What can looking at fish poo tell you about your fish health?

In most fish, faecal trails do not hang on for a long time since their normal swimming action would break the trail. Goldfish tend to have a longer trail because they swim slowly and their trail is of larger diameter, making it ‘tougher’ to break. But these should come off easily when the fish is disturbed.

Healthy faeces should be dark and not contain gas bubbles. If it contains bubbles, causing the faecal trail to float (see picture below), then there might be issues. Bacterial imbalance or parasites may be possible reasons. The way to investigate it is to examine the faeces under the microscope to look for evidence of parasites and to culture the gut flora to check for presence of pathogenic bacteria. Over feeding is obvious when the faeces produced is the same colour as the food you fed them.