Search

The Australian lungfish, Neoceratodus forsteri Krefft, 1870, is a threatened species whose long-term persistence is at risk due to land-use intensification, water resource development, and other human pressures. Changes to the hydrology of rivers has the potential to alter the availability of certain high-quality food resources for this species, that may impact recruitment success, and contribute to population declines. This study analysed the fatty acid (FA) composition of lungfish eggs and fin tissues from two locations upstream and downstream of a large dam in the Brisbane River. We tested the hypothesis that river impoundment and flow alteration associated with the dam have altered the dietary composition and the FA composition of important dietary items for N. forsteri which translates to the body tissues and eggs. The contribution of each food source was estimated with mixing models using carbon and nitrogen stable isotopes. The total FA content in lungfish fin and eggs was significantly higher in downstream sites compared to upstream. Few significant differences in FA contents of the nine potential lungfish food sources were found between sites upstream and downstream of the dam. Stable isotope analyses of lungfish fin tissues revealed the most likely food sources were gastropods, bivalves, and crustaceans, however their relative importance differed upstream and downstream of the dam. Collectively, these results indicate that the dam did not negatively affect food quality for lungfish downstream. The most likely mechanism for potential FA deficiency and subsequent impacts on recruitment success in N. forsteri would be due to changes to the availability of high-quality food sources. This study highlights the need for future research to determine whether the low FA contents we observed in lungfish, is a function of broader environmental changes, or if FA contents are naturally low for this sub-tropical species. [ABSTRACT FROM AUTHOR]

We isolated and characterized 21 microsatellite loci in the vulnerable and iconic Australian lungfish, Neoceratodus forsteri. Loci were screened across eight individuals from the Burnett River and 40 individuals from the Pine River. Genetic diversity was low with between one and six alleles per locus within populations and a maximum expected heterozygosity of 0.774. These loci will now be available to assess effective population sizes and genetic structure in N. forsteri across its natural range in South East Queensland, Australia. [ABSTRACT FROM AUTHOR]

The effects of oxygen partial pressure ( $$ P_{{{\text{O}}_{2} }} $$) on development and respiration were investigated in the eggs of the Australian lungfish, Neoceratodus forsteri. At 20°C, embryonic survival and development was optimal at 15 and 20.9 kPa. Development was slowed at 5 and 10 kPa and embryos did not survive 2 kPa. At lower $$ P_{{{\text{O}}_{2} }} $$, the rate of oxygen consumption also decreased. Embryos responded to hypoxia by hatching at an earlier age and stage of development, and hatching wet and dry gut-free masses were reduced. The role of oxygen conductance ( $$ G_{{{\text{O}}_{2} }} $$) in gas exchange was also examined under selected environmental $$ P_{{{\text{O}}_{2} }} $$ and temperatures. The breakdown of the vitelline membrane changed capsule geometry, allowed water to be absorbed into the perivitelline space and increased capsule $$ G_{{{\text{O}}_{2} }} $$. This occurred at embryonic stage 32 under all treatments and was largely independent of both $$ P_{{{\text{O}}_{2} }} $$ and temperature (15, 20 and 25°C), demonstrating that capsule $$ G_{{{\text{O}}_{2} }} $$ cannot adaptively respond to altered environmental conditions. The membrane breakdown increased capsule diffusive $$ G_{{{\text{O}}_{2} }} $$ and stabilised perivitelline $$ P_{{{\text{O}}_{2} }} $$, but reduced the convective $$ G_{{{\text{O}}_{2} }} $$ of the perivitelline fluid, as the large perivitelline volume and inadequate convective current resulted in a $$ P_{{{\text{O}}_{2} }} $$ gradient within the egg prior to hatch. [ABSTRACT FROM AUTHOR]

The rate of oxygen consumption throughout embryonic development is used to indirectly determine the 'cost' of development, which includes both differentiation and growth. This cost is affected by temperature and the duration of incubation in anamniote fish and amphibian embryos. The influences of temperature on embryonic development rate, respiration rate and energetics were investigated in the Australian lungfish, Neoceratodus forsteri, and compared with published data. Developmental stage and oxygen consumption rate were measured until hatching, upon which wet and dry gut-free masses were determined. A measure of the cost of development, the total oxygen required to produce 1 mg of embryonic dry tissue, increased as temperature decreased. The relationship between the oxygen cost of development ( C, ml mg) and dry hatchling mass ( M, mg) in fishes and amphibians is described by C = 0.30 M, r = 0.52. The scaling exponent indicates that the cost of embryonic development increases disproportionally with increasing hatchling mass. At 15 and 20°C, N. forsteri cost of development is significantly lower than the regression mean for all species, and at 25°C is lower than the allometrically scaled data set. Unexpectedly, incubation of N. forsteri is long, despite natural development under relatively warm conditions, and may be related to a large genome size. The low cost of development may be associated with construction of a rather sluggish fish with a low capacity for aerobic metabolism. The metabolic rate is lower in N. forsteri hatchlings than in any other fishes or amphibians at the same temperature, which matches the extremely low aerobic metabolic scope of the juveniles. [ABSTRACT FROM AUTHOR]

Genetic variation at allozyme and mitochondrialDNA loci was investigated in the Australianlungfish, Neoceratodus forsteri Krefft1870. Tissue samples for genetic analysis weretaken non-lethally from 278 individualsrepresenting two spatially distinct endemicpopulations (Mary and Burnett rivers), as wellas one population thought to be derived from ananthropogenic translocation in the 1890's(Brisbane river). Two of 24 allozyme lociresolved from muscle tissue were polymorphic.Mitochondrial DNA nucleotide sequence diversityestimated across 2,235 base pairs in each of 40individuals ranged between 0.000423 and0.001470 per river. Low genetic variation atallozyme and mitochondrial loci could beattributed to population bottlenecks, possiblyinduced by Pleistocene aridity. Limited geneticdifferentiation was detected among rivers usingnuclear and mitochondrial markers suggestingthat admixture may have occurred between theendemic Mary and Burnett populations duringperiods of low sea level when the drainages mayhave converged before reaching the ocean.Genetic data was consistent with theexplanation that lungfish were introduced tothe Brisbane river from the Mary river. Furtherresearch using more variable genetic loci isneeded before the conservation status ofpopulations can be determined, particularly asanthropogenic demands on lungfish habitat areincreasing. In the interim we recommend amanagement strategy aimed at conservingexisting genetic variation within and betweenrivers. [ABSTRACT FROM AUTHOR]