Is my yabby a boy or a girl?

Hi there, Russel - please see above for a detailed description of how to differentiate male and female yabbies. The underside of the tail of a female is the one on the right-hand side of the illustration.

Hi Karen - Yes Robert is certainly Roberta, and what you are looking at are in fact eggs. You don’t need to do anything special - just keep looking after her as per usual, but avoid any disturbances such as doing a major clean of the tank etc. If the eggs are infertile she will sort things out herself, and most probably eat them. If they are fertile you will ultimately see tiny babies clustered under her tail, which soon after will drop off and become independent.

Hi Keely - Our Live Exhibits staff would be happy to help you discover the sex of your yabbies. Perhaps you could take some pictures of the yabbies you have just purchased as email them to us via our 'Ask the Experts' enquiry service. Please also read out 'Identifications' guidelines before you submit your enquiry.

Hi Keely! We're glad your yabby is ok, and Happy Easter to you too! For specific questions for which you need a timely answer, I'll direct you again to our 'Ask the Experts' service. Whilst we do check these comments threads for questions, they are more used for facilitating dialogue between visitors.

Hi Keely, we have checked with our Live Exhibits team and they have suggested that perhaps your yabby was responding to a change in water temperature, or perhaps there were more additives in the water in the new tank, but it is great to hear that all is well with your yabby!

 

Hi Keely - It sounds like there is a fair bit of aggression and fighting going on with your yabbies. There can be a few reasons why they may be behaving that way:

*There may be too many yabbies for the space provided

*There may be too few hiding spots

*There may be not enough protein in the food, or food in general (ie attacking each other through desire to eat other yabbies)

 

It’s hard for us to say exactly which (if any) of these factors may be affecting your yabbies, as we do not know all of the circumstances.

 

 

Hi Dibs, the term yabby is used for the large, native freshwater crayfish Cherax destructor. There is no special term for a juvenile yabby, they are just referred to as a juvenile yabby.

62 yabbies in a 2 cm tank – that is a lot of mouths to feed in a very small space! At the museum we keep yabbies for display as well as breeding them to feed to other animals – including our Australian Lungfish in the 600 Million Years exhibition. We work out the minimum size / maximum number of individuals by watching the animals behaviour. If our yabbies do not have enough hiding spaces within the tank they will start fighting – leading to injuries and death. So as soon as we see this we separate our population and keep the numbers low.

Hi Aaron, it is always nice to have other animals in a tank – especially for one lone yabby. The only problem you may be faced with is that yabbies are quite territorial and you need to provide ‘hiding’ spots for all the yabbies. If you know if your yabby is a boy or girl, it might be nice to get him or her a boyfriend/girlfriend so you could see a whole life cycle. You should not keep more than 2 or 3 adult yabbies in a tank you described, but having babies in there would be great.

 

Hi Jenni, eggs hatch after about 40 days of being stored under the female's tail, this amount of time can vary depending on the temperature of the water. Once hatched they spend the next couple of weeks continuing to be under her tail developing. So it can be a fair while before you have the tiny yabbies ‘free swimming’.

Hi Jen, it sounds like your yabby eggs have hatched and the hatchling yabbies are currently in a stage that do not look like yabbies yet and are still attached to the females swimmerets under her tail. They will look like they have a domed shaped back for about three days and then moult again. At this point they look a bit more like a yabby but will still be attached to mum. They will remain this way for around 10 days until they moult again to look like a ‘yabby’. It is at this point that they will start to move away from mum’s tail and be a bit more active around the tank.

At this point when the young leave mum they will be looking for food to feed on. At the museum we try to provide small amounts of food at regular intervals. The young animals can’t fit much into their bellies and so need small meals daily. Apart from that they can be looked after the same way you look after your adults.

Best of luck from the Live Exhibits team

Hi Jen, if you leave mum in the tank you will find she may nibble on some of the babies over the coming weeks. You will have a lot of young yabbies so losing a few here and there may not be too much of an issue for you. We have a tank here at the museum that is 4 foot and has held the mum and all her young successfully for the last couple of months. We provided lots of hiding spaces for the young to keep out of the clutches of their parent.

Hi Amanda. It's hard to answer if your yabby is male or female as there could be a couple of things that may change what you are looking at. My first guess is to confirm your yabby has not lost any legs – if the last pair of legs have come off the yabby maybe this is what is causing the confusion.

Hi Renee, it is hard to know what your yabby is up to. We generally have our females yabbies with eggs behaving just like normal – except they have their tail curled under to protect their eggs. Possibly the water conditions or her safe refuge in the tank has been disturbed and she is a little uncomfortable. Keep an eye on her and maybe do a partial water change to give her some fresh water.

Hi Adam, once your yabbies leave their mothers tail refuge they can be potential prey for your fish. There are two main things you can do to help your young yabbies out. The best thing you can do is provide lots of hiding places for your young yabbies and this should help reduce the chances that fish will find them. You can also have a spare tank available and if you find your fish, and other yabbies eating your young ones when they emerge transfer them away. Otherwise, enjoy watching a food chain in progress. Once you fish have had their fill they should stop eating the young and it may be a great display tank.

Hi Kaiden, the term yabby is used for the large, native freshwater crayfish Cherax destructor. There is no special term for a juvenile yabby, they are just referred to as a juvenile yabby.

Hi Napooleon, if you scroll back up this sheet to the 5th and 7th October and look at the questions and answers for Jen you should get the answers to your questions.

Hi BJ - Our live exhibits staff say that yabbies generally lose their natural colour if kept out of sunlight for long periods, rather than becoming white through age alone. The loss of pigment exposes the underlying structure, which is naturally white. There may be some influence from the type of food they eat, but the main cause is generally lack of sunlight, and some colour may return if they once again experience natural light.
Young yabbies tend to be light pinkish or light blue and become darker as they get older, so the variation in colour in this case is due to age. Once again if they aren’t exposed to sunlight this dark colour will fade eventually to white as well.
Their colour doesn’t indicate anything other than the amount of pigment in their exoskeleton, and the sexes are distinguished by structures on the bases of the legs.

Hi Dana, the things you are looking at on the underside of your yabbies tail are most likely pleopods  which are also known as swimmerets. For female yabbies these are very important as the edge of each pleopod is lined with fine hairs, or setae, to which they attach their eggs. So you are looking in the right spot if you are looking for eggs.

Hi Millie, we have checked with our Live Exhibits Team and unfortunately we do not have an answer for you.  It has been suggested that the yabbies here at the museum 'wave' a claw when they are reaching out for food, so perhaps that is what they are doing.

Hi David, if you go back up to the information sheet before all the comments it explains how to tell if a yabby is a boy or a girl.

Hi Charlie, the "wriggling suckers" sound like a common parasite to yabbies called Temnocephids, which are relatively harmless in low numbers. Other than manually removing them I can't think of any other way to get rid of them without having an effect on the yabby.

Hi Hoani - sorry to hear you're having trouble with your yabbies. If you find you have no luck with the diagrams and instructions given above, then I would suggest you try exploring some of the documents listed in the "Further Reading" section.

Hi Michaela,

Yabbies can be territorial and can become aggressive and cannibalistic if they don’t have enough space. The Australian Museum will provide you with some information on what your yabbies will require. 

 

Courtney, thanks for your query. We have asked for some comments from our Live Exhibits team here at Melbourne Museum, and they have said the following:

Yabbies will readily fight in captivity and a dominant yabby, if given the opportunity, may slowly dismember another one over a short period of time. A female yabby will also consume her offspring if they don’t have enough places to hide . When keeping yabbies together, the key is to provide as many hiding places as possible, so vulnerable individuals will always have a handy bolthole in which to escape. Some yabby keepers use thin strips of corrugated plastic, laid on top of each other, which affords a large number of cavities in a small amount of space.

While it is true that the limbs will grow back after successive moults, this process is slow. Very young yabbies may moult every week, but older yabbies may moult only once a year, depending on the food supply. Limbs don’t grow back completely after a single moult, but take several moults to get to a usable size.  Depending on the age of your yabby, the limbs may take a very long time to return, if ever. In the meantime, your yabby will be unable to move around under its own power, other than the occasional tail-flick.

In addition to the yabby’s quality of life, there is also the question regarding pain and suffering. This subject has been widely debated for many years, and a 2005 report by Advocates for Animals, entitled ‘Cephalopods and Decapod Crustaceans – Their Capacity to Experience Pain and Suffering’, stated there was evidence that suggested “there is a potential to experience pain and suffering in these animals”. As the yabby’s carer, its fate is up to you. If you choose to euthanase, a report by the Australian and New Zealand Council for the Care of Animals in Research and Teaching, entitled ‘Euthanasia of Animals Used for Scientific Purposes’ recommended a number of euthanasia methods but the simplest method was to place in the fridge to cool the animal down, and then to freeze.

Hi Trini,

Even though yabbies lay hundreds of eggs they may not all hatch.  If you have only one female yabby, and no male, the eggs would not be fertile and the yabby most likely ate them. Yabbies often eat their young.  For further information, visit the NSW Department of Primary Industry website, which provides useful information on keeping yabbies, their reproduction and their diet.

Nicholas - when a yabby loses its claws or legs, they will start growing back the next time it moults. If the yabby is young and the claw or leg is small, it may grow back completely during a single moult. Most of the time, however, three or four moults are required to fully restore the limb.

In the meantime, your yabby may need to be offered a diet that it can easily consume without the need of claws. Just to make life a bit easier for it. The more the yabby eats, and the warmer the temperature of the water (up to 26 degrees), the sooner it will moult and the quicker its claws and legs will return.

Hi Destiny and Chloe, if you scroll to the top of this information sheet you will find that is about how to tell if your yabby is a boy or girl, so you will find the answer there. The yabby Cherax destructor can attain a total length of around 16cms. 

Hi Chloe,

Female yabbies produce 100 to 500 eggs per individual, depending upon their size. You can find more information about yabbies on the Department of Primary Industries website.

Hi Catherine.

We forwarded your question about Bill to Museum Victoria's animal keepers, and they provided us with the following answer:

There are a number of causes that would explain the behaviour of Bill. The most likely is that he’s having trouble moulting, as this is the period when yabbies are most vulnerable and when the death rate is highest. Yabbies lose the ability to move around during the moulting process and at this time a yabby will often be seen lying on its back or its side. However, moulting should take no more than 20 minutes, so if the yabby continues to behave in this way, it may be stuck in its old skin.

Hi Megan,

The information above should be able to assist you identify the sex of your yabby. Eggs will be produced if the yabby is a female and the water temperature and other conditions allow it. If you believe your yabby is producing eggs, and there has been no contact with a male yabby, the eggs will not develop and they will most likely be eaten. In regards to the curling of the abdomen, this may indicate that the female is readying herself to reproduce. However there could be a variety of other reasons for this too.

Hi Leanne, yabbies are well adapted to feeding with only one claw and even with no claws. They use their claws to defend themselves, to capture living prey and to tear food apart. Your yabby shouldn't have too many problems feeding, other than the fact that it won't be able to tear up its food, so it will only be able to cope with smaller portions. You may want to pay extra attention to feeding it small portions, but even so there are generally enough small pieces of food in an average tank for it to get by. It will also be more vulnerable to attack from other yabbies now, so make sure there are plenty of hiding places in the tank.

Hi Sam, Yabbies moult throughout their lives, but as they get older and bigger the frequency of moulting declines. So what you're experiencing is not unusual for an old yabby, and it would be the case regardless of the size of the tank.

When more than one yabby is held in a tank, there does tend to be aggression and the bigger yabby will almost always attack and dismember any smaller ones. We don't think the older yabby is at risk from the younger ones, even if there are a number of them.

The risk of aggressive encounters is greatly reduced by giving the yabbies places to hide, and with the right set-up a number of yabbies can live together for many years. Many yabby keepers use strips of corrugated plastic sheeting, layered on top of each other at the back of the tank, to form a kind of apartment block with dozens of small rooms that are more easily defendable by each occupant.

Hi Zak, Moulting occurs frequently when the yabby is young, as often as every 10 days. Older yabbies will moult only every couple of months. If a yabby is missing a claw or two, all its energy will go into regrowing those claws, at the expense of overall growth, so the yabby's increase in size will be much slower. But if the yabby is young enough, both claws may reach full size by the time it becomes adult. Keeping the yabby slightly warmer with plenty of food will encourage it to grow more quickly.

Hi Brodie, there is a fantastic illustration above that shows you the difference between a male and female yabby, hope that helps!

Hi Elanor,
We asked our live animal keepers for some advice:
In the wild, yabbies dig burrows that are open at the entrance and closed at the other end, which is how they feel most comfortable. With the claws at the front of the body, yabbies are designed to defend these burrows and as a general rule have no problem doing so, but are not designed to defend themselves from behind. An opening at the back makes them feel vulnerable from a rear echelon assault. The best option, therefore, is to give them a cave-like shelter rather than a tunnel.

Hi Huseyin, we have checked with the Live Exhibits Team about molting yabbies and yabbies, like all arthropods, produce a moulting hormone that causes nutrients etc from the old skin to be reabsorbed into the body as the skin separates. This is an internal hormone and it’s not known whether any is released into the water, or whether predators are able to pick up on it. It would be in the yabby’s interest to contain the hormone, but it’s a very good question and would make an interesting research project!