)
Décor (ocean rock or replica rock)
Test kit (marine version, of course)
Water conditioner (if using tapwater)
This article was first published in the May 2008 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.