Last week I came across an article in the New York Times that described a species with which I am very familiar. It is a species that lived in my home for over a decade entertaining both my children and my cats. It is a species for whom many friends of mine devote a great deal of time, resources and energy to keep in luxurious captivity. The article, though, looked at this remarkably innocuous animal, an animal that is the poster species for a calm, quiet, peaceful existence, from an extremely unexpected point of view. The article described goldfish (Carassius auratus) as quite possibly the most dangerous and destructive exotic, invasive species affecting our aquatic ecosystems today!
Goldfish? Really? I might have expected that Burmese pythons, or walking catfish, or sea lampreys, or zebra mussels, or even sewer-reared crocodiles would take on the mantle of “worst exotic aquatic species.” After reading the article, though, I can understand the case being made against the goldfish!
I have frequently written about invasive species in this blog. Looking back over the posts published in just the past year I found many exotic, invasive plants (like multiflora rose, Japanese knotweed, Amur honeysuckle, garlic mustard, and tree-of-heaven) mentioned in the context of hikes and explorations of my yard and field. I also found several exotic invasive birds (English sparrows, European starlings) in my discussions of my bird feeder and surrounding nesting communities. There were also exotic invasive insects both invading my house and garden (pavement ants and brown marmorated stink bugs) and also threatening the trees in my woodlot and in the surrounding forests (emerald ash borers, wooly adelgids, and Asian long horned beetles). There are also exotic, invasive insects lurking in the margins of our ecosystems (like the Asian tiger mosquito) that may act as vectors for serious human diseases!
I have described house cats as exotic invasive species (their ability to destroy populations of birds and small mammals is almost human in its pace and completeness!), and have even reported that some ecologists look at the wide array of introduced European earthworms (including the very familiar “nightcrawler”) as remarkably destructive exotic species that have decimated the leaf litter habitats of a wide range of invertebrate species. A few years back, I also wrote about the invasive consequences of introduced eucalyptus trees in Peru. The eucalyptus’ allelopathic root and leaflet chemicals poison the soil they grow in for many decades even after the trees have been cut and removed!
Humans have sculpted entire biomes out of invasive species! It is the world in which we live!
But, back to goldfish.
My own experience with goldfish started in the early 1990’s. I bought a ten gallon aquarium for my children and then took them to the pet store to let them pick out two goldfish each. At the pet store neither child noticed that the tank from which they were going to make their selections was labeled “feeder fish.” These fish had a very short expected life span and were destined to be given to larger, carnivorous fish as meals and snacks. The four fish they picked out were very distinctively colored and patterned so it was easy to tell them apart. They were named according to a popular cartoon video of the time (“The Land Before Time”) so, without any sense of irony at all we had goldfish named “Little Foot,” “Big Foot,” “Sara” (which was actually “Cera” from the triceratops in the cartoon), and, in a return to goldfish standard names, “Goldie.” Big Foot, because of her great appetite and rapid growth rate eventually came to be called “The Hog.”
The four fish were wonderful. All four grew into substantially sized individuals (Hog, of course, was the largest). They all would have grown even larger if I had put them in a larger aquarium (and this is a characteristic of the species that we will come back to in a few minutes!). Watching the fish tank was almost as good as watching television (our cats actually seemed to prefer the tank to any of the TV shows or video cartoons regularly shown in our living room).
Little Foot, Hog, Sara, and Goldie lived for just over ten years, and many people have expressed surprise that goldfish were able to live that long (cleaning the tank every week helped to keep their environment free of toxins and pathogens. The tank cleaning was my job, of course). Ten years, though, is not really an unexpected time frame for goldfish. They can live for up to twenty years in the wild or up to thirty years in captivity. The way we have been exposed to goldfish, though, has not stressed their amazingly long potential life spans. Instead, starting with U.S. government (Commission on Fisheries) programs that gave away goldfish to Washington D.C. residents back in the late 1800’s (over 20,000 free fish a year!) up to every carnival or fair that had glass bowls and plastic bags of goldfish for game prizes or giveaways, goldfish have been presented to the public as a disposable ornamentation, and this brings us back to discuss some of their characteristics that make them such a dangerous exotic invasive species.
As we mentioned before goldfish will grow to a size that fits the environment in which they live. In a small aquarium, the fish will stay small. In a larger aquarium, the fish will get larger. If a goldfish, though, lives in a pond or a river, they can really exert their growth potentials almost without limits! Four pound goldfish, sixteen inches long are regularly found in the wild! And, with humans thinking of goldfish as disposable knick-knacks, many of them have ended up in previously wild ponds and streams!
The behavior of the feral goldfish in their habitats is also quite destructive. They swim just above the soft bottoms of their rivers and lakes and uproot aquatic plants and roil up sediments causing the water to become turbid and throwing its nutrient composition out of balance. Out of control algae growth often follows (further spurred on by the nitrogen rich excretions of the goldfish themselves). The goldfish also eat everything (especially small invertebrates and fish eggs) and destroy established food chains and reproductive cycles. They can also transmit a number of exotic parasites and diseases which can decimate the other fish in their streams and ponds.
Female goldfish can produce up to forty thousand eggs a year! Goldfish can also interbreed with many species of wild carp and generate an invigorated array of hybrid species. With an absence of effective, natural predators a large percentage of the young goldfish survive to breeding age setting up an explosive cycle of exponential growth.
Goldfish are also very active swimmers. A single individual can regularly swim many hundreds of yards up and down a river each and every day. One monitored, feral goldfish swam over 140 miles along a river during an observation year! Goldfish are also able, possibly instinctively, to find suitable spawning habitats in which their offspring have very high probabilities of success and survival.
The other characteristic of goldfish that add to their potential to be an extremely destructive, invasive species is their intelligence. They can be trained to do complex tasks and even to recognize and respond to different pieces of music! The Times article mentioned an engineer from Pittsburgh who trained his goldfish to push soccer balls into nets. While the abilities to play soccer and to tell Mozart from Beethoven are not direct survival aids in the wild, the high cognitive skills displayed by this species make it an efficient problem solver and rapid learner and a formidable adapter to almost any ecological milieu.
So, as we consider the world and our geological era as re-made by humans, that “Anthropocene” all around us, let us not forget out dear friend (and mortal, ecological enemy?) the goldfish!