by Richard Lunsford

This question is very common & controversial. We have neither the controlled scientific research nor a narrow enough focus to definitively answer all the specific questions, but I can lay down basic feeding theory and offer insight. I can summarize what I’ve learned from others, read, seen and think. There are holes and I’ll try to highlight those. There are controversial points others may debate. Ordinarily I don’t write articles with such gaping holes but the need for one on this topic justifies it, despite its incompleteness.

             To answer these questions, we’ll break it down into a discussion of what turtles are, general principles of herbivores, carnivores & omnivores, establish an environmental frame of reference, review dietary-related health concerns & lay out a basic dietary plan. Don’t miss the Resources section at the end; there’s great stuff out there you can read online for free, and the books are worth having. If you just want recommendations, go to Section X.) I Recommend. The rest of the article revolves around knowledge & theory to back it up.

             Scope of this article: North American semi-aquatic basking (RES, Painted, Cooters, Maps, perhaps Chicken Turtles) & aquatic bottom-walker (mud, musk, to some degree snappers) from temperate climates. The focus is on species with at least some degree of omnivory. General principles may generalize to foreign species. Links to Tortoise Trust articles on tortoise dietary management are included at the end, with other links & references of interest.

 Contents:

I.) What Turtles Are

II.) General Principles of Herbivores, Carnivores & Omnivores

III.) Environmental Frame of Reference

IV.) Size vs. Age

V.) Dietary-related Health Concerns

VI.) Feeding Quantities

VII.) Calcium Supplementation Concerns

VIII.) Vitamin D3 Concerns

IX.) Dietary Theory Synthesis

X.) I Recommend

Appendix I.) Online Resources You Should Read On Feeding

Appendix II.) Recommended Books

 

 I.) What Turtles Are:

 

1.)    Turtles are currently classified as reptiles. There is a move underway to define them separately from other reptiles, on the grounds turtles and other reptiles arose from amphibians separately without a distinct common ancestor, just as birds and mammals arose separately from reptiles.

 

2.)    Turtles are ‘cold-blooded’ (poikilothermic; ectothermic) animals & much more ‘fuel efficient’ (a.k.a.: have less metabolic overhead) than warm-blooded animals (homeothermic; endothermic) because they do not burn up many additional calories maintaining a stable body temperature. In winter it costs fuel to keep your house warmer than the surrounding environment. Same’s true for living things. This is why some snakes can fast for months, and some shrews eat over their own weight daily or starve to death in hours. Small animals have a higher surface area to mass ratio & small mammals lose body heat much faster (& must eat much more to maintain temp.s higher than surroundings) than large mammals. Not maintaining an elevated body temp. is why small reptiles don’t need huge food volumes like mice, rats, shrews & moles do. ‘Cold-blooded’ and ‘Warm-blooded’ have different advantages; energy efficiency vs relative environmental independence & constancy. Which is ‘better’ depends on the animal’s environment.

 

3.)    Cold-blooded animals vary widely in food requirements. An Anaconda may take down a large prey item and not eat again for months. A green anole may eat many small insects daily. Note the former is a more sedentary beast designed for rare feeding of large meals, & the latter an active hunter for frequent feeding of small prey.

 

4.)    Most turtles seem more active than large constrictors (more time spent foraging for food; a large constrictor will go lay up a long time after a big meal). Still, most aren’t active 24 hours/day and some spend quite awhile basking. (Note: adult alligator snappers can be very sedentary). Most common U.S.A. native turtles will forage daily & expend energy via exercise in the process. Despite the temperate climate many warm themselves in the sun & so increase metabolic activity vs. what a strict aquatic existence would entail.

 

What I don’t know:
  • I don’t know specifically how turtle metabolic needs compare to other reptiles.
  • Turtle species vary widely in activity & in theory metabolism. Softshells are reputedly higher metabolism turtles; alligator snappers & mata matas are more sedentary ambush predators. Most turtles fall between the extremes.
  • How to factor in hibernation (& lack thereof) in wild vs captive turtles’ needs.
  • How to factor in behavioral differences (food choice & activity level) in wild turtles at different seasons (early Spring vs mid. Summer) & times (Afternoon vs. midnight).

 

II.) General Principles of Herbivores, Carnivores & Omnivores:

            In nature, few turtles are exclusively herbivorous or carnivorous given that even grazing herbivores accidentally take in an occasional invertebrate. And even such famous ‘carnivores’ as common snappers eat some vegetation in the wild. Some tortoises do come pretty close the total herbivory. You must research what your turtle’s natural diet is before planning its captive diet regimen.

            Herbivores tend to take in large volumes of low-nutrition bulk greenery (a.k.a. grazing) that is difficult to digest (& thus G.I. transit time is prolonged). Consider the multiple stomachs and chew/swallow/regurgitate as cud/chew cud/swallow again pattern of cattle! No turtle goes quite that far, but you see the point.

Carnivores tend to be sporadic feeders on smaller quantities of high nutrition easily digested foods, with shorter digestive tracts & more rapid G.I. transit times. Consider the domestic ferret, a small mammalian carnivore with a G.I. transit time of perhaps 4 hours.

Omnivores tend to run an intermediate pattern. Humans, noted mammalian omnivores, keep food in the stomach alone about 4 hours, and much longer in the intestines.

 

III.) Environmental Frame of Reference:

            To understand what turtles are, we must understand the rules of the environments they’re designed to live in. Turtles did not evolve in predator-free 55 gallon glass aquariums with Ebo-Jager submersible heaters & daily feedings. We need to look at the practical realities & demands of the natural environment, & consider what’s different about a captive environment. Note that wild environs vary wildly with latitude, longitude, altitude, seasonal variation, habitat type & degree & type of human disturbance. A wild slider in a heavily vegetated Florida marsh leads a different life than one in a sparsely vegetated Indiana cattle pond…

 

Natural Environment Basics:

1.)    Turtles are not domesticated; they are at best captively-maintained docile wild animals.

2.)    Turtles rely on instinctive drives to determine food choice & foraging.

3.)    A turtle will not reorder its instincts for a captive environment food supply.

4.)    Natural environments are often very competitive with frequent lean times.

5.)    Growing season is climate-limited & only part of the year.

6.)    Food supply is unpredictable.

7.)    Meat-based foods are nutritionally much richer than general vegetation.

8.)    Meat-based foods tend to be quite small & hard to catch.

9.)    Opportunity to eat meat-based foods must not be squandered. Omnivores like sliders & Painted will ignore plants to focus on meat-based food if offered both at once. Plants don’t run or hide, so they can wait. Turtles instinctively eat meat-based foods as though their lives depend on it because in nature they might.

10.)            Wild turtles seldom have opportunity to gorge buffet-style on meat-based foods. Wild turtles can sometimes graze at will, but meat-based foods are harder to catch and require much more energy expenditure to acquire. Therefore while adult sliders prefer meat to vegetation, wild adult sliders have more vegetation in their stomachs.

11.)            Many wild turtles need to eat well during times of plenty to carry them during times of want (i.e.: hibernation; cold weather with diminished activity & food supply; over-land migration to new water bodies).

12.)            Plants are often present in good supply & need not be ‘hunted down.’ Ergo, those turtles who eat them may graze without needing the strong instinctive drive necessary to motivate pursuit of meat-based prey.

13.)            Meat-based food intake occurs in the form of sporadic intake of small volume prey (snacking).

14.)            Plant-based food intake occurs in the form of frequent (daily) larger volume intake (frequent meals).

15.)            It’s believed wild sliders (and possibly even Kinosternids) shift to more herbivory during winter; this is discussed later in this article.

 

Captive-Care Basics:

1.)    Longer growing season (All year).

2.)    Warmer water – day & night, all year; may increase food intake & digestive efficiency.

3.)    Guaranteed steady food supply.

4.)    Captives – More sedentary. Wild - More foraging/exercise.

5.)    Captives – few worries/distractions. Wild – alert for predators; need keep lower profile.

6.)    No slowed hibernation period. Growing season 365 days/year.

7.)    No ‘time off’ to wander overland looking for new habitat or nests.

8.)    Higher protein diet. Humans offer plants & meats, the turtle is instinctively driven to take advantage of the meat opportunity, & the owner reasons the turtle won’t eat plants (& doesn’t offer them) or overfeeds meats (like letting a kid choose to eat nothing but hamburgers once he learns to ‘hold out.’)

9.)    Less low-nutrition roughage.

10.)            Captives – Eat large meals, more widely spaced (daily or every other day) - the meal/buffet model. Wild - Eat small amounts rather often (catch as catch can) – the snack model.

11.)            Hunger: Nature – hunger is normal & common, part of daily life. Survival of the Fittest creates a balance where adequate food is the rule. Humans – view hunger as a state of want, a painful, miserable craving indicative of negligence & suffering. Humans act to prevent hunger & err on the side of over-feeding.

12.)            Captive diet less varied & often unnatural (i.e.: marine-caught frozen shrimp, brine shrimp, beef heart, processed commercial foods).

13.)            Just maintaining turtles at a warm temperature 365 day/year may lead them to abnormal dietary choices (no shift to winter herbivory).

14.)            Captive-Bred captives may not have the metabolic overhead of carrying parasites.

15.)            Captives get either no UV-B light or commercial lights of much less intensity than natural sunlight in most setups; oral supplementation appears effective but exact equivalency is unclear.

16.)            Too little is known about the nutritive content of the vegetative component of wild turtle diets, making replication of this portion impossible.

 

IV.) Size vs. Age:

We could use growth charts with carapace length & weight ranges considered appropriate for individual species of turtles of various ages. It’d be nice to have online ‘bench mark’ sets for milestones (hatchling, 6 months, 1 year, 1.5 years, 2 years) for RES, Southern & Western Painted (the extremes in painted sizes), common or Mississippi maps, stinkpots, 3-striped mud and common and alligator snappers.

            Growth rates vary between individuals under the same conditions; captives not hibernated have a much longer growing season & steadier food supply than wild turtles. Wild turtle populations vary by locale in terms of length of growing season & capacity of local environments to sustain growth. Even if you get good figures for wild turtles, taking those figures & projecting healthy sizes for captive individuals at varied ages is an inexact science. At the time of this writing there is not yet a size vs. age chart I can refer you to. Such a project would be an article in its own right.

 

V.) Dietary-related Health Concerns:

Anecdotal reports of renal (kidney) failure have been attributed to rapid growth and high protein diets might be at issue. Since the RES is the leading pet aquatic turtle I figure this is the aquatic we’re most likely to hear about, but there’s info. on tortoises, too. It’s been suggested maybe this is due to the increased load on the kidney (nitrogenous wastes from protein breakdown, for example), toxic metabolic byproduct buildup, or from the rest of the animal growing faster than some organ systems, putting the strain of maintaining a large body on still small organs. The kidney removes nitrogen-based wastes from the body & maintains appropriate levels of substances in the blood such as ions (sodium, potassium, chloride & bicarbonate) and, in humans, impacts blood pressure. Note: The kidney is not the only organ suspected of suffering from rapid-growth effects. Liver failure has also been implicated in deaths. The liver metabolizes toxic substances (like medication) from the blood, produces bile salts to aid in fat digestion, & serves as a store house for starch to convert to ‘blood sugar’ (glucose) for release into the blood stream.

Metabolic Bone Disease is a condition where inadequate calcium is placed into the skeleton, or too much calcium is removed. Calcium is an important constituent of bone, giving it hardness & strength. Calcium is also critical in shell-hardening in juveniles. This condition can cause irreparable damage & even kill.

Pyramiding is a condition of grossly deformed shell common in rapidly grown tortoises & turtles. In a nut shell, the carapace scutes (plates on the top shell) bulge out & may have a ‘wood grain’ like appearance. Some turtles have naturally bulging scutes, and some have naturally ‘grained’ scutes. Pyramiding can permanently disfigure a turtle. Some grotesque examples & explanation can be seen at Turtlestuff.com - http://www.turtlestuff.com/pyramid.html and Tortoise Trust - http://www.tortoisetrust.org/care/faq.html#pyramiding.

 

Some Observations:

 

1.)    High-Volume High-Protein Diets cause excessive growth far in excess of natural norms & very early sexual maturity, years in advance of what is seen in wild populations. A captive-raised hatchling on such a diet may reach a size comparable to a 4 or 5 year old wild adult in one year & display mating behavior well within 2 years of age.

 

2.)    Excessively high-protein diets are known to cause pyramiding in tortoises, many of which in nature eat very low protein diets. Pyramiding can occur in basking aquatics, including red-eared sliders (RES) & Painted turtles. RES are initially carnivorous & become progressively herbivorous with age and size, although adults still usually choose meat-based foods if available. Painteds have a similar behavioral pattern. Mild pyramiding is perhaps a cosmetic disfigurement; more severe pyramiding can cause skeletal abnormality & functional impairment. A. C. Highfield notes (http://www.tortoisetrust.org/articles/d3.html) that high enough protein content can cause problems despite adequate calcium & Vit. D3.

 

3.)    I asked Phil. Peak (a mud/musk enthusiast in Louisville, KY) about pyramiding in mud/musk, snappers & softshells; he said “I have seen mild cases of what could be viewed as pyramiding in mud turtles. Not nearly to the same degree as tortoises or even emydid turtles, but clearly a similar type condition. In muds this seems to result in a slightly more bumpy appearance to the carapace, instead of the smooth, almost polished stone look they are supposed to have. I have not seen it in any of the other species mentioned, including musk. I would be interested to know if it does occur in those other types.”

 

Plants are a wild card in turtle diets. Some see plant matter as harmless in the diet (if proper species of organic produce or aquatic vegetation are used); a belly-filling ‘bulk filler.’ It’s actually more complicated than that. Some plants are poisonous. Some, like spinach, contain oxalic acid (that binds calcium) & despite having considerable calcium may actually deplete a turtle of calcium if fed often in large amounts. My article on dietary menu options discusses this in the section on plants so refer to that; in brief, fruits aren’t natural for many turtles & if fed much & often can cause problems. A. C. Highfield noted concerns about pesticide residues on commercial produce, particularly given that a turtle consumes amounts far in excess of a human, relatively speaking (unless you eat several pounds of lettuce daily!). It’s been pointed out iceberg lettuce has almost no nutritional value; it’s like feeding water. Romaine lettuce is similar, but has more Vitamin A. But if your turtle gets a solid comprehensive nutritional program from other food, who cares if it munches on a lot of iceberg or romaine lettuce? Green vegetation should add to the bulk & fiber of stools, achieving a more natural consistency.

      The USDA's Searchable Nutrient Database is a wonderful free online tool for getting nutrient info. on commercial vegetables. Using it, let’s look at the nutrient value for some common things you might have handy (100 mg samples; raw):

                           % Water        Energy   Protein     Fiber     Vit. A    Calcium  P.____

Iceberg Lettuce:      95.89%    12 kcal    1.01 g      1.4 g     330 IU     19 mg    20 mg

Romaine Lettuce:   94.91%    14 kcal     1.62 g      1.7 g   2,600 IU    36 mg   45 mg

Celery:                   94.64%     16 kcal     0.75 g      1.7 g     134 IU     40 mg   25 mg

Pinto Beans:           81.30%     62 kcal     5.25 g          ?           2 IU     43 mg   94 mg

     (Raw, Sprouted)

Green Beans:         90.27%     31 kcal     1.82 g      3.4 g     668 IU      37 mg   38 mg

     (Raw, snap)

Zucchini:                 95.28%     14 kcal     1.16 g      1.2 g     340 IU      15 mg   32 mg

Banana:                  74.26%     92 kcal      1.03 g      2.4 g      81 IU        6 mg   20 mg

Dandelion Greens  85.60%      45 kcal     2.70 g     3.5 g 14,000 IU   187 mg   66 mg

                  Note: P = Phosphorous. The calcium:phosphorous ratio is critical. We see not all ‘plants’ are created equal. And Dandelions have a lot of Vitamin A & Calcium, & a great Calcium:Phosphorous ratio.

            Let’s compare that to wild vegetation the turtle might eat. I don’t have a nifty tool for that. In Life History and Ecology of the Slider Turtle, by J. Whitfield Gibbons, it’s noted there’s a citation of research (Boyd, C. E. 1970 - Amino acid, protein, and calorie content of vascular aquatic macrophytes. Ecology 51:902-906. 20) stating the mean crude protein content of aquatic plants from Par Pond, South Carolina was 13.1% +/- 1.3%. Of course, turtles vary by degree of herbivory & which plants & how much they will eat, so we can’t assume even a typical slider plant portion of the diet is 13% protein. Gibbon’s book also cites research (Avery, H. W. 1987 – Roles of diet protein and temperature in the nutritional energetics of juvenile slider turtles, Trachemys scripta. Master’s thesis. State University of New York College at Buffalo. 20) on the effects of 10, 25 & 40% protein diets on captive slider growth at four temperatures (15º, 22º, 28º & 34º C). Avery found higher consumption, digestive rate and digestive efficiency at warmer temperatures, & that high-protein diets saw a greater temperature response in their digestion rate. Sliders on a 10% diet had posterior plastron curling so their length actually shortened & they didn’t gain significant weight; those on 25 & 40% diets grew & gained weight @ similar rates over the 12 weeks shown on the graphs. The point is that juvenile sliders require over a 10% protein diet to grow & develop normally. It’s noted fish carrion in Pars Pond has a crude protein content around 20%, so carnivory/omnivory helps augment protein intake during juvenile slider growth. On the other hand, many tortoises have diets averaging significantly less protein so we can’t generalize this to all turtles. Avery’s study was also noted to show sliders displayed greater consumption rates, digestion rates & digestive efficiencies at warmer temperatures. And another study (Parmenter, R. R. 1980 – Effects of food availability and water temperature on the feeding ecology of pond sliders (Chrysemys s. scripta). Copeia 1980:503-514. 1-3, 9, 11, 17, 18, 20, 21).showed slider intake to be a function of body temperature with maximum intake at 29º C (84.2º Fahrenheit).

            Life History and Ecology of the Slider Turtle (Seasonal Changes in Diet, Pages 258-259) notes seasonal shifts in slider diet composition have been shown (by Parmenter, R.R., 1980 – Effects of food availability and water temperature on the feeding ecology of pond sliders (Chrysemys s. scripta). Copeia 1980:503-514. 1-3, 9,11,17,18,20,21); Schubauer, J.P. and Parmenter, R.R., 1981 – Winter feeding by aquatic turtles in a southeastern reservoir. Journal of Herpetology 15:444-447. 10, 16.18, 20, 22), with the summer diet containing plants & animal prey but the winter diet almost entirely aquatic vegetation. A similar shift (summer omnivory to winter herbivory) was noted in Kinosternids (Mahmoud, I. Y., 1968a – Feeding behavior in kinosternid turtles. Herpetologica 24:300-305. 18, 20). They even noted related drastic declines in trapping success using fish or meat bait for omnivorous turtles (Cagle, F.R., 1950 – The life history of the slider turtle, Pseudemys scripta troostii (Holbrook). Ecological Monographs 20:31-54. 1, 3, 8-17, 19, 20, 22, 24); Ernst, C.H., 1972 – Temperature-activity relationship in the painted turtle, Chrysemys picta. Copeia 1972:217-222. 18, 20).

            My Points: Learn about your species of turtle. Don’t overdo the protein, but don’t grossly under-do it, either. Younger turtles are growing & often need a higher protein diet than older ones. This is important because some commercial foods market the same food for all aquatic turtles from hatchling to adult. Not all plants are created equal. Romaine & Iceberg lettuce are equivalent to feeding your turtle water (so I see no need to limit them, if they eat a complete nutritious diet otherwise). This may not hold for other plants, including some like Anacharis, where protein levels are likely lower than meat but may remain significant. Since wild turtles have frequent access to ‘plant buffet’ it’s reasonable to offer Anacharis & other aquatic greenery often, even daily, but perhaps not as a 24/7 buffet (so once or twice daily).

 

What I Don’t Know:
  • The percentage of kidney &/or liver failure cases in rapid-grown turtles.
  • The extent of kidney &/or liver damage in rapid-grown turtles.
  •  How much this affects predominantly carnivorous turtles (i.e.: stinkpots & snappers).
  • Whether omnivores with a more carnivorous bent have better tolerance than other turtles (Painted > RES > Cooter, for example).
  • Whether this organ-damage phenomenon occurs during the juvenile rapid growth spurt or over long-term exposure to high volume high protein diets.
  • Whether this organ-damage phenomenon can occur after reaching adult size.
  • Whether this organ-damage is reversible with a shift to a healthy diet (like a 40 year old obese man losing weight, getting in shape & eating healthy).
  • Whether organ-damage is a function of rapidly increased size (big body, small organs) or the strain of processing so much nutrition (wearing organs out by overuse).
  • I don’t know if pyramiding occurs in predominantly carnivorous baskers (map & chicken turtles), softshells or bottom walkers (mud, musk, common & alligator snappers).
  • I don’t know if pyramiding is due solely to rapid growth, solely to total high protein content in and off itself, to high protein foods themselves (relevant if you feed small quantities of high-protein diet) or to the combination.
  • I’m uncertain at what point pyramiding is permanent & irreversible.
  • I have raised young RES who grew quickly when I was a kid; I don’t remember strong pyramiding on them. I have a Southern Painted whose scutes do have a mildly pyramided look; seen in glare they look like a stack of very thin concentric plates, or to have a ‘wood grain’ effect.
  • Whether 24/7 Buffet of aquatic plants including Anacharis is always harmless.

 

VI.) Feeding Quantities:

            Let’s look at some common forum recommendations re: how much to feed at a single meal.

1.)    All they can eat in 5 minutes (some say 15 minutes).

2.)    All they can eat, period.

3.)    What you think would fit in the head if it were hollow (presumably from nose to behind the red patches on a RES).

4.)    Feed to partial satiation, where there's a noticeable drop-off in appetite & you subjectively feel you've fed 'quite a bit' but the animal would eat considerably more, were it provided. (I recommend this one).

Quite an inexact science, you see. There are other variables to factor in:

1.)    Food volume is one variable in the equation. It can only be considered relative to what they’re fed, how often they’re fed, their activity level, age, size and the species in question. Softshell turtles are thought to be high metabolism turtles who need more food. Alligator snappers can be very sedentary (a friend of mine did college research tagging them, so I know). RES are probably intermediate.

2.)    Food type is key; letting your turtle gorge on romaine lettuce is probably a non-issue. Letting it gorge on ReptoMin, guppies, ghost shrimp, etc, is another thing entirely. When people talk about feeding 3 times/week & smaller quantities, they’re generally talking about more nutrient-rich foods (i.e.: Mazuri, ReptoMin, crickets), not vegetation (by which I mean greenery, not fruits!).

 

VII.) Calcium Supplementation Concerns:

            It’s typically recommended a reptile diet contain a calcium to phosphorous ratio of at least 2:1. So it’s important to have both enough calcium & the right ratio. The problem is, many foods contain either too little calcium or a poor calcium to phosphorous ratio (feeder crickets, for example). Calcium is more critical during the rapid growth & shell-hardening phase of the early juvenile, but it remains important through the life of the turtle. A turtle with calcium deficiency may fail to harden its shell & this is referred to as ‘soft shell.’ Turtles are born with soft shells but these quickly firm up with size & age. Further, a turtle with low calcium levels will mobilize calcium from the bones, weakening them. You can read a discussion of this in a Tortoise Trust article at: http://www.tortoisetrust.org/articles/aquaticdiet.htm (read the section on metabolic bone disease).

            I’m no Vet but I do work in human health care. Humans have small glands called parathyroid glands on the back of the thyroid gland in the neck. The parathyroid glands produce parathyroid hormone that mobilizes calcium from the skeleton. Calcium is used for much more in the body than just bone. Calcium concentration variations inside & outside human cells can trigger such responses as muscle contractions. Some medications to treat high blood pressure in humans are called Calcium Channel Blockers, which demonstrates yet another important role of calcium in the body. The upshot is your turtle’s body will struggle to maintain adequate calcium levels in the blood at the expense of the skeleton if you don’t give it enough calcium.

            One of the most common means of calcium supplementation is offering a Cuttlebone from the pet store’s bird section. You can read about it in my dietary option article at http://www.austinsturtlepage.com/menu.htm (go to Section G.) Supplements). Be sure to remove the hard backing from cuttlebone, since turtles can choke on it. To do this, break the cuttlebone in two, take a ‘case knife’ (blunt metal knife; called case knives where I grew up) & drive it under the hard backing (the main cuttlebone is soft enough to do this); then turn the knife, breaking loose a big piece of backing.

            It is generally thought your turtle will not overdose on calcium; you can read a Tortoise Trust clip on this at http://www.tortoisetrust.org/care/faq.html#supplement.

            Your turtle’s body cannot utilize calcium effectively without Vitamin D3.

 

VIII.) Vitamin D3 Concerns:

            Vitamin D occurs in different forms, but is ultimately converted into the final form, vitamin D3, in the skin by action of sunlight’s UV-B wavelength light on sterols in the skin. Vit. D3 is necessary for the body to properly utilize calcium. You may have heard of rickets, the condition of humans who are chronically D3 deficient. One of my old college teachers actually knew a ‘night owl’ colleague who got this!!! It takes very little sunshine exposure for humans to meet their needs, but many captive turtles don’t get any natural sunlight for years on end. Some Vit. D3 can be absorbed during digestion, & so many commercial turtle foods (i.e.: Mazuri, ReptoMin) are fortified with it, and varied oral supplements are sold.

            Ultraviolet (UV) light does not pass through normal glass. Letting your turtle get sunlight through the window, or putting a ReptiSun 5.0 UV-B light bulb in an aquarium hood with a sheet of glass between bulb & turtle, is likely useless. UV Light can pass through water but loses strength rapidly.

            Normal fluorescent & incandescent light bulbs do not produce UV-B light. So-called ‘full spectrum’ & ‘daylight’ fluorescent bulbs do not produce significant UV-B light! Any bulb that produces useful amounts of UV-B light will be actively marketed as such. This production is done via a special coating in the bulb that is consumed producing the UV-B; therefore these bulbs need replacing at least every year. Note: UV-A & UV-B are both ultraviolet wavelengths but are not the same. Do not buy a bulb listed only for UV-A & think you’re giving UV-B…

            Plant matter generally does not provide Vitamin D3; some animal foods may.

            A critical point: You can overdose Vitamin D3!!! Unlike calcium, you can overdo it. While a turtle will not overdose by basking or getting some D3 in its Mazuri or ReptoMin, it very well may if you use oral D3 supplements excessively.

            So, how important is it to provide UV-B lighting or oral supplements to turtles? Does this hold equally true for tortoises, semi-aquatic baskers, bottom-walkers like mud/musk/snappers, partially nocturnal species (i.e.: Stinkpots), etc…? That is widely debated & easily an article in its own right. Here are my thoughts, based on what I’ve read:

1.)    Plants contain little if any Vit. D3; tortoises must have UV-B lights or oral supplementation. I recommend this with strong confidence.

2.)    Basking turtles (RES, Painted, Map, etc…) evolved with frequent strong sunlight exposure. Some (RES & Cooters) are fairly strongly herbivorous as adults (if you’re feeding properly). Some people have raised these species without supplemental UV-B. I recommend UV-B supplementation (light or oral) for semi-aquatics. My Southern Painted has pyramiding and I’m a believer.

3.)    Bottom-Walkers (Snappers, musk, mud) – I have found stinkpots basking up during the day both Spring & Summer (July & August) several times & have photo.s to prove it. I have more rarely found adult common snappers basking. Since sunlight produces much stronger UV-B than most commercial bulbs, & UV light can penetrate water to some degree, these turtles may benefit from ‘basking’ in shallow water. I recommend they get UV-B, too.

 

IX.) Dietary Theory Synthesis:

            Warning: Much of this is scientifically unsubstantiated opinion.

 

1.)              Green, leafy vegetation (not fruits): daily feeding acceptable (examples: Romaine lettuce, Dandelions, Anacharis, Water Hyacinth). RES eat a lot of plant matter naturally. I have personally assumed (rightly or wrongly) that green, leafy vegetation (for my Southern Painted, Anacharis and romaine lettuce) is probably not harmful to graze on. This assumption is based on the high-volume grazing seen in herbivores to account for the low nutritional value of vegetation. I believe that providing romaine lettuce and Anacharis daily for grazing is acceptable and allows the turtle to placate itself. I reason many wild turtles can probably enjoy vegetation buffet at will.

2.)              Meat-based products (live food, frozen food, freeze-dried food, processed foods including ReptoMin and Trout Chow) – once daily feeding for the first 6 months of age is good. From 6 months to a year is controversial; a predominant carnivore may eat daily, an omnivore might eat daily, and an omnivore eating a lot of plant matter every other day).

a.)    Beware wild-caught aquatic live foods due to parasite concerns (lung flukes in a particular type of snail; some of us suspect fish may carry a tapeworm than can infect turtles). Some suggest freezing for several months may ‘sterilize’ live-caught food; if you can catch large quantities (small fish, crawdads) and have a large collection, this may be important.

b.)    Land-based live foods are often used for aquatic turtles (earth worms, slugs, grasshoppers, crickets and pill bugs, etc…) if there’s no spraying of pesticides, herbicides, etc…locally.

3.)              Many people recommend at least part of your turtle’s diet consist of high-grade commercial food specially formulated for turtles (Mazuri & ReptoMin, for instance).

4.)              Recommendations on commercial vs. processed natural (freeze-dried or frozen) vs. natural foods vary. The cases:

a.       Commercial – presumed to be professionally formulated to contain all needed vitamins and minerals. Aren’t species specific, degree to which science knows what turtles need isn’t clear, packaging isn’t always reassuring (ReptoMin cans say feed 2-3 times daily & say small quantities, but doesn’t define small), they’re not species specific, and they may be ‘too nutritious’ (high protein, etc…). How can one food be right for RES and alligator snappers both? One major plus: many are vitamin D3 & calcium-fortified. Processed foods like ReptoMin have lower-moisture content and higher protein than many natural foods. ReptoMin is maximum 8.0% moisture, minimum 42.5% crude protein. Compare to living things. Isn’t the human body, like, 70% water? What about all those invertebrates whose exoskeletons are made out of indigestible chitin? Processed foods likely have a much higher usable nutritional payload relative to their volume, compared to natural foods.

b.      Processed natural – supposedly kills the parasites (ex: they recommend you don’t use live blood worms, but frozen are cool). Thought to be tasty; I haven’t done taste-testing to compare preferences of ReptoMin vs. freeze-dried shrimp, etc…). I suppose freeze-drying and freezing could destroy some nutrients, but I’ve seen no real confirmation.

c.       Natural – Live Feeders are not ‘natural;’ many wild turtles seldom get to eat fish, earthworms or crickets, yet that’s what many people think is ‘natural.’ There’s a parasite risk, particularly with prey taken from native habitat (snails, fish, etc…). Live food provides stimulation, particularly in large enclosures where the turtle can actually hunt for extended periods. Purchased feeders (guppies, red rosies, ghost shrimp, red wriggler earth worms) are examples. The first 3 examples help clean the tank while present. Many people assume turtles prefer live food, enjoy the hunt and kill, and find it tastier…I haven’t tested this. My stinkpot loves snails, though. If the prey item is large enough to need shredding, it may make a mess. Some people can’t handle the Circle of Life. Rare prey items can be dangerous (large crawdads; giant water bugs; etc…). A bacterium linked to shell rot has also been linked to ghost shrimp and crayfish, although many of us don’t find this to be a practical concern. Most wild turtles (rare exceptions: mata matas, Chitras, Alligator snappers) have fish as a very small percentage of the diet, so captive diets shouldn’t include fish over once weekly, tops. Crickets do not have a favorable calcium to phosphorous ratio, although gut-loading them can change that.

 

X.) I Recommend:

 

1.)    Leafy Greens (Romaine lettuce, Anacharis, Dandelions) daily. (Makes it easier to ignore their begging, since they CAN eat something they like). You can give all the lettuce you want; don’t offer Anacharis & other ‘substantial’ aquatic plants over twice daily (once is fine).

2.)    Meat-based foods daily x 6 months, then every other day for omnivores/herbivores (Painted, RES, Cooters) or every day another 6 months for carnivores (mud, musk, softshell), then feed 3 times weekly but not quite so close to satiety, if health is your highest priority (pleasure vs. longevity is a tradeoff made for our turtles just like ourselves). I find a Sunday-Wednesday-Friday schedule works well; if you try for ‘every other day’ you’ll get confused by the shifting schedule (odd number of days in a week).

3.)    Feed meat-based products to the point of diminished appetite but not to the point of absolute stuffedness. When you’re done, you should feel you’ve fed plenty but the turtle would eat more if offered.

4.)    If you have the discipline to do so, daily feeding of under half the meat-based food amount established by 3.) is fine and more natural. Not recommended for most people; too hard to keep consistent!

5.)    An occasional small low-value snack (like a small snail) on an off-day is okay, particularly for carnivores. My stinkpot & mud get a small snail or two.

6.)    If you can handily afford frozen fish food, consider making occasional use of these for part of your turtle’s meat-based dietary portion:

a.)    Frozen blood worms.

b.)    Frozen Spirulina-enriched brine shrimp.

c.)    Frozen Krill.

d.)    Frozen Plankton.

e.)    Live ghost shrimp.

f.)      Live or fresh-killed feeder fish (once or twice a month).

g.)    Red-wriggler earth worm.

h.)    Captive-bred snails (not wild-caught).

i.)      Wild-caught slugs.

j.)      Feeder crickets (especially gut-loaded).

7.)    Make at least ¼’th of the meat-based portion of the diet Mazuri, ReptoMin, or another ‘made for turtles’ high-grade commercial food. I do not trust trout chow for anything but a rare treat. Check into using Tortoise or Box Turtle foods for part of the diet for largely herbivorous semi-aquatics like RES & Cooters, but I wouldn’t use exclusively with more carnivorous maps & bottom-walkers (I do use some!).

8.)    Don’t feed wild-caught snails or wild-caught fish without freezing at least 1 month.

9.)    Drop broken up cuttlebone without the backing (they can choke on the hard backing) into the tank at least 3 times weekly for calcium supplementation.

10.)            Use a balanced Calcium/Vit. D3 supplement like Rep Cal, & a multi-vitamin supplement like Herptivite (by the Rep Cal people; you’re supposed to mix them just before use). Use it once or twice weekly (I base this on A. C. Highfield’s advice at: http://www.tortoisetrust.org/care/faq.html#supplement). Oral supplementation appears a workable alternative to natural sunlight or UV-B lighting. If you use outdoor setups with natural sunlight or indoor setups with good UV-B bulbs, I do not recommend oral D3 supplementation (unless you have a bottom walker who never gets near the bulb; outdoors he’ll still get enough sunlight…).

11.)            Do not use ‘liquid sun drop’ type Vit. D3 supplements (I’m basing this solely on A. C. Highfield’s recommendation against them in an article at Tortoise Trust (http://www.tortoisetrust.org/articles/webdiet.htm).

12.)            If you use UV-B lighting (i.e.: ReptiSun 5.0 UV-B bulbs) instead of oral Vit. D3 supplementation, you must change them every 6 – 8 months because they quit producing UV-B as a special coating burns off.

13.)            Remember: You must not succumb to constant begging! They will beg whether you feed them or not; it’s a conditioned response. You can offer most all the Romaine lettuce (even iceberg lettuce) & cuttlebone they want, so your turtles need not ‘starve.’ Would you let a 2 year old child gorge all day on M&M’s because he wanted to? Same deal.

 

Appendix I.) Online Resources You Should Read On Feeding:

 

Tortoise Trust Articles:

1.)    Feeding Aquatic Turtles - http://www.tortoisetrust.org/articles/aquaticdiet.htm

2.)    Feeding Tortoises - http://www.tortoisetrust.org/articles/webdiet.htm

3.)    Feeding Red-foot & Yellow-foot Tortoises: http://www.tortoisetrust.org/articles/feeding_redfoots.html

4.)    Vitamins, Minerals & Tortoises: http://www.tortoisetrust.org/articles/dietcons.html

5.)    When Tortoises won’t Eat: http://www.tortoisetrust.org/articles/fedart.html

6.)    Live Food Choices for Turtles: http://www.tortoisetrust.org/articles/live.html

7.)    Dietary Constituents For Terrestrial Chelonians & Effects on Growth & Development: http://www.tortoisetrust.org/articles/dietcons.html

8.)    Pyramiding: http://www.tortoisetrust.org/care/faq.html#pyramiding

9.)    How Often To Use Vitamin & Mineral Supplements: http://www.tortoisetrust.org/care/faq.html#supplement

10.)    High Growth Rate Diets & Vit. D3 – a response: http://www.tortoisetrust.org/articles/d3.html

 

Austin’s Turtle Page Articles:

1.)    Dietary Options for Turtles: http://www.austinsturtlepage.com/menu.htm

2.)    Food & Feeding Sections under General Care: http://www.austinsturtlepage.com/basic.htm#Food

3.)    Care Sheets for Specific Info.: http://www.austinsturtlepage.com/caresht-1.htm

 

David T. Kirkpatrick, Ph.D’s Articles:

1.) On Feeding Turtles: What and How Much: http://www.unc.edu/~dtkirkpa/stuff/turtfeed.html

 

Turtle Stuff:

1.)    Pyramiding: http://www.turtlestuff.com/pyramid.html

 

Appendix II.) Recommended Books:

 

Practical Encyclopedia of Keeping and Breeding Tortoises and Freshwater Turtles (Softcover) by A. C. Highfield. The title is definitive. If you want an ‘owners guide’ to turtles, buy it. Highfield speaks from extensive husbandry experience with a large variety of both tortoises and turtles. His section on nutrition includes a breakdown by nutrient of symptoms of deficiency & how to prevent it. Many color photo.s of disease conditions. Many species profiles giving an overall synopsis and often such tidbits as incubation info. and what incubation temp.s produce males or females. Both native and exotic turtles are discussed. Worth the money.

 

Turtles of the United States and Canada (Hardcover)

Turtles of the United States and Canada (Softcover)

            Outstanding book depicting the natural history of our native turtles. Divided into section by species, with sections broken down into Recognition, Karyotype, Fossil Record, Distribution, Geographic Variation, Confusing Species, Habitat, Behavior, Reproduction, Growth & Longevity, Food Habits, Predators & Defense, Populations, and Remarks. It surveys the 56 species of the U.S. & Canada. Includes research study information on such matters as stomach contents, how long the turtle can survive underwater, chromosome number, homing ability if removed from original site and activity cycle by time of day and year. If you want to ‘know’ your turtle from his wild origins, this is the book.

 

            The Tortoise and Turtle Feeding Manual (Paperback)

            By A. C. Highfield. I don’t own a copy (yet) but it was recommended by Tom C. as relevant & worthy for recommendation, and between that and the author, I’m backing it. Currently at Amazon.com for $8.95 albeit with a wait.

 

            Life History and Ecology of the Slider Turtle (Softcover).

            By J. Whitfield Gibbons. If you own a slider & enjoy natural history, scientific research & state-of-the-art information from many research authors on sliders, this is the book. It tackles questions like whether tropical sliders are true tropical turtles or temperate immigrants, the purpose of melanism in some, dietary behavior & other matters. It collects a large body of formal scientific research articles on sliders.

 

Article by Richard Lunsford.

            Special thanks to Tom Coy, Phil. Peak (Phil. in Louisville) and Kory Steele (Colchicine) for editorial recommendations.