Expert: Ron Coleman - 10/30/2009

Question
We began our 20 gallon cichlid tank about 2 months ago with 3 cichlids. We do not know the specific species-- one is orange and black, another is dark blue with a yellow tail, and the 3rd was bright orange.  The bright orange one died within a month or so, but did not seem to have been attacked--we thought perhaps it was bloat.  Then we added a light blue, but vibrant cichlid, which was slightly smaller than the other two.  It held its own for a while, then I noticed it was not eating like the others---it would eat if the food happened across its path, but it wouldn't seek out food on its own, so the other fish would usually finish all food well before it had time to find "Blue" as we called “it” (we have no idea how to distinguish the sexes with any certainty.)  Within a couple days of the original change of eating behavior, I noticed the orange and black fish do a shimmy in front of Blue, so I thought maybe they were mating, and then the next day Blue had barely a tail fin.  I removed Blue and put it in a vase with water from the tank and it was dead within 12 hours.  I'm afraid to introduce any new fish because it seems that the 2 we have are EXTREMELY aggressive.  What the heck happened? How can I prevent this in the future?

Answer
Hi Erin,
 Your two fish have claimed that tank as their territory and it is very likely that if you put other fish in there, they will meet the same end as "blue".  There isn't really a whole lot you can do about it, other than getting a larger tank.   You can try adding a lot of structure (wood, rock, plastic plants, etc) to divide up the space, and then it is more likely that a newcomer would be able to survive. A single plant or rock, however, is not going to do it.  You need a LOT of structure.

-- Ron
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