Salt Glands in the Tongue of the Estuarine Crocodile Crocodylus Porosus

The apparent absence of salt glands in marine and estuarine Crocodilia has long been a puzzle. However, we have identified glands in the tongue of Crocodylus porosus which exude a concentrated secretion of sodium chloride. The glands are similar in ultrastructure to other reptilian salt glands and undoubtedly play a major role in electrolyte regulation.

Kidney and cloaca function in the estuarine crocodile (Crocodylus porosus) at different salinities: Evidence for solute-linked water uptake

Kidney function and the role of the cloacal complex in osmoregulation was investigated in estuarine crocodile (Crocodylus porosus) exposed to three environmental salinities: hypo-, iso- and hyperosmotic to the plasma. Plasma homeostasis was maintained over the range of salinities. Antidiuresis occurred with increased salinity. Although urine from the kidneys retained an osmotic pressure between 77% and 82% of the plasma, over 93% and 98% of plasma chloride filtered at the glomeruli was reabsorbed during passage through the kidneys under hypo and hyperosmotic conditions, respectively, and only 64% in iso-osmotic water. The kidneys were the primary site of sodium reabsorption under hypo-and hyperosmotic conditions. Secondary processing of urine during storage in the cloaca varied with salinity. During post renal storage of urine, the difference in urine osmotic pressure increased from -26.1 +/- 15.5 to 35.66 +/- 9.29 mOsM with increased salinity, and potassium concentration of urine increased over 3-fold in C. porosus from freshwater. The almost complete reabsorption of both sodium and chloride under hyperosmotic conditions indicates the necessity for secretory activity by the lingual salt glands. The osmoregulatory response of the kidneys and cloacal complex to environmental salinity is both plastic and complementary. (C) 1998 Elsevier Science Inc.

Peptidergic control of gastrointestinal blood flow in the estuarine crocodile, Crocodylus porosus

Peptidergic mechanisms influencing the resistance of the gastrointestinal vascular bed of the estuarine crocodile, Crocodylus porosus, were investigated. The gut was perfused in situ via the mesenteric and the celiac arteries, and the effects of different neuropeptides were tested using bolus injections. Effects on vascular resistance were recorded as changes in inflow pressures. Peptides found in sensory neurons [substance P, neurokinin A, and calcitonin gene-related peptide (CGRP)] all caused significant relaxation of the celiac vascular bed, as did vasoactive intestinal polypeptide (VIP), another well-known vasodilator. Except for VIP, the peptides also induced transitory gut contractions. Somatostatin and neuropeptide Y (NPY), which coexist in adrenergic neurons of the C. porosus, induced vasoconstriction in the celiac vascular bed without affecting the gut motility. Galanin caused vasoconstriction and occasionally activated the gut wall. To elucidate direct effects on individual vessels, the different peptides were tested on isolated ring preparations of the mesenteric and celiac arteries. Only CGRP and VIP relaxed the epinephrine-precontracted celiac artery, whereas the effects on the mesenteric artery were variable. Somatostatin and NPY did not affect the resting tonus of these vessels, but somatostatin potentiated the epinephrine-induced contraction of the celiac artery. Immunohistochemistry revealed the existence and localization of the above-mentioned peptides in nerve fibers innervating vessels of different sizes in the gut region. These data support the hypothesis of an important role for neuropeptides in the control of the vascular bed of the gastrointestinal tract in C. porosus.

Hypoxia stimulates cerebral blood flow in the estuarine crocodile (Crocodylus porosus)

The effect of N-2 respiration on cerebral blood flow (CBF) velocity on the dorsal surface of cerebellum was examined in the estuarine crocodile, Crocodylus porosus, using epi-illumination microscopy. Twelve minutes of N-2 respiration resulted in a 126% increase in CBF velocity. N-2 respiration had no effect on blood pressure, indicating an underlying cerebral vasodilation. In addition, heart rate increased significantly. Systemic injections of aminophylline and the NO synthase (NOS) inhibitor nitro-L-arginine (L-NA) did not affect the hypoxia induced increase in CBF. We conclude that C. porosus responds to hypoxia with adenosine and nitric oxide (NO) independent cerebral vasodilation, and that this is likely to be a mechanism protecting the brain from energy deficiency during prolonged dives. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.

Morphology of the cloaca in the estuarine crocodile, Crocodylus porosus, and its plastic response to salinity

The cloacal complex of Crocodylus porosus is composed of three chambers (proctodaeum, urodaeum, and coprodaeum) separated by tight, muscular sphincters. The proctodaeum is proximal to the cloacal vent and houses the genitalia. The urodaeum is the largest chamber, is capable of storing large quantities of urine, and is lined with an epithelium with the capacity for transepithelial water and ion exchange. The coprodaeum, the most orad cloacal chamber, is a small, only marginally expandable chamber that has an epithelium composed almost entirely of mucus-secreting cells. The coprodaeum and lower intestine are reported to be the site(s) for urine modification in birds and bladderless lizards. A radiographic trace of urine storage in C. porosus kept for 2 months under hyperosmotic conditions showed no signs of retrograde movement of urine into the coprodaeum or rectum. Instead, urine was stored in the urodaeum of C. porosus. Examination of the mucosal surface of the urodaeum by SEM showed a plastic response to environmental salinity, with a possible increase in surface area in animals kept in hyperosmotic water compared with animals from fresh water. We propose the urodaeum as the primary site for postrenal modification of urine in C, porosus. (C) 2000 Wiley-Liss, Inc.

Nitric oxide, a potent vasodilator of the aortic anastomosis in the estuarine crocodile, Crocodylus porosus

The effects of five neuropeptides (CGRP, SOM, SP, NPY, VIP), L-NAME (nitric oxide synthase inhibitor), and adrenaline on the contractile tone of the aortic anastomosis in the estuarine crocodile, Crocodylus porosus, were investigated. None of the neuropeptides, which had previously been found to be present in the aortic anastomosis, had any direct effect on the tension developed by ring preparations. L-NAME itself significantly increased the basal tone of the vascular ring preparations, suggesting a tonic release of nitric oxide in the preparation. Adrenaline produced concentration-dependent vasoconstrictions that were counteracted by profound reflex vasodilatations that were susceptible to blockade by L-NAME. Immunohistochemistry revealed the presence of nitric oxide synthase and tyrosine hydroxylase-containing (indicating the presence of a adrenergic innervation) nerve fibres in the adventitia and adventitio-medial border of the aortic anastomosis. These data demonstrate opposing actions of adrenaline and nitric oxide on the vascular smooth muscle in the anastomosis of the C. porosus. The morphology of the anastomosis, with the extremely thick muscular vessel wall, suggests a sphincter-like function for this vessel that could be controlled mainly by adrenergic and nitrergic mechanisms, (C) 2001 Academic Press.

The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus

The effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions; (2) heated via radiant energy while half-submerged in flowing water at 23degreesC and (3) heated via convective transfer by increasing water temperature from 23degreesC to 35degreesC. Cooling was achieved in all treatments by removing the heat source and with C. porosus half-submerged in flowing water at 23degreesC. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate ('rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (

Comparison of stress induced by manual restraint and immobilisation in the estuarine crocodile, Crocodylus porosus

This study compared the stress induced in captive estuarine crocodiles, Crocodylus porosus, by two different handling methods: manual restraint (noosing with ropes) and immobilization by electro-stunning. To stun, a short charge (approx. 6 s) at 110 V was delivered to the back of the necks of C. porosus using a custom-built device, which immobilized the animals for 5-10 min. Immobilized and restrained animals were measured and sexed, and the condition of the skin assessed. Blood samples were taken from some animals immediately after restraint or immobilization. Other animals were returned to their pens to recover for periods of 30 min, 1, 4, 12, 24 or 48 hours after which they were stunned and blood samples taken. Individual animals (mean body length 1.96 m, N=99) were bled only once. Haematocrit and haemoglobin concentrations were measured and plasma samples were analysed for corticosterone, glucose and lactate levels. Following restraint, there were significant increases in haematocrit, haemoglobin, glucose, lactate and corticosterone concentrations in C. porosus. For restrained animals, recovery to baseline levels occurred after approximately 8 hours. The stress response of stunned animals was significantly reduced compared to manually captured and restrained crocodiles. Both groups showed a significant increase in haematocrit, haemoglobin concentration and lactate levels, however the magnitude of change was significantly reduced, and recovery was faster in stunned animals. No increase in either glucose or corticosterone levels occurred with immobilisation. The results imply that immobilization by electro-stunning is much less stressful. (C) 2003 Wiley-Liss, Inc.

Cholinergic and adrenergic innervation of lingual salt glands of the estuarine crocodile, Crocodylus porosus

Many marine reptiles and birds possess extrarenal salt glands that facilitate the excretion of excess sodium and chloride ions accumulated as a consequence of living in saline environments. Control of the secretory activity of avian salt glands is under neural control, but little information is available on the control of reptilian salt glands. Innervation of the lingual salt glands of the salt water crocodile, Crocodylus porosus, was examined in salt water-acclimated animals using histological methods. Extensive networks of both cholinergic and adrenergic nerve fibres were identified close to salt-secreting lobules and vasculature. The identification of both catecholamine-containing and cholinergic neurons in the salt gland epithelium and close to major blood vessels in the tissue suggests the action of the neurotransmitters on the salt-secreting epithelium itself and the rich vascular network of the lingual salt glands.

From anatomy to angioscopy: 164 years of crocodilian cardiovascular research, recent advances, and speculations

This paper present: a synthesis of current research on the crocodilian cardiovascular system with a view to encourage discussion and debate about the intricacies of this unique system and to provide ideas and suggestions for future studies. Innovative experimental approaches combined with new technologies have helped to resolve the complex flow and pressure patterns observed during non-shunting conditions that predominate in resting instrumented animals and during pulmonary to systemic shunting, which has been observed to occur spontaneously and during diving. The mechanisms and structures that may induce and regulate shunting are presented and the functional significance of a pulmonary to systemic shunt is discussed. (C) 1997 Elsevier Science Inc.

A Report on the Managment of Saltwater Crocodiles (Crocodylus porosus) in the Northern Territory: Results of a Survey of Pastoralists

The management of saltwater crocodiles (Crocodylus porosus) in the Northern Territory is an important component of the State’s wildlife management policy. It encompasses saltwater crocodile control (the removal of problem crocodiles dangerous to humans and livestock), and the regulation of harvesting, farming and ranching of saltwater crocodiles for the production of commercial products. The distribution of saltwater crocodiles and their habitats often extend onto private and communal lands along the coastal belt of the Northern Territory, and therefore are a concern of landholders both Aboriginal and pastoral. This report presents the findings of a study of managers of Northern Territory cattle properties (pastoralists). Their attitudes are surveyed towards saltwater crocodiles on their properties and their views of the Northern Territory Parks and Wildlife Commission’s saltwater crocodile management plan are outlined. This report addresses social, economic and environmental aspects of the issue: pastoralists’ attitudes towards saltwater crocodiles in general, the impact saltwater crocodiles have on their cattle-raising business, their opinions of the Northern Territory Government’s saltwater crocodile plan and its operation, and their views of saltwater crocodile harvesting, its potential as an income earner and its contribution to the conservation of the saltwater crocodile. Opinions of pastoralists about new management schemes such as trophy hunting of saltwater crocodiles are also analysed. A concluding statement ties up the findings of the study and provides a snapshot of the current views of pastoral landholders of saltwater crocodiles and their management in the Northern Territory.

Osmoregulation of the Australian freshwater crocodile, Crocodylus johnstoni, in fresh and saline waters

An unusual saltwater population of the "freshwater" crocodilian, Crocodylus johnstoni, was studied in the estuary of the Limmen Bight River in Australia's Northern Territory and compared with populations in permanently freshwater habitats. Crocodiles in the river were found across a large salinity gradient, from fresh water to a salinity of 24 mg.ml-1, more than twice the body fluid concentration. Plasma osmolarity, concentrations of plasma Na+, Cl-, and K+, and exchangeable Na+ pools were all remarkably constant across the salinity spectrum and were not substantially higher or more variable than those in crocodiles from permanently freshwater habitats. Body fluid volumes did not vary; condition factor and hydration status of crocodiles were not correlated with salinity and were not different from those of crocodiles from permanently fresh water. C. johnstoni clearly has considerable powers of osmoregulation in waters of low to medium salinity. Whether this osmoregulatory competence, extends to continuously hyperosmotic environments is not known, but distributional data suggest that C. johnstoni in hyperosmotic conditions may require periodic access to hypoosmotic water. The study demonstrates a physiological capacity for colonisation of at least some estuarine waters by this normally stenohaline freshwater crocodilian.

Hydrodynamics of the Itapocu river and the Barra Velha lagoon estuarine system, SC, Brazil

A hydrodynamic characterization of the Itapocu river and Barra Velha lagoon estuarine system was carried out with the objective of evaluating how the current regime in this area is affected by astronomical and meteorological tides and the river discharge. Meteorological, water level and current velocity and direction data were gathered hourly during a twenty-day period, from 22-July until 10-August, 2004. Current meters were positioned at the inlet, at the entrance of the north and south lagoons and at the lower estuary of the river along with a tide gauge. The estuarine system showed distinct current behavior among the different sectors within the estuary, responding to the different forcings. The strongest currents were observed at the inlet while the weakest values were observed at the northern lagoon, a location that showed little dynamic. The general flow was ebb-dominated flux, in response to fluvial discharge, even during local wind water set-up event.

INTERANNUAL VARIABILITY IN TROPICAL ESTUARINE COPEPOD ASSEMBLAGES OFF NORTHEASTERN BRAZIL

We studied copepod assemblage variability among years, seasons, and tidal states in the Mucuri River estuary (Bahia State, Brazil). Zooplankton samples were collected seasonally through five years (2002-2006) at three sampling stations, one of which was sampled over a complete tidal cycle (two ebb and two flood tides). Temperature, salinity, river flux, and rainfall data were collected. Winter and summer represented dry and wet seasons, respectively. Copepod abundances ranged from 40 to 63% of the total zooplankton assemblage and comprised 46 taxa, among which, common estuarine species such as Temora turbinata (first record for the studied area), Parvocalanus crassirostris, Acartia lilljeborgi, Oithona hebes were the most abundant (euryhaline species). Interannual and seasonal variations were most marked in stenohaline species, e.g.. Notodiaptomus sp. and Thermocyclops minutus; density variations of euryhaline species, which made up the majority of the abundant taxa, were most closely related to tides. Diversity and richness also followed an intertidal pattern of variation.