Description
Conraua goliath is the largest frog in the world, with some individuals weighing as much as 3.3 kilograms and reaching ~32 cm snout–vent length (Krüger 1912; Sabater-Pi 1985. Channing and Rödel 2019). The largest reported individuals are females, with males ranging from 22 – 32 cm snout–vent length (1.5 – 2.7 kg) and females ranging from 15 – 32 cm snout–vent length (0.6 – 3.3 kg) (Sabater-Pi 1985).

The species description by Boulenger (1906 - Annals) was based on one specimen. The depressed head is wider than long with an obtusely pointed snout. The nostril is closer to the snout tip than the eye. The canthus rostralis is obtuse and the loreal region is deeply grooved. The interorbital space is shorter than the length of the upper eyelid. The tympanum is small relative to the large head, and bordered above by a prominent fold or ridge. The short fingers each have one large, flat, oval subarticular tubercle. The first and second fingers are about equal and the third is longer than the fourth (Boulenger 1906 - Annals). The hindlimbs are powerful and long relative to the body length (~150% of snout–vent length; Sabater-Pi 1985). When extended along the body, the tibiotarsal articulation reaches the tip of the snout. The feet are as long as the crus (Boulenger 1906 - Annals) and fully webbed with relatively thick interdigital membranes extending along the full length of the toes and ending at the disc-like toe tips (see photograph in Zahl 1967). The foot has a flat, elliptical inner metatarsal tubercle and no outer tubercle. As with the fingers, the moderate toes have large, flat, oval subarticular tubercles. There is a strong dermal fringe on the outer side of the fifth toe (Boulenger 1906 - Annals). The skin on the dorsum and on top of the limbs is granular with many fine ridges (Pawley 1987). The flanks have small warts. The upper surface of the thighs and tibias have longitudinal granular folds. The belly and throat also have small granules (Boulenger 1906 - Annals).

Conraua goliath can be differentiated from Conraua robusta, the only other large Conraua that co-occurs with C. goliath, via the ventral coloration, which is white or gray in C. robusta (Channing and Rödel 2019). Though some species of Conraua retain lateral line organs as adults, these organs are lost at metamorphosis in C. goliath and C. robusta (as well as the other Central African C. crassipes; Gutsche et al. 2023).

In life, the background dorsal coloration ranges from dark green to orangey green with darker spots on the dorsum. There are irregular cross-bars on the limbs and the posterior surface of the hindlimbs are blackish with white spots. The abdomen and ventral part of the limbs are yellowish orange (Boulenger 1906 - Annals; Channing and Rödel 2019).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Cameroon, Equatorial Guinea

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (1 records).

The distribution of Conraua goliath is limited to a small region of Central Africa in the countries of Cameroon and Equatorial Guinea. In this region, C. goliath occurs in the tropical lowland forests of the Lower Guinean Forest Zone, extending 150 – 200 km inland and from near sea level to ~700 m (Gonwouo et al. 2022). Its distribution extends from the Sanaga river basin in Cameroon in the north to the Benito river basin in the Republic of Equatorial Guinea in the south, and is found in rivers including the Benito, Kienké, Laña, Nkebe, Ntem, Nyong, Sanaga, and Uoro (Boulenger 1906 - Annals; Perret 1957; Sabater-Pi 1985; Lasso et al. 2002; Herrmann et al. 2005).

Adult goliath frogs are found in rapids and cascades of rivers with a sandy bottom and clean, slightly tannic, cool (16 – 22 ^oC), oxygen-rich waters (Sabater-Pi 1962, 1985; Zahl 1967). Typically, these rivers are large enough to not be enclosed within the forest canopy (Amiet 1986).

Life History, Abundance, Activity, and Special Behaviors
While adults of C. goliath are generally nocturnal, during the day adults may bask on rocks emerging from streams and rivers for up to a half hour at a time before returning to the water (Sabater-Pi 1985; Channing and Rödel 2019). The escape behavior of individuals in or near rivers is to jump into the water, typically with a single leap. In some cases, however, individuals have been observed to skitter across the surface of the water with as many as seven consecutive short leaps over as much as 3.5 m (Herrmann and Edwards 2006). On land, however, individuals typically appear exhausted after five or six leaps (Sabater-Pi 1967) making them easy to capture by humans. Once in the water, adults have been observed to bury themselves in the sediment and leaves on the river bottom (Gonwouo et al. 2022).

Large adults are often observed on rocks close to or within waterfalls and rapids spaced at a distance of 3 - 5 m, whereas subadults are found more often on mid-stream rocks. Metamorphs and juveniles in pools adjacent to the river that have more slow-moving water (Gonwouo et al. 2022).

In Río Muni of Equatorial Guinea, reproduction occurs during the dry season (July and August) as well as during the short dry season of December and January (Zahl 1967).

Egg masses are deposited underwater and attached to vegetation or stones in pools near rapids (Sabater-Pi 1985; Channing and Rödel 2019). In some cases, frogs (likely males) create nests in existing pools and washouts that may be expanded, whereas in others frogs actively dig depressions into the gravel banks of rivers (Schäfer et al. 2019). In all cases, these pools and depressions are actively cleaned of leaf litter and detritus by the frogs. Most nests contain 150 – 350 eggs, though in some cases might have as many as 2,800 eggs (Schäfer et al. 2019). Multiple nests may be deposited in these pools and depressions, with up to three cohorts of tadpoles being involved in some nests, and tadpoles appear to finish development within these nests (Schäfer et al. 2019). Larval development takes approximately 3 months to go through metamorphosis (Zahl 1967; Sabater-Pi 1985). Female frogs attend these nests for some period of time after oviposition (Schäfer et al. 2019).

Freshwater shrimp have been observed feeding on eggs of C. goliath within the nests constructed by adults (Schäfer et al. 2019).

The diets of adults include insects (beetles, ants, dragonflies, caddisflies), millipedes, freshwater shrimp, spiders, scorpions, freshwater snails, as well as larval and adult anurans (Perret 1957, 1960; Sabater-Pi 1962, 1967, 1985; Gewalt 1977). In captivity, when fed young mice, frogs have been observed to feed out of the water, though will also feed while their bodies are submerged in the water, capturing prey on the water’s surface (Pawley 1987). Suction-feeding, however, has not been reported in these aquatic frogs.

Despite previous assertions that adults do not call (Perret 1957; Sabater-Pi, 1985), C. goliath has a repertoire of call types, including brief whistles, chirping, and even a “sighing deep roar” (Channing and Rödel 2019). The advertisement call of Conraua goliath is a high frequency sound of long duration (4.1 kHz, and up to 1.5 minutes; Pawley and Hutchison 1989; Hutchison 1998; Amiet and Goutte 2017). Strangely, claims were made in jest during the early 20th-century that this very large frog might have a high frequency call (Claybird and Wanawiwi 1939), and this appears to be the case. Similar to C. crassipes, the advertisement call of C. goliath is produced with the mouth open (Hutchison 1998).

In captivity, males have been observed to exhibit territorial behaviors including lunges at one another, wrestling venter to venter, and biting (Pawley and Hutchison, 1989). These may be sometimes accompanied by vocalizations varying between guttural calls (1.6 – 2.3 kHz) and high-frequency squeaks (4.5 – 5.8 kHz) (Pawley and Hutchison 1989; Hutchison, 1998). These interactions were only observed during the day and ranged from occurring once per week to as rarely as every three or four months.

Larva
Tadpoles have robust and muscular tails and mouths with prominent, heavily keratinized jaw sheaths, 7 rows of keratodonts surrounding the mouth (keratodont formula: 7(5 – 7)/7(1)), and many small papillae, especially around lateral and ventral borders (Lamotte et al. 1959; Channing et al. 2012). The straight, short spiracular tube is located on the left side of the posterior half of the body. The vent tube is nearly one-third the length of the body and opens on the right side of the ventral fin (Channing et al. 2012).

In life, the coloration of the body of tadpoles is a somber grey with darker round spots on the dorsal surface, with equally large but more irregular spots on the tail. The spiracular tube is unpigmented (Lamotte et al. 1959; Channing et al. 2012).

Sabater-Pi (1985) reported that tadpoles of C. goliath feed on the leaves of the aquatic plant "Dicraea warmingii"; the genus Dicraea is currently considered a junior synonym of the genus Podostemum (Podostemaceae), which does not occur in Africa, and the taxon to which Sabater-Pi (1985) is likely referring, Inversodicraea warmingiana, is a high elevation Angolan endemic. Thus, the identity of this aquatic plant remains unknown, though is plausibly a member of the Podostemaceae (M. Cheek, pers. comm. to D.C. Blackburn).

Trends and Threats
This species has a limited geographic distribution, narrow ecological requirements, is actively hunted by peoples in both Cameroon and Equatorial Guinea, and is threatened by the conversion of forests into agricultural lands, logging, water pollution (including by agrochemicals), and potentially hydroelectric dams (Gonwouo et al. 2022). Conraua goliath persists at least at some sites with documented agrochemical contamination (Gonwouo et al. 2022), though what impact this has on their biology is not clear. There are currently ex situ conservation efforts beginning in Cameroon in an attempt to rear this species in captivity (Ruoso 2018).

Relation to Humans
The Goliath frog is hunted frequently for food, including using poisons, nets, traps, and snares, including above oviposition sites (Perret 1957; Sabater-Pi 1985; Schäfer et al. 2019). Likely due to this hunting pressure, C. goliath is more abundant and attains larger body sizes farther from human settlements (Gonwouo et al. 2022). As of 2019, it remains the only amphibian species afforded special protection status in Cameroon, which is why it is subject to the US Lacey Act even though it is not protected by CITES.

See Comments below for relevant news of the week.

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)

Comments
A phylogenetic study of relationships among species of Conraua (Blackburn et al. 2020) found a strongly supported sister relationship between C. goliath and C. robusta; both are large-bodied species that can occur in syntopy in Cameroon. Recent phylogenomic analysis have recovered Conrauidae, which contains only the genus Conraua, as the sister lineage of the Petropedetidae (Feng et al. 2017; Yuan et al. 2019). Conrauidae and Petropedetidae are, in turn, sister to the Pyxicephalidae.

Since their discovery, goliath frogs have proved fascinating to scientists and the public alike (Boulenger 1906 - Proceedings; Krüger, 1912), inspiring work both in the field and at zoos and aquaria (Gewalt, 1976, 1977; Pawley, 1987) and many popular articles (Sabater-Pi, 1962, 1967, 1972; Zahl, 1967; Ruoso, 2018). Some of what we know of the basic biology of these large, charismatic frogs is due to the study of captive animals (e.g., Pawley and Hutchison, 1989; Hutchison, 1998).

Hutchison (1998) found C. goliath to have a somewhat lower metabolic rate than other ranoid frogs. The volume of air brought in during a breath is typically small, but the frogs take frequent breaths and oxygen uptake is higher than other frogs of similar mass.

Several recent videos highlighting behaviors in Conraua goliath

Conraua goliath in the wild [in Spanish]:

Conraua goliath guarding nest in the wild:

This species was featured as News of the Week on October 15, 2019:

Despite having been described in 1906, little is known about the natural history of the largest frog in the world, Conraua goliath. In their recent paper, Schäfer et al. (2019) shed light on the species' reproductive behavior by documenting their construction of nest sites. The authors described three types of nesting sites they found in West Cameroon that protect developing offspring from river torrents and predators: rock pools, existing washouts, and dug-out depressions in gravel riverbanks. The different types of nest sites have differing levels of construction effort and risk of flooding or drying. However, in each of these sites, the breeding adults cleared the area of detritus and leaf-litter and deposited eggs on multiple occasions. Camera traps showed that adults guarded nests at night, which is consistent with local knowledge. The authors speculate that because large, heavy objects must be moved for nest construction, this type of nest construction may have favored large size in this species (Written by Ann T. Chang).

This species was featured as News of the Week on November 20, 2023:

The largest known frog—even bigger than the extinct frog Beelzebufo from Madagascar—is the Goliath Frog, Conraua goliath, found only in Cameroon and mainland Equatorial Guinea. Though it has long been known that local people hunt this species, there has been little quantitative study of local knowledge and use of Goliath Frogs. Tasse Taboue and colleagues (2023) provide data from interviews of over 200 people from 11 ethnic groups as well as observations of frog hunters to document practices and inform conservation management. They document that in some communities hunting Goliath Frogs is a traditional and celebrated rite of men who hunt frogs for local consumption. Hunters prefer to hunt the largest individuals (typically females), and usually do so with fishing nets or spears. Most frogs are eaten locally, but some are sold to others in the community or to travelers, including for export to other countries. Though Goliath Frogs are formally protected by the Cameroonian government, their collection, hunting, and export remain common, and the relevant government ministry appears to not be tracking exportation. (Written by David C. Blackburn)

References

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Amiet, J.-L., Goutte, S. (2017). Chants d'amphibiens du Cameroun. Locus Solus Publishing House, Chateaulin, France. [link]

Blackburn, D.C., Nielsen, S.V., Barej, M.F., Doumbia, J., Hirschfeld, M., Kouamé, N.G., Lawson, D., Loader, S., Ofori-Boateng, C., Stanley, E.L., Rödel, M.-O. (2020). "Evolution of the African slippery frogs (Anura: Conraua), including the world’s largest living frog." Zoologica Scripta 49: 684–696. [link]

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Channing, A., Rödel, M.-O. (2019). Field Guide to the Frogs and Other Amphibians of Africa. Penguin Random House South Africa, Cape Town, South Africa.

Feng, Y.-J., Blackburn, D.C., Liang, D., Hillis, D.M., Wake, D.B., Cannatella, D.C., Zhang, P. (2017). ''Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary.'' Proceedings of the National Academy of Sciences, USA, 114(29), E5864-E5870. [link]

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Gonwouo, N.L., Schäfer, M., Tsekané, S.J., Hirschfeld, M., Tchassem, F.A.M., Rödel, M.-O. (2022). “Goliath Frog (Conraua goliath) abundance in relation to frog age, habitat, and human activity.” Amphibian & Reptile Conservation, 16(2), e319. [link]

Gutsche, A., Lingelbach, K., Neira-Salamea, K.D., Rödel, M.-O. (2023). “Postmetamorphic retention of a lateral line system in African slippery frogs (Amphibia: Anura: Conraua).” Zoologischer Anzeiger, 304, 21–31. [link]

Herrmann, H.-W., Böhme, W., Herrmann, P.A., Plath, M., Schmitz, A., Solbach, M. (2005). ''African biodiversity hotspots: the amphibians of Mt. Nlonako, Cameroon.'' Salamandra, 41(1/2), 61–81.

Herrmann, H.-W., Edwards, T. (2006). ''Conraua goliath: skittering locomotion.'' Herpetological Review, 37(2), 202–203. [link]

Hutchison, V.H. (1998). The Goliath Frog (Conraua goliath): physiological ecology of the largest anuan. Extended abstracts of the 1998 International Symposium on Animal Adaptation, Institute of Zoology, Academia Sinica, Taipei, Taiwan, Republic of China. 5 pp.

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Lasso, C.A., Rial, A.I., Castroviejo, J., De la Riva, I. (2002). ''Herpetofauna del Parque Nacional de Monte Alén (Río Muni, Guinea Ecuatorial).'' Graellsia, 58(2), 21–34. [link]

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Pawley, R. (1987). ''The management of the Goliath Frog, Conraua goliath: a goliath problem?'' Bulletin of the Chicago Herpetological Society, 22(5), 96–97.

Pawley, R., Hutchison, V.H. (1989). ''Territorial behavior and vocalizing in the Goliath Frog, Conraua goliath, in the Chicago Zoological Park.'' Abstracts of the First World Congress of Herpetology, Canterbury, UK.

Perret, J.-L. (1957). ''Observations sur Rana goliath.'' Blgr. Bulletin de la Société Neucthâteloise des Scienes Naturelles, 80, 195–202.

Perret, J.-L. (1960). ''Études herpétologiques africaines II.'' Bulletin de la Société Neucthâteloise des Scienes Naturelles, 83, 93–100.

Perret, J.-L. and Mertens, R. (1957). ''Étude d’une collection herpétologique faite au Cameroun de 1952 á 1955.'' Bulletin de l’Institut fondamental d’Afrique noire, Série A, 19, 548-601.

Ruoso, Cyril. “Taking Down Goliath.” Biographic.com, 8 Mar. 2018, www.biographic.com/posts/sto/taking-down-goliath.

Sabater-Pi, J. (1972). ''Der größte Frosch der Erde ist ein fast unbekanntes Tier.'' Das Tier, 1972, 36–37.

Sabater-Pi, J. (1985). ''Contribution to the biology of the Giant Frog (Conraua goliath, Boulenger).'' Amphibia-Reptilia, 6(2), 143-153.

Schäfer, M., Tsekané, S.J., Tchassem, F.A.M., Drakulić, S., Kameni, M., Gonwouo, N.L., Rödel, M.-O. (2019). ''Goliath frogs build nests for spawning – the reason for their gigantism?'' Journal of Natural History, 53(21–22), 1263–1276. [link]

Yuan, Z.-Y., Zhang, B.-L., Raxworthy, C.J., Weisrock, D.W., Hime, P.M., Jin, J.-Q., Lemmon, E.M., Lemmon, A.R., Holland, S.D., Kortyna, M.L., Zhou, W.-W., Peng, M.-S., Che, J., Prendini, E. (2019). ''Natatanuran frogs used the Indian Plate to step-stone disperse and radiate across the Indian Ocean.'' National Science Review, 6, 10–14. [link]

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Species Account Citation: AmphibiaWeb 2023 Conraua goliath: Goliath Frog <https://amphibiaweb.org/species/4691> University of California, Berkeley, CA, USA. Accessed Dec 17, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 17 Dec 2024.

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