TRIGGERS IN THE REEF TANK

 

 The redtooth or niger triggerfish (Odonus niger) is a handsome fish that can be kept in a reef aquarium. Of all the potentially reef-safe triggerfishes, this is one with a more dubious reputation. It will eat ornamental crustaceans and as it grows larger, it may attack and even kill fish tankmates.

Triggerfishes have long had a bad reputation for being voracious predators and aquarium bullies. Many of the triggers are some of the most polyphagous of all fishes, eating everything from algae, sponges and corals, to all kinds of crustaceans and even smaller fishes. So the idea of adding one of these beasts to a reef aquarium, packed with succulent invertebrates, seems a bit daft! While it is true, the majority of triggerfishes are not appropriate invertebrate aquarium neighbors,  there is a relatively small group of triggers that have more specialized diets that can be housed with sessile invertebrates. 
In this post we will examine these triggerfishes and look at the calculated risk of keeping some of the less suitable species with your invertebrates.

 

 The members of the genus Xanthichthys (like this Sargassum triggerfish, X. mento) are the best triggerfishes for the reef aquarium. They are a threat to crustaceans, especially as they get larger.

Reef Trigger Differences

Those triggerfishes that are best-suited to the reef aquarium have some special qualities. First of all, most of these species feed primarily on zooplankton or floating algae. As a result, their “designed” a little differently than their less selective cousins. They have slightly smaller mouths, not well-suited for destroying aquarium equipment (including heater tubes!), that are a bit higher up on the head. They also tend to spend more time in the water column hunting their Lilliputian food. Some of these species (e.g., crosshatch triggerfish, Xanthichthys mento) form large shoals because they are more vulnerable when they are farther from the reef. They choose to feed together because there is safety in numbers.

 

 The pinktailed triggerfish (Melichthys vidua) is another potential reef aquarium inhabitant that typically feeds on zooplankton and free-floating algae in the wild. It is a threat to shrimps and crabs. 

The Best Triggerfish Genera for the Reef Aquarium:
Melichthys 
Odonus
Xanthichthys

Those triggerfish that feed more heavily on benthic invertebrates also have other bad habits that can cause problematic in the reef aquarium. When searching for prey, these species will lift bits of rubble in their jaws and blow jets of water out of their mouth at the sand to uncover buried prey. They may even lay on their sides and paddle with the pectoral fin nearest the sea floor to produce holes in the sand. The sand moving is not necessarily a big deal – although they may bury corals placed on or near the aquarium bottom, but the lifting and dropping of debris, rubble and even small coral colonies can cause mechanical injury to coral polyps. By the way, these behaviors are fascinating to observe! If you want a fish that exhibits an amazing behavioral repertoire, you may consider dedicating a whole tank to one of these personable pets.  The reef safe triggerfishes listed above do not engage in these more destructive habits.

 

 The Indian triggerfish (Melichthys indicus) is an attractive species that can become very aggressive as it gets larger. On more than one occasion, we have had these fish pester piscine neighbors to death.

One of the most appealing differences between the reef-safe triggers and their more dubious cousins is their level of pugnaciousness. The genera that do best in reef tanks tend to be the least aggressive members of the family. That said, even these species may “go bad” and try to eat a smaller fish that is added to a tank where they are residents and many are a threat to ornamental crustaceans. In most reef communities, these triggers should be the last fish added to any community tank. The aquarist should be aware that with any triggerfish the problem of aggression is exaggerated if they are kept in smaller aquariums or in crowded conditions. I should point out, that almost all triggerfish species (and most other fishes) display some degree of individual variation. A final note: of all the potential reef aquarium triggers, I have seen individual Indian triggerfish (M. indicus) behave badly more than any of the other potential balistid candidates. I have had individuals in large tanks (over 700 gallons) that bullied, nipped and even dispatched their tankmates (in some cases, piscine neighbors that were as long as they were). Also be aware that Odonus niger can also be belligerent toward fish tankmates as it gets larger.

 

 An orange-striped triggerfish (Balistapus undulatus) in a reef aquarium? While it is not a suitable tankmate for many fishes and invertebrates,  it is possible to keep this bellicose beauty with soft corals that contain ichthyotoxic substances. 

A Note to the More Adventurous

Some aquarists are more adventuresome than others and are willing take risks when it comes to mixing fishes with their invertebrates. For those of you that fall into this category, it is possible to keep some of the triggers that have a more catholic diet in a reef tank with certain invertebrates. For example, I once saw a clown triggerfish (Balistoides conspicillum) in a reef tank!  The owners said they had the trigger in the tank for over a year and that it had not caused any problems. The cnidarian community consisted mainly of soft coral “trees” (e.g., Sinularia, Litophyton, Lemnalia). Many of these soft corals have toxins that make them unpalatable to the general predator. The tank contained no crustaceans, as the trigger would most likely make short work of these, but there were small demoiselles (Chrysiptera spp.) that would dart into tight hiding places when the triggerfish got too close!  The other thing that helped reduce the level of destruction wrought by the trigger was the feeding regimen – the triggerfish was fed chunks of seafood several times a day. Not only does frequent feeding mean your trigger if fat and happy, it also means the balistid is less likely to eat its neighbors.

In conclusion, if you are careful about the invertebrates you select for your reef tank, it is even possible to keep some of these potentially-destructive triggers in your reef. For those that do not want to take as much of a risk, there are also a number of plankton-feeding balistids that are even better-suited to the reef tank environs.


©  Scott W. Michael- Reef Tectonics

 Reef Tectonics Aquarium Maintenance and Design - Lincoln, Omaha, Des Moines, Kansas City