THE URBAN RESEARCHER



CRAYFISH
Cherax quadricarinatus or the Australian Red Claw Crayfish is the only edible crayfish that can be owned in the United Kingdom without a specific licence. This was a self-generated research study on the behaviour, life cycle, habitat requirements and diet of the Redclaw. Three Redclaws: two female, one male, were kept in a 100 litre tank with a 90x30cm base, providing a 30x30cm square habitat for each crayfish, aligned with online stocking suggestions. The aim of the research was to establish the suitability and a potential specification for keeping Redclaw in an aquaponic system. The research project ran for 6 months.

The majority of aquaponic systems are stocked with tilapia or catfish due to their robust nature and preferential stocking density. Crayfish, along with other crustaceans, have unique habitat requirements compared to fish. The total surface area at the bottom of the tank is the key limiting factor for stocking of crayfish; with fish, the total volume of the tank is key metric for correct stocking. This means that over 60% of the volume of a standard tank will not provide extra habitable space for crayfish.



Crayfish like insects with hard exoskeletons, go through a series of moults during which they shed their hard exoskeleton to allow further growth of their body within, displayed below. After moulting the skin of a crayfish is very soft, taking in some cases multiple days to harden. In the wild, crayfish would naturally hide from predators as well as their own species in burrows in the riverbank or under rocks and wood until this process has finished. Crayfish will often eat their own moulted shell to help reabsorb nutrients and build a new one.

Due to the size limitations of tanks, preferential stocking densities, limitation of hide numbers and territory sizes of individual crayfish, moulting proved a tension point. If newly moulted crayfish were left alone with another crayfish it would be at danger of being killed. Even during non-moulting stages, crayfish would display strong territorial tendencies to defend a specific hide or burrow. This often lead to fighting, resulting in injury of a smaller or weaker crayfish.



The research concluded that crayfish are not viable or suitable for aquaponic systems if fair living conditions are the aim. Fish farming in general has questionable levels of overcrowding however in the case of crayfish this leads to a potentially high mortality rate, which is not acceptable. In addition overcrowding can dramatically decrease quality of life with crayfish continuously fighting for preferred burrows.