Goldfish expert reporting for duty.
I don't quite understand what they mean, polarized vision used by goldfish to hunt? I thought goldfish were primarily vegetarians (grass carp?)
I thought polarized vision didn't work under water, only above water looking through the reflection.
Goldfish will eat a wide range of foods, including algae, plants, invertebrates, fish eggs and small fish.
Many books and websites say that the goldfish is a domesticated form of the carp. This is incorrect. They are different species, and both have been domesticated separately. Some goldfish and carp may look almost identical, but the carp (
Cyprinus carpio) grows much larger and has barbels, unlike the goldfish (
Carassius auratus).
The grass carp is yet another species, with the impressive Latin name of
Ctenopharyngodon idella. It feeds mostly on plants and algae.
I don't know how polarized vision would help them, maybe to see insects which have landed on the surface, or to spot predators above the surface?
Although the goldfish and carp are mostly bottom-feeders, some related fish are surface and midwater feeders, such as the Orfe. If they also have polarized vision, they may benefit more from it. They hunt mostly by sight, and feed on plankton, surface insects and small fish. The goldfish and carp use a combination of sight, smell and random 'vacuum-cleaning'.
I have seen goldfish eating their young in the fish pond. Lucia?
They will often eat their eggs and young if given the chance. Once the young are past the transparent fry stage and look like small fish, they are less likely to be eaten. In a pond with lots of plants and other hiding places, some will survive. It is often better that only a few survive, as they produce thousands of eggs, and overcrowding will produce stunted fish.
On the subject of grass carp, they are often sold for algae control. They do eat blanketweed algae in the wild, but in captivity they will eat almost anything else to avoid it. If given a choice of foods, they prefer to eat commercial carp food, invertebrates and small fish. If these are not available they will turn to plants, eating first the leafy ones and then the tough ones such as waterlily stems. Only if none of these is available will they start to eat the blanketweed. It must taste as bad as it looks. rofl
