The Black Trigger

By Kevin Thurston
From CAS Newsletter and Aquarist, Colorado Aquarium Society
Aquarticles.com

The black trigger sounds like some sort of cloak and dagger villain, but of course I am referring to Odonus niger, also known as the Niger trigger and red-toothed trigger. The triggers are a group of marine fish that are named for their ability to lock themselves into an opening of rock or coral with a trigger-like mechanism of the fins.

I've always had a mild interest in the triggers but I was always put off by their reputation as very aggressive fish. I'd even experienced it first hand when a clown trigger demolished a lionfish at a store I was working in. I had asked a local retailer once, "what can you put in with triggers?" "Nothing," was his immediate reply. However, about the same time, I noticed in a large marine display aquarium at the office I was working in, a few new fish including a black trigger. I knew the black trigger had a reputation for being a little more sedate than the others, so I kept my eye on this situation to see how it would develop. This group seemed to work out fairly well, even though there were fish in there that were somewhat smaller than the trigger. I left that job, as well as my home, and moved to a larger house where I was able to set up a marine tank that was a little larger than what I had been maintaining. I started this tank with a small lionfish (Pterois volitans) that quickly grew significantly larger than the purchase size. I had in my mind that I would try a black trigger with it. A few weeks later I found one that was smaller than the lionfish (about 2½ inches total length), but large enough that it was not at risk of being eaten by the lionfish. A few weeks later I added a moon wrasse, Thalassoma lunare. As those three fish grew, they continued to live together in reasonable peacefulness. At the start, the wrasse was the most aggressive fish in the tank, but as they grew the black trigger has become the more aggressive. It has been about two and a half years since I started those three fish together. The lionfish is about ten inches long (there's a photo of it on page 96 of the November 2002 issue of Tropical Fish Hobbyist magazine, if you want to see what it looks like). The wrasse is about seven inches long and the black trigger is about three and a half inches long from tip of the nose to the caudal peduncle.

After this trio lived together for over two years, I took a risk and added a harlequin tusk (Choerodon fasciatus). If you've ever priced a harlequin tusk, you know what I mean by risk. The risk was compounded by the fact that the harlequin tusk would be the smallest fish in the tank at about three inches total length. In fact the lionfish attacked the bag that the harlequin tusk came in while it was floating to be acclimated. The lionfish continued to look at the harlequin tusk as if it might be food for several days. The moon wrasse chases after the harlequin tusk occasionally and the black trigger pretty much ignores the harlequin tusk. After all this time, I feel I can confirm that the black trigger is not nearly as aggressive as the other triggers.

Despite my experiences, there is another consideration that I have to keep in mind and that is that the bigger a trigger gets, the more aggressive it gets. The black trigger can be expected to grow to ten inches in an aquarium, so my trigger still has some growing to do. The nice thing is that the triggers are very hardy and mine has been no exception. My black trigger has eaten just about anything including some of the larger foods that I use to feed my lionfish such as cichlid sticks and freeze dried krill. When I offer the lionfish some feeder fish, the black trigger shows some interest in them, but the lionfish usually has them eaten before the trigger has decided to do anything about it. The moon wrasse on the other hand has bitten the heads off of some of the feeder fish.

Based on my experiences, I can recommend the black trigger for anyone who has ever wanted to try a trigger, but was worried about how aggressive they are. The black trigger is hardy and not quite as aggressive as the other triggers. Some might think that the black trigger is not as colorful as they want a marine fish to be, but the name is not entirely accurate. The color of the black trigger can vary from purple to blue to green depending on different factors that I'm not sure if anyone has pinned down definitively. These colors are usually not shown very effectively in photographs, probably due to the lighting conditions and other factors involved in a photo shoot, so they are more colorful in life than they are in photographs. Another positive about the black trigger is that just like many other "aggressive" fish, it has some personality. Taking all these factors into consideration, I'm very happy that I decided to try the black trigger. Maybe now you'll be motivated to give them a try too.