That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

In Part I of this article we discussed the origin and current state of the problems associated with the long term use of goldfishes as a staple food for reptiles and amphibians.

Bait and Tropical Fishes

Fathead minnows, golden shiners and related fishes are preferable to goldfishes as a reptile and amphibian food, and may be used as dietary staples where appropriate. They are generally raised in outdoor ponds or wild-caught, and have fed on a variety of invertebrates, plants and other natural food items. This renders them a highly nutritious food item.

Whenever possible, you should alternate the species of fish offered. This is especially important for water and tentacled snakes, mata mata and alligator snapping turtles, Surinam toads and other species that feed primarily upon fish. Many common pet trade tropical fishes are nutritious and easily-reared, including swordtails, platys, guppies and mollies.

Food Market Fishes

Food market fresh water fishes (i.e. Tilapia and catfish), especially those which can be obtained whole, are another useful option. I fed the Bronx Zoo’s gharials (large, piscivorous crocodilians) on trout for many years…but that cost upwards of $1,000/month – 20 years ago!

Collecting Native Fishes

Where legal, you can add vital nutrients to your pets’ diets by collecting freshwater fishes via seine net, trap or pole. I always remove the dorsal and pectoral spines of catfishes, sunfishes and other well-armed species, just to be on the safe side.

Fish and Vitamin E

The Vitamin E question has also been investigated…I’ll write more on that in the future. For now, please be aware that frozen fish of any kind, used as a dietary staple for crocodilians and turtles, has been implicated in Vitamin E and other deficiencies. Marine fishes, frozen or fresh, seem to block vitamin absorption when fed in quantity to fresh water animals.

Further Reading

I must say that, food considerations aside, I like goldfish! Please check out our blog article Carnival Fish for some interesting background on their habits, care and long history as pets.

The books Snakes: the Keeper and the Kept and Snakes and Snake Hunting, written by Staten Island Zoo curator Carl Kauffeld, turned “Okeetee, South Carolina” into a household name for legions of snake enthusiasts worldwide (myself included). An incredibly productive snake collecting area, Okeetee was especially noted for its brilliantly colored corn snakes, Elaphe (Pantherophis) guttata, and abundant Eastern diamondback rattlesnakes (Crotalus adamanteus). A road sign from the area still graces the corn snake exhibit at the Bronx Zoo, where I worked for many years, and photographs taken from collecting trips to Okeetee in the 60’s and 70’s line the back rooms of the zoo’s 100 year old reptile house.

The Influence of Okeetee

These “Okeetee corns”, as they became known, were largely responsible for the explosion of interest in captive snake breeding in the late 60’s and 70’s, and ushered in a new age of husbandry innovations; today the corn snake remains the world’s most commonly bred snake species. Corn snakes have provided untold numbers of aspiring herpetologists with an introduction to snake keeping and snake breeding, and have played an important role in a number of research efforts.

Preparing Snakes for the Breeding Season

For those of you who plan to breed corn snakes, now (late summer) is the time to begin preparations. Your snakes should be fed heavily until autumn, at which time they can be chilled to 50-59 F (after a 2 week fast) for 6-8 weeks. Although corn snakes may reproduce at the tender age of 11 months, breeding should be withheld until they are at least 2 years of age…females that are bred too early often fail to attain full size, and tend to produce small clutches and weak offspring.

Mating occurs from March to June in most regions, with the eggs being laid 25-50 days thereafter. A second clutch may be produced in late summer/early fall. An average clutch consists of 16 eggs, but may range from 6-26. At 82 F, incubation time averages 62 days in length, and the young are 8-11 inches long upon hatching.

As we will see in Part II of this article, years of intense captive breeding efforts have produced a mind-boggling array of corn snake morphs, strains and hybrids. The reproductive cycle of all parallels that just described, but individual details, such as clutch size, etc., will vary among the various types of corn snakes.

Further Reading

The Southwestern Center for Herpetological Research has posted some informative notes and blog entries concerning the influence that Carl Kauffeld and Okeetee, SC have had on the snake-keeping community:
http://southwesternherp.com/cgi-bin/yabb2/YaBB.pl?num=1215719054.

The care of corn snakes roughly parallels that of black rat snakes. Please see my article The Captive Care of Black Ratsnakes for more information.

I remember well my shock when the news concerning temperature dependant sex determination (TDSD) among reptiles first broke.  Imagine…a turtle or crocodile egg can develop as either a male or female, depending upon the incubation temperature!  Well, it now seems that at least one species of lizard, the three-lined skink (Bassiana duperreyi), complicates matters even further.

Egg Size and Sex

Writing in the June, 2009 issue of Current Biology, University of Sydney biologists have revealed that large skink eggs develop into females, while small eggs become males.  Furthermore, removing yolk from a large egg resulted in a male hatchling, despite the fact that female genes were present; adding yolk to a small egg over-rode the effect of the male genes already in the egg, producing instead a female.

Temperature and Sex

Extreme nest temperatures, it seems, can also affect the hatchlings’ sex, regardless of its genetic makeup, resulting in xx chromosome males (males are usually xy) and xy females (females are typically xx).

Survival and Conservation Implications

The question that begs answering, of course, is why has this lizard evolved such a unique and complicated reproductive strategy?  Researchers are now looking into its ecology to determine the answer.

Understanding such matters has greatly assisted those working to conserve reptiles and amphibians.  Knowing the parameters of TDSD has allowed us to pick and choose the sexes of highly endangered species being bred in zoos, so that a favorable sex ratio can be maintained.

Of course, there were some problems early on.  I was working with green sea turtle head-start programs in Costa Rica when TDSD first came to light.  The organization I was with had been gathering sea turtle eggs for 30 years, incubating them, and then releasing the young when they had grown past the vulnerable stage.  Great in theory…but by using a single incubation temperature, we may have produced only female green turtles for the entire 3 decades!

Further Reading

You can read more about the natural history of the three-lined skink and its relatives at http://www.jcvi.org/reptiles/species.php?genus=Bassiana&species=duperreyi.

I frequently recommend wild-caught invertebrates as food for captive herps, birds, invertebrates and fishes. Today I’d like to address the thoughtful comments posted by some of our blog readers regarding potential pesticide contamination.

Secondary Poisoning

Secondary poisoning, the killing of animals other than the species that is the target of a pesticide, is an important concern whenever toxins are used.

Modern Pesticides

Commercial pesticides have evolved quite a bit since the secondary poisoning effects of DDT were documented in the 1960’s. Today, a combination of species-specific products and short half-lives (the time the pesticide remains lethal once applied) greatly reduces the risk to non-target species. This is especially true where West Nile Virus control and similar programs are undertaken by local municipalities…the chemicals used are carefully evaluated, and follow-up studies are implemented.

Secondary Poisoning Facts

As regards captive animals, the concern is that they will be affected by a pesticide after consuming food animals that have themselves been exposed.

While valid, such is not quite as likely as it may appear at first glance. Even as regards the highly publicized DDT scenario, the effects of DDT were manifested largely among top consumers (eagles, ospreys and other raptors) that consumed, over many years, fishes and birds that had concentrated the toxin in the course of feeding upon insects.

The non-target species were not killed outright, but the cumulative effects of the concentrated DDT rendered bird eggshells brittle and subject to breakage. There are, of course, exceptions…but, in any event, pesticides now in use are formulated so as to exert far less radical effects on non-target species.

Zoo Practices

During my 30+ years working with major zoos, aquariums and nature centers in the USA and Japan, wild-caught invertebrates have often been used to supplement the diets of reptiles, amphibians, birds and other creatures. The use of light-based insect traps (i.e., the Zoo Med Bug Napper) has been a standard practice in zoos long before my time in the field; laboratory analysis of invertebrates so collected has supported the safety of the practice as regards most species.

All major zoos use insecticides to kill roaches and rodenticides for mice and rats. Except in very unique situations, it is simply impossible to control such pests by other means. Roaches and mice survive for varying periods after being sprayed or consuming poison. During that time, they enter enclosures housing animals that prey upon them (this is well documented by cameras installed to record nocturnal behavior). During my time in the zoo field, the only local case of secondary poisoning that occurred involved a wreath-billed hornbill that consumed poisoned mice nearly exclusively over a period of years.

My Collection

In my collection, the use of native invertebrates dates back over 40 years. In a great many cases, animals that I have kept on such diets have reproduced and even set or approached longevity records (musk turtle, still alive at age 40; marine toads, 20+ years; African clawed frog, 19 years; weather loach, 19 years). My experience is echoed by many of the prominent hobbyists and herpetologists with whom I have long worked.

That being said, there are specific species and situations that warrant caution. I’ll cover these in Part II of this article.

Further Reading

Please see my article Collecting Invertebrates: an Entomologist’s Technique and the articles referenced there for further information.

One of the world’s rarest amphibians is being bred by dedicated hobbyists and is now available in the US pet trade. Anderson’s salamander, Ambystoma andersoni, which was only formally described in 1984, is limited in range to a single high altitude (6,000+ feet above sea level) lake and stream in south-central Mexico (Laguna de Zacupa, Michoacan, Mexico).  The IUCN lists it as “Critically Endangered”.

Rare Aquatic Salamanders of Mexico’s Highlands

Anderson’s salamander is part of a complex of similar aquatic, neotenic salamanders which includes the Mexican axolotl (A. mexicanum).  Neotenic species retain larval characteristics such as external gills and an aquatic lifestyle upon maturity.

A dozen or more species of these unique, poorly-studied amphibians inhabit mountain lakes in Mexico.  Most are found only in a single lake or, in the case of the axolotl, may exist only in canals and other habitat remnants. Some, including the Dumeril’s salamander (A. dumrelii), seem to have adapted to waters that are somewhat saline in nature.

Hope for the Species’ Survival

The sole population of Anderson’s salamanders is threatened by pollution, habitat loss and collection for the (human) food trade.  Its relative, the Mexican axolotl, was saved from extinction by captive breeding efforts, and is now in the unique position of being one of the most common captive and rarest wild salamanders.

Originally surfacing in Europe, captive-bred Anderson’s salamanders are now available in the USA as well.  This represents a unique opportunity for serious hobbyists to help learn about and conserve an endangered species. As a bonus, Anderson’s salamander is large, beautifully patterned and relatively hardy as well.

Keeping Anderson’s Salamander

The captive husbandry of Anderson’s salamander is similar to that of the Mexican axolotl (please see article referenced below)…please write in if you are interested in becoming involved what may become a most worthwhile amphibian breeding effort.  At this point, noted salamander specialist Michael Shrom is likely the only person breeding Anderson’s salamanders in the USA. You can contact Michael at shrommj at ptd.net.

Further Reading

You can read more about the natural history of Anderson’s salamander and its relatives at http://www.mexico-herps.com/caudata/ambystoma/ambystoma-andersoni.

For information on the Mexican axolotl, please see my article The Natural History and Care of the Mexican Axolotl http://blogs.thatpetplace.com/thatreptileblog/2008/12/19/the-natural-history-and-captive-care-of-the-mexican-axolotl-ambystoma-mexicanum-natural-history-part-1/.

Photos courtesy of Michael Shrom.