Description: Fejervarya cancrivora has a SVL of 68.2 mm. The sides of the head have small glandular warts. Parts of the flanks have glandular folds and the lower part has glandular warts. The back has interrupted dorsolateral folds. The dorsal sides of the limbs have warts and folds, while the ventral surfaces are smooth. It has a medium sized, narrow head. The snout is oval. F. cancrivora has a rounded canthus rostralis, a concave loreal region, and a flat interorbital space. The nostrils, which are closer to the tip of the snout than the eye, are oval and have a small flap. The tympanum is distinct. The pupil is rounded. It has a few teeth between the choanae on the vomerine ridge. The tongue is large. It has a supratympanic fold. No parotoid glands are present. The fingers are long and the finger tips are pointed. Some of the fingers have dermal fringes, but have no webbing. Subarticular tubercles are present and are rounded. Toes are long and have webbing and dermal fringes (Dubois and Ohler 2000).
Diagnosis: F. cancrivora can be distinguished from F. limnocharis by having a deeper head and a more pointed beak-like snout (McKay 2006).
Coloration: Color varies from brown, or greenish-brown, to gray, with irregular darker bars scattered on the lips and hindlimbs. The venter is whitish, sometimes with scattered darker markings (McKay 2006).
Coloration in Preservation: The dorsum and flanks are brown with indistinct brown spots. A wide, light brown mid-dorsal band runs from the tip of the snout to the vent. Vocal sacs are dark brown. The belly and undersides are white with light brown spots (Dubois and Ohler 2000).
Variation: Males have nuptial spines on the nuptial pads and vocal sacs are present (Dubois and Ohler 2000). Mature males may or may not have dark throats and thumbs, and sometimes lack slits opening to the vocal sac (McKay 2006).
Tadpole Morphology: Tadpoles have a maximum total length of 40 mm. The body is oval-shaped and dark-colored with dark spots. The tail is less than twice the body length. The spiracle is centered on one side of the body. The mouth is situated under the snout. The upper lip has a single row of papillae and the lower lip has two rows. (McKay 2006).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Brunei Darussalam, Cambodia, India, Indonesia, Lao People's Democratic Republic, Malaysia, Myanmar, Singapore, Thailand, Viet Nam. Introduced: Guam.
Malaysian region distribution from AmphibiaWeb's database: Peninsular Malaysia, Sabah, Sarawak
F. cancrivora is widely distributed in southeastern Asia, including Brunei Darussalam, India (Great Nicobar Island), Indochina (Cambodia, Lao People's Democratic Republic, Malaysia, Thailand, Viet Nam), coastal southern China (Hainan and Guangxi provinces), the Philippines, Sulawesi, Nusa Tenggara, and Irian Jaya (Ren et al. 2009; Zhigang et al. 2009), as well as in Bali (McKay 2006). It has been introduced to Guam (Christy et al. 2007) and to Papua New Guinea (Zhigang et al. 2009). Along the coast of the Gulf of Thailand and in Singapore, F. cancrivora is usually found in mangrove swamps (Dicker and Elliott 1970). It is also common on the banks of brackish meanders, at the edges of tidal prawn ponds, and in fresh water areas (Elliott and Karunakaran 1974; Ren et al. 2009). In Bali, F. cancrivora is found in lowland rainforests, lower montane forests, monsoon forests, forest edges, mangroves, other brackish waterways, and agricultural areas up to 1300 m asl (McKay 2006).
Life History, Abundance, Activity, and Special Behaviors
Although it is not the only amphibian that can withstand salinity (Xenopus laevis and Bufo viridis can tolerate 20 and 26 ppt of salinity, respectively), F. cancrivora is the only living amphibian species that can inhabit saline waters constantly (Ren et al. 2009). This species can adapt to environments of widely different salinity. It can adapt from freshwater pools to full-strength sea water, in only a few hours. The rate of water movement through its skin is the same at any osmolarity, whether the external medium consists of NaCl, sucrose, or urea. F. cancrivora accomplishes this by raising the osmolar concentration of its plasma greater than that of the external fluids (Dicker and Elliott 1970); it rapidly accumulates urea through inducing a key enzyme in urea synthesis (Ren et al. 2009). The animal's skin glands may also contribute to its salinity tolerance. Unlike other species, F. cancrivora has three types of skin glands: mucous glands, mixed glands, and vacuolated glands, in respective order of abundance (Seki et al. 1995). F. cancrivora has been reported to tolerate external salinities from 650 to 950 mOsm/L for several months (Dicker and Elliott 1970).
F. cancrivora forages in sea water of about 1000-1100 mOsm/L (Dicker and Elliott 1970). The diet of frogs near brackish water is predominantly crustacean, including crabs. On the other hand, the diet of frogs near fresh water is comprised mainly of insects and some small vertebrates frogs. The choice-limiting factor appears to be prey size only (Elliott and Karunakaran 1974).
F. cancrivora breeds year-round, but is most active at the beginning of the wet season. The call sounds like a fast throat gargle (McKay 2006).
Trends and Threats
Although the species is abundant, over-harvesting, habitat destruction, wood harvest from mangrove forests, human settlement expansion and road construction may threaten populations (Zhigang et al. 2009).
Relation to Humans
As much as 75% of Indonesia's exported frog legs for food consumption consists of F. cancrivora. Frogs are captured mostly in Java and are generally large and sexually mature (Kusrini and Alford 2006).
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intentional mortality (over-harvesting, pet trade or collecting)
F. limnocharis is the most closely related to F. cancrivora (Ren et al. 2009).
Christy, M. T., Clark, C. S., Gee II, D. E., Vice, D., Vice, D. S., Warner, M. P., Tyrrell, C. L., Rodda, G. H. and Savidge, J. A. (2007). ''Recent records of alien anurans on the Pacific Island of Guam.'' Pacific Science, 61(4), 469-483.
Dicker, S.E. and Elliott, A.B. (1970). ''Water uptake by the Crab-eating Frog Rana Cancrivora, as affected by osmotic gradients and by neurohypophysial hormones.'' Journal of Physiology, 207, 119-132.
Dubois, A. and Ohler, A. (2000). ''Systematics of Fejervarya limnocharis (Gravenhorst, 1829) (Amphibia, Anura, Ranidae) and related species. 1. Nomenclatural status and type-specimens of the nominal species Rana limnocharis Gravenhorst, 1829.'' Alytes, 18(1-2), 15-50.
Elliott, A.B., and Karunakaran, L. (1974). ''Diet of Rana cancrivora in fresh water and brackish water environments.'' Journal of Zoology, London, 174, 203-215.
Kusrini, M.D., and Alford, R.A. (2006). ''Indonesia’s exports of frogs’ legs.'' TRAFFIC Bull, 21, 13-24.
McKay, J.L. (2006). A Field Guide to the Amphibians and Reptiles of Bali. Krieger Publishing Company, Malabar, Florida.
Ren, Z., Zhu, B., Ma, E., Wen, J., Tu, T., Cao, Y., Hasegawa, M., and Zhong, Y. (2009). ''Complete nucleotide sequence and gene arrangement of the mitochondrial genome of the crab-eating frog Fejervarya cancrivora and evolutionary implications .'' Gene, 441, 148-155.
Seki, T., Kikuyama, S., and Yanaihara, N. (1995). ''Morphology of the skin glands of the Crab-eating Frog (Rana cancrivora).'' Zoological Science, 12(5), 623-626.
Zhigang, Y., Zhao, E., Haitao, S., Diesmos, A., Alcala, A., Brown, R., Afuang, L., Gee, G., Sukumaran, J., Yaakob, N., Ming, L. T., Chuaynkern, Y., Thirakhupt, K., Das, I., Iskandar, D., Mumpuni, and Inger, R. (2009). Fejervarya cancrivora. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. www.iucnredlist.org. Downloaded on 11 November 2011.
Originally submitted by: Christine Lu (first posted 2010-10-25)
Edited by: Kellie Whittaker, Mingna (Vicky) Zhuang (2012-04-05)
Species Account Citation: AmphibiaWeb 2012 Fejervarya cancrivora: Crab-eating Frog <https://amphibiaweb.org/species/4748> University of California, Berkeley, CA, USA. Accessed Jan 22, 2022.
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Citation: AmphibiaWeb. 2022. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Jan 2022.
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