Red-Eared Sliders, Snapping Turtles, Red-Bellied Turtles, Soft-shelled Turtles, Reeve’s Turtles and the various Side-necks and Snake-necks are among the world’s most popular reptilian pets. While we know much about their care, the importance of calcium in the diet is, judging from the questions I receive on this blog, still not fully realized by all keepers. One feeding tip I received from an animal importer for whom I worked as a boy has served me well throughout my career as a zookeeper, and remains the simplest way to assure adequate calcium intake. Today I’ll review it and some other very useful calcium sources.
Whole Freshwater Fishes
Whole freshwater fishes such as minnows and shiners are the best, “fool-proof” source of calcium for aquatic turtles. I rely heavily on commercially available fathead minnows (a/k/a/ “rosy reds”) and golden shiners. Both are usually raised in outdoor ponds, and have therefore consumed insects and other invertebrates in addition to prepared diets. This may give them a superior nutrition profile. Depending upon the turtle species in question, I offer fish at least once weekly.
I also use minnow and fish traps to catch local species, such as various dace and sunfishes (all of which also make fascinating aquarium inhabitants…but not with turtles!). I trim spiny pectoral and dorsal fins as a precaution. I also trap mummichugs (“killies”), shiners and other marine fish on occasion (these can also be purchased in bait stores). I’ve seen no problems when using these as part of the diet, but I rely primarily on freshwater species.
Freshwater food market species such as Tilapia, trout and white perch can be used for adult Common Snapping Turtles and other large pets. You can also feed sections of large fish to smaller turtles in order to add variety to their diets, but whole fishes with bones and internal organs should be their mainstay.
Years ago, a Bronx Zoo co-worker of mine linked goldfish-dominated diets to Mata-Mata Turtle (Chelus fimbriatus) deaths in several collections. Liver and kidney damage seem to have been involved. Used sparingly, goldfishes seem are harmless, but most zoos now avoid them. Please see the article linked below.
Pre-killed pinkies (newborn, fur-less mice) are eagerly accepted by most aquatic turtles. Over-use has, however, led to kidney and liver disease in insectivorous lizards and frogs. I’ve not seen this with turtles, but have not used pinkies long term for any save several species of Australian Snake-Necks. I suggest erring on the side of caution and focusing on fish as a calcium source. I do not use furred rodents other than as a rare meal for large (“large” as in a 205 lb. Alligator Snapper and 45-60 lb. Common Snappers!) specimens.
Crayfish, Earthworms and other Invertebrates
Crayfish and other crustaceans, if fed with the exoskeleton/shell intact, are especially high in calcium. Earthworms have also proven to be a good calcium source, but levels will vary with diet. Earthworm calcium content (as well as that of crickets, roaches and others) is easy to improve if you feed them properly. Please see the articles linked below, or post here for further information.
Commercial foods from Zoo Med and other well-respected companies can provide your pets with calcium and other important nutrients, but should not be used to the exclusion of whole fishes. Some that I favor and have used, for years in some cases, include Zoo Med products such as Aquatic Turtle Food, ReptiStcks and Gourmet Diet and Reptomin Food Sticks.
Anecdotal evidence from several of my zoo colleagues indicates that shrimp (and krill) are an excellent calcium source for a variety of turtles…and I cannot recall many individuals that will refuse them! Frozen and freeze-dried shrimp and krill have long been used in tropical fish diets, and are readily available. You can also buy shrimp in food markets – “un-cleaned”, with shell intact, are the most healthful and least expensive choice. Most will be marine species, so I would not use as a basis of the diet.
Zoo Med’s Sun Dried Red Shrimp is, in my opinion, the best shrimp-option because a freshwater species (the Oriental River Shrimp, Macrobrachium nipponense) is used.
Some turtles will feed directly on calcium blocks and cuttlebone, which also provide beak-trimming exercise. Try offering Turtle Bone or similar products.
Turtles that bask in the sun (termed “heliothermic” species) cannot use the calcium that we provide in their diets unless they have access to UVB light of the proper wavelength. This is because they must manufacture Vitamin D3 in the skin – dietary sources of D3 are not sufficient for these species. There are some exceptions, perhaps, but if denied UVB, especially when young, most will suffer severe-to-fatal health problems brought on by a calcium deficiency. Fortunately, we now have a huge array of UVB-emitting bulbs at our disposal.
Highly-aquatic species such as Common and Alligator Snappers, Pig-Nosed Turtles, Matas-Matas and Softshells usually do fine without UVB if provided a proper diet. However, as several of these bask at the surface in the wild, or occasionally on land, a UVB source would be useful as “insurance”. Please see the article linked below and post here if you need specific information on UVB sources.