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The Freshwater Crocodile

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The Freshwater Crocodile

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TABLE OF CONTENTS

1 INTRODUCTION………………………………………………………………………………………………………………………………………………………3

2 DESCRIPTIONS

2.1 The Source of the Word………………………………………………………………………………………………………………………………3

2.2 Natural History………………………………………………………………………………………………………………………………………………4

2.3 Showing the Evolution of the Crocodilian…………………………………………………………………………………………….4

3 APPEARENCES

3.1 Size and Age……………………………………………………………………………………………………………………………………………………6

3.2 Internal Organs

3.2.1 Tooth……………………………………………………………………………………………………………………………………………………….7

3.2.2 Skin…………………………………………………………………………………………………………………………………………………………7

3.2.3 Skeleton………………………………………………………………………………………………………………………………………………...8

3.2.4 Heart………………………………………………………………………………………………………………………………………………………8

3.3 Sensory Organs…………………………………………………………………………………………………………………………………………….10

4 DIET……………………………………………………………………………………………………………………………………………………………………………11

5 BREEDING

5.1 Mating System……………………………………………………………………………………………………………………………………………….12

5.2 Reproduction Condition

5.2.1 Females………………………………………………………………………………………………………………………………………………….14

5.2.2 Males…………………………………………………………………………………………………………………………………………………….15

6 BEHAVIOR……………………………………………………………………………………………………………………………………………………………….15

7 HEALTH REQUIREMENTS………………………………………………………………………………………………………………………………….15

7.1 Infection Diseases…………………………………………………………………………………………………………………………………………16

7.2 Non Infection Diseases……………………………………………………………………………………………………………………………….18

8 CONSERVATION STATUS………………………………………………………………………………………………………………………………….18

9 REFERENCES………………………………………………………………………………………………………………………………………………………….19

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1 Introduction

The Freshwater Crocodile ‚Crocodylus johnstoni‛ is a member of the Crocodilidae, Crocodilians are

the largest worlds that include the largest living reptile, and that have been evolving on earth for

the past 250 million years. They have survived major upheavals such as the breakup of the

continents and the ice ages. Crocodilians are well established predators in their respective food

chains and are among the most deadly and efficient predators in the world. They have incredible

strength, stealth and are excellent ambush predators. Crocodilians have adapted many

characteristics to suit an aquatic predatory lifestyle including the powerful blade-like tail used for

propulsion when swimming, and three webbed toes on its hind limbs, water-tight valves in the

nostrils which sit high on the head, the possession of nictitating membranes covering the eyes as a

third eyelid, and most noticeably an elongated head with sharp teeth.

All crocodilians are ectothermic (an ectothermic animal is one who cannot regulate its own body

temperature, so its body temperature fluctuates according to its surroundings), and although most

comfortable in the water, the crocodilian’s physical traits allow them to be successful swimmers.

They have a streamlined body that enables them to swim swiftly. They also tuck their feet to their

sides while swimming, which make them faster by decreasing water resistance. Moreover, they

spend quite a lot of time on land, usually basking on river banks, logs, and rocks in the sun in

order to raise their body temperature. They are some of the most impressive animals in the world

that people know about them. Hopefully by understanding them, people may develop an

appreciation of crocodilians which in turn may lead to some rational decisions being made about

their long-term conservation and management.

The freshwater crocodiles are superb predators, of amazing strength and are potentially dangerous

to people. It is for this reason that security and safety are two very important issues when

considering housing freshwater crocodiles. This species is an important part of educating people

on conservation and of the amazing, efficient and well adapted crocodilians. They are now a

protected species and can no longer be hunted for their skins, something which was unfortunately

done by many during the 1950s to 1980. The freshwater crocodiles are often thought of as being

just as aggressive and dangerous as the larger saltwater crocodile, therefore the freshwater

crocodiles are important in educating young children.

2 Descriptions

2.1 The Source of the Word

The word crocodile comes from the Ancient Greek κροκόδιλος (crocodilos), "lizard," used in the

phrase ho krokódilos ho potamós, "the lizard of the (Nile) river." There are several variant Greek

forms of the word attested, including the later form κροκόδειλος (crocodeilos) found cited in

many English reference works. In the Koine Greek of Roman times, crocodilos and crocodeilos

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would have been pronounced identically, and either or both may be the source of the Latinized

form crocodīlus used by the ancient Romans. Crocodilos/crocodeilos itself is a compound of krokè

("pebbles"), and drilos/dreilos ("worm"). The form crocodrillus is attested in Medieval Latin. It is

not clear whether this is a medieval corruption or derives from alternate Greco-Latin forms (late

Greek corcodrillos and corcodrillion are attested). A (further) corrupted form cocodrille is found in

Old French and was borrowed into Middle English as cocodril(le). The Modern English form

crocodile was adapted directly from the Classical Latin crocodīlus in the 16th Century, replacing

the earlier form. The use of -y- in the scientific name Crocodylus (and forms derived from it) is a

corruption introduced by Laurenti (1768).

From the top: Head of an American alligator (Alligator mississippiensis), a Nile crocodile (Crocodylus niloticus), and

an Indian gharial (Gavialis gangeticus).

2.2 Natural History

The Freshwater Crocodile (C.

johnstoni) is a member of the

Crocodylidae family, a group in

which there are 23 living

species worldwide, and one that

includes all crocodile, alligator,

caiman and gharial species. The

distribution of crocodilians is

largely confined to the tropical

regions, with their distribution

ranging from Northern

Australia, through Asia, India, Africa and South America to the temperate regions of The United

States of America and China. Within the Crocodylidae, there are three subfamilies like the

Alligatorinae (Alligators and Caimans), the Crocodylinae (Crocodiles, dwarf crocodiles, and false

gharials) and the Gavialinae (Indian Gharial) – and of these, only two species are found in

Australia – the saltwater crocodile (Crocodylus porosus) and the Freshwater Crocodile (Crocodylus

johnstoni).

2.3 Showing the evolution of the crocodilian

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Modern crocodiles evolved from prehistoric crocodiles which were quite varied in their body

structure – some having long legs and being able to hunt and run on land; and some being much

larger and spending a large proportion of time in the water. Professor Roger Seymour from the

Discipline of Environmental Biology at The University of Adelaide says that the earliest crocodiles

were among a group of animals known as archosaurs which evolved to cause dinosaurs along one

lineage, which then gave rise to birds; and crocodiles on a separate lineage. It is thought that

crocodilians diversified between 200 and 65 million years ago and gave rise to more than 150

genera in all kinds of habitats from land-based to fresh water and the ocean. When the mass

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extinction had occurred 65million years ago, there was a small group of crocodilians that survived

and inhabited aquatic environments, evolving into the modern crocodilian species present today.

3 Appearances

3.1 Size and Age

Some people are less well-known crocodile is the Freshwater Crocodiles, also called Johnston’s

Crocodiles, Fish Crocodiles or simply ‘Freshie’. This species is unique to Australia, occurring only in

the tropics of Queensland, the Northern Territory and Western Australia. Apart from their much

smaller size, distinctive the freshwater crocodiles are light brown with darker bands on body and

tail; bands which break up near the neck on many specimens. Their scales are comparatively large

and the back is protected by broad, closely-knit armored plates. The flanks and the outsides of the

legs are covered in rounded, pebble-like scales. The snout of this species is very slender and

tapering and has sharper teeth. The males grow no bigger than 2.5-3 meters (9.8 feet), the females

generally stay smaller than 2.1 meters (6.9 feet), and males weigh no more than 60 kilograms

Females weigh half as much. It normally takes at least 30 years for a male to reach that length.

Dwarf/pygmy populations of freshwater crocodile growing no bigger than 1.5 m (5 feet) have been

identified, but they are not considered subspecies. These small freshwater crocodiles are darker

than their larger counterparts and reach sexual maturity at half the normal size. Their diminutive

size may be linked to a scarcity of food. They can certainly live for 40 to 60 years, and possibly up

to 100 years of age! Individual growth rates vary greatly depending on the availability of food, so

size is no indicator of age. In fact, rocky habitats far upstream, mature animals may be only half

the size of well-fed crocs of the same age living farther downstream, where food is more plentiful.

They move overland more readily, using a fast gait to move between pools of water. Speeds of up

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to 18 kilogram per hour (11 mph) may be obtained, but the animal is soon exhausted. They have a

flexible semi-erect (semi-sprawled) posture that can walk in low, sprawled "belly walk," or hold

their legs more directly underneath them to perform the "high walk". Most other reptiles can only

walk in a sprawled position, and chameleons are the only modern reptiles with a more erect

posture than crocodilians. The semi-erect posture makes it possible for some species to run fast on

land if necessary.

3.2 Internal organs

3.2.1 Tooth

Their dentition (teeth set in bony sockets) they replace their teeth throughout life (though not in

‚extreme‛ old age). Immature crocodiles replace teeth with larger ones at a rate as high as 1 new

tooth per socket every month. After reaching adult size in a few years, however, tooth replacement

rates can slow to two years and even longer. Very old members of some species have been seen in

an almost ‚toothless‛ state, after teeth have been broken and replacement slowed or ceased. The

result of this is that a single crocodile can go through at least 3,000 teeth in its lifetime. Each

tooth is hollow, and the new one is

growing inside the old. In this way, a new

tooth is ready once the old is lost. The

skull of an adult Freshwater Crocodile

shows its sharp pointed teeth. The fourth

tooth on the lower jaw and the notch on the upper jaw are visible in this photo.

3.2.2 Skin

The skin is covered with non-overlapping scales composed of the protein keratin (the same protein that

forms hoofs, skin, horns, feathers, hair, claws, and nails in other tetrapods), which are shed individually.

On the head, the skin is actually fused to the bones of the skull. There are small plates of bone, called

osteoderms or scutes, under the scales. Osteoderms are found especially on the back, and in some

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species also on the belly. The overlapping rows of scutes cover the crocodile's body from head to tail,

forming a tough protective armor. Beneath the scales and osteoderms is another layer of armor, both

strong and flexible and built of rows of bony overlapping shingles called osteoscutes, which are

embedded in the animal's back tissue. The blood-rich bumpy scales seen on their backs acted as solar

panels.

3.2.3 Skeleton

The spool-shaped vertebra in their ancestors went from

being biconcave to having a concave front and a convex

back in the modern forms. This made the vertebral

column more flexible and strong, a useful adaptation

when hunting in water. They possess ribs of dermal origin

restricted to the sides of the ventral body wall. The collar

bone (clavicle) is absent.

3.2.4 Heart

They have a secondary bony palate that enables them to breathe when partially submerged, even if

the mouth is full of water. Their internal nostrils open in the back of their throat, where a special

part of the tongue called the "palatal valve" closes off their respiratory system when they are

underwater. This way they can open their mouths underwater without choking. When under water

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and stationary, their heart rate drops to as low as two or three beats per minute and they expel

most of the air from their lungs. Blood of them has a remarkable capacity to release the oxygen it

carries as it is needed. The blood themself has a unique chemistry that enables them to utilize

more oxygen from a breath of air than any other animal. The reptilian heart has three chambers.

Oxygenated blood travels into the heart from the lungs, and oxygen-exhausted blood from the

muscles and internal organs. The blood is mixed in a common ventricle and begins to circulate

again. Not all blood that goes to the muscles and organs has been re-oxygenated, and some of the

oxygenated blood returns to the lungs. However, the crocodilian heart has a partitioned ventricle

so, in effect, has four chambers like a mammal. The system becomes really impressive when the

crocodilian goes under the surface of water. If a crocodilian can’t get fresh air into its lungs, it

effectively disengages them. A unique valve, known as the foramen of panizza, closes off the lung

circuit and redirects the blood to the organs. They can control the flow so precisely that the blood

goes directly to the brain and heart, where it is most needed. They are the only animals that have

actively controlled muscular valves in their hearts.

They are poikilothermic that their internal body temperature depends primarily on their

surrounding environment and they are cold blood because most of them are only comfortable in

tropical environments or we can stay that they can tolerate cooler temperatures, their blood is

rarely cold. They prefer to keep their body temperature between 26ºC and 33ºC. They maintain

their body temperature by their behavior. They bask in the sun to raise their body temperature. If

they become too hot, they simply move to the shade or back into the water. They will also laze in

river mud, which is warmer than surrounding water. In addition, they have built-in solar panels on

their backs. Infra-red cameras have shown that the scutes, or bony ridges, on their backs trap the

sun’s heat, giving the animals an extra source of warmth. The scutes are also known as osteoderms

(osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of

the skin.)

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American alligators alternate between the sun and the shallows to regulate their body temperature. (Courtesy

Damian Kelly)

3.3 Sensory organs

They have a small brain, but it is more advanced than in other reptiles. Among other things it has

a true cerebral cortex. As in many other aquatic or amphibian tetrapod, the eyes, ears, and nostrils

are all located on the same plane. They see well during the day and may even have color vision,

plus the eyes have a vertical, cat-like pupil that also gives them excellent night vision. The iris is

silvery (a layer of crystals behind the retina at the back of the eye, present in many animals. This

layer is known as the tapetum lucidum, and the crystals reflect the light that passes through the

retina back onto the retina, thus increasing their ability to see in weak light), making their eyes

glow in the dark.

A third transparent eyelid moves sideways across the eye (nictitating membrane). This eyelid

protects the otherwise ‘open’ eyes when they submerge and attack under water. The third eyelid

also conceals the liquid excretions produced by the crocodilian tear glands. However, if it is out of

the water for any length of time, the resulting dryness in its eyes will cause visible tears to be

formed. This is possibly why both factual and fictional accounts tell of crocodilians weeping over

their prey on a river bank. They cannot focus underwater, meaning other senses are more

important when submerged underwater. While birds and most reptiles have a ring of bones

around each eye that supports the eyeball (the sclerotic ring), the crocodilians lack these bones,

just like mammals and snakes. The light receptors in crocodilians’ eyes include both cones and

numerous rods, so it is assumed all crocodilians can see colors.

A crocodilian’s pupil can close to a narrow,

slit-like aperture in bright light, while

opening to a full, circular pupil to allow

maximum light collection in the dark. So,

they can hunt both during the day and at

night, though they tend to hunt mostly at

night and in the dim light of dawn and

dusk. Bright sunlight means that it is time

for basking on the river bank. The

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eardrums are located behind the eyes and are covered by a movable flap of skin. This flap closes,

along with the nostrils and eyes, when they dive, preventing water from entering their external

head openings. The middle ear cavity has a complex of bony air-filled passages and a branching

eustachian tube (a narrow tube that joins the throat to the middle ear). There is also a small

muscle (which is also seen in geckos) next to or upon the stapes, the stapedius, which probably

functions in the same way as the mammalian stapedius muscle does, dampening strong vibrations.

The upper and lower jaws are covered with sensory pits, seen as small, black speckles on the skin,

the crocodilian of the lateral organ seen in fish and many amphibians. But they have a completely

different origin. These pigmented nodules encase bundles of nerve fibers that respond to the

slightest disturbance in surface water, detecting vibrations and small pressure changes in water,

making it possible for them to detect prey, danger, and intruders even in total darkness. These

sense organs are known as DPRs (Dermal Pressure Receptors). While alligators and caimans only

have them on their jaws, they have similar organs on almost every scale on their body. The

function of the DPRs on the jaws is clear, but it is still not quite clear what the organs on the rest

of the body in crocodilians actually do. They are probably doing the same as the organs on their

jaws, but it seems like they can do more than that, like assisting in chemical reception or even

salinity detection.

4 Diets

The most commonly eaten foods are insects and fish. Freshwater Crocodiles will also eat

crustaceans such as shrimps and crayfish, and spiders, frogs, lizards, snakes birds and mammals. If

freshwater crocodiles are fed, hatchling and yearling freshwater crocodiles should be fed a range of

insects and aquatic invertebrates, and as they grow larger, small fish and worms may be added to

the diet. In captivity, crickets (a small brown jumping insect that makes aloud high sound by

rubbing its wings together) are often supplied as the main or sometimes only source of diet for

smaller crocodiles, but caution must be taken when this is done as a varied diet allows the

crocodiles to be in better condition and health.

Larger juvenile and adult freshwater crocodiles are suggested to be fed a diet consisting primarily

of fish, however small mice, day-old chicks, and other small mammals may be offered. They may be

fed rats, mice, rabbits and chickens but it is recommended to only feed animals or parts of animals

that will be easily swallowed in one gulp. The table below (table 6.1) shows the recommended food

types for freshwater crocodiles of varying ages.

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Recommendations of food types to be offered to Freshwater Crocodiles of varying ages or sizes.

They are known to swallow stones, gastroliths ("stomach-stones"), which act as a ballast in

addition to aiding post-digestion processing of their prey. The stomach of them is divided into two

chambers; the first one is described as being powerful and muscular, like a bird gizzard. This is

where the gastroliths are found. The other stomach has the most acidic digestive system of any

animal, and it can digest mostly everything from their prey; including bones, feathers, and horns.

They have a very slow metabolic rate, compared to the rapid mammalian digestive system. The

metabolic rate is influenced by temperature, and if a crocodile eats and become too cool to digest

its food properly, the food may in fact rot in its stomach before it is completely digested.

However, this is why wild crocodilians lose interest in food when the temperature falls. They

expend a large amount of energy killing their prey, large chunks of which are swallowed whole and

then digested in their entirety. The stomach is relatively small for its size, so they have to rest and

digest after each kill. It’s never safe to assume, however, that the crocodile basking on the river

bank has just eaten and therefore isn’t dangerous. They have also been observed to gorge in times

of plenty and build up extra fat stores, particularly before the onset of the colder months.

5 Breeding

5.1 Mating System

The mating system of freshwater crocodiles is quite advanced, and involves various courtship

behavioral displays by both the males and females. The mating season generally commences in

June/July at the beginning of the dry season, when ambient temperatures are quite cool. The

stimulus for breeding and courtship is unknown for them.

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Generally, they have relatively long courtship rituals and behaviors, whereas mating and actual

intercourse is completed in minutes. After mating the males play no role in the nesting process

and may even mate with another female. It is unknown whether or not males play a role in nesting

processes. They take years to reach this size. A male of breeding size may be 17 to 20 years old. By

then he will be about 1.68 meters long (5 ½ ft) and weigh about 14 kilos (31 lbs). Females may

mature at about 15 to 20 years of age, when they reach a length of about a meter and a half (4 ¾

ft) and a weight of about 9 1/2kilos (21 lbs).

About three weeks after mating, the females will start to search for an appropriate nest site and

begin to excavate her nest. The females will often dig several test holes first before choosing her

nest site. Once the nest site is chosen and the nest prepared the females will prepare to lay her

eggs, usually six weeks after mating. Egg-laying usually occurs at night. It is quite unusual but the

freshwater crocodiles have been known to often ‚pulse nest‛, where all the females in a specific

population lay their eggs within a period of three weeks.

The females normally deposit her eggs roughly six weeks after mating and they will place them 12-

20 cm (5-8 in) below the surface of the nest. If the eggs are burrowed to shallowly, they risk

becoming overheated by the sun.

The nesting period for this crocodilian species varies from location to location but generally occurs

between July and September. Usually, all the females in a certain location will nest within the same

three week period, and it is common for a lot of nests to be excavated near each other. If the nest

density becomes too high, females may dig up and destroy the nests of other females. The female

digs a nesting hole in a sandbank close to a permanent body of water and lays an average of 13

eggs. Clutch size can vary from 4 to 20 eggs. Like all oviparous animals, the crocodilians spend a

certain time developing within the egg while it is being incubated, before the hatchlings break the

shell and emerge. Development in the egg is aided by several membranes – the amnion; the

chorion; the allantois; the yolk; and the albumen. The amnion acts as protection for the developing

embryo; the chorion allows gas exchange to occur; the allantois is a receptacle for metabolic

wastes; and the yolk and the albumen provide nutrition to the developing embryo.

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Diagram shows the different stages of embryonic development within the egg in Freshwater Crocodiles.

Incubation takes 65-95 days during which an average temperature of 30-33° C (86-91° F) is

desirable. Embryos incubated at 32° C (89.6° F) become male, while those expose to slightly

warmer or cooler conditions become female. Fluctuating nest temperatures are believed to result

in greater sexual differentiation. The parents will leave the nest unguarded and predation from

lizards is common. On average for all nests, no more than one egg out of three survives long

enough to hatch. When the young are ready to

emerge they will emit chirping sounds that prompts

the female to return and help them out of the nest.

She may also carry them to the water in her

mouth. The female will watch over her hatchlings for

some time to protect them from predators, but the

exact period varies. All crocodilians are relatively slow

growing animals, and may take up to 15 or 20 years

to reach maturity. In the wild growth rates vary

greatly between populations, regions and even between seasons. Some years may have provided

individuals with ample food where their growth rate would have increased; and in years that

provided less food and resources their growth rate would have decreased.

5.2 Reproductive Condition

5.2.1 Females

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Before females can reproduce they must reach maturity which is both age and size dependent.

Females are required to be healthy and strong in order to produce healthy and strong young. They

must be healthy in order to produce enough nutrients and calcium to protect the eggs and allow

them to develop. In captivity, it is the responsibility of the keepers to ensure all animals but

particularly breeding animals are kept in their optimal condition.

5.2.2 Males

Before males can reproduce they too must reach maturity. Males will also require to be healthy

and strong, more so for the reason of competing for females with other males. All across the

animal kingdom, males compete to impress females. Males want to display how strong and healthy

they are, with good genes to pass onto the next generation. If male freshwater crocodiles are not in

their peak condition it may mean they lose the chance to breed for that season. In captivity, it is

the responsibility of the keepers to ensure all any but particularly breeding animals are kept in

their optimal condition.

6 Behavior

In areas where there is a permanent water source, freshwater crocodiles are active throughout the

year; however in areas where the water source disappears during the dry seasons, crocodiles may

aestivate, i.e. become dormant, until the rains return.

The daytime is usually spent between basking on the river banks and sitting in the water hiding in

amongst the murky water and reeds. The water offers many methods of predator avoidance such

as water plants, reeds, algae, murky water, logs, and branches. When basking, freshwater crocodiles

often sit with their mouths open, which may help them to prevent overheating and regulate their

body temperature. They spend a large amount of their time in water, but they do come to land to

bask, nest and defend their territory. Hatchlings and juvenile crocodiles probably spend more time

in water than other adults, as there is more safety in amongst reeds and murky water.

They tend to be more active at night, when there is a lesser threat of being attacked or being

eaten by predators. It is at night when freshwater crocodiles hunt for food, taking invertebrates,

fish, frogs and other reptiles. It is also at night when females come to land to dig their nests and

lay their eggs. Crocodilians generally have relatively long courtship rituals and behaviors, whereas

mating and actual intercourse is completed in minutes. However, males will come to gather at

water sources at the beginning of the dry seasons where they will compete against one another for

the right to mate with a female. The stimulus for breeding and courtship is unknown for the

freshwater crocodile, but it may be related to a period of cooler temperatures and lack of rainfall.

Males may mate with several females; however, females will only mate with single males. Males

then have no further role in the reproductive cycle.

7 Health Requirements

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When servicing freshwater crocodile enclosures on a daily basis, the general physical condition of

each individual should be checked to ensure each crocodile has no signs of stress, physical injury,

or ill health. General observation of behavior checking for abnormalities like test the crocodile’s

strength and check the skin, the feet, tail, dorsal (back) and ventral (underside) surfaces and the

head, including the eyes, nostrils, snout, inside mouth, teeth, vent area, or changes can be done

from a non-invasive distance, and can be done continually throughout the day.

It is incredibly important to check the temperature of the water; the ambient temperature; and the

heating and/or filtration systems. If one of these factors is unusual or not functioning it could

potentially cause the environmental conditions to fall outside of the optimum.

It may even be possible on some occasions to perform a general physical examination quickly

whilst the crocodile is being handled for certain tasks such as in shows, training, moving exhibits.

All freshwater crocodiles kept in captivity should be regularly checked and treated for any diseases

or conditions that could potential cause illness or injury to the crocodile. Crocodiles in captivity

consume food items that have already been killed. This may expose them to microorganisms that

may be potentially harmful. It may be suggested that freshwater crocodiles like other reptiles be

administered regular ‚worming‛ medications to help prevent disease by endoparasites.

Hygiene is extremely important for hatchling Freshwater Crocodiles, both to prevent disease

transfer between animals as well as to keepers. The EAPA lists specific hygiene and cleaning

requirements that need to be met in order to provide adequate housing for crocodilians. Hatchling

Freshwater Crocodile holding enclosures may have the ponds as well as the terrestrial areas of the

enclosures spot cleaned daily where any debris, feces or discarded food is removed, and perform a

complete change of pond water twice weekly. Each of the enclosure furnishings should be sprayed

and scrubbed with a light chemical agent such as F10, which may help in disinfecting the

furnishings and also does not cause harm to the animals.

For keeper hygiene, gloves and sinks must be provided as reptiles can carry bacteria and other

pathogens that may be ingested by any person who touches a reptile and these pathogens may be

harmful to humans also. Gloves should also be worn and changed between handling each

individual hatchling to minimize the spread of disease.

7.1 Infectious Diseases

The table below lists the known infectious and non-infectious diseases that can occur in the

freshwater crocodile (Crocodylus johnstoni).

Bacteria Salmonella sp.; bacterial dermatitis (Dermatophilus spp.); Mycoplasma crocodyli; respiratory infection

Viruses Adenoviruses; Parapoxvirus Fungi fungal dermatitis; respiratory infection Endoparasites Trematodes; Nematodes; Ectoparasites Mites; ticks

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Protozoans Coccidia Bacterial Disease

Some species of crocodile are susceptible to Dermatophilus spp., a bacterium which causes brown

to red lesions between the scales, and is sometimes associated with ulcerative lesions. This disease

is difficult to treat with medications as it has limited response to antibiotic drugs; therefore strict

hygiene procedures are necessary to prevent and control this disease. Samonella sp. is common in

normal body flora, however, at low concentrations. If the numbers of cells increases too greatly

infestation will occur. This disease is zoonotic and can be easily passed on to humans even if the

individual is not showing signs of infection. Treatment can be with antimicrobial medications such

as metronidazole, a medication used for the treatment of many diseases.

Mycoplasma crocodyli is quite prevalent too in captive populations, and signs of infection are

rather general – lethargy; weakness; anorexia; white discharge from the eyes – however, these signs

must not be overlooked as pneumonia and other conditions can develop and cause death. Again

treatment should include the use of antimicrobial medications.

Viruses

Freshwater crocodiles have been known to suffer from parapoxvirus, and usually show signs of

lesions forming on the skin. These lesions can be yellow to brown, wart-like nodules that can

either be raised or unraised, and can be found on the head, nostrils, mouth, oral cavity, ventral

neck among other sites. The only treatment for this virus is to improve husbandry and maintain to

a high standard, and all signs of the virus may subside in 3-4 weeks.

Fungal

Many fungal infections can be treated with specialised antifungal medications; however, it is often

improvement in husbandry practices and a high level of hygiene that can effectively treat these

conditions.

Endoparasites and Ectoparasites

There is little information specific to the freshwater crocodile; however, generalised information

has been gathered on reptile ecto- and endo-parasites.

Freshwater crocodiles are susceptible to both endo- and ecto-parasites. As captive crocodiles may

be fed rodents, they may be exposed to Cryptosporidium from the gut of the rodent. Many mites

and ticks exist as reptile parasites, and this may be similar for the freshwater crocodiles. Some

ticks can spend their whole life cycle on the skin whereas some change hosts, but all are usually

difficult to see. Mites are also difficult to see but infestations can be quite visible. In general for

other reptile species, medications such as Ivermectin and Flagyl can be administered to treat both

internal and external parasites, however, information is lacking on specific treatment for freshwater

crocodiles.

Protozoans

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The most common of these is Coccidia sp., a pathogen which can cause infection and disease in

many reptiles. It is known to often infect young animals and there has been important in captive

crocodile rearing in Zimbabwe, and so may be a problem in freshwater crocodiles also. In young

animals it can cause stunted growth, and Mader (2006) states that the disease is slightly different

in the Zimbabwe captive crocodiles. Clinical signs here included hemorrhagic enteritis and swelling

and congestion of the small intestine.

7.2 Non Infectious Diseases

Nutritional Anorexia; obesity; malnutrition; growth deformities; Neoplastic None known Physical Trauma Integumentary disease (from lacerations etc. due to fighting); Capture

Myopathy Chemical Toxicities None known Allergies None known Genetic/Metabolic Growth deformities; Environmental Hypothermia; Hyperthermia; Respiratory discomfort or infection,

Thyamine deficiency 8 Conservation Statuses

Freshwater crocodiles were hunted for their skins from the late 1950s until protection in 1962,

1964 and 1974. A ranching program based on hatchlings was established in the Northern Territory

in 1982, but by the early 1990s farming had largely ceased due to the relatively low commercial

value of the skin. Harvesting of C. johnstoni is permitted in Western Australia and the Northern

Territory through management programs. The Northern Territory is currently updating its C.

johnstoni management programs. No use of the wild resource is permitted in Queensland. A

limited pet market exists in some States and Territories whose legislation allows for the keeping of

crocodiles. Webb et al. (1987a) estimated the Northern Territory population of C. johnstoni to

comprise 30,000-60,000 nonhatchlings. In Western Australia, the population in the Fitzroy and

Ord Rivers and Lake Argyle and Lake Kununurra was estimated to be at least 47,000 individuals.

Population size in Queensland is unquantifi ed johnstoni populations remain in areas in

Queensland exposed to cane toads for several decades suggests that extinction is not the prime

issue of concern. Freshwater crocodiles are more sensitive to the cane toad toxin than C. porosus.

Most information on the impact of cane toads as they spread across the Northern Territory has

been anecdotal, and limited to observations of mortality. The McKinlay River population, which has

been intensively studied since 1978, offers a unique opportunity to quantify precisely the impact of

cane toads on population size, structure and dynamics. Studies on the impact of toads have been

initiated in Western Australia, including investigation of Conditioned Taste Aversion Learning as a

means of minimizing impact. The establishment of populations of C. porosus in Lakes Kununurra

and Argyle in Western Australia, through human mediated movements may reduce the C.

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johnstoni populations in the future. Studies on the impact of toads on ‚stunted‛ populations in

marginal escarpment populations are ongoing in the Northern Territory and Western Australia.

9 References

From Book

Allen & Unwin. 2006. Evolution’s Greatest Survivor Crocodile. Lynne Kelly’s Press. Australia.

Lisa Manson. June 2008. Husbandry Guidelines for The Freshwater Crocodile. Lisa Manson’s Press.

Burbidge A.A. (1987). The management of crocodiles in Western Australia. In: G.J.W. Webb,

S.C. Manolis and P.J. Whitehead (Eds.), Wildlife Management: Crocodiles and

Alligators. Surrey Beatty & Sons Pty. Ltd. in association with the Conservation

Commission of the Northern Territory, Sydney,

From Internet

http://www.aquaticcommunity.com/crocodiles/freshwater.php

http://www.proserpineecotours.com.au/crocs.htm

http://en.wikipedia.org/wiki/Crocodilia