Abstract

The Puerto Rican crested toad is critically endangered with a greater than 80% population decline in the last decade, and fewer than 250 mature individuals residing in the wild in Puerto Rico. Captive breeding and reintroduction programs began in the early 1980s. Recently, metamorphs found at release sites demonstrate the development of a second viable population. Since 2004, the success of the captive breeding program at the Toronto Zoo has been hampered by a condition known as “Brown Skin Syndrome.” Adult and juvenile toads develop dark shiny skin on their dorsal and ventral surfaces, with apparent dysecdysis. Fragments of the outer layer of epidermis adhere to the underlying skin layer, rather than being shed in sheets, and occasionally dark pigmented debris accumulates within the oral cavity. Affected toads have chronic weight loss, fail to thrive, and eventually die. Histopathologic findings include cutaneous epithelial hyperkeratosis, ulceration, a thick Eberth-Katschenko dermal calcium layer, and occasionally glomerulonephropathy, enteritis, and squamous metaplasia of lingual glands. Response to soaking, antibiotics, antifungals, and various nutritional supplements has been inconsistent. A cause has not been identified, but a nutritional imbalance is suspected. In 2003, ‘Specified Risk Materials’ were removed from the food supply, and various animal-derived constituents of dietary supplements were replaced with synthetic forms. While these supplements, used to gut load and dust crickets, the primary dietary component of the captive toads, appear to contain adequate vitamin A on analysis, it may not be fully bioavailable or bioactive.