Popular as pet fish all over the world, goldfish are often the target consumers of a wide variety of fish feeds. Their reliance, as pets, on this artificial formulation makes it difficult to comprehend what they could possibly eat in the wild to survive. As they are chiefly bred for use as domesticated animals, they don’t have strains that exist purely in the wild. In fact, those that are found in public waterways are usually escapees or their offspring.
Today’s goldfish breeds are the product of artificial selection and captive breeding between wild Carassius auratus specimens. These ancestors, which are native to southern China, don’t typically have the characteristic orange, gold, or red colors of the domesticated breeds. Their wild-type coloration is more olive, silvery, or bronze-toned, and is somewhat unremarkable. Despite this difference, they are still considered one and the same species as goldfish because they share an identical genetic code. Domesticated strains are sometimes given a subspecies name of C. auratus auratus.
Wild-type C. auratus have a fairly diverse diet and can easily survive in natural systems with ample vegetation and structure. Though goldfish can adjust their diet to survive in the wild, just as their ancestors do, freeing them into natural systems is frowned upon and potentially harmful to the environment.
The Natural C. auratus Habitat
In the wild, C. auratus and escaped domesticated goldfish are able to thrive in a wide range of freshwater systems. As coldwater fish, they favor calm ponds, lakes, rivers, ditches, and lagoons with mild temperatures. The optimal temperature for peak survival rates is 25˚C (77˚F), though they can tolerate dips of up to 0.3˚C (32˚F) in winter and hikes of up to 30˚C (86˚F) in summer.
Wild goldfish can also survive in brackish environments with a salinity of up to 15 ppt. Their habitat preferences are quite similar to those of Asian carp, their close relatives. Slow-moving water allows them to navigate through the water column and find food with ease. Domesticated goldfish escapees may struggle to persist in poorly oxygenated waters, particularly if they have been bred under optimized conditions. In contrast, their wild counterpart has a tolerance for low dissolved oxygen levels.
Fancy goldfish breeds, such as the lionheads and orandas, are the least capable of adapting to wild conditions as they are highly sensitive to sudden changes in water parameters. Low temperatures can compromise their health. The robust varieties (e.g. feeder goldfish) have been known for surviving in natural freshwater systems. Far from endangered, these farmed fish can easily overcrowd local waterways with ample bottom structure.
Goldfish as Omnivores: Captive vs Wild Diet
As a close relative of koi carp, goldfish share their food preferences. One of the key differences between the nutritional needs of both domesticated species lies in their need for high-protein sources. Mature goldfish are more likely to persist on a selection of low-protein food choices. Nonetheless, their omnivorous nature still entails the need for substantial protein.
Captive goldfish are usually fed fish flakes or pellets, along with the occasional high-protein treat (e.g. bloodworms, brine shrimp). These treats are not necessarily harder for them to come by in the wild, particularly if they occupy ecologically stable systems. In natural ponds and lakes, wild goldfish and escapees subsist on a mixed diet of the following items:
- Plants
- Algae
- Detritus
- Small crustaceans
- Aquatic insects and their larvae
- Small snails
- Worms
- Zooplankton
- Amphibian larvae
- Fish eggs, fry, and smaller fish species
Their capacity to metabolize vegetation, including detritus, may give them an edge compared to native fish species that have a preference for live, moving food. Pet goldfish are quite accustomed to eating immobile food items, so they may be less picky when it comes to feeding in the wild. Conversely, wild-type goldfish may have a harder time adjusting to fish feeds if they are introduced into an aquarium setup.
Feeding Habits of Captive vs Escaped Goldfish
Escaped goldfish may be called opportunists as they’ll readily feed on most types of organic matter. They may feed across all levels of the water column, particularly in shallow bodies of water. Wild-type C. auratus, however, are typically bottom-feeders. In tanks, domesticated goldfish may be accustomed to feeding on the surface as many types of fish feeds tend to float or must be drenched in water to sink.
It is fully normal for pet goldfish to look for food along the bottom of a tank, especially if there are excess feeds trapped in between bottom substrates. Observe bottom feeders from time to time to monitor their energy levels. If they appear pale and remain immobile, it is more likely that they are gravitating toward the bottom due to stress instead of hunger.
In the absence of live prey in the wild, goldfish obtain the necessary nutrients by nibbling on plant or algal material. They may also occasionally scavenge on decaying meat, particularly if they have been fed with frozen, high-protein treats in captivity. Their fry will likely consume microbes, zooplankton, and floating plant material.
How Often Do Goldfish Eat in the Wild?
Goldfish are poikilothermic fish, which means the frequency with which they eat and how much they can consume on a daily basis is largely dependent on water temperature. During warmer months, they are able to metabolize a higher amount of food and are thus capable of eating at a higher frequency. In the wild, they tend to eat small amounts of food at multiple periods throughout the day. However, if they are able to consume considerably-sized prey, they are likely to eat at a lower frequency.
Once temperatures drop in winter, their rate of food consumption will likewise drop significantly. They are unable to metabolize at efficient rates in low temperatures, so feeding at this time may be detrimental to their survival. In large waterways, where the lower reaches of the water column remain fairly warm, they may eat minimal amounts of food. They are also more likely to consume plant material at this time for two reasons – the breakdown of carbohydrates requires less energy and the chances of finding live prey in the cold may be reduced.
This feeding behavior may be observed in outdoor garden ponds that are fully exposed to changing temperatures throughout the year. This is why the frequency with which pond goldfish (and all carp species in general) are fed must be altered through the seasons. Feeding during winter may simply result in the accumulation of rotten feeds and eventually de-optimize water parameters.
Ecological Impact of Goldfish Escapees
As C. auratus auratus is not native to North America or Europe, it has the potential to become an invasive species in these areas. In the US, goldfish that have escaped from the pet trade have eventually proved to be a pest fish in public waterways. In some areas, they have even managed to produce self-sustaining populations that have drastically altered the ecological structure.
The first goldfish releases in the US took place centuries ago. As early as the 1800s, ornamental varieties of C. auratus began to reproduce in natural freshwater systems. They may have been released into these systems in an effort to diversify the existing fauna. More accidental and intentional introductions into wild systems have occurred since then, resulting in feral populations of this beloved pet.
As generalists with schooling behavior, goldfish may place heavy grazing pressures on well-established freshwater systems. As a result, they directly compete with native fish species for food. With their tolerance for aquatic pollutants, they are more likely to survive in disturbed systems compared to many secondary consumers. When found in large feral populations, they can disrupt sediments and increase turbidity levels due to their bottom foraging behavior. These combined effects make them a nuisance species that threatens local biodiversity.
Despite their impact on wild freshwater bodies, they are continuously introduced by pet owners who aren’t aware of the resulting ecological implications. Escapees also include goldfish that find their way out of hatcheries, overflowing ponds, or those that are used as baitfish. In some cases, they are introduced into the wild as a mechanism for mosquito control in stagnant waters. Nonetheless, there are now regulations that make their casual release and use as bait fish illegal.
Turning the Tables – Wild Predators of Goldfish
Fortunately, a goldfish’s own capacity to eat a wide range of food types doesn’t make it immune to the appetites of carnivorous fish. Virtually any type of apex predator can easily consume a fully grown goldfish. The problem is there simply may not be enough of them to regulate goldfish populations. Goldfish may also grow remarkably large in the wild – up to several times their typical length in an aquarium setup. This makes them more difficult for carnivorous fish to consume.
Alligators, waterfowl, mammals, reptiles, and other river monsters will readily feast on the largest of goldfish, but this vigorous pet may reproduce at rates that are far too fast for them to be depleted. Goldfish have become quite the anomaly in the natural world as they are a domesticated species with a knack for surviving in the wild. The next time you intend to let a goldfish lose, think again! They’re cute in an aquarium, but definitely villainous in the natural world.
