Why don’t my fish poo?
I have a 200 l community aquarium. My problem is that my fish often seem constipated, and this sometimes causes what I think are swimbladder issues. Currently one of my Rosy Barbs has been hanging at the surface
(it’s doing this constantly, not just after being fed). It swims down but keeps going back to the surface and staying there, and almost points its nose out of the water. All the other fish seem fine. I have isolated it and have it in a hospital tank, and I’m using Interpet Swimbladder Treatment. I can't think of any other disease that presents this type of behaviour.
I feed a combination of Bug Bites, Repashy Soilent Green, with peas and some gel foods like shrimp and Daphnia. My plec also likes pleco wafers.
Why don't my fish poo? I never see them doing it and it’s a mystery as I can't work out what’s causing this constipation. I only feed once a day. Any ideas would be much appreciated. HEATHER REID, VIA EMAIL
PETER SAYS:
I suspect that your fish are producing solid wastes — it’s just that you won't often catch them doing it. I have just sat in front of my mixed community aquarium and observed my fish for about 30 minutes: I didn't see any signs of poo being released. I'd be far more worried to see lengths of poo (or white mucus) hanging from my fish's vents, as this can be a sign of something wrong with the diet and/or their digestive systems.
The frequency and quantity of faecal wastes will vary depending on the species of fish and other factors, notably the diet. In the wild, food items are likely to contain more indigestible materials (fruit and nut fibre, insect exoskeletons; snail and crustacean shells) compared to the ‘highly digestible’ aquarium diets that we feed in captivity. Regarding your Rosy Barb, it’s unlikely to be a water quality problem, given only one fish is affected. Fish may hang at the surface because they’re struggling to get enough oxygen to their tissues.
If only one fish is affected, as in this case, one likely cause is gill damage or gill disease — if so then you will probably see that the respiratory rate (measured as gill beats per minute) is higher on the affected barb compared with the other Rosy Barbs. A buoyancy problem, such as an over-inflated swimbladder (perhaps due to gas accumulation as a result of a swimbladder deformity or infection) can also make fish float at the surface.
Where several fish are affected, it could be due to a water problem such as a high ammonia level that will ‘burn’ the gills; high nitrite, which will inhibit the blood from transporting oxygen; low oxygen levels in the water; or some sort of infectious gill disease, such as caused by gill flukes or gill-parasitic protozoa, each of which can make several or all the fish surface-gasp and/or have fast gill beats.