That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information
Concerns over the use of goldfishes (Carassius auratus) as a food item for reptiles and amphibians have long been recognized, yet there remains a bit of confusion on the topic. References to Vitamin E deficiencies in animals kept on fish-based diets, a separate problem entirely, often further clouds the issue. Prompted by recent comments on our blog, I thought I might address the subject in this article.
Goldfishes and Large Pets
The controversy is important because goldfishes are the least expensive and most readily available “feeder fish”. They are also available in a wide variety of sizes, allowing owners of large reptiles and amphibians to offer their pets a whole fish, and a more substantial meal than a large golden shiner. This is preferable, from a nutritional standpoint, to feeding cut pieces of a Tilapia or other large food-market fish.
A Valuable Resource for Live-Food Specialists
Goldfishes are also quite hardy and usually remain alive when introduced into an aquarium, even when subjected to large temperature changes (drastic temperature changes quickly kill other typical feeder fishes, such as golden shiners and fathead minnows). This allows us to more easily feed aquatic live-food specialists, such as mata mata turtles and tentacled snakes, and American bullfrogs and other large amphibians.
I once cared for a large, wild-caught alligator snapping turtle that refused to eat fishes unless, as in nature, they investigated his tongue’s “fishing lure”. Goldfishes adjusted so well to the exhibit’s water that they would try to eat the turtle’s worm-like lure in short order.
The Origin of the Goldfish Problem
I was fortunate in having been involved in the specific incident that led to the discovery of the nutritional problems associated with goldfish-based diets. During my early years at the Bronx Zoo, it was noticed that mata mata turtles (Chelus fimbriatus) that were fed solely upon goldfish thrived for about 5 years, and then died suddenly. The odd phenomenon, it turned out, was not limited to the Bronx Zoo, and had occurred in several other collections.
Necropsies of the turtles revealed liver and kidney damage, and problems indicative of Vitamin A overdose (this last was later disputed, and has not been proven conclusively).
Using Goldfishes
Experience has since established that goldfishes may be safely fed to reptiles and amphibians on an occasional basis, i.e. once monthly, but should not be used as a dietary staple.
Another Concern?
Some years ago, I came to learn that some commercial goldfish farms raised their stock largely on chicken droppings supplied by local poultry farms (goldfishes, it seems, are quite hardy…and goldfish farm owners equally resourceful!). I do not know if this is still the case, but often wondered about the possibility of Salmonella contamination. I’ve never run across or read of a problem…but looking into it might make for an interesting project.
Further Reading
Please check out the following article for another experienced turtle keeper’s view on goldfishes as a food item, and for a description of the mata mata turtle’s unique strategy of “herding” fishes and other prey.
http://www.tortoise.org/archives/matamata.html.
Great article. I was always wondering if goldfish could be a replacement to rodents… I raise a tegu at home, and goldfish are great LIVE food for them, as it is very difficult to purchase a live mouse or a rat in Japan.
I have given those fishes maybe as often as once a month so I’m guessing that won’t be a problem…
Thanks Frank.
Hello Jake, Frank Indiviglio here. Thanks for your kind words and interest in our blog.
Fish are a fine substitute for rodents, at least for the black and white tegu (Tupinambis merianae) and most likely for the red (T. rufescens) as well. During field research in Venezuela I noticed that black and white tegus moved out into the flooded grasslands during the rainy season when forging. Although based on only casual observations, I noted that they took a great many fishes (and frogs, freshwater crabs, small turtles) at this time. I have also used fish extensively for captive animals.
A once monthly feeding of goldfish will cause no harm. Of course, you’ve quite a food market selection there in Japan as well – I spent some time there, in zoos and aquariums, and was floored by Tokyo’s giant Tsukiji fish market. Stay with small, whole freshwater species when possible, perhaps some small crabs or large prawn as well. If you are near any of the coasts, bait shops might be an option in terms of dietary variety as well.
Tegu generally switch onto non-living food readily, if that might be helpful to you.
You may be interested in some tegu field notes I have included in another article on this blog. Please check out Notes From the Field: an Aggressive Black Tegu when time permits.
Please be in touch if you need further information. Good luck and please keep me posted.
Best regards, Frank Indiviglio.
Hi Frank,
Glad to find such an interesting blog. I have 1 year old matamata, and used to feed him gold fishes. He can normally consume 4-5 fishes/day. It has been almost 2 weeks now that he refused to eat. I tried to change the fish to platies, also change the goldfish size with no success. He still look active during his short-daily basking, but go back to sleep as soon as he is returned to his aquarium. Any suggestion of what might be the cause? Thanks a lot Frank.
Hello Benny, Frank Indiviglio here. Thanks for your kind words and interest in our blog.
You mentioned “daily basking”…by this do you mean that the turtle is being removed from the water each day? If so, this would be a source of stress, even if the animal had adjusted to it early on. Mata mata turtles are entirely aquatic and inhabit murky waters with plenty of cover. Some UVB might be absorbed when they are in very shallow water, which is rare, but they obtain the bulk of their D3 from dietary sources. Absent shell fungus or related problems, they should not be removed from the eater for basking.
You might also check that the turtle has enough space, and try adding extra cover in the form of floating plastic plants. Mata mates are fairly shy, and, although not very active, do not take well to close quarters.
I’m not sure how long you’ve had the animal, but newly imported turtles sometimes gorge for a time no matter how they are kept. As they gain weight environmental factors take precedence over hunger.
Daily feedings may be a bit too much…bear in mind that a captive animal is expending very little energy in most cases. Growth does take calories, of course, but it can only account for so much. If the turtle commences feeding, try offering food every other day or so, and add in longer fast periods from time to time.
If you have not done so, please also check your water quality, i.e. ammonia and pH (please write back if you need further information).
Of course, any number of physical maladies might be at work as well. Fecal tests and follow up treatment of parasites are usually indicated for wild-caught animals. A veterinary exam would be in order as well if the animal continues to refuse food.
Good luck and please keep me posted.
Best regards, Frank Indiviglio.
I have a 18 month old Matamata female. Her diet mainly consists of goldfish. I read that can be dangerous. I want to ensure she will live a healthy and long life. What can I feed her? In addition keep in mind her “food” is dropped in her tank live and she eats them live.
Any information you can give me would be great.
Hello Todd, Frank Indiviglio here.
Thanks for your interest in our blog. Yes it’s inevitable that a solid goldfish diet will kill the turtle after a few years. Minnows are available at some pet stores, but are small. Golden shiners are ideal, but you may need to order from a bait store supplier (check local bait stores, if there are any near you as well) in large quantities. Storage requires a cool, filtered aquarium etc….not an easy task. A minnow trap or seine net can be used to catch native freshwater fishes if legal. Saltwater baitfish (mummichogs, etc) can also be bought or collected, but should not be used as the sole diet.
Another option is to accustom your turtle to feeding from a long-handled tong; most I’ve worked with have taken to this, even wild0caught adults. Then you can order shiners and freeze most.
Fresh water fishes can also be purchased at food markets (tilapia, trout, perch, etc); they can be cut and fed via tongs. This is not ideal, as organs and skin are important, but useful to add variety to the diet.
Lots of work, but well-worth it; these unique turtles are quite special, and we need to learn more about breeding them in captivity,
Please let me know if you need further info,
Good luck and please keep me posted.
Best regards, Frank Indiviglio.
Hi,
I have an 8 cm mata mata I have for 4 months now.. I had been feeding it a mixture of feeder goldfish and and feeder guppy (not the fancy colorful tailed one)
After reading this article and several others I think goldfish is a bad idea.. Should I now completely remove goldfish from the diet? How about a feeder guppy only diet will it be ok?
My local petstore only have feeder goldfish and feeder guppies
Hi Vincent,
You raise a very good question. Unfortunately, no studies have been done, as far as I know, re the effects of diets containing some goldfish along with other species. The Bx Zoo and others have removed goldfish completely from the diet. I’m not sure that is absolutely necessary, and I know of several adult turtles that are in good health and receive goldfishes on occasion, but I have no specifics as to how many, etc. The safest course of action would be to remove goldfishes entirely.
In zoos, we rely mainly on minnows and shiners; try looking at other stores, if there are any, or bait stores. If you find one that is far away, perhaps you can make an occasional trip and stock up. The fish can be kept alive, but this is easiest if you have a cool basement available (when warm, they eat alot, produce waste, etc). Try habituating the turtle to dead food offered via tweezers/tongs, or just nudged towards it with a hand. Then you’d be able to freeze feeders, or purchase trout, tilapia etc at a food store and cut into strips (whole fishes better, but this fine as a filler)
Frozen silversides and other whole fishes sold for aquarium use may also be tried; however, these are salt water species and should not be used as the sole diet, if accepted at all.
Guppies alone should be fine, but you’ll need a lot of them in time; you can add platies, mollies, etc, but this will become expensive.
Please let me know of you need further info, Best, Frank
Hi frank, thanks for the info.. You speak about stocking live fish and adding mollies/platies…
I was thinking.. I have an outdoor pond which used to have koi fishes until for some strange sickness it all died… Country I live in have really bad constant rain season which I think is bad for fishes needing good water quality
Im thinking to breed the guppy/platy and mollies you suggested in the pond instead of stocking it up so later I can have constant food for my mata.. Are they easy fish to breed? Are they hardy fishes? Are they suitable outdoor pond fish? Is there a good care sheet for these fishes and can I mix them all up in a pond?
Also, I keep my mata in a 40x30x30 cm tank without filter but I change it’s tank water once a week.. Is that okay or will the constant weekly changes stress the turtle? If I change the water, is it better to keep some of the water or is it fine to change all of the water?
Thank you your help is much appreciated
Hi Vincent,
Mollies, guppies, platies, swordtails usually breed explosively in an outdoor pond (mollies do best with a bit of salt in the water, so stay with the others); all are live bearers. They will eat the young but if you stock with plenty of plants most will escape. They are small, so insect predators can cause losses if they become established. In some cases, you need not feed them at all, they will do fine on mosquito larvae, daphnia etc that will establish in the pond, and insects that fall in. Adding fish flakes each day will boost growth and breeding. Water should be 72-82, growth best at higher temps (where are you located?) Other live bearers or in some cases egg layers can be used. weather loaches get large, and are a good food source, but may not breed in all ponds. You can mix all, swrds and platies will hybridie and produce interesting offspring. Mosquito fish, if available, also breed readily.
Try partial changes 1-2x weekly (just scoop out and add fresh water) and a full change. Change can be stressful, but water quality impt to matas (seems you favor interesting but delicate species!). During change, place turtle in a container of water with floating plants for cover. Full change is fine as long as you avoid drastic temperature changes.
Pl keep me posted, enjoy, frank
Thx frank,
Since you mention water quality, what quality/ ph of water do matas prefer?
Also You mention floating plants for cover, I assume that function is to reduce stress so can I just use a plastic one? Anything else I should add to the setup that is easily washable/cleaned for regular weekly water changes?
Thx
Thx
Hi Vincent,
pH of 5-6 is preferable; water quality should be managed as for tropical fishes – ammonia near 0/ low nitrites, etc.
Yes, plants are for cover, so plastic is fine. If you can arrange very strong lighting, live water hyacinth, water lettuce and related species will assist in water quality control between water changes. Removing substrate will help (in the wild they burrow into mud, dead leaves, but most will adjust to resting below floating/submerged plants, etc.) A few large smooth stones will assist with traction if that seems to be a concern. Scooping or siphoning some water out and replacing each day, even if water appears clear, is useful (sorry if obvious, but never start a siphon with your mouth, as was common practice in years past).
Please keep me posted, best, Frank