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
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
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
Lifespan of goliath frogs is not well documented, although individuals in the wild seem to live longer than those in captivity.
The geographic range of goliath frogs is restricted to coastal, equatorial Guinea and Cameroon in West Africa.
Biogeographic Regions: ethiopian (Native )
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 )
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.
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
There are no known adverse effects of goliath frogs on humans
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
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
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
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)
The goliath frog (Conraua goliath), otherwise known commonly as the giant slippery frog and the goliath bullfrog, is a species of frog in the family Conrauidae. The goliath frog is the largest living frog.[3][4] Specimens can grow up to 32 centimetres (12.6 in) in length from snout to vent, and weigh up to 3.25 kilograms (7.2 lb). This species has a relatively small habitat range in Cameroon and Equatorial Guinea.[5] Its numbers are dwindling due to habitat destruction and its collection for food and the pet trade.[1]
Sexual dimorphism between the sexes is minimal.[6] In a sample of 15 individuals, weights ranged between 600 and 3,250 g (1.3 and 7.2 lb), and snout-vent lengths were between 17 and 32 cm (6.7 and 12.6 in).[5] Their eyes can be nearly 2.5 cm (1.0 in) in diameter. The conspicuous tympanum has a diameter around 0.5 cm (0.20 in) and is separated from the eye by about 5 cm (2.0 in) in adults. Goliath frog eggs and tadpoles are about the same size as other frogs despite their 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.
The Goliath frog is mainly found near waterfalls in Equatorial Guinea and Cameroon. Their habitat is divided into two main seasons: the dry season which occurs from November to April and the rainy season which occurs from May to October.[7]
The Goliath frog is one of the largest frogs and since it has such a large size, it has an extremely selective distribution. This species is primarily located in a dense equatorial forest fringe which is somewhat parallel to the coast and surrounded by rivers. The Goliath frog was located in Sanaga Basin mainly appearing near the Nachtigal cascades and in the Sakbayeme rapids, in Kienke Basin, Ntem Basin mainly being located near the rapids of the Mensolo and Nsana, in Mbía Basin where it was found to be very abundant in the rapids and cascades. These distribution patterns emphasize its limited environment which tends to have a clear preference for water territories.[8]
The primary threat to the goliath frog is hunting, as it is considered a food source in its native range.[1] The IUCN has highlighted the need for conservation measures, in cooperation with local communities, to make sure the hunting is at sustainable levels.[1] To a lesser extent they are also threatened by habitat loss and degradation.[1] They were extensively exported to zoos and the pet trade, but have proven shy and nervous in captivity.[9] Although captives may live longer than their wild counterparts, the species has not been bred in captivity.[9][10] Due to their classification as an endangered species, the Equatorial Guinean government has declared that no more than 300 goliaths may be exported per year for the pet trade, but few now seem to be exported from this country.[3]
It was determined in a study that the goliath frog consumes a wide variety of food which suggests that the frog is omnivorous with a carnivorous preference. Their prey are terrestrial, aquatic, and semi-aquatic, indicating that they hunt both on land and in water. Food preferences were different among the different weight groups of each frog which could be correlated to different stages of development. For frogs who weigh less than 400 g (14 oz) (could be equivalent to the young), they consumed annelids, arachnids, myriapods, insects, crustaceans, gastropods, and reptiles. For frogs who weigh more than 1,000 g (35 oz) (could be equivalent to a fully developed frog), they consumed arachnids, myriapods, insects, crustaceans, and gastropods with a significantly higher occurrence of myriapods. This shows that annelids and reptiles are present only in the diet of low weight frogs which emphasizes the more diversified diet for younger goliath frogs.[11] Fully developed frogs are also believed to prey on fish, small mammals, and amphibians, including newts, salamanders, and smaller frogs.[12]
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 generally present in frogs and toads.[5] The egg masses consist of several hundred to a few thousand eggs, approximately 3.5 mm (0.14 in) each, and often attached to aquatic vegetation.[13] There are three main nest types, all semi-circular in shape and located in or near a river: In the first they clear a section in a river pool. In the second they expand an already existing pool, daming it off from the river. In the final they dig a pool, roughly 1 m (3 ft) wide and 10 cm (4 in) deep, sometimes moving quite large stones in the process. This may partially explain the goliath frog's large size, as larger frogs may be more successful at moving heavy objects when constructing their nests. Adults have also been shown to guard the nests at night. Although not confirmed, there are indications that the nest is constructed by the male, while the female guards the nest with the eggs.[13] Larval development takes between 85 and 95 days.
While the reproductive behavior for this species is mostly not well-known, studies by Lamotte, Perret, and Zahl have allowed an overall chronological table of larval development to be created.[5]
Typically after 24 hours, the cover of the egg mass becomes yellow and the eggs become dark gray-brown. These egg masses were found attached to the bottom of plants. [5]
First Month: no organs were differentiated and only the ocular region showed significant pigmentation and transparent external gills. The lengths were 8–10 mm (0.31–0.39 in) and while the body/tail appeared to be slightly pigmented, the abdomen was always nearly white.[5]
Second Month: The activity of the tadpoles increased greatly for they are now beginning to feed on leaves. Furthermore, they have developed a denser pigmentation, and the spiraculum and anal tube are now beginning to become visible. Additionally, the mouth and the eyes are beginning to function. Sizes range 19–21 mm (0.75–0.83 in). As the month continues, pigmentation is becoming more intense via the presence of nearly black spots, two rows of teeth are developing on both the upper and lower lip, feeding increases greatly, and their size becomes 24 mm (0.94 in).[5]
Third Month: The posterior legs are now beginning to form and the length of the tadpoles are around 40mm. As the month progresses, the posterior legs become larger and joints/fingers are becoming more distinguishable. The total length of the tadpoles is now 45 mm. Finally, at the end of the month, anterior legs have fully appeared, posterior legs are grown with long and powerful fingers accompanying this growth, the mouth has become an arched slot line, tail regression has begun, and these tadpoles begin to put their head out of the water in order to breathe.[5]
Fourth Month: All of the specimens in the experiment reached the final stage of metamorphosis. The tail has been either completely or nearly reabsorbed, the shape and color of adults is obtained with slightly lighter and greener pigmentation, the total length is 35 mm (1.4 in). The large size characteristic of these frogs is not obtained yet. The entire process of larval development takes approximately 85–95 days to complete. [5]
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, Nile monitors, and humans, among other predators.
The goliath frog creates nests as sites for their offspring as a form of parental care. There are three main types of nests: type 1 mainly contains rock pools that were cleared from detritus and leaf litter, type 2 contains existing washouts at riverbanks, and type 3 were depressions dug by the frogs into the gravel riverbanks. Each nest type contains advantages and disadvantages. Nest type 1 was the easiest to create since only cleaning of the substrate was required to create the nest. Consequently, these types of nests were the least reliable since they were usually positioned in the river bed which makes them extremely vulnerable to being washed out by the rising water levels and to having predators enter the nest. Both nest types 2 and 3 were less likely to be washed out, however, they have an increased risk for being dried-up during the dry season. Consequently, while each nest promotes clear advantages, nests are typically constructed depending on the environment cues (whether it is the dry season or the rainy season). All nest types can be used several times, and can consist of three distinct cohorts of tadpoles.[14] The construction of these nests can also explain how the goliath frog became the largest frog. Digging out these nests which exceed 1 m in diameter is an extremely arduous task. Other species which perform this task are also quite large in size. This includes: male African Bullfrogs, Gladiator Frogs, and the Bornean Giant River Frog.[13]
Typically, the goliath frog attaches its eggs either underwater, in small groups to rocks, or in gravel or larger pieces of wood. The construction of the nests may help reduce predation for it would be more difficult for the fish and shrimp (species which typically eat the eggs) to find the eggs and it may prevent the eggs from being washed away by the rapid current. However, in contrast, the changing water levels may also cause an increase in predation, cause more of the eggs to spill out, and increase tadpole morality as well since the tadpoles and eggs may remain trapped within the nests. Additionally, these nests allow the Goliath frogs to become less dependent on existing structures for egg deposition which can allow these frogs to prolong their breeding season and also increase the amount of suitable breeding sites (they are determined to be suitable by the absence of predators or water presence since water is required for the offspring to survive).[13]
The process of constructing a nest for the offspring is used as a method of promoting a male’s reproductive benefits to the females. It also serves as the main parental investment since once the female deposits the eggs after fertilization, there is no more parental investment. [13]
The goliath frog is endangered due to deforestation, overhunting, and parasites. One particular parasite is one species of microfilaria which belongs to the Icoseilla genus. This parasite is often found within the blood and lymphatic system and its spread throughout the lymphatic system can cause lethargy and mortality when the infection is serious. This parasite was more prevalent during the dry season which is primarily due to the water speed decreasing thereby allowing more potential breeding sites created. Since there are more breeding sites (it is important to note that their primary habitat is near rivers and waterfalls, but in the dry season, they tend to create breeding sites in areas that contain less water), there would be more opportunity for the mosquitos to infect the frogs thereby increasing the contagion rate. Furthermore, there was a positive relationship detected between host size and parasite abundance: the greater the size of the host, the more intense the infection would be. Within this species, male goliath frogs were found to be more significantly infected when compared to the females which can be due to the weight difference between the two. Additionally, as within most species, as age increases, the severity of the infection will also increase.[15]
There are also parasites that mainly target the gastro-intestinal tract of this frog. These parasites are called helminth parasites which are worm-like parasites divided into three main groups: flukes which are leaf-shaped flatworms, tapeworms which are elongated flatworms that inhabit extraintestinal tissues, and roundworms which inhabit intestinal and extraintestinal sites. The Goliath frog, however, was mainly infected by Nematodes (90.5%) which is a specific type of roundworm. The helminth species discovered within the Goliath frog was extremely similar to those discovered in amphibian hosts in other African countries emphasizing that its location/habitat is the main cause of the prevalence of this predator. However, the Goliath frog was also infected by the nymph of Sebekia sp which could be primarily due to these frogs sharing the same habitat of crocodiles (definitive host) and fishes (intermediate host). Frogs that originate in Loum and Yabassi which are places within Cameroon had the largest variety of helminth species whereas frogs from Nkondjock had the smallest variety. This could be explained by the difference in agricultural activities, deforestation, and poaching. Liver weight was examined to reveal that there is a higher accumulation of toxic products at Loum due to the significant increase in agriculture practice. Consequently, land use effects and their impact on water habitats plays a significant role in the pattern of parasitism and land use by goliath frogs. Additionally, the direct life cycles of the helminths may play an important role in species diversity Parasites which have direct life cycles spend a majority of their adult life within one host which allows their offspring to be spread from one host to another. These types of parasites also often lack an intermediate stage which means that they must be able to survive in the outside environment as well and be able to establish themselves within a new host. This ability to adapt to new environments contributes greatly to the complexity of helminth communities of goliath frogs.[16][17][18]
Chytridiomycosis is an infectious disease which affects many different species of amphibians worldwide. It is caused by the chytrid fungus which has the capability of causing random deaths due to its high mortality rate. This fungus tends to invade the surface layers of the skin thereby causing damage to the outer keratin layer (this fungus only attacks the parts of the frog’s skin that contains keratin). As the tadpole continues to grow, more keratin becomes present on the skin thereby allowing the fungus to spread to many parts of the body resulting in the death of the tadpole. Amphibian skin is vital because it is physiologically active meaning it plays important roles in regulating respiration, water, and electrolytes. While the method of how this fungus kills frogs is not known, it can be hypothesized that its invasion through the skin is related since it can cause an electrolyte depletion, osmotic imbalance, and make it more difficult for the frog to breathe. When infected with this fungus, a frog may have discolored skin, peeling on the outside layers of its skin, be sluggish, and have its legs spread slightly away from itself. This fungus is also transmittable since it can be directly transferred through contact between frogs and tadpoles or through exposure to infected water. Thus, it is highly spreadable and with its high mortality rate among frogs, it is extremely deadly.[19][20]
The goliath frog contains extensive skin folds to promote respiratory gas exchange at high altitudes. Additionally, the lungs within these frogs are reduced to about one-third of the volume of other frogs and they also contain a smaller heart. This is primarily due to their difference in predation methods. Goliath frogs are typically sit-and-wait predators. This means that they tend to capture/trap their prey either by luring them or using elements of surprise by acting extremely stealthy. As a result, they have a reduced metabolic rate and a unique method of breathing. When attempting to breathe, each buccal movement (a method in which the mouth expands and contracts in order to promote the movement of air into the lungs) pumps air at a rapid rate and the process of getting the oxygen removed from the air is slightly more efficient in this species of frog. These adaptations are very useful for the production of territorial and reproductive calls created by these frogs. Typically, the call of the goliath frog which is produced by the frog opening its mouth is admitted at a high frequency of 4.4 kHz. Furthermore, the goliath frog does not contain a vocal sac which causes the process for making noises/calls for reproduction to be different than most frogs.[21]
While effects of climate change, agriculture, and deforestation greatly affect this species to the extent of making them endangered, they are also mainly captured by the locals who use lanterns to get their attention and then shortly after, they immobilize them using meshed nets. In Nkombia, they are also captured with nets during the day while they are resting on the rocks. However, this method of capture is not very effective for they are able to escape quite well due to their ability to jump 1.2 to 3 m (3.9 to 9.8 ft) high. Humans are the main predators for this species and are the main cause of their endangerment. In order to save the species, hunting and evironmental destruction should be limited.
The goliath frog (Conraua goliath), otherwise known commonly as the giant slippery frog and the goliath bullfrog, is a species of frog in the family Conrauidae. The goliath frog is the largest living frog. Specimens can grow up to 32 centimetres (12.6 in) in length from snout to vent, and weigh up to 3.25 kilograms (7.2 lb). This species has a relatively small habitat range in Cameroon and Equatorial Guinea. Its numbers are dwindling due to habitat destruction and its collection for food and the pet trade.
