Overview

Brief Summary

Biology

Unlike most other frogs and toads, goliath frogs have no vocal sac and therefore courtship does not involve displaying any calls (2). Females lay large clutches of several hundred eggs onto vegetation on the river bottom (3). Once the tadpoles hatch they feed on the food plant, which is only located near to waterfalls and rapids (2). It takes around 85 to 95 days for complete metamorphosis into the adult form (3). Adults feed on insects, crustaceans and fish (2).
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Description

The massive goliath frog, as its name alludes, is the largest frog in the world with individuals weighing over three kilograms (2). The granular skin is greenish in colour with a yellowish-orange underside, and the feet and hands are webbed (3).
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Comprehensive Description

Summary

Conraua goliath is the largest frog species in the world with one of the largest recorded specimens weighing 3.3 kg. This species is found only in Cameroon and Equatorial Guinea and is considered Endangered.

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Etymology

This species was named for the enormous Philistine warrior, Goliath, who was famous for his combat with young David, the future king of Israel.

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Description

This is reported to be the largest frog in the world, with some individuals weighing well over 3 kilograms! In a sample of 15 individuals, weights ranged between 600 and 3250 grams, and snout-vent lengths were between 17 and 32 cm.The conspicuous tympanum has a diameter of about 0.5 cm and is separated from the eye by about 5 cm in an adult. A lateral fold extends from the eye to the posterior portion of the tympanum. Toes are fully webbed, with large interdigital membranes extending down to the toe tips, and the second toe is the longest. The skin on the dorsum and on top of the limbs is granular. Dorsal coloration is green sienna, while the abdomen and ventral part of the limbs are yellow/orange.

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

This species is known only from south-western Cameroon from the region of Nkongsamba, and south to Monte Alen in mainland Equatorial Guinea (Amiet, 2004).

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The geographic range of goliath frogs is restricted to coastal, equatorial Guinea and Cameroon in West Africa.

Biogeographic Regions: ethiopian (Native )

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Range Description

The world's largest frog is known only from south-western Cameroon from the region of Nkongsamba, and south to Monte Alen in mainland Equatorial Guinea. It is generally found at low to medium altitudes, below 1,000m asl.
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Distribution and Habitat

C. goliath has a discontinuous distribution. The range extends from the last 200 km of the Sanaga basin in Cameroon in the north to the last 150 kms of the Benito river basin in the Republic of Equatorial Guinea in the south. This area runs roughly parallel to the coast, and includes the basin of the Sanaga river south to the basin of the Benito, Wolo, and Mbini rivers. It is defined as a dense equatorial forest fringe, with an average width of 150 to 180 km,

C. goliath is found in rapids and cascades of rivers with a sandy bottom and clean, slightly tannic, oxygen-rich waters. The surrounding vegetation can be described as West African (congolid) rainforest. A particular species of plant, Dicraea warmingii warmingii, always covers the rocks among the cascades and rapids and is the exclusive food source of the tadpoles in the first weeks of larval development.

  • Sabater-Pi, J. (1985). ''Contribution to the biology of the Giant Frog (Conraua goliath, Boulenger).'' Amphibia-Reptilia, 6(2), 143-153.
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Historic Range:
Cameroon, Equatorial Guinea, Gabon

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Range

Found in a narrow range in Equatorial Guinea and Cameroon, south from the basin of the Sanaga River to the Benito, Wolo and Mbini Rivers (3).
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Physical Description

Morphology

Goliath frogs are the largest frogs on Earth. They are from 17 to 32 cm long and from 600 to 3250 grams in weight. They have a flattened, wide body with a triangular head. Their dorsal skin is granular and greenish brown and the ventral skin is a lighter yellowish green. The hind legs are long, front legs are shorter and stout, and all of the feet are extensively webbed. Their eyes can be nearly 2.5 cm in diameter.

Range mass: 600 to 3250 g.

Range length: 17 to 32 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

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Vomerine teeth are present in two very strong oblique series, narrowly separated in the middle with their outer extremeties touching the choanae. The head is significantly depressed, a little broader than long. Snout is obtusely pointed, as long as the orbit. Canthus rostralis is very obtuse, and loreal region is deeply grooved. Nostril is slightly closer to the tip of the snout than to the eye. Interorbital space is as broad as the upper eyelid. According to the original description (Boulenger, 1906), the tympanum is small and hidden, whereas Sabater-Pi (1985) reports that there is a very conspicuous tympanum with an average diameter of 0.5 cm and separated from the eye by approximately 5 cm. A lateral fold is present from the eye to the posterior portion of the tympanum. Fingers are rather short, obtuse, and bordered by a very distinct dermal fold. The first and second are equal, and the fourth is slightly shorter than the third. One large, ovular, flat subarticular tubercle is present under each finger. Toes are moderate; tips are dilated into small but very distinct discs, which are embraced by the very broad, full web. The second toe is the longest; this digit can be as long as 13 cm in specimens larger than 2.500 kg (Sabater-Pi, 1985). Subarticular tubercles on toes are also large, ovular, and flat. A flat, elliptical inner metatarsal tubercle, measuring 3.5 its distance from the end of the inner toe is present. There is no outer metatarsal tubercle. A strong dermal frige is present on the outer side of the fifth toe. The tibio-tarsal articulation reaches the tip of the snout. The tibia is as long as the foot, and slightly more than half the length of the head and body.The skin is finely shagreened above, with small warts, especially on the sides. The upper surface of the thigh and tibia have narrow longitudinal, glandular folds. The throat and belly have small granules. A strong curved fold is present from the eye to the shoulder. The dorsum is dark olive-brown above with small, darker spots. Irregular cross-bars are present on the limbs. The hinder sides of the thighs are blackish, dotted with white. The venter is yellowish-white (Boulenger, 1906).

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Size

This species is the largest frog in the world, and a specimen collected by Sabateri-Pi (1985) in Nkombia on 23 August 1960, weighed 3.3 kg. This is assumed to be the maximum known weight for this species. A sample of 15 individuals in this study weighed between 600 and 3250 grams, and measured between 17 and 32 cm in snout-vent length. The holotype specimen measured 250 mm from snout to vent (Boulenger, 1906).

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Ecology

Habitat

Habitat and Ecology

It lives in the vicinity of fast-flowing rivers and streams in rainforest. Rivers and streams have a sandy bottoms and clean, slightly tannic oxygen-rich waters (Sabater-Pi, 1985). It can survive in secondary habitats close to rivers, as well as in forest, but not in very heavily degraded areas (farm bush). It is generally found at low to medium altitudes, below 1,000m asl. (Amiet, 2004).

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Goliath frogs are found in or near fast-flowing rivers and waterfalls in dense, humid and relatively high-temperature rain forests. The water is usually clean, oxygen rich, slightly acidic and usually around 67°F. The presence of larval food also determines where goliath frogs occur.

Habitat Regions: tropical ; freshwater

Terrestrial Biomes: rainforest

Aquatic Biomes: rivers and streams

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Habitat and Ecology

Habitat and Ecology
It lives in or near fast-flowing rivers and streams in rainforest, preferring warmer, slower rivers than Conraua robusta, though faster rivers than C. crassipes. It can survive in secondary habitats close to rivers, as well as in forest, but not in very heavily degraded areas (farm bush). Breeding occurs in streams and small rivers. The young rest by flowing water during the day. Around Nkongsamba in western Cameroon, C. goliath, C. crassipes and C. robusta occur sympatrically.

Systems
  • Terrestrial
  • Freshwater
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Inhabits fast-flowing rainforest rivers and cascades, which have sandy bottoms and rocks covered with Dicraea warmingii warmingii, the primary food source for the goliath frog tadpoles (3).
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Trophic Strategy

Adult goliath frogs feed on insects, crustaceans, fish, mollusks, small mammals and amphibians, including newts, salamanders, and smaller frogs. Goliath tadpoles are vegetarians and feed only on one aquatic plant, Dicraea warmingii, found only near waterfalls and streams.

Animal Foods: mammals; amphibians; insects; terrestrial non-insect arthropods; mollusks

Plant Foods: algae

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods, Molluscivore )

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Associations

Around Nkongsamba in western Cameroon, C. goliath, C. crassipes and C. robusta occur sympatrically. It prefers warmer, slower rivers than Conraua robusta, though faster rivers than C. crassipes (Amiet, 2004).

The diet consists of approximately 60 % arthropods, 20% crustaceans, 10 % amphibians and 10% indeterminate (Sabater-Pi, 1985). Stomach and intestinal contents of several specimens included:

Molluscs: Podomona freethi guineensis; Potadoma graptoconus

Insects: Zabalius lineolatus; Chrysomya putoria (larvae); Libellula depressa: Coleoptera, Elateridae, gen. sp. indet; Carabidae, gen. Platynus

Aracnids: Mygale sp.

Myriapods: Spilorobus sp.

Scorpionids: Family Buthidae

Crustaceans: Palaemon sp. (Palaemonidae); Potamonantes sp. (Potamonidae)

Amphibians: Bufo regularis (adults and larvae); Bufo gracilipes (adults and larvae)

Plants: Dicraea warmingii Engler, 1894 (Rosales) only eaten by the young larvae

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Being carnivores, frogs occupy an intermediate position in food webs and their numbers can be indicators of the health of a broader ecosystem. Generally frogs regulate insect populations and also feed on other frogs, fish, small mammals and other small amphibians. Frogs in turn serve as food for birds, reptiles and mammals.

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The greenish brown dorsal skin of goliath frogs camouflages them well with the wet-moss covered rocks that adult frogs bask on. Goliath frogs are only known to be preyed on by humans, although other predators are possible.

Known Predators:

Anti-predator Adaptations: cryptic

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Population Biology

It has decreased significantly as a result of harvesting for food (Amiet, 2004).

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Life History and Behavior

Behavior

Activity and Special Behaviors

Young (<1000 g) spend 60 % of the day under the water with only the anterior part of their heads above the surface, specially during hot and sunny days. Adults (>2000 g) rest on rocks emerging from rapids, exposing their backs to the sun but keeping their skin moist via splashing water. They periodically change their positions, most likely to adjust their heat and water balance, and they remain exposed for periods of about 35 min, returning to the water for about 15 min. The frogs are active during the night., coming out of the water to jump around in the humid river margins. Animals weighing 2 to 3 kg have been seen making 1.2 to 3 m jumps. Adult specimens may be territorial; Hunting grounds within the rapids of the Mbia river range between 20 and 40 square meters (Sabater-Pi, 1985).

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Goliath frogs do not have vocal sacs and are often considered mute. As a mating call, goliath frogs hold their mouths open and make a whistling noise.

Communication Channels: visual ; acoustic

Perception Channels: visual ; tactile ; acoustic

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Life Cycle

Goliath frog tadpoles are not much larger than those of other frogs, but the majority of growth occurs in the first 75 to 90 days of development. The goliath frog's young tadpoles are not much larger than other frogs'. So the majority of the growth process occurs during the 75-90 days. As in other frogs, goliath frog larvae undergo metamorphosis to become adult frogs.

Development - Life Cycle: metamorphosis

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Metamorphosis

Sabater-Pi (1985) reported on the metamorphosis of this species. In the final stage of metamorphosis (body length 14 mm) the tail has been reabsorbed completely or nearly completely. Specimens are similar to adults in shape and color, though slightly lighter and greener.

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Life Expectancy

Lifespan of goliath frogs is not well documented, although individuals in the wild seem to live longer than those in captivity.

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Lifespan, longevity, and ageing

Maximum longevity: 5.9 years (captivity) Observations: Weighting over 3Kgs, this is considered the largest frog in the world (http://amphibiaweb.org/).
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Reproduction

Little is known about goliath frog mating systems. The little research that has been done suggests that male goliath frogs perform the calling ritual differently from most other frogs. Instead of sucking in air into vocal sacs and blowing it out to make calls, goliath frogs hold the mouth open to make a long whistling noise. Goliath frogs do not have vocal sacs. Females then follow this noise to the male.

Mating System: polygynous

Female goliath frogs lay several hundred eggs at a time that are about 3.5 mm in diameter. They stick to vegetation at the bottom of the rivers and streams in which they reproduce. The eggs then hatch into tadpoles that grow to about 5 cm long over the next 75 to 90 days. There is no information about the seasonality or frequency of breeding or time to sexual maturity.

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

There is no parental investment in goliath frog young after the female deposits the eggs after fertilization.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female)

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Breeding occurs in streams and small rivers. Sabater-Pi (1985) observed a female laying eggs amongst the rocks in a pool amongst the rapids of the Mbia river, known as Nkombia. This individual (1,200 kg) was later captured and continued laying eggs at a rate of 50 eggs/h for 2 h. Dissected females with a weight of 0.600 kg were found to be sexually mature. A clutch of ten eggs included a mean diameter of 3.47 mm with a jelly mass covering each egg that was on average 4 mm thickness; eggs weighed 0,028 g.

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Advertisement Call

Locals confirm that this animal does not emit any sound (Sabater-Pi; 1985).

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Growth

Tadpole morphology

Sabater-Pi (1985) reported on the tadpole morphology, including a chronological table of larval development.

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Larval development takes between 85 and 95 days; the giantism that is characteristic of adults is not yet noticeable (Sabater-Pi, 1985).

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Conservation

Conservation Status

The IUCN sites goliath frogs as an endangered species because of a 50% decline in population size in the last three generations. The most significant threats to the species include hunting for food, destruction of forest habitat because of human settling, sedimentation, commercial logging and agriculture, and exportation for zoos, the pet trade, and competitive frog races. Some of the goliath frogs natural habitats have been declared protected areas including the Monte Alen National Park in Equatorial Guinea. Three wildlife sanctuaries in Littoral Province have also been approved as protected areas in Cameroon. The Equatorial Guinean government has set a limit of 300 on the frogs that may be exported per year. However, local conservation efforts and captive-breeding programs also need to be considered in order to maintain population sizes.

US Federal List: threatened

CITES: no special status

IUCN Red List of Threatened Species: endangered

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IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2d+3d

Version
3.1

Year Assessed
2004

Assessor/s
Jean-Louis Amiet

Reviewer/s
Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson and Neil Cox)

Contributor/s

Justification
Listed as Endangered because the number of mature individuals is believed to have declined by more than 50% over the last three generations because of harvesting for food, and it is projected to decline by a similar amount over the next three generations. A generation is assumed to be approximately five years.

History
  • 1996
    Vulnerable
  • 1994
    Vulnerable
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Vulnerable
    (IUCN Conservation Monitoring Centre 1986)
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Current Listing Status Summary

Status: Threatened
Date Listed: 12/08/1994
Lead Region: Foreign (Region 10) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: T

For most current information and documents related to the conservation status and management of Conraua goliath , see its USFWS Species Profile

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IUCN Red List Category and Justification of Conservation Status

The IUCN Red List (2009) categorizes this species as Endangered because the number of mature individuals is believed to have declined by more than 50% over the last three generations because of harvesting for food, and it is projected to decline by a similar amount over the next three generations. A generation is assumed to be approximately five years (Amiet, 2004).

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Status

Classified as Endangered (EN) on the IUCN Red List 2007 (1).
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Populations of this species are decreasing (Amiet, 2004).

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Population

Population
It has decreased significantly as a result of harvesting for food.

Population Trend
Decreasing
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Life History, Abundance, Activity, and Special Behaviors

Egg masses consist of about several hundred eggs and are attached to vegetation at the bottom of rivers. Larval development takes between 85 and 95 days.

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

Major Threats
The most important threat to this species is hunting for food, and new, sophisticated traps for catching this species are now being used in the Nkongsamba area of Cameroon. Animals are also imported from Cameroon to the USA on a regular basis by animal dealers for zoos, the pet trade and competitive frog races (one estimate of this trade is 300 animals per year). It is also adversely affected by the loss of forest habitat for agriculture, logging, and human settlements, as well as by sedimentation of its breeding streams.
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Life History, Abundance, Activity, and Special Behaviors

The species has a limited distribution and a limited ecological range, and is considered threatened. The two major threats are habitat destruction (from conversion into farmland) and predation by humans. The people who inhabit the areas where the Goliath frog lives consider them a delicacy.

  • Sabater-Pi, J. (1985). ''Contribution to the biology of the Giant Frog (Conraua goliath, Boulenger).'' Amphibia-Reptilia, 6(2), 143-153.
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The most important threat to this species is hunting for food as new, sophisticated traps for catching this species are now being used in the Nkongsamba area of Cameroon. Animals are also imported from Cameroon to the USA on a regular basis by animal dealers for zoos, the pet trade and competitive frog races (one estimate of this trade is 300 animals per year). It is also adversely affected by the loss of forest habitat for agriculture, logging, and human settlements, as well as by sedimentation of its breeding streams (Amiet, 2004).

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Much of the dense rainforest of the goliath frog's habitat has been deforested for timber and to make way for agriculture. The construction of dams also threatens the breeding habitat of these frogs and this species is particularly vulnerable to habitat alteration due to its highly restricted range (2). Additionally, goliath frogs are considered a delicacy and are collected by local people for food (3); their large size has also encouraged collection for the pet trade in the past (2).
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Management

Conservation Actions

Conservation Actions
It presumably occurs in several protected areas, and is confirmed from Monte Alen National Park in Equatorial Guinea. Measures are needed to work with local communities to manage the harvest at sustainable levels. A captive-breeding programme should be considered.
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Conservation Actions and Management

It presumably occurs in several protected areas, and is confirmed from Monte Alen National Park in Equatorial Guinea. Measures are needed to work with local communities to manage the harvest at sustainable levels. A captive-breeding programme should be considered (Amiet, 2004).

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Conservation

The goliath frog is not currently protected under any trade restrictions and collection continues to threaten remaining populations. Captive breeding programmes have not proven successful and the only method of effectively preserving this amphibious giant is to safeguard areas of remaining habitat (2).
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Relevance to Humans and Ecosystems

Benefits

There are no known adverse effects of goliath frogs on humans

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Because of their size, goliath frogs are valued for the international pet and zoo trade. They are also a valuable food source for local communities.

Positive Impacts: pet trade ; food

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Uses

This species is considered a delicacy by local people.

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Risks

Relation to Humans

The Goliath frog is a significant food source for some human populations.

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

Goliath frog

The goliath frog (Conraua goliath) is the largest extant anuran on Earth.[1] The largest known specimens can grow up to 33 cm (13 in) in length from snout to vent, and weighs up to 3 kg (7 lb). This animal has a relatively small habitat range, mainly in Cameroon and Equatorial Guinea. Its numbers are dwindling due to habitat destruction and its collection for consumption and the pet trade.

Description[edit]

In a sample of 15 individuals,[2] weights ranged between 600 and 3,250 g (1.32 and 7.17 lb), and snout-vent lengths were between 17 and 32 cm (6.7 and 12.6 in). Their eyes can be nearly 2.5 cm (0.98 in) in diameter. The conspicuous tympanum has a diameter of about 0.5 cm (0.20 in) and is separated from the eye by about 5 cm (2.0 in) in adults. The next largest extant anurans are the Cane toad, about a third smaller than the Goliath in the largest specimens, and the African bullfrog, which is just over half the size of the Goliath. Goliath frog eggs and tadpoles are about the same size as other frogs despite its very large adult form.

A lateral fold extends from the eye to the posterior portion of the tympanum. Toes are fully webbed, with large interdigital membranes extending down to the toe tips. The second toe is the longest. The skin on the dorsum and on top of the limbs is granular. Dorsal coloration is green sienna, while the abdomen and ventral part of the limbs are yellow/orange. They have acute hearing but no vocal sac, and also lack nuptial pads.

Habitat and distribution[edit]

The goliath frog is normally found in and near fast-flowing rivers with sandy bottoms in the Middle African countries of Cameroon and Equatorial Guinea.[2] These rivers are usually clear and highly oxygenated. Their actual range spans from the last 200 km (120 mi) of the Sanaga basin in Cameroon to the north to the last 50 km (31 mi) of the Benito River basin in Equatorial Guinea to the south. The river systems in which these frogs live are often found in dense, extremely humid areas with relatively high temperatures.

Ecology and behavior[edit]

Reproduction[edit]

Like most amphibians, water is vital for their reproduction. Because the goliath frog lacks a vocal sac, it does not produce mating calls, a behavior unusually absent among frogs and toads.[2] Males construct spawning and breeding areas alongside and within rivers by pushing rocks into semicircular patterns. The egg masses consist of several hundred eggs, approximately 3.5 mm each, attached to vegetation at the bottom of rivers.[3] Larval development takes between 85 and 95 days.

Diet[edit]

Goliath tadpoles are vegetarian and feed on a single aquatic plant, Dicraeia warmingii, found only near waterfalls and rapids, which may help explain their restricted range.[1] Adult goliath frogs feed on worms, and insects, such as dragonflies and locusts. They also eat smaller frogs, crabs, baby turtles, and young snakes.

Mortality[edit]

The goliath frog can live up to 15 years in the wild. In captivity, they can live up to 21 years. It is preyed upon by snakes, Nile crocodiles, and Nile monitors.

Conservation[edit]

Preserved specimen at the Harvard Museum of Natural History

Goliath frogs were considered to be a source of food in some parts of west Africa.[4] They were also highly exported to zoos and animal dealers to be sold as pets. Unfortunately, these frogs fail to thrive in captivity and almost never reproduce there. Due to their classification as an endangered species, the Equatorial Guinean government has declared that no more than 300 goliaths may be exported out of the country per year.[1] Some are captured and kept as pets.

References[edit]

  1. ^ a b c "Goliath Frog". The American Museum of Natural History. 2007. Retrieved 2012-02-09. 
  2. ^ a b c Sabater-Pi, J. (1985). "Contribution to the biology of the Giant Frog (Conraua goliath, Boulenger)". Amphibia-Reptilia 6 (1): 143–153. 
  3. ^ "True Frogs: Ranidae - Goaliath Frog(conraua Goliath): Species Accounts". Net Industries. 2008. Retrieved 2012-02-09. 
  4. ^ Amiet, J. (2004). Conraua goliath. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006.
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