The relationship between spindly leg syndrome incidence and water composition, overfeeding, and diet in newly metamorphosed harlequin frogs (Atelopus spp.)

Abstract

Spindly Leg Syndrome (SLS) is a persistent animal welfare issue associated with the rearing of amphibians in captivity. We conducted two experiments to investigate the effects of diet, water composition and overfeeding on prevalence of SLS in newly metamorphosed harlequin frogs (Atelopus spp.). In our first experiment, we offered 400 full-sibling tadpoles of Atelopus certus isocaloric diets in treatments of 31%, 37%, 42% and 48% crude protein respectively. Tadpoles fed higher protein diets metamorphosed faster, but the incidence of SLS exceeded 80% in all treatments leading to the conclusion that variation in dietary protein was not responsible for causing SLS. We used 720 full-sibling Atelopus glyphus tadpoles in a second experiment to examine the effects of diet type, water composition and diet ration on SLS. We found that an overall incidence of 58% spindly leg in tadpoles reared in tap water, but reduced to about 10% in water treated by reverse osmosis and then reconstituted. It is possible that the reverse osmosis treatment removed some factor that caused the SLS, or that the reconstitution may have added a mineral lacking in the original tap water. Within tap water treatments, overfeeding tadpoles in tanks increased the incidence of SLS. We recommend further experimental research into this condition to identify the causative factors in the water. Additional research into the nutritional composition of food available to wild tadpoles would be useful in formulating captive diets, that have to date been solely based on surrogate species.

Spindly leg syndrome in Atelopus varius is linked to environmental calcium and phosphate availability

“…Spindly leg syndrome (SLS) is a musculoskeletal abnormality commonly associated with captive-rearing of amphibian aquatic larvae, resulting in underdeveloped limbs that cannot support the body of newly metamorphosed animals [1][2][3][4][5]. Animals have malformed joints and reduced numbers of shortened, thinner muscle fibers in the limbs, some of which are detached [6].…”

“…While there are many speculated causes of SLS, there have been few adequately replicated studies on the topic. Nutritional deficiencies in the diet have been most widely postulated as the causative factor in SLS, but one recent study found that SLS was prevalent, even when feeding presumed nutritionally-complete diets [4].…”

“…Four independent studies suggested that soft water was related to skeletal deformities in tadpoles and metamorphs [4,[6][7][8]. Calcium is an important mineral for tadpoles because as they metamorphose, their cartilage skeletons begin to ossify, creating a high demand for calcium [9].…”

“…Tadpoles reared in deionized water experience poor neurological development leading to limb malformation [7], but addition of calcium improves survival [6], reduces larval deformities [8], and reduces the incidence of malformations in the limbs [7]. A previous study by our own research group found that SLS incidence was aggravated by overfeeding tadpoles, and ameliorated by filtering the water through a reverse-osmosis (RO) membrane and then reconstituting it [4]. We hypothesized that soft tap water at our facility may have led to calcium being a limiting factor and that adding calcium chloride to RO water may have reduced SLS prevalence.…”

“…We hypothesized that soft tap water at our facility may have led to calcium being a limiting factor and that adding calcium chloride to RO water may have reduced SLS prevalence. We also hypothesized that phosphates released from uneaten food may have altered the Ca:P ratio of the water in the overfed treatments, further aggravating the problem [4,5].…”