Queensland lungfish

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Queensland lungfish

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sarcopterygii
Order: Ceratodontiformes
Family: Ceratodontidae
Genus: Neoceratodus
Species: N. forsteri
Binomial name
Neoceratodus forsteri
Krefft, 1870

Contents

[edit] General

The Queensland lungfish, Neoceratodus forsteri (also known as the Australian lungfish, Burnett salmon, and barramunda) is the sole member of the family Ceratodontidae and one of only six existing lungfish species in the world. Native only to Australia, [1] the Ceratodontidae is an ancient family belonging to the subclass Sarcopterygii, or fleshy-finned fishes. Fossil records of this group date back 380 million years, making the lungfish one of the oldest living vertebrate genera on the planet.[2] It is one of five extant representatives of the ancient air-breathing Dipnoi (lung fishes) that flourished during the Devonian Period (c. 413-365 million years before present) and is the most primitive surviving member of this lineage.[3]
The five other freshwater lungfish species, four in Africa and one in South America, are very different morphologically to N. forsteri.[2] The Queensland lungfish can live for several days out of the water if it is kept moist, but will not survive with total water depletion unlike its African counterpart.[1]

[edit] Range and Distribution

The Queensland lungfish is native only to the Mary and Burnett river systems in south-eastern Queensland.[4] It has been successfully distributed to other more southerly rivers including the Brisbane, Albert, Stanley, and Coomera Rivers, and the Enoggera Reservoir in the past century. The Queensland lungfish has also been introduced to the Pine, Caboolture, and Condamine Rivers, but current survival and breeding success are unknown.[1] Formerly widespread, at one time there were at least seven different species of lungfish in Australia.[2]

[edit] Habitat

This species lives in slow-flowing rivers and still water (including reservoirs) that have some aquatic vegetation present on banks. It occurs over mud, sand, or gravel bottoms.[2] Australian lungfish are commonly found in deep pools of depths between 3-10 meters[5] and live in small groups under submerged logs, in dense banks of aquatic macrophytes, or in underwater caves formed by the removal of substrate under tree roots on river banks. The lungfish is cold hardy, but prefers waters with temperatures between 15-25 °C.[6]
N. forsteri is incapable of surviving complete desiccation of its habitat, although it can live out of water for several days if the surface of the skin is constantly moist. Unlike the African species, Protoperus, it does not survive dry seasons by secreting a mucous cocoon and burying itself in the mud.[7]
The Queensland lungfish is essentially a sedentary species, exhibiting strong site fidelity within a restricted area. Its home range rarely extends beyond a single pool or occasionally, two adjacent pools. It does not follow a set migratory path, but may actively seek out suitable spawning habitats between July and December.[8]

[edit] Physical Description

Lungfish are olive-green to dull brown on the back, sides, tail, and fins and pale yellow to orange on the ventral surface (chin, chest, and belly).[4] They have been described as having a reddish coloring on their sides which gets much brighter in the males during the breeding season. This coloration is the only distinguishing sexual characteristic of the lungfish.[9] They have stout, elongated bodies and flattened heads with small eyes.[2] The mouth is small and in a subterminal position.[6] The lungfish can grow to a length of about 150 cm, or 1.5 m, and a weight of 43 kg,[4] or approximately 95 lbs. It is commonly found to be about 100 cm and 20 kg on average.[2] Both sexes follow similar growth patterns, excepting that the females grow to a slightly larger size.[6] They are covered in slime when taken from the water.[4]
The skeleton of the lungfish is partly ossified, partly cartilaginous. The vertebrae are pure cartilage while the ribs are hollow tubes filled with a cartilaginous substance.[10] The body of the lungfish is covered with large, bony scales.[2] There are ten rows on each side, grading to small scales on the fins. Each scale is embedded in an epithelial pocket and overlap extensively such that vulnerable areas of the body are covered by a thickness of at least four scales. Two unusually large and thick interlocking scales cover the back of the head where the bony skull is thin. They have powerful diphycercal tails[6] that are long and paddle-shaped.[4] The pectoral fins are large, fleshy, and flipper-like. The pelvic fins are also fleshy and flipper-like and situated well back on the body. The dorsal fin commences in the middle of the back and is confluent with the caudal and anal fins.[2]
The dentition of the lungfish is unusual: two incisors, restricted to the upper jaw, are flat, slightly bent, and denticulated on the hind margin. These are followed by dental plates on the upper and lower jaws.[10]
Juveniles have different body proportions than those of mature adults. The head is rounder, the fins are smaller, and the trunk is more slender. The mouth is initially terminal, but shifts back as the fish grows. The dorsal fin typically reaches to the back of the head in young juveniles, and gradually moves caudally until it only extends to the mid-dorsal region in adults. They show a gradual change in body form as they develop, but there is no externally detectable metamorphosis and no obvious point at which they can be termed adult.[11] As a juvenile the lungfish is distinctly mottled with a base color of gold or olive-brown. Patches of intense dark pigment will persist long after the mottling has disappeared.[6] Young lungfish are capable of rapid color change in response to light, but this ability is gradually lost as the pigment becomes denser.[9]

[edit] Breathing

The unique characteristic of the lungfish is the presence of a lung-like swim bladder. Modified into a vascularized air-breathing organ, it is used to supplement the oxygen supply through the gills.[2] During times of excessive activity, times of drought or high temperatures (when water becomes deoxygenated), or when prevailing conditions inhibit normal functioning of the gills, the lungfish can rise to the surface and swallow air into its lung.[4] It has been shown that more frequent air breathing is correlated with periods of greater activity at night when it uses the lung as a supplementary organ of respiration.[12]
The lung is a single long sac situated above and extending the length of the coelomic cavity. It is formed by a ventral outgrowth of the gut. Internally, the lung is divided into compartments formed by the infolding of the walls. Each compartment is further divided to form a spongy alveolar region. Blood capillaries run through this region close enough to the air space in the lung to enable gas exchange. Inhalation is achieved via a buccal force-pump similar to that of amphibians. The contraction of smooth muscles in the walls of the lung results in exhalation.[13]
The sound of the lungfish exhaling air at the surface prior to inhaling a fresh breath has been compared to that made by a small bellows.[2] Young lungfish come to the surface to breathe air when they are about 25 mm long.[6]

[edit] Reproduction and Development

The Queensland lungfish spawns and completes its entire life cycle in freshwater systems.[6] The age of first breeding is estimated to be 17 years for males and 22 years for females. Males typically become mature at 738-790 mm and females at 814-854 mm.[8] After an elaborate courtship, the lungfish spawn in pairs, depositing large adhesive eggs amongst aquatic plants.[2] They spawn from August until November, before the spring rains, in flowing streams that are at least a meter deep.[1] Eggs are most abundant during September and October. The stimulus for spawning is believed to be day length. The lungfish is known to spawn both during the day and at night.[14] The lungfish is selective in its choice of spawning sites. Eggs have been recorded on aquatic plants rooted in gravel and sand, slow and fast-moving waters, in shade and in full sun, but never on aquatic plants covered with slimy algae, in stagnant water, or where there was loose debris on the water’s surface.[9]
The lungfish does not make a nest and there is no guarding or parental care once the eggs are laid.[14] When spawning does take place, the pair of fish will lie on their sides or become entwined. Eggs are usually deposited singly, occasionally in pairs, but very rarely in clusters. The male lungfish fertilizes each egg as it emerges and the eggs are deposited in dense aquatic vegetation. The newly laid egg is hemispherical in shape, delicate, heavily yolked, and enclosed in a single vitelline and triple jelly envelope.[9] The egg itself is approximately 3 mm in diameter. With the jelly envelope it has a total diameter of about 1 cm.[11] The egg is sticky for a short while until silt and small aquatic organisms have covered it, but long enough for it to become attached to submerged vegetation. It is negatively buoyant and if it falls to the lake or river bed it is unlikely to survive to hatching.[9]
The female Queensland lungfish has a large ovary and the potential to lay many eggs, but only produces hundreds of eggs at most in her lifetime in the wild. In captivity, anywhere from 200 to 500-600 eggs have been laid in a single event. The lungfish does not necessarily spawn every year. A good spawning season occurs approximately once every five years, with no correlation to environmental conditions.[6]
The eggs and young of N. forsteri are similar to those of frogs.[4] Within the egg, head structures and pigmentation start to appear by day 17. They hatch after 3-4 weeks and resemble tadpoles.[2] Upon hatching the young fish is close to 10 mm. During the first week it lies on its side, hiding in the weeds and moving only when stimulated by touch. It will swim spontaneously, and often retreat back into the gelatinous envelope when disturbed. Newly hatched larvae develop a ciliary current over the skin and gill surfaces.[14] This is believed to either provide respiratory exchange across the skin and gills without necessitating any movements of the jaw or brachial apparatus or to keep the skin of the unprotected larvae free of debris, parasites, and predatory protozoans.[15] Larvae are reported to not feed for 2-3 weeks while the yolk is still present. By the time the yolk is fully utilized, a spiral valve has developed in the intestine and the fish starts to feed. The young are slow growing, but under optimal conditions may reach a length of 25 cm in 6 months.[2]
Neoceratodus forsteri has very complex courtship behavior made up of three distinct phases. The first is the searching phase, when the fish will range over a large area, possibly searching for potential spawning sites.[16] A pair of fish will perform circling movements at the surface of the water close to beds of aquatic plants. They breathe air more frequently and more noisily than normal, possibly reflecting a greater physiological requirement for oxygen. Individual fish have been observed to breathe air at regular intervals of about 20 minutes, with air breathing accompanied by a distinct loud burp made in the air. It has been suggested that the noisy breathing is a form of a mating call. Observations have been made that lungfish seem to do their noisy breathing in concert, even responding to each other, but never in close vicinity of where the eggs are laid.[14] The next phase involves behavior similar to “follow-the-leader” during which one fish, the male, shows interest in the female and nudges her with his snout. Up to eight individuals may be involved in follow-the-leader behavior. The male lungfish may occasionally take a piece of aquatic plant into its mouth and wave it around..[6] In the third phase, the fish dive together through aquatic vegetation, the male following the female and presumably shedding milt over the eggs.[16]
Adults have a high survival rate and are long-lived (at least 20-25 years), with a few claims that they may possibly live 60-100 years.
The Queensland lungfish has an unusually large karyotype, very large chromosomes and cells, and a high nuclear DNA relative to other vertebrates but less than what is reported for other lungfishes. In spite of this, it displays low allelic diversity between populations from the Mary, Burnett, and Brisbane catchments.[6] This low level of genetic variation could be attributed to population “bottlenecks” associated with periods of range contraction, probably during the Pleistocene, and in recent times during the periods of episodic or prolonged drought that are known to reduce some reaches of these river systems.[3]

[edit] Diet and Feeding Habits

N. forsteri is nocturnally active for the most part and is essentially carnivorous. In captivity it will feed on frogs, earthworms, pieces of meat, and pelleted food.[1] In the wild its prey includes frogs, tadpoles, fishes, a variety of invertebrates, and plant material.[2] No quantitative dietary data is available, but anecdotal observations clearly indicate that the diet of the lungfish changes with development. This is proven to be correlated with a change in dentition. Lungfish larvae are bottom feeders. They eat micro crustaceans and small Tubifex worms, occasionally supplementing their diet with filamentous algae. Soft foods such as worms and plants are partially crushed with a few quick bites and then swallowed. In the adult lungfish, movement of the prey in and out of the mouth is accompanied by strong adduction of the jaws. This crushing mechanism is coupled with hydraulic transport of the food, achieved by movements of the hyoid apparatus, to position the prey within the oral cavity.[17] The Queensland lungfish exhibits the most primitive version of these biomechanical feeding adaptations and behaviors.

[edit] Conservation Status

Although the status of Neoceratodus forsteri is secure, it is a protected species under the Queensland Fish and Oyster Act of 1914 and capture in the wild is strictly prohibited.[2] It was placed on the CITES list in 1977. The lungfish is currently protected from fishing and collection for education or research purposes requires a permit in Queensland, under the Fisheries Act of 1994, and from the Commonwealth Government. It is included on the list of “vulnerable” species, as studies have failed to show that it meets the criteria needed to be considered a threatened or endangered species.[6]
Human activities currently threaten the Queensland lungfish, particularly water development. It is potentially at risk in much of its core distribution in the Burnett and Mary Rivers as 26% of these river systems are presently impounded by weirs and dams. Barriers to movement and altered flow regimes downstream of dams for irrigation purposes could lead to the disruption of existing population structure and cause even more loss of genetic variation.[3]
Queensland lungfish are slow growing with a delayed first breeding age. For a long-lived species with naturally low mortality rates, successful spawning and juvenile recruitment is not essential every year and may only occur irregularly in medium to long cycles, even in natural environments.[18] The length of these cycles could easily mask the potentially deleterious impacts on recruitment for many years. Additionally, large adults could remain common for decades and give no indication of a declining population in the longer term.[6]
The Mozambique mouth brooder, or tilapia, has been declared a noxious and threatening alien species to the lungfish in Queensland.

[edit] Miscellaneous

All the remaining freshwater fishes of Australia are the modern bony fishes and all are ray-finned. The lungfish is distinct from this group as it is fleshy-finned.[1]
Fossils almost identical to Neoceratodus forsteri have been uncovered in northern New South Wales, indicating that it has remained virtually unchanged for well over 100 million years.[2]
The lungfish is reputed to be sluggish and inactive, but it is capable of rapid escape movements with the use of its strong tail.[19] It is usually quiet and unresponsive by day, becoming more active in the late afternoon and evening.[6]

[edit] Recent events

Proposed damming projects on both the Mary and Burnett rivers[20] threaten the habitat of the remaining lungfish. The dams would change the flow of the rivers eliminating the slow shallow areas the fish need for spawning. Scientists worldwide have become involved in saving the habitat for these lungfish citing their evolutionary importance.[21]

[edit] References

  1. ^ a b c d e f Lake, John S.. Australian Freshwater Fishes. Nelson Field Guides. Melbourne: Thomas Nelson Australia Pty. Ltd., 1978, 12. 
  2. ^ a b c d e f g h i j k l m n o p Allen, G.R., S.H. Midgley, M. Allen. Field Guide to the Freshwater Fishes of Australia. Eds. Jan Knight/Wendy Bulgin. Perth, W.A.: Western Australia Museum, 2002, 54-55. 
  3. ^ a b c Frentiu, F.D., J.R. Ovenden, and R. Street. "Australian lungfish (Neoceratodus forsteri: Dipnoi) have low genetic variation at allozyme and mitochondrial DNA loci: a conservation alert?". Conservation Genetics 2 (2001): 63-67. 
  4. ^ a b c d e f g Whitley, G.P.. in Ed. Jack Pollard: G.P. Whitley’s Handbook of Australian Fishes. Victoria: Wilke and Company Ltd., 1960, 334. 
  5. ^ Kemp, A.. "Threatened Fishes of the World: Neoceratodus forsteri (Krefft, 1870) (Neoceratodontidae)". Environmental Biology of Fishes 43 (1995): 310. 
  6. ^ a b c d e f g h i j k l m Pusey, Brad, Mark Kennard, and Angela Arthington. Freshwater Fishes of North-Eastern Australia. Nathan, QLD: CSIRO Publishing, 2004, 49-59. 
  7. ^ Joss, J.. "Australian Lungfish, Neoceratodus forsteri". Fishes of Sahul 16 (2002): 836-844. 
  8. ^ a b {{cite journal | author = Brooks, S.G. and P.K. Kind. | title = Ecology and demography of the Queensland lungfish (Neoceratodus forsteri) in the Burnett River, Queensland with reference to the impacts of Walla Weir and future water infrastructure development | journal = Queensland Department of Primary Industries, Brisbane, Report No. QO02004 (2002)
  9. ^ a b c d e Kemp, A.. "The biology of the Australian lungfish, Neoceratodus forsteri (Krefft 1870)". Journal of Morphology 1 (1986): 181-198. 
  10. ^ a b Krefft, G.. "Description of a gigantic amphibian allied to the genus Lepidosiren from the Wide-Bay district, Queensland". Proceedings of the Zoological Society 16 (1870): 221-224. 
  11. ^ a b Kemp, A.. "The embryological development of the Queensland lungfish, Neoceratodus forsteri (Krefft)". Memoirs of the Queensland Museum 20 (1982): 553-597. 
  12. ^ Grigg, G.C.. "Studies on the Queensland lungfish, Neoceratodus forsteri (Krefft) III. Aerial respiration in relation to habits". Australian Journal of Zoology 13 (1965): 413-421. 
  13. ^ Grigg, G.C.. "Studies on the Queensland lungfish, Neoceratodus forsteri (Krefft)". Australian Journal of Zoology 13 (1965): 243-253. 
  14. ^ a b c d Kemp, A.. "Spawning of the Australian lungfish, Neoceratodus forsteri (Krefft) in the Brisbane River and in Enoggera Reservoir, Queensland". Memoirs of the Queensland Museum 21 (1984): 391-399. 
  15. ^ Whiting, H.P. and Q. Bone. "Ciliary cells in the epidermis of the larval Australian dipnoan, Neoceratodus". Zoological Journal of the Linnean Society 68 (1980): 125-137. 
  16. ^ a b Grigg, G.C.. "Spawning behaviour in the Queensland lungfish, Neoceratodus forsteri". Australian Natural History 15 (1965): 75. 
  17. ^ Bemis, W.E. and G.V. Lauder. "Morphology and function of the feeding apparatus of the Lungfish, Lepidosiren paradoxa (Dipnoi)". Journal of Morphology 187 (1986): 81-108. 
  18. ^ Johnson, J.W.. "Review of draft lungfish scientific report 4 July 2001". Unpublished report. 2001. 
  19. ^ Kemp, A.. "A relic from the past – The Australian lungfish". Wildlife Australia (Autumn) (1990): 10-11. 
  20. ^ Ministerial Media Statements
  21. ^ http://www.theaustralian.news.com.au/story/0,20867,19859367-30417,00.html

[edit] External links