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.

Bent-toed geckos (Genus Cyrtodactylus, i.e. C. louisiadensis and C. irianjayaensis) are becoming ever more popular in captivity but, while a fascinating group, their care is often fraught with difficulties, and there is a great deal of conflicting information being circulated. A recent note from blog reader Dave, upon whom I can always count for interesting comments and questions, brought these wonderful creatures to mind again.

Dave noted the scarcity of husbandry information regarding bent-toed geckos, and mentioned that his lizard, purchased as a giant bent-toed gecko, was not feeding with very much vigor. Following are some exerts from my response to Dave, along with a few additional notes.

The Genus Cyrtodactylus
So far, 115 species have been described in the genus Cyrtodactylus. The giant bent-toed gecko is often sold as the “New Guinea phase” of C. louisiadensis, but is actually a separate species, C. irianjayaensis. To further confuse matters, stores sometimes mix up the various species, and coin their own names.

There are still many questions as regards the husbandry and natural history of the giant bent-toed gecko. Over the years, I’ve had a number of little known species of the same genus (Cyrtodactylus) pass through my hands, and have found the following general principles to be of use.

The Importance of a Secure Environment
Give the animal as much space as possible, with lots of cover and places to climb…suspended pieces of rolled cork bark make perfect shelters. Bent-toed geckos are very stress-prone, but don’t always exhibit the behavioral signs of stress – flight, panting, threat displays – so commonly seen in other lizards; disturb it as little as possible. These are definitely animals to observe, not handle. A night-viewing bulb will allow you to watch the lizard as it goes about its nocturnal wanderings without undue disturbance.

Providing Security
One useful technique that works with animals of all types is to provide a solid wall or two. You may notice that well-run zoos rarely exhibit animals in cages having all sides are open to view.

In an aquarium, you can cover some of the glass with dark paper or cardboard. Even where shelters are available, this simple step often makes a great difference in the animal’s welfare, and brings about immediate changes in its behavior.

Next time I’ll cover lighting and feeding, including a note on the use of snails in the diet of this and related geckos.

Further Reading
A listing of all species with the genus Cyrtodactylus, along with range information, may be found at
http://www.jcvi.org/reptiles/search.php?submit=Search&exact%5B%5D=genus&genus=Cyrtodactylus

The image pictured above  was referenced from Wikipidia and features a related species; not the Giant Bent Toed Gecko. Originally posted by W.A. Djatmiko.

Charles Darwin said of the lowly earthworm (Lumbricus terrestris): “It may be doubted that there are many other animals which have played so important a part in the history of the world as these lowly organized creatures”….this in deference to the fact that the 50,000 earthworms that may populate each quarter acre of farmland aerate and fertilize 18 tons of soil annually!

More to the point here, earthworms come close to being a complete nutritional package for many amphibians and certain reptiles.  Although based largely upon experience, this statement is also borne out by research…one study showed that earthworms provide adequate levels of several important nutrients, including Vitamins E and A, for many vertebrate species.

A Valuable Food for Many Pets

I have raised spotted and red salamanders and green, bronze and leopard frogs from metamorphosis through adulthood on an earthworm-only diet, and use them for 50-75% of the diets of many other amphibians.  Although refused by many lizards (but relished by American and European glass lizards), earthworms are taken by most predatory reptiles.

Larger earthworms, collectively termed “nightcrawlers”, offer a healthful alternative to rodents for those keeping largely insectivorous species (i.e. basilisks, African bullfrogs), which are often erroneously fed a rodent-based diet in captivity.

I’ve also had excellent results when using earthworms as the main food for bullheads and other fishes and for certain tarantulas and centipedes. They may also be fed to marine animals, but expire and decay rapidly in salt water.

Using Earthworms

Earthworms may be broken into small pieces to feed tiny pets.  However, a whole, small earthworm is more nutritionally complete than is a piece of a larger worm. Uneaten earthworms will remain alive in aerated freshwater for up to eight hours, but decompose rapidly upon death.

Obtaining, Storing and Breeding Earthworms

Earthworms may be purchased from bait stores and commercial breeders or collected, and store well in damp sphagnum moss under refrigeration.

Earthworms breed readily in captivity but, being intolerant of temperatures much above 70F (50-65 F is ideal), are best raised in a cool basement.  They can be easily cultured in a screen-covered garbage can filled with alternating layers of moist soil and dead leaves.  Ample air flow is important, but they will wander at night if left uncovered.

Earthworms can be raised on a variety of diets.  I use dead leaves, tropical fish food flakes, oatmeal and cornmeal, into which is mixed a powdered calcium supplement.  Placing the food on the surface, beneath a layer of damp burlap, simplifies collection.

Nutrient Loading

Earthworms consume large amounts of soil while feeding, and therefore their nutritional profile will vary with collection location.  If you buy eathworms for immediate use, try to feed the worms for a day or so as described above before offering them to your pets.

Earthworms and Pesticides

In the course of tunneling through the ground, earthworms may ingest pesticides and other harmful substances.  I’ve not had any problems with wild-caught worms, but a diet of earthworms contaminated with organochlorine pesticides has tentatively been linked to the disappearance of striped skunks on Long Island, NY.  If unsure, purchase your earthworms from commercial farms.

Further Reading

For more information on using earthworms and other invertebrates, please see my article Feeding Large Insectivorous Reptiles and Amphibians.