Originally Posted by dazeek
Hello, I was wondering if someone could help me figure this out. I have a 150 gallon aquarium with 2 neon tetras (I had 6 but four didnt survive the first two days), 6 serpae tetras, 2 green barbs, 2 tiger barbs, 5 platys, and 3 phantom barbs. I did have one more green barb, one more tiger barb, and 2 more phantom tetras. However, every day this week I awake to one fish MIA. I'm thinking I have a hungry fish? Any ideas who it may be?? They all seem to get along well when I watch them. I have one serpae who is the biggest fish in the tank (although not much bigger than the rest) who tends to sit under a bridge all the time and will chase the others out if the come by but that's his space it seems and he doesnt want to share. One of the phamtoms that is mia was the second largest fish in the tank. I really am clueless as to what is happening to my fish and it seems to be just one fish each night?? The aquarium store said all of these fish can be together other than possibly the barbs but that they should keep to themselves. Any thoughts??
You really must take anything told to you by staff in fish stores to be "questionable" at the very least. And before you buy any fish, always research the species. We have a Profile section here, and most if not all of the fish you mention are included; there is information on maintenance, compatibility, how many you need of each, tank size, etc. Plus you can always ask and those with experience in the fish can comment.
A dead fish can very quickly be eaten, or the corpse can be well hidden. But I am only going to comment on the fish you have in your tank, as you are asking for some problems.
Tiger Barb and Serpae Tetra are notorious for being aggressive; the extent of this aggression can be influenced by several things, including the number of fish of their species and the other fish in the tank, and the size of tank. Both species should only be maintained in groups of 8 or more, and in your 150g you have no problem doing this--assuming you really like them. However, be aware that they will establish a pecking order within the group, and fin nipping and harassment is almost guaranteed--though again, some fish don't. But it is in their nature to do so, and you must accept that it may happen.
The other fish also need larger groups; six is the minimum number usually given for tetras, but this is only because most of us have tanks that are not large enough to accommodate larger groups. With all the shoaling fish--tetras, rasbora, barbs, Corydoras, loaches (with a couple exceptions)--a group of 8 or 9 or more is well worth it. The fish will behave more naturally within the group (some of the male displays can be awesome) and this means they will be more "comfortable" and that means less stress. And stress is the largest single factor to fish disease, poor health and death.
And that brings me to the Tigers and Serpae. They will, just by their very presence, cause stress to more quiet fish like Black Phantoms and Neon Tetra. And even if they do not actively chomp on them, the stress caused by their presence takes its toll. Fish release pheromones into the water, and some other species as well as their own can pick up on these. An "aggressor" sends out a signal that he is tough and rough, even if this is not followed up with enforcement.
Stress weakens the fish's immune system, and it tires them out. This is no different for fish than it is for humans. They are then more susceptible to other issues that would otherwise probably never arise. I can't say for certain that a Tiger Barb or a Serpae Tetra killed the missing fish. But I can say they probably had a part to play, whatever the actual cause.