Yabby Frequently Asked Questions
Am I going to get a disease that will wipe out all my yabbies?
No. There is a rather nasty tail-wasting disease (Thelohania) in eastern states yabbies but the original stock of yabbies introduced to WA was free of it. (This is a good reason for no one being foolish enough to smuggle in yabbies or other crayfish from the east or, much worse, from overseas where there are worse diseases.) Some (very few) marron do have a disease that lab tests show is harmful to yabbies, so you shouldn't mix the two species in a dam.
My yabbies have tiny crawling, leech-like animals and pinhead-size eggs under their tails?
These are called "temnos" (temnocephalids) by farmers and occur naturally on all crayfish. They are not a disease organism, but what is called an "ectocommensal". They feed on the scunge (epiphytes) growing on the crayfish shell, so they tend to be a symptom of a slow growing stock and larger crayfish (which don't cast of their shells frequently) and rich, clearer water conditions. We need to do more research on these, and other, so-called, "epibionts" on crayfish. The adult crawling stage of the temno can be removed by immersing the Yabby in salty water, briefly; however, we don't know how to remove the temno eggs (glued onto the pleopods or swimmerets under the tail). These eggs appear as black spots on a cooked Yabby and detract from marketing appearance.
My crayfish are covered with small, buff coloured eggs? 
These eggs are laid by a small aquatic insect, the water boatman or "corixid", which is beetle-shaped and has two oar-like rear legs. These insects can be seen darting, very quickly, back and forth to the surface of the dam in shallow water to breath air. Large numbers of these insects mean that a dam is highly organically polluted with very little oxygen, even in shallow water (summer floods are a common cause, but overfeeding can cause this condition, too). The corixids lay eggs on any stationary object (a stick) or slow moving crayfish. Marron are badly affected in polluted dams, but we've had no reports for yabbies, which are less slowed down by low oxygen. However, large numbers of corixids are a good indication of a dam which is too rich in decomposing organic matter and microscopic algae.
On the other hand, a good indication of a dam with well-oxygenated shallow water is the presence of a small crustacean called a scud (amphipod); these get their oxygen from the water, not the air. Sometimes scuds are mistaken for baby yabbies; out of water, on your hand, yabbies can crawl upright while scuds have curved, side-flattened bodies and lie or spin helplessly on their sides.
My crayfish are covered in fur?
The fur is one of a number of microscopic colonial protozoans (stalked peritrichs, usually Epistylis). This organism is symptomatic of dam conditions described above for corixids and again is usually found on a few surviving marron suffering in a polluted dam.
I can see a lot of small red worms near the edge of my dam? 
These segmented "blood worms" are the aquatic larvae of an insect and eventually hatch into a fly, the non-biting midge (chironimid). The red colour is an oxygen carrying blood pigment, since these larvae live on organic matter in the mud under stagnant water where oxygen is very low. Many larvae can be seen after pollution from a summer rain; otherwise they indicate over feeding; they are a good natural source of food for yabbies.
The depot I deliver to complains that my yabbies are dying and blame me?
If you have a competent depot, you are probably to blame in poor handling causing dehydration, heat stress or bacterial infection, i.e. stressed out and unhealthy yabbies- see the answers to the earlier questions on this topic of catch handling and delivery, which is very important.
I washed my hands in a Yabby dam after dipping the sheep; next day we found that the yabbies had walked out and died; any connection?
Since crustacea (crayfish) are the same group of animals (Arthropods) as insects, any insect poison like sheep dip is also very deadly for them, too. The old, now banned, chlorine based insecticides (DDT, etc) were doubly bad because they did not break down for decades and accumulated in soil, water and animals. The "new" phosphorous based and synthetic pyrethroid (sheep dip, etc) poisons are biodegradable within a day, or so, but fresh from the tin are extremely toxic in very small amounts to arthropods. We've done research on using sheep dip to clear a dam of a crowded, stunted Yabby stock so as to restock it, properly- see the answers on Yabby biology.
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