Most yabbies are either male or female, but some have characteristics of both, and are called ‘intersexes’.
A yabby, Cherax destructorPhotographer: Alan Henderson, Source: Museum Victoria
As in humans, the most reliable character to use to distinguish male and female yabbies is the position of the reproductive openings or gonopores. To see these openings you must turn the animal upside down and inspect the base of their walking legs. Live animals don’t like this much – watch the claws! There are five pairs of legs, called pereopods. The first pair are the chelae (also called claws or nippers) and the second to fifth pairs are the walking legs. The legs are attached to a narrow ridge called the sternum, the same name we give to our breastbone.
In males the gonopores are on the first hinging segment of the fifth pereopod or last pair of walking legs and are often seen as small bumps or ‘pimples’ (arrowed in left-hand diagram).
Look near the middle of the animal. In females the gonopores are on the bases of the third pair of pereopods, second walking legs (arrowed in right-hand diagram). It is a larger opening than in the male and looks transparent and oval-shaped. But make sure to look on the base of the legs, not on the sternum that runs down the middle of the animal’s belly, because in some species that ridge may have openings as well.
It is easy to pick the sexes when the animals are reproducing, or ‘in berry’. Only females carry the eggs. They carry their eggs on the appendages of the abdomen (the pleopods), and the eggs look like bunches of grapes. If you can find a female in berry, look for her genital openings on the second walking legs. Then you will know what the female genital openings look like and you can look for the same feature in non-reproductive animals.
Male FemaleIllustration: Jo Taylor / Source Museum Victoria
Fallu, R., 1994. Yabbies for Fun, Fishing and Farming. Department of Food and Agriculture: Melbourne.
Kailola, P. J., Williams, M. J., Stewart, P. C., Reichelt, R. E., McNee, A. and Grieve, C., 1993. Australian fisheries resources. Bureau of Resource Sciences, Department of Primary Industries and Energy, and Fisheries Research and Development Corporation: Canberra.
Yearsley, G. K., Last, P. R. and Ward, R. D. 1999. Australian Seafood Handbook. An Identification Guide to Domestic Species. CSIRO Marine Research: Hobart.
In the wild, yabbies dig into the banks of a pond during winter and become inactive - you generally won't find yabbies during any month without an 'R' in it. In addition, yabbies will not feed if the water temperature is below 10 degrees Celsius, and won't grow below about 15 degrees. Room temperature is usually above 10 degrees even if unheated, so it may be that your yabby is simply slowing down and not feeding as often. If you're leaving food in the tank, the excess nutrient may explain the orange film covering the yabby's claws. The best option is to reduce the quantity of food offered and remove excess food from the tank if not eaten within a day.
Although yabbies tend to hide in crevices and holes most of the time, they will generally leave their hiding places to moult, presumably needing an open space to manoeuvre out of the old shell. Your yabby may have decided the tank needs rearranging before this task can be undertaken. Moulting takes place at irregular intervals, depending on the conditions and the amount of food available, and reduces in frequency as the yabby grows. Young yabbies may moult up to five times per year, whereas older ones will moult once every two years, and males tend to moult more often than females. There is plenty of information on the internet on sexing yabbies, including Melbourne Museum's website 'Is my yabby a boy or a girl'
Hi Hailey, we have checked with our Live Exhibits Team and whenever more than one yabby is present in a tank, the larger one(s) will attack the smaller one(s), even if the size difference is minimal. And once the attacks begin, they will continue until the smaller yabby(s) are in pieces. The only way to avoid this is to provide plenty of places to hide, so that the larger yabbies don’t feel their territory is being encroached upon, and the smaller yabbies have a handy retreat. Hides can include empty plant pots, PVC pipes or any suitably sized object. Breeders with many yabbies place layered pieces of corrugated plastic sheeting inside the tank to provide dozens of hiding places. We hope this helps with the care of your yabbies.
Hi Rhys - we've passed your question on to our Live Exhibits team here at the Museum, and they have prepared the following response for you:
If the yabbies are in a small tank they will certainly have started fighting due to lack of space. If one of the yabbies is dominant it will rapidly pull the legs and nippers off the other yabby, and if they are evenly matched they may pull each other’s legs off over a longer period of time. The first thing to do is to give them more hiding places, using PVC piping or layered strips of corrugated plastic, or some more natural arrangement. There should be at least 10 suitable places to hide within the tank. The next step is to give them a bigger tank if the extra hiding places don’t do the trick.
Hope this helps!
Hi Amanda; we've checked with our Live Exhibits team, and they have the following response for you:
If a dominant yabby is allowed constant access to a more vulnerable one, the dominant yabby may slowly dismember it until it has no legs or nippers left. It could be a case of not enough hiding spots – in most situations any yabby can protect itself from any other as long as there are enough places to hide. If there are enough hiding places but you’re still concerned, the only other option is to give them two separate tanks
Hi Huseyin, We forwarded your enquiry to Museum Victoria’s Live Exhibits team, the Museum’s animal keepers, who responded with the following information:
A standard four foot (120cm) tank will house about eight full sized yabbies or approximately 30-35 yabbies of the size you describe. So your tank is suitable at the moment, but will need to increase in size as the yabbies do (or you'll need to downsize your yabby collection). You can keep higher numbers of yabbies together if they all have suitable hiding places.
Yabbies are basically carnivores but will feed on any organic material available. High protein pellets are better than vegetable-based varieties, as yabbies will always choose meat-based food over anything else, and they will always breed better on a higher protein diet. Special yabby pellets are available from some pet shops or directly from RBM Aquaculture (http://www.rbmaqua.com.au/).
Earthworms, brine shrimp and bloodworms are all good food items, as well as fruit and vegetables such as carrots, spinach, potatoes, peas, apple and peach. Although they do favour meat, variety is very important to them and it is also important that the food offered is fresh. Don't overfeed them as the food may go off and foul the water (it's always safer to underfeed, if anything) - one pellet per yabby every second day plus a small earthworm and a piece of fruit per yabby per week is a good guide.
Calcium is important for a strong exoskeleton, and can be provided by washed sea shells or pieces of coral from the beach, or from calcium blocks available in pet shops.
Adults or yabbies approaching adulthood can be sexed by looking underneath - males have a small projection at the bases of the fourth pair of walking legs, whereas females have a small round patch on the bases of the third pair of walking legs. In general, males are larger than females and have larger claws, with a more narrow tail, and this applies throughout their development.
We love receiving comments, but can’t always respond.
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 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.
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.
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.
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.
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.
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.
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.
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.
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 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 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 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 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 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 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 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 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 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.
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 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.
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 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! 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 - 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 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 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 Joey, Baw Baw Frog numbers have collapsed in recent years, this link to the Melbourne Zoo website will provide you with some information on possible reasons ...
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