Crocodylus Johnstoni Research Articles

Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in freshwater crocodiles (Crocodylus siamensis) after intravenous and intramuscular administration.

To the best of the authors' knowledge, pharmacokinetic information to establish suitable therapeutic plans for freshwater crocodiles is limited. Therefore, the purpose of this study was to clarify the pharmacokinetic characteristics of enrofloxacin (ENR) in freshwater crocodiles, Crocodylus siamensis, following single intravenous and intramuscular administration at a dosage of 5mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168hr. The plasma concentrations of ENR and its metabolite ciprofloxacin (CIP) were measured by liquid chromatography tandem-mass spectrometry. The concentrations of ENR and CIP in the plasma were quantified up to 144hr after both the administrations. The half-life was long (43-44hr) and similar after both administrations. The absolute i.m. bioavailability was 82.65% and the binding percentage of ENR to plasma protein ranged from 9% to 18% with an average of 10.6%. Percentage of CIP (plasma concentrations) was 15.9% and 19.9% after i.v. and i.m. administration, respectively. Based on the pharmacokinetic data, susceptibility break point and PK-PD indexes, i.m. single administration of ENR at a dosage of 5mg/kg b.w. might be appropriate for treatment of susceptible bacteria (MIC>1μg/mL) in freshwater crocodiles, C.siamensis.

The curious case of the endemic freshwater crocodile Crocodylus mindorensis as incidental host of marine fish acanthocephalan

We performed the first host-parasite survey of the Philippine crocodile, Crocodylus mindorensis, a critically endangered species for which ecological information is lacking. We collected by gastric lavage samples of the stomach contents of crocodiles (n = 10) residing at the Palawan Wildlife Rescue and Conservation Center in Puerto Princesa, Palawan, Philippines. The only parasite detected was an acanthocephalan, which was identified as Neorhadinorhynchus nudus (n = 68), a parasite typically found in the marine fish species consumed by three crocodile individuals. Given the known hosts of N. nudus, its parasitism of C. mindorensis in captivity is likely established by consumption of marine fish. Our findings have implications for the conservation management of C. mindorensis, particularly in terms of preventing introduction of parasites that could lead to development of infectious disease or alter the fitness of captive animals.

Surveying death roll behavior across Crocodylia

The “death roll” is an iconic crocodylian behaviour, and yet it is documented in only a small number of species, all of which exhibit a generalist feeding ecology and skull ecomorphology. This has led to the interpretation that only generalist crocodylians can death roll, a pattern which has been used to inform studies of functional morphology and behaviour in the fossil record, especially regarding slender-snouted crocodylians and other taxa sharing this semi-aquatic ambush predator body plan. In order to test this hypothesis, we surveyed death roll behaviour across animals representing all extant crocodylian species. Animals were prompted to death roll using two methods of stimulation: a feeding cue and an escape cue. The feeding cue involved presenting each animal with a bait item, to which resistance would be applied during a biting event. The second cue involved capturing each animal with a rope or catch pole, a standard technique for capturing crocodylians, but one that also often prompts an attempt to escape. All species tested, except Paleosuchus palpebrosus, exhibited the behaviour in response to at least one of the stimuli. This included the following slender-snouted species: Gavialis gangeticus, Tomistoma schlegelii, Mecistops cataphractus, Mecistops leptorhynchus, Crocodylus johnstoni, and Crocodylus intermedius. The patterns of death roll behavior observed in this survey suggest that this behaviour is not novel to any one crocodylian clade, morphotype, or dietary niche. Also, the prevalence of death rolling behaviour across Crocodylia in response to perceived threats indicates that it is not solely, or maybe even primarily, a feeding behaviour, but is also utilised during inter- and intra-specific conflict as a means to escape or injure an opponent. The results of this case study highlight the importance of using multiple modern analogues when attempting to correlate form and function across diverse clades, both living and extinct.

Observations of mammalian feeding by Australian freshwater crocodiles (Crocodylus johnstoni) in the Kimberley region of Western Australia

Observations of mammalian feeding by Australian freshwater crocodiles (Crocodylus johnstoni) in the Kimberley region of Western Australia

Australia's Northern Safari

[Extract] Filmed during a 1955 family trip from Perth to the Gulf of Carpentaria, Keith Adams’s Northern Safari showed to packed houses across Australia, and in some overseas locations, across three decades. Essentially a home movie, initially accompanied by live commentary and subsequently by a homemade sound track, it tapped into audiences’ sense of Australia’s north as a place of adventure. In the film Adams interacts with the animals of northern Australia (often by killing them), and while by 1971 the violence apparent in the film was attracting criticism in letters to newspapers, the film remained popular through to the mid-1980s, and was later shown on television in Australia and the United States (Cowan 2; Adams, Crocodile Safari Man 261). A DVD is at present available for purchase from the website of the same name (Northern Safari). Adams and his supporters credited the film’s success to the rugged and adventurous landscape of northern Australia (Northeast vii), characterised by dangerous animals, including venomous spiders, sharks and crocodiles (see Adams, “Aussie”; “Crocodile”). The notion of Australia’s north as a place of rugged adventure was not born with Adams’s film, and that film was certainly not the last production to exploit the region and its wildlife as a source of excitement. Rather, Northern Safari belongs to a long list of adventure narratives whose hunting exploits have helped define the north of Australian as a distinct region and contrast it with the temperate south where most Australians make their lives. This article explores the connection between adventure in Australia’s north and the large animals of the region. Adams’s film capitalised on popular interest in natural history, but his film is only one link in a chain of representations of the Australian north as a place of dangerous and charismatic megafauna. While over time interest shifted from being largely concentrated on the presence of buffalo in the Northern Territory to a fascination with the saltwater crocodiles found more widely in northern Australia that interest in dangerous prey animals is significant to Australia’s northern imaginary.

Serological survey of Australian native reptiles for exposure to ranavirus.

Ranaviruses have been isolated from many ectothermic vertebrates, and serological surveys of both amphibians and reptiles have shown the presence of ranaviral antibodies in a proportion of these populations. An enzyme-linked immunosorbent assay (ELISA) was developed to measure serum antibodies against ranavirus in Australian reptiles. The ELISA was validated with serum from challenge trials with Bohle iridovirus (BIV) in 6 reptilian species. A preliminary sero-survey of northern Queensland riparian reptile fauna (saw-shelled turtles Myuchelys latisternum, Krefft's river turtles Emydura macquarii krefftii, freshwater crocodiles Crocodylus johnstoni, as well as the snakes Boiga irregularis, Dendrelaphis punctulatus, Tropidonophis mairii, Morelia spilota, Liasis childreni and L. fuscus) revealed evidence of past exposure to Bohle iridoviral antigens in part of the population at several locations sampled. Furthermore, in Krefft's river turtles and freshwater crocodiles, a statistically significant trend was apparent for larger reptiles to be more likely to have BIV-reactive sera than smaller individuals. The use of adult tortoise populations as sentinels can assist in monitoring the presence of BIV in northern Australian freshwater streams, and thereby the potential dangers to native fauna from this agent.

Morphometric analysis of the Australian freshwater crocodile (Crocodylus johnstoni)

We conducted a morphometric analysis of 279 Crocodylus johnstoni, using specimens from the McKinlay River (n = 265) and Arnhem Land (n = 14), to meet the management need for predicting body size of C. johnstoni from isolated body parts. The results also allow reconstruction of C. johnstoni dimensions for comparison with other crocodilian species. We detected sexual dimorphism in some body measurements from the McKinlay River, and geographic variation in the morphology of McKinlay River and Arnhem Land populations, but differences were slight. There is pronounced allometric growth in C. johnstoni in the immediate post-hatching phase, largely due to elongation of the snout after exiting the confines of the egg. We compared the size, shape and relative growth of C. johnstoni with that of other crocodilian species for which equivalent data are available, but particularly the other Australian crocodile, Crocodylus porosus. C. porosus has a proportionately longer tail and a shorter but wider snout than C. johnstoni, and we discuss possible ecological correlates of these and other differences.

Hematology and Serum Biochemistry for Free-ranging Freshwater Crocodiles (Crocodylus johnstoni) in Western Australia

We determined reference ranges for hematology and serum biochemistry in 39 free-ranging freshwater crocodiles ( Crocodylus johnstoni ). Animals were captured from Windjana Gorge in Western Australia and physically restrained for blood sampling from the supravertebral vein. No significant sex differences were found. Four animals were infected with a haemogregarine-like intraerythrocytic parasite.

Pharmacokinetics of marbofloxacin in freshwater crocodiles (Crocodylus siamensis) after intravenous and intramuscular administration.

To evaluate the fate and disposition of marbofloxacin (MBF) in freshwater crocodiles (Crocodylus siamensis), MBF was administered either intravenously (i.v.) or intramuscularly (i.m.) at a dosage of 2.0mg/kg body weight. The concentrations of MBF in plasma were measured using high-performance liquid chromatography equipped with a fluorescence detector. The concentrations of MBF in the plasma were measurable up to 144h after i.v. and i.m. administration. After the first 45min, the mean pharmacokinetic profiles produced by the two administration routes were almost identical. No statistically significant differences in the pharmacokinetic parameters between the groups were observed. The half-life was long (about 2.5days), the volume of distribution was large (about 1.44L/kg), λz was small (0.01 h-1 ), and the clearance was slow (22.6mL/h/kg). The absolute i.m. bioavailability (F%) was 105.36%. The dose of MBF administered in this study seems to produce appropriate PK-PD parameters that predict antibacterial success for disease caused by susceptible bacteria. More studies are warranted to evaluate the likely residues after administration of multiple doses.

Croc eyes fine-tuned to lurk at water surface

Crocodiles and alligators have perched at the water's edge waiting for the perfect dining opportunity to pass for millions of years. Explaining how the animals also spend much of their time immersed in water with only their eyes and nostrils protruding above the surface, Nicolas Nagloo from The University of Western Australia adds that this posture provides them with a unique perspective on the world. ‘The water surface makes up the majority of the bottom of the visual field and the visual horizon occurs along the riverbanks where the crocodile sees best’, he says. However, while the visual worlds of saltwater and freshwater crocodiles are essentially identical above the water's surface, the light conditions are significantly different when the animals are submerged: ‘In freshwater habitats, there is an abundance of long wavelength [red] light… In contrast, saltwater habitats transmit a broader range of wavelengths, providing a greater amount of short wavelength [blue] light’, Nagloo explains. Knowing that crocodiles cannot see clearly when submerged but they have a fantastic assortment of adaptations that help them to see and hunt in dim conditions, Nagloo and his colleagues Shaun Collin, Jan Hemmi and Nathan Hart decided to gaze into the eyes of two Australian crocodile species to find out more about their colour vision and visual clarity.Investigating the structure of the retina at the back of the eyes of juvenile saltwater crocodiles (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni), Nagloo discovered that instead of having a compact fovea (a depression in the retina where there is a high density of photoreceptors that provide a high-resolution view of the world), the foveae of saltwater and freshwater crocodiles are stretched across the back of the eye in line with the horizon. Describing the elongated structure as a foveal streak, Nagloo says, ‘[it] gives greater visual clarity’, adding that the elongated shape of the structure allows both species to keep a close eye on events on the riverbank without moving their heads.However, when Nagloo investigated the sensitivity of the different photoreceptors in both species’ eyes, he was surprised to find that the crocodiles have relatively sophisticated colour vision, provided by three colour-sensitive cones that are tuned to violet, green and red wavelengths. Also, the sensitivity of the saltwater crocodiles' colour photoreceptors was slightly shifted to shorter (bluer) wavelengths compared with that of the photoreceptors of the freshwater crocodiles, even though neither species can focus underwater, suggesting that they may use their vision underwater more than had been thought.Considering the subtle differences between the visual systems of the two Australian species, Nagloo says that the crocodiles have finely tuned visual systems that give each species an advantage while in their own environments. And he is now keen to find out how the vision of both species adapts as they grow. ‘We know that eye size has a big effect on visual clarity and we also know that saltwater crocodiles reach much greater maximum body sizes than freshwater crocodiles, so it would be interesting to find out whether the eye of saltwater crocodiles also gets much bigger than the freshwaters’ and what impact that would have on visual clarity,’ he says.

Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni

Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semi-aquatic lifestyle and ambush hunting mode are reflected in specific adaptations in the peripheral visual system. Design-based stereology and microspectrophotometry were used to assess spatial resolving power and spectral sensitivity of saltwater (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni). Both species possess a foveal streak that spans the naso-temporal axis and mediates high spatial acuity across the central visual field. The saltwater crocodile and freshwater crocodile have a peak spatial resolving power of 8.8 and 8.0cyclesdeg(-1), respectively. Measurement of the outer segment dimensions and spectral absorbance revealed five distinct photoreceptor types consisting of three single cones, one twin cone and a rod. The three single cones (saltwater/freshwater crocodile) are violet (424/426 nm λmax), green (502/510 nm λmax) and red (546/554 nm λmax) sensitive, indicating the potential for trichromatic colour vision. The visual pigments of both members of the twin cones have the same λmax as the red-sensitive single cone and the rod has a λmax at 503/510 nm (saltwater/freshwater). The λmax values of all types of visual pigment occur at longer wavelengths in the freshwater crocodile compared with the saltwater crocodile. Given that there is a greater abundance of long wavelength light in freshwater compared with a saltwater environment, the photoreceptors would be more effective at detecting light in their respective habitats. This suggests that the visual systems of both species are adapted to the photic conditions of their respective ecological niche.

Cationic Antimicrobial Peptides Derived from Crocodylus siamensis Leukocyte Extract, Revealing Anticancer Activity and Apoptotic Induction on Human Cervical Cancer Cells.

Known antimicrobial peptides KT2 and RT2 as well as the novel RP9 derived from the leukocyte extract of the freshwater crocodile (Crocodylus siamensis) were used to evaluate the ability in killing human cervical cancer cells. RP9 in the extract was purified by a combination of anion exchange column and reversed-phase HPLC, and its sequence was analyzed by mass spectrometry. The novel peptide could inhibit Gram-negativeVibrio cholerae(clinical isolation) and Gram-positiveBacillus pumilusTISTR 905, and its MIC values were 61.2µM. From scanning electron microscopy, the peptide was seen to affect bacterial surfaces directly. KT2 and RT2, which are designed antimicrobial peptides using the C. siamensis Leucrocin I template, as well as RP9 were chemically synthesized for investigation of anticancer activity. By Sulforhodamine B colorimetric assay, these antimicrobial peptides could inhibit both HeLa and CaSki cancer cell lines. The IC50 values of KT2 and RT2 for HeLa and CaSki cells showed 28.7-53.4 and 17.3-30.8µM, while those of RP9 were 126.2 and 168.3µM, respectively. Additionally, the best candidate peptides KT2 and RT2 were used to determine the apoptotic induction on cancer cells by human apoptosis array assay. As a result, KT2 and RT2 were observed to induce apoptotic cell death in HeLa cells. Therefore, these results indicate that KT2 and RT2 with antimicrobial activity have a highly potent ability to kill human cervical cancer cells.

Squamous cell carcinoma with hepatic metastasis in a saltwater crocodile (Crocodylus porosus)

Squamous cell carcinomas (SCC) are uncommon in reptiles and there have been few reports of neoplasia in Australian crocodiles, despite increased numbers being raised in captivity. We report a locally invasive SCC in the hindlimb of a wild-caught saltwater crocodile (Crocodylus porosus) with hepatic metastasis. The gross appearance was soft tissue swelling adjacent to the nail bed, progressing to abscessation incorporating multiple toes. Diagnosis was achieved by biopsy during amputation of the affected toes. Hepatic metastasis was identified at necropsy, with a similar gross appearance resembling an abscess. Neoplasia is an uncommon finding in crocodilians and metastatic neoplasia is rarely documented. This is the first report of SCC in a crocodilian.

Hatchability Problem Of Exsitv Conservation Of The Freshwater Crocodile Crocodylus Palustris(Lesson 1831) At Dulahazra Safari Park, Cox’s Bazar, Bangladesh

In this research hatchability problems of freshwater crocodile in Dulahazra Safari Park have been discussed. The findings focused on meteorological factors, lack of suitable habitat in semi-captive enclosures and some physiological factors which are mainly responsible for non-hatchability of freshwater crocodile in the park environment. The research emphasized on finding rationale that interrupts breeding failure of this crocodile in this park. The hatchability problem was identified with some influential factors which are main barriers to escalate and proliferate the reintroduce program in Bangladesh. The findings showed that the influential factors including high stock density in a small space, low water deepness and narrow sandy bank of the enclosure with lack of nesting materials, high temperature and heavy rainfall are mainly responsible for the failure of freshwater crocodile breeding potentiality.
 Asiat. Soc. Bangladesh, Sci. 41(2): 155-161, December 2015

Contribution of Quantitative Methods of Estimating Mortality Dynamics to Explaining Mechanisms of Aging.

Accumulation of various types of unrepaired damage of the genome because of increasing production of reactive oxygen species and decreasing efficiency of the antioxidant defense system and repair systems can cause age-related diseases and emergence of phenotypic signs of senescence. This should lead to increasing vulnerability and to mortality monotonously increasing with age independently of the position of the species on the evolutionary tree. In this light, the survival, mortality, and fertility curves for 45 animal and plant species and one alga published by the Max Planck Institute for Demographic Research (Germany/Denmark) are of special interest (Jones, O. R., et al. (2014) Nature, 505, 169-173). We divided all species treated in that study into four groups according to the ratio of mortality at the terminal age (which corresponds to 5% survival) and average mortality during the entire studied period. For animals of group IV (long-lived and senescent), including humans, the Jones method makes it possible to trace mortality during the entire life cycle. The same applies to short-lived animals (e.g. nematodes or the tundra vole), whether they display the Gompertz type of senescence or not. However, in long-lived species with a less pronounced increase in mortality with age (e.g. the freshwater crocodile, hermit crab, or Scots pine), as well as in animals of average lifespan that reach the terminal age earlier than they could have enough time to become senescent, the Jones method is capable of characterizing only a small part of the life cycle and does not allow judging how senescence manifests itself at late stages of the life cycle. Thus, it is known that old trees display signs of biological senescence rather clearly; although Jones et al. consider them non-senescent organisms because less than 5% of sexually mature individuals survive to display the first manifestations of these characters. We have concluded that the classification proposed by Jones et al. makes it possible to approximately divide animals and plants only by their levels of the Gompertz type of senescence (i.e. actuarial senescence), whereas susceptibility to biological senescence can be estimated only when principally different models are applied.

Molecular identification of three novel herpesviruses found in Australian farmed saltwater crocodiles (Crocodylus porosus) and Australian captive freshwater crocodiles (Crocodylus johnstoni)

As part of a larger investigation into three emerging disease syndromes highlighted by conjunctivitis and pharyngitis, systemic lymphoid proliferation and encephalitis, and lymphonodular skin infiltrates in farmed saltwater crocodiles (Crocodylus porosus) and one emerging syndrome of systemic lymphoid proliferation in captive freshwater crocodiles (Crocodylus johnstoni), cytopathic effects (CPE), including syncytial cell formation, were observed in primary crocodile cell lines exposed to clarified tissue homogenates from affected crocodiles. Ten cell cultures with CPE were then screened for herpesviruses using two broadly-reactive herpesvirus PCRs. Amplicons were obtained from 9 of 10 cell cultures and were sequenced. Three novel herpesviruses were discovered and the phylogenetic analysis of these viruses showed there was a 63% Bayesian posterior probability value supporting these viruses clustering with the subfamily Alphaherpesvirinae, and 100% posterior probability of clustering with a clade containing the Alphaherpesvirinae and other unassigned reptile herpesviruses. It is proposed that they are named Crocodyline herpesvirus (CrHV) 1, 2 and 3. CrHV1 and 2 were only isolated from saltwater crocodiles and CrHV3 was only isolated from freshwater crocodiles. A duplex PCR was designed that was able to detect these herpesviruses in formalin-fixed paraffin-embedded tissues, a sample type that neither of the broadly-reactive PCRs was able to detect these herpesviruses in. This work describes the isolation, molecular detection and phylogeny of these novel herpesviruses but the association that they have with the emerging disease syndromes requires further investigation.

Encephalitozoon hellem Infection in a Captive Juvenile Freshwater Crocodile (Crocodylus johnstoni)

Microsporidiosis is reported rarely in reptiles and has never been reported in any species of crocodilian. Microsporidiosis was diagnosed histologically in a juvenile captive freshwater crocodile (Crocodylus johnstoni) that was found suddenly dead in its enclosure. Ultrastructural and molecular testing revealed infection to be due to Encephalitozoon hellem. This is the first report of E. hellem infection in any species of reptile.

Long‐term monitoring reveals declines in an endemic predator following invasion by an exotic prey species

AbstractInvasive predators can cause population declines in native prey species, but empirical evidence linking declines of native predators to invasive prey is relatively rare. Here, we document declines in an Australian freshwater crocodile Crocodylus johnstoni population following invasion of a toxic prey species, the cane toad Rhinella marina. Thirty‐five years of standardized spotlight surveys of four segments of a large river in northern Australia revealed that the density of freshwater crocodiles decreased following toad invasion and continued to decline thereafter. Overall, intermediate‐sized freshwater crocodiles (0.6–1.2 m) were most severely impacted. Densities of saltwater crocodiles Crocodylus porosus increased over time and were generally less affected by toad arrival, although toad impacts were inconsistent across survey sections and size classes. Across the entire river, total freshwater crocodile densities declined by 69.5% between 1997 and 2013. Assessments of the status of this species within other large river systems in northern Australia, where baseline data are available from before the toads arrived, should be prioritized. Our findings highlight the importance of long‐term monitoring programmes for quantifying the impacts of novel and unforeseen threats.

Surveys of endogenous retroviruses (ERVs) in the freshwater crocodile (Crocodylus johnstoni) suggest that ERVs in Crocodylus spp. vary between species.

Endogenous retroviruses (ERVs) are one of many families of transposable elements present in vertebrate genomes. We have examined the ERV complement of the freshwater crocodile (Crocodylus johnstoni) in order to investigate the diversity of ERVs present and possibility of ERV or retroviral activity in a diseased individual of this species. Amplification and sequencing of the highly conserved retroviral pro-pol domains revealed high levels of sequence variation in these ERVs. Phylogenetic analyses of these ERVs and those previously identified in other crocodilian species suggest that although many crocodilians share the same ERV lineages, the relative numbers of retroelement insertions from each of these lineages may vary greatly between species. The data generated in this study provide evidence for the presence of a unique and varied complement of ERVs in crocodilians. This study has also demonstrated the presence of species-specific evolution in ancient retroviral infections.

Chlorinated, brominated, and fluorinated organic pollutants in Nile crocodile eggs from the Kruger National Park, South Africa

Repeated annual episodes of Nile crocodile deaths in two isolated areas of the Kruger National Park prompted the investigation of possible organohalogen pollutant involvement. Crocodile eggs were collected close to one of the mortality sites (Gorge) as well as from a crocodile farm (CF) as reference. ∑DDT was significantly higher in Gorge (450ng/g wm) than in CF eggs (85ng/g wet mass). Percentage DDT of ∑DDT was significantly higher in CF (14 per cent) than in Gorge eggs (5 per cent). Mean ∑DDT was almost 70 times higher than mean ∑PCB in Gorge eggs. HCB, β-HCH, mirex, brominated flame retardants (BFRs), and perfluorinated compounds (PFCs) occurred at lower concentrations. We believe that the BFR and PFCs data represent the first published results for any crocodile egg. Thickening of the outer eggshell layer of Gorge eggs was significantly associated with higher concentrations of ∑DDT. Concentrations of ∑DDT and other pollutants were in the same range as eggs from elsewhere, where there were no mortalities. Concentrations of ∑DDT in eggs from healthy Australian crocodiles were of the same orders of magnitude as the current study, making it highly unlikely that the concentrations of pollutants measured in the present study would have caused or substantially contributed towards the mortalities observed. Concerns about reproduction and behaviour remain. As large predators, crocodilians are at the apex of the freshwater aquatic food web. More research is needed to guide measures to manage African freshwater systems so that it will also sustainably accommodate these large, long-lived animals.