Tara Lee Gilson, of Balclutha Primary School, asks :-

My goldfish was swimming on its side and the pet shop told me to put a pea in his bowl to eat. He died but we were wondering what a pea has in it to make him better?

Christine Thompson, of Massey University's Institute of Veterinary Sciences, responded.

Goldfish can develop swimming problems. They may swim on their side if they have problems with their balance or using their fins. Alternatively, they may swim at the bottom or the top of the water, or even upside down if they have a buoyancy problem. Goldfish regulate their buoyancy with an organ called a swim bladder. The swim bladder is an air-filled, membrane-lined space located underneath their spine.

To adjust its depth in the water, the goldfish changes its buoyancy by increasing or decreasing the amount of air in the swim bladder. To increase its buoyancy, air absorbed into the bloodstream via the gills, can be secreted into the swim bladder. To decrease its buoyancy, the goldfish releases air from the swim bladder via a narrow duct into the oesophagus/front part of the digestive tract. The goldfish then excretes the excess air.

Feeding peas to goldfish is rumoured to help food pass through the digestive tract and thus keep the swim bladder opening clear, so that the goldfish can release air and adjust its buoyancy. Perhaps peas assist the passage of food through the gut by being high in fibre, or maybe peas contain some chemical that keeps goldfish digestive tracts healthy.

However, despite contacting several goldfish experts around the world and searching the scientific literature, I could not find any scientific evidence to support feeding peas to goldfish to help their swim bladder function. Lack of evidence doesn’t mean the rumour is incorrect, it just means that a scientific study has yet to be done to determine whether this rumour is true. Perhaps an enterprising fish owner like yourself may become an ichthyologist and do a scientific study to determine whether feeding garden peas to goldfish keeps them swimming properly.