Frogs House

Many of the mangrove reptiles are aquatic and live wholly in saline waters. Amphibians on the whole are intolerant of saline conditions, but the Crab-eating frog is among the very few exceptions.

It is found in the brackish-water of mangrove streams and also in adjacent damp, grassy areas. The adults are large enough to be of some culinary value, and the newly-metamorphosed froglets are commercially raised for sale as live food for predatory pet fish.

The Crab-eating frog (Fejervarya cancrivora formerly Rana cancrivora), is a frog native to south-eastern Asia including the Philippines and more rarely as far west as Orissa in India6. It inhabits mangrove swamps and marshes and is the only known modern amphibian which can tolerate salt water. It is locally favored for its eating quality and is often farmed for its edible legs. Call described as …dododododok …dododok.

This frog can tolerate marine environments (immersion in sea water for brief periods or brackish water for extended periods) by increasing urea production and retention, and also by remaining slightly hyperosmotic within urea and sodium flux3,4,5.

1. A study has been made of kidney function in the Crab-eating frog, Rana cancrivora, of south-east Asia.

2. This frog can live in full-strength sea water; in such concentrated media its blood is slightly hypertonic to the medium, and a considerable part of the osmotic concentration is due to urea.

3. In concentrated media the excretion of urea is greatly diminished. This is not due to active tubular reabsorption of urea, but primarily to a low urine flow caused by increased tubular reabsorption of water and reduced glomerular filtration.

4. In concentrated media, as compared with dilute media, only a few percent of the filtered urea appears in the urine.

5. Osmoregulation of the Crab-eating frog in sea water resembles that of elasmobranchs except in that there is no evidence of active tubular reabsorption of urea in the frog.

In the Crab-eating frog Rana cancrivora, taken from a full-strength seawater pond, the in situ levels of serum Na, Cl, K, Ca, Mg, Pi, urea, and osmolarity were examined. The levels were higher than those usually reported for freshwater anurans. However, values for the monovalent salts, urea, and osmolarity were lower than those reported by Gordon et al. (1961, J. Exp. Biol. 38, 659-678) following immersion of this species in 80% seawater for 7 days. The histological features of the ultimobranchial gland and parathyroid gland were coincident with those known in usual freshwater frogs, in spite of the peculiarity of the habitat of this species. The ultimobranchial gland was composed of a single follicle or multiple follicles. In most parenchymal cells, immunoreactive calcitonin was detected using the PAP method with anti-salmon calcitonin antiserum. In the parathyroid gland, cells in the central part of the gland were smaller than those in the peripheral part.