The goliath frog (Conraua goliath), also known as the giant slippery frog or goliath bullfrog, is the largest frog on Earth. These impressive amphibians are found in the equatorial regions of Africa. This article delves into the specifics of their diet and habitat, as well as the conservation challenges they face.
Habitat and Distribution
Goliath frogs are endemic to the dense, humid, and relatively high-temperature rainforests of West Africa, specifically in Equatorial Guinea and Cameroon. Their geographic range extends from southwestern Cameroon south across the northern half of Río Muni (Continental Equatorial Guinea). They thrive in or near fast-flowing rivers and waterfalls.
Specific Habitat Requirements
The goliath frog has fairly specific habitat requirements. The water bodies they inhabit are typically characterized by:
- Cleanliness: The water is usually clean.
- Oxygenation: It is rich in oxygen.
- Acidity: It is slightly acidic.
- Temperature: The temperature hovers near 19.4 °C (67 °F).
They are also found near riverbanks and humid, undisturbed old-growth or secondary-growth forests (see also secondary succession). The presence of larval food also determines where goliath frogs occur.
Adult goliath frogs spend most of their time in the river to avoid daytime heat, venturing out of the water at night to search for food. Larger adults sometimes bask in the sun on rocks, with occasional dips in the water to stay moist.
Read also: The Hoxsey Diet
Physical Characteristics
Goliath frogs are the largest frogs on Earth. They exhibit several distinctive physical traits:
- Size: They range from 17 to 32 cm (6.7 to 12.6 inches) in length (snout-vent lengths).
- Weight: They weigh from 600 to 3250 grams (1.3 to 7.2 lb). The heaviest verified specimen weighed 3,305 g (7.3 lb) and had a snout-vent length of 34.0 cm (13.4 in). The longest verified specimen had a snout-vent length of 35.6 cm (14.0 in). In total length, including outstretched legs, the largest specimens can slightly exceed 80 cm (31 in).
- Body Shape: They have a flattened, wide body with a triangular head and muscular limbs.
- Skin: Their dorsal skin is granular and greenish-brown, which camouflages them well with the wet-moss covered rocks that adult frogs bask on. The ventral skin is a lighter yellowish-green or yellow-orange.
- Limbs: The hind legs are long, front legs are shorter and stout, and all of the feet are extensively webbed, with large interdigital membranes extending down to the toe tips. The second toe is the longest.
- Eyes: Their eyes can be nearly 2.5 cm (1 inch) in diameter.
- Tympanum: 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. A lateral fold extends from the eye to the posterior portion of the tympanum.
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.
Diet and Feeding Habits
The goliath frog has different dietary habits at different stages of its life.
Tadpole Diet
Goliath tadpoles are vegetarians and feed only on one aquatic plant, Dicraea warmingii, found only near waterfalls and streams. Having such an exclusive diet at this critical life stage may partially explain the species’ narrow habitat range.
Adult Diet
Adult goliath frogs are carnivores with a diverse diet. They feed on insects, crustaceans, fish, mollusks, small mammals and amphibians, including newts, salamanders, and smaller frogs. They also eat spiders, worms, and insects, such as dragonflies and locusts. In captivity, they have been known to eat adult white mice.
Read also: Walnut Keto Guide
Food preferences were different among the different weight groups of frogs, possibly correlating to different stages of development. Frogs weighing less than 400 g (14 oz) consumed annelids, arachnids, myriapods, insects, crustaceans, gastropods, and reptiles. Frogs weighing more than 1,000 g (35 oz) consumed arachnids, myriapods, insects, crustaceans, and gastropods with a significantly higher occurrence of myriapods.
Reproductive Behavior and Life Cycle
Little is known about goliath frog mating systems.
Mating Ritual
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 and are often considered mute. Females then follow this noise to the male.
Nest Building
In preparation for breeding, males create water-filled egg deposition sites made by clearing leaf litter and other debris from rock pools and river-scoured depressions or by excavating holes in gravel riverbanks. In some cases, males move rocks up to half of their body weight. 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.
There are three main nest types, all semi-circular in shape and located in or near a river:
Read also: Weight Loss with Low-FODMAP
- The first type of nest is constructed by clearing a section in an existing river pool.
- The second is constructed by expand an already existing pool, damming it off from the river.
- The third is constructed by digging a new pool roughly 1 m (3 ft) wide and 10 cm (4 in) deep, sometimes moving quite large stones in the process.
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. All nest types can be used several times and can consist of three distinct cohorts of tadpoles.
Egg Laying and Tadpole Development
Female goliath frogs lay several hundred to a few thousand eggs at a time that are about 3.5 mm (0.14 in) in diameter. They stick to vegetation or rocks at the bottom of the rivers and streams in which they reproduce. Females may guard the pools for a short time before abandoning them.
The eggs then hatch into tadpoles that grow to about 5 cm long over the next 75 to 90 days. The entire process of larval development takes approximately 85-95 days to complete. As in other frogs, goliath frog larvae undergo metamorphosis to become adult frogs.
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.
The chronological table of larval development:
- First Month: no organs were differentiated and only the ocular region showed significant pigmentation and transparent external gills.
- 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).
- 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.
- 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).
Lifespan and Maturity
Researchers note that goliath frogs likely become sexually mature at 10-12 months of age. Individuals can live up to 15 years in the wild, and some live as long as 21 years in captivity.
Conservation Status and Threats
The IUCN sites goliath frogs as an endangered species because of a 50% decline in population size in the last three generations. The International Union for Conservation of Nature (IUCN) has listed the goliath frog as an endangered species since 2004. Researchers estimate that goliath frog numbers fell by 70 percent between 2004 and 2019. 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.
Threats to Goliath Frog Populations
Several factors contribute to the endangered status of the goliath frog:
- Habitat Destruction: Deforestation and environmental degradation from agriculture, logging, and infrastructure development have significantly reduced their natural habitats. The frog has fairly specific habitat requirements, and the habitat where it occurs has become increasingly fragmented. Some of the frog’s habitat has been degraded by water pollution, specifically pesticide contamination and possibly by the development of hydroelectric dams.
- Overhunting and Poaching: The Goliath frog is hunted extensively for its meat, which is considered a delicacy in certain regions.
- Collection for Pet Trade: Because of their size, goliath frogs are valued for the international pet and zoo trade. They are sought after by zoos and pet collectors, with some in the latter category using them in frog-jumping contests; however they are unable to breed in captivity. They were extensively exported to zoos and the pet trade but have proven shy and nervous in captivity. Although captives may live longer than their wild counterparts, the species has not been bred in captivity.
- Parasites: Goliath frogs are also threatened by parasites. One particular parasite is one species of microfilarial nematode which belongs to genus Icoseilla. 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. 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.
- Chytridiomycosis: Chytridiomycosis is an infectious disease affecting amphibians, caused by the chytrid fungi Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans. It has the capability to cause random deaths due to its high mortality rate.
Adaptations
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. 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.
Conservation Efforts
Goliath frog exports are regulated in Equatorial Guinea, and the goliath frog is protected from collecting, trade, and wanton killing in Cameroon; however, local residents continue to hunt it. The southern extent of its geographic range lies in the Monte Alén National Park in Equatorial Guinea.
The IUCN has highlighted the need for conservation measures, in cooperation with local communities, to make sure the hunting is at sustainable levels. Local conservation efforts and captive-breeding programs also need to be considered in order to maintain population sizes.