Editing Crayfish (section)

==Diet==
Crayfish are opportunistic [[omnivorous]] scavengers, with the ability to filter and process mud.<ref name="OBrien1990">{{cite journal |last=O'Brien |first=Brett G. |title=Feeding Biology of Marron Cherax tenuimanus Decapoda: Parastacidae |journal=National Symposium of Freshwater Crayfish Culture Proceedings |date=1990 |pages=89–104}}</ref> In [[aquaculture]] ponds using [[isotope analysis]] they were shown to build body tissue selectively from the animal protein portion of pelleted food and not the other components of the pellet.<ref name="OBrienDavies2002">{{cite journal |last1=O'Brien |first1=B.G. |last2=Davies |first2=P.M. |title=The structure of marron ''(Cherax tenuimanus)'' food webs in commercial ponds: results from multiple stable isotope analyses. |journal=Freshwater Crayfish |date=2002 |volume=13 |issue=1 |pages=155–163}}</ref>
  
They have the potential to eat most foods, even nutrient poor material such as grass, leaves, and paper, but can be highly selective and need variety to balance their diet. The personalities of the individual crayfish can be a key determinant in the food preference behaviour in aquaria.{{cn|date=December 2023}}

Crayfish all over the world can be seen in an [[ecological]] role of [[benthic]] dwellers, so this is where most of their food is obtained – at the sediment/water interface in ponds, lakes, swamps, or burrows. When the gut contents are analysed, most of the contents is mud: fine particulate organic matter (FPOM) and mixed particles of lignin and cellulose (roots, leaves, bark, wood).<ref name="OBrien1995">{{cite journal |last1=O'Brien |first1=Brett G. |title=The natural diet of the freshwater crayfish ''Cherax tenuimanus'' (Smith 1912) (Decapoda: Parastacidae) as determined by gut content analysis. |journal=Freshwater Crayfish |date=1995 |volume=10 |issue=1 |page=151–162}}</ref> Some animal material can also be identified, but this only contributes a small portion of the diet by volume. 

They feed on submerged vegetable material at times, but their ability to catch large living animal material is restricted. They can feed on [[interstitial fauna|interstitial organisms]] if they can be grasped in the small feeding claws. They can be lured into traps with an array of baits from dog biscuits, fish heads, meat, etc., all of which reinforces the fact that they are generalist feeders. 

On a day-to-day basis, they consume what they can acquire in their immediate environment in limited space and time available - [[detritus]]. At a microbial level, the FPOM has a high surface area of organic particles and consists of a plethora of [[Substrate (marine biology)|substrate]] and [[bacteria]], [[fungi]], [[micro-algae]], [[meiofauna]], partially decomposed organic material and mucus. This mucus or "slime" is a [[biofilm]] and can be felt on the surface of leaves and sticks. Also crayfish have been shown to be [[coprophagic]] – eating their own faeces, they also eat their own [[exuviae]] ([[moult]]ed [[carapace]]) and each other.<ref name="OBrienDavies2002"/> They have even been observed leaving the water to graze.<ref>{{Cite journal |last=Grey |first=Jonathan |last2=Jackson |first2=Michelle C. |date=2012-08-03 |editor-last=Carlson |editor-first=Stephanie M. |title=‘Leaves and Eats Shoots’: Direct Terrestrial Feeding Can Supplement Invasive Red Swamp Crayfish in Times of Need |url=https://dx.plos.org/10.1371/journal.pone.0042575 |journal=PLoS ONE |language=en |volume=7 |issue=8 |pages=e42575 |doi=10.1371/journal.pone.0042575 |issn=1932-6203 |pmc=3411828 |pmid=22880039 |doi-access=free |quote=Isotopic analysis confirmed limited nocturnal observations that these individuals were consuming living terrestrial plants}}</ref>

Detritus or mud is a mixture of dead [[plankton]] (plant and animal), organic wastes from the [[water column]], and debris derived from the aquatic and terrestrial environments. Mostly detritus is in the end phase of decomposition and is recognised as black organic mud. The crayfish usually ingest the material in only a few minutes, as distinct from grazing for many hours. The material is mixed with digestive fluids and sorted by size. The finer particles follow a slower and more exacting route through to the [[hindgut]], compared to the coarser material. The coarser material is eliminated first and often reappears in approximately 10 to 12 hours, whereas the finer material is usually eliminated from 16 to 26 hours after ingestion.<ref name="O'Brien1994">{{cite book |last=O'Brien |first=Brett G. |title=The Feeding Biology of Marron |date=1994 |publisher=The University of Western Australia |page=273}}</ref>

All waste products coming out through the hindgut are wrapped in a [[peritrophic membrane]], so they look like a tube. Such an investment in the wrapping of the microbial free faeces in a protein rich membrane is most likely the reason they are coprophagic. Such feeding behaviour based on selection, ingestion, and extreme processing ensures periodic feeding, as distinct from continuous grazing. They tend to eat to satiation and then take many hours to process the material, leaving minimal chance of having more room to ingest other items. Crayfish usually have limited home range and so they rest, digest, and eliminate their waste, most commonly in the same location each day.

Feeding exposes the crayfish to risk of predation, and so feeding behaviour is often rapid and synchronised with feeding processes that reduce such risks – eat, hide, process and eliminate.

Knowledge of the diet of these creatures was considered too complex since the first book ever written in the field of zoology, ''The Crayfish'' by [[T.H. Huxley]] (1879), where they were described as "[[detritivores]]". This is why most researchers have not attempted to understand the diet of freshwater crayfish. The most complex study which matched the structure and function of the whole digestive tract with ingested material was performed in the 1990s by Brett O'Brien on [[marron]],<ref name="O'Brien1994"/> the least aggressive of the larger freshwater crayfish with aquaculture potential, similar to redclaw and yabbies.