Could Corydoras be killing other fish? One of readers asks us if this is why some of their Neons are going missing...
Q) I think my Corydoras might be eating some of my fish. My tank is about 120l and has been set up for three months. I haven't had any obvious problems up until now and water tests have been fine, but I have had a couple of small Neons go missing. Yesterday, I came down and switched on the tank lights to find one of the Corys eating a Neon. I thought they were peaceful but I’m now wondering if they are killing and eating the Neons as they are still very small. Is this sort of thing unusual?
MARTY HUMPHRIES, VIA EMAIL
Bob replies: You can rest easy — you don't have killer corys! These catfish are entirely peaceful and simply don't have the dentition (or even the jaws) to eat anything but the tiniest fry or eggs. It sounds like they are just fulfilling their natural scavenging role and 'tidying up' fish that have died for one reason or another.
You don't mention any fish you have in the tank apart from the Corys and Neons, so I can't point an accusatory finger at other inhabitants. But you do mention how small the Neons are, and this could be a factor. They are often imported at a very small size, and when they are this young, they require more frequent feeding of appropriately sized foods to get them growing. With correct nutrition, Neons are fast-growing (in the wild they are more or less an annual species), so it may simply be a case of them not getting enough to eat. Small 'micro granule' foods and frozen Cyclops are ideal to prevent this.
Similarly, Neons can be rather delicate at first, so if your tank’s water chemistry is less than perfect you may have problems. Newly set up tanks can suffer from sudden fluctuations in water conditions that you might miss unless you are carrying out daily testing with a good quality test kit.