Species

Australian Lungfish

April 25, 2013, 7:18 pm
Content Cover Image

Captive Australian lungfish (Neoceratodus forsteri). © Dr. Solomon R. David, http://primitivefishes.com

The Australian lungfish Neoceratodus forsteri is one of six species and three genera in the sub-class Dipnoi (lungfishes). N. forsteri is the lone member of the family Ceratodontidae, the remaining families of Dipnoi being Lepidosirenidae and Protopteridae. Protopteridae contains four species in the genera Protopterus, which are all endemic to South and Central Africa. The family Lepidosirenidae contains one species, Lepidosiren paradoxa, endemic to South America. The extinct Scaumenacia, one of the earliest lungfishes, swam through ancient Devonian waters 400 million years ago. The Australian lungfish is thought to be the least derived of the extant lungfishes as N. forsteri shares many morphological traits with ancient Dipnoans (including Scaumenacia). These shared traits include a single lung, deep bodies, large cycloid scales, muscular paired fins and broad diphycercal tails. Fossilized toothplates, identical to those of living N. forsteri, have been found in Early Cretaceous deposits, attesting to the notion that the Australian lungfish is 140 million years old. The Australian lungfish may just be the oldest living vertebrate.

 

Embryonic Australian lungfish developing within the eggs.                     Photo courtesy of Dr. Roger Guo, www.ceratodus.com.


10-12 inch Juvenile Neoceratodus forsteri.                                             Photo courtesy of Dr. Roger Guo, www.ceratodus.com.


1.4 meter wild adult Australian lungfish Neoceratodus forsteri.         Courtesy of Heinz Machacek, www.fishing-worldrecords.com.

Conservation Status

 

Scientific Classification

Kingdom: Animalia
Phylum: Chordata
Class: Sarcopterygii

Order: Ceratodontiformes
Family: Ceratodontidae
Genus: Neoceratodus
Species: forsteri (Krefft 1870)

Physical Description

The body is large and deep with dark brown coloration covering the dorsal region and white to pink coloration on the ventral region. The head is flattened with small eyes and a small mouth that is gape limited. Large, cycloid scales run the length of the body. The Australian lungfish has paddle-like pelvic and pectoral fins (compared to the thread-like paired fins of the African and South American lungfishes). The caudal fin is broad and diphycercal. A single lung is thought to function more in buoyancy or to sustain elevated levels of activity than for respiration. N. forsteri grows to 1.5 meters in length and up to 40 kilograms in weight. Sometimes called the "Burnett River salmon" due to its pink flesh.

Behavior

The Australian lungfish is a facultative air breather, relying mostly on well-developed gills to respire. Intake of atmospheric oxygen only occurs frequently when the fish is stressed, such as living in polluted waters or during the breeding season. This is a stark contrast to the African and South American species of lungfishes, which are obligate air breathers, relying more on atmospheric oxygen for respiration. African and South American lungfishes can survive desiccation (drought) by constructing underground burrows and enveloping themselves in a cocoon for roughly 7 to 8 months, emerging with the returning rainy season. The Australian lungfish does not exhibit such estivation behavior. Although, Australian lungfish do burrow in submerged substrates, presumably to rest or avoid predation.

Reproduction

Sexual maturity is attained at an age of approximately 15-20 years of age. An increasing photoperiod (longer days) produces the onset of egg production in females. The bellies of N. forsteri become increasingly colorful when preparing to breed. Spawning occurs between August and December in the clean, flowing rivers of Southeastern Queensland and individuals habitually return to the same spawning sites. Spawning of N. forsteri includes elaborate courtship behaviors between mating pairs. Eggs are laid on aquatic plants or roots along the bank throughout the day or night. Females lay between 50-100 eggs per spawning event. Offspring develop directly, meaning there is no larval stage typical of many fishes. Unlike the South American and African lungfishes, the Australian lungfish does not construct a nest and there is no parental care following the breeding event. Hatchling lungfish are sheltered from predators by a mass of vegetation and an egg capsule, which the young fish can dart into when predators are near. Young lungfish not only respire through gills, but also through the skin (cutaneous respiration) much like many larval fishes and certain amphibians.

Lifespan/Longevity

Australian lungfish are long-lived fish that do not reach sexual maturity until approximately 15-20 years of age. Individuals in captivity have lived as long as 70 years. Wild individuals have been estimated as living up to 100 years. This milestone in age is seen in other fishes that reach sexual maturity late in life and grow slowly, like the sturgeon fishes (Acipenseridae) of North America and Eurasia.

Distribution & Movements

Endemic to Southeastern Queensland with historical populations in the Mary and Burnett Rivers, two bodies of water with similar water parameters and wildlife. The species was first described in the Auburn River, a tributary of the Burnett River system. There has been some debate on whether populations have occurred naturally or have been introduced into the Brisbane, Fitzroy, and North Pine Rivers. Since the 1800's, the Australian lungfish has been introduced into many other small reservoirs south of the Mary River to aid in the recovery of the species. Though, it is unknown whether the introduced populations will subsist or become extirpated.

Habitat

Australian lungfish are benthic fishes, living in or near the bottom of the water column. They can be found in both lotic and lentic environments, but are found mainly in the flowing waters or deep pools of rivers systems. In the Brisbane River, temperatures range from 13-25ºC and the pH ranges from 6.0-7.8 in waters where the species is found. Many of the rivers in which the Australian lungfish inhabits are turbid due to tannins, thus restricting light levels. Prime microhabitat for N. forsteri is sheltered areas such as submerged logs, caves, leaf litter, vegetation, and detritus. Submerged aquatic plants or dense root systems near the bank are essential spawning and nursery habitat for young lungfish. Since 1999, a prolonged drought in Southeast Queensland has restricted the spawning habitat of lungfish.

Food & Feeding Habits

The Australian lungfish begins foraging in the evening and continues throughout the night. Ampullary receptors in the skin of N. forsteri act as electroreceptors, enabling the fish to locate prey buried in sediments and leaf litter. A well-developed lateral line system aids in the location of prey during foraging hours when light levels are low. Olfactory (smell) organs in the mouth add to the list of tools for prey location. The diet consists of crustaceans, mollusks, small fishes (including young lungfish), amphibians, and plant matter. Heavily armored prey items (mollusks and crustaceans) are light work for the Australian lungfish's crushing toothplates. Once prey is caught by a powerful suction mode, prey are repeatedly sucked in the mouth, crushed with the toothplates, and spit back out until the prey is ready to be ingested. Hatchling lungfish feed mainly on zooplankton and algae. As the fish continues to grow into a juvenile, the diet will expand to include worms, prawns, snails, and eventually aquatic plants.

Predation

Australian lungfish are not utilized as food as they are protected by the Australian federal government. Historically, lungfish could succumb to the powerful jaws of crocodiles (crocodylidae); though, crocodiles have long since been extirpated from Queensland. Adult lungfish live relatively free from predation as submerged shelters act as protection. If needed, a quick thrust of the muscular trunk and broad caudal fin can act as an escape mechanism. Young lungfish can fall prey to a number of predators including other fishes and insects.

Threats & Conservation Status

The Australian lungfish was deemed Vulnerable in 2003 by Australia's federal Environmental Protection and Biodiversity Conservation Act. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) lists the Australian lungfish in Appendix II, meaning that the species is not currently threatened, but may become threatened in the future if not properly protected. Wild populations of N. forsteri are protected by the Fisheries Act of 1994, which requires a special permit to collect an Australian lungfish in Queensland. The destruction of spawning and nursery habitat, pollution, invasive species, and low recruitment are the major factors contributing to the decline of the Australian lungfish in its native range. Fluctuating water levels, due to the establishment of dams in the past 50-60 years, has prevented the growth of aquatic plants along the littoral zone, which is crucial breeding and nursery habitat for lungfish. Invasive species like the tilapia Oreochromis mossambicus, a cichlid native to Africa, compete with Australian lungfish through egg predation and habitat space.

Further Reading

  • Graham, Jeffrey B. 1997. Air-Breathing Fishes: Evolution, Diversity, and Adaptation. Academic Press.
  • Helfman, Gene S., Bruce B. Collette, Douglas E. Facey, & Brian W. Bowen. 2009. The Diversity of Fishes: Biology, Evolution, and Ecology. 2nd edition. Wiley-Blackwell West Sussex, United Kingdom.
  • Kemp, Anne. 2008. The Natural History of the Australian Lungfish. Center for Marine Studies, University of Queensland.
  • Threatened Species Scientific Committee (TSSC). 2011. Neoceratodus forsteri (Queensland Lungfish, Australian Lungfish). http://www.environment.gov.au/biodiversity/threatened/species/n-forsteri.html.
  • Watt, M., C. S. Evans, & J. M. Joss. 1999. Use of electroreception during foraging by the Australian lungfish. Animal Behavior Vol. 58: pg. 1039.
Glossary

Citation

Loos, J. (2013). Australian Lungfish. Retrieved from http://www.eoearth.org/view/article/51cbfa177896bb431f6bc7e8