I am dissecting many invasive signal crayfish, Pacifastacus leniusculus, stomachs from Scottish populations in order to obtain general dietary information, but specifically to understand what the level of cannibalism is. I will have weekly crayfish samples from May through until September or October (10-40 crayfish per sample), so would be interested in finding out the seasonal pattern of cannibalism frequency, and quantifying the size/ sex affect on cannibalism incidence. All crayfish will be frozen prior to dissection. I have dissected many crayfish in the past in order to extract reproductive organs (which I will not be wasting in this data set), but I have never looked at the stomach contents. I would be very grateful for any advice, guidance or links to papers outlining the methodology, including what equipment is required.
Have you ever thought about using stable isotopes to trace the diet ?? it could be also a nice way for you to get some results from the stomach content of the crayfish.
I attach some articles where you can see this appoach, but also you can have an idea about a general methodology for gut analysis procedures.
Basically, you sampled your crayfish and immediately put on ice and frozen on their return to the laboratory. Gut content analysis : Percentage volume of each food type was assessed visually through a binocular microscope. Particulate organic matter (c. >0.5 mm CPOM) was identified as leaf detritus, grass, woody detritus, fern detritus, macrophytes and moss, filamentous green algae (FGA), terrestrial invertebrates, or aquatic invertebrates. Invertebrates were identified to the lowest practicable level using the keys of Winterbourn & Gregson (1989) and Winterbourn (1973), and whole individuals were counted. Stabe Isotope: Crayfish abdomen muscle is dried at 50 °C for 24 h, then ground in a mortar and pestle. A small sub-sample (0.1–0.3 mg) is analysed for stable carbon and nitrogen isotopes using continuous flow, isotope ratio mass spectrometer (NIWA, Wellington, New Zealand). But check the articles to have more details ¡¡
For a less expensive study I would perform a lab experiment to check how the carapace fragments of con-specifics in a stomach look like (this is the fraction that certainly remains for the longest time in the stomach, even when compared to other food items) and how long crayfish needs to break down such carapace fragments. Then you could check the stomach contents of your field samples according to standart protocols that could be found via google. Good luck!
Thank you very much for your responses. This project will be given to an undergraduate project student, so I suspect that conducting both stable isotope and gut content analysis would be too involved for a single project. However I might refreeze the unused tail muscle tissue for potential analysis in the future. I will check to see if we have an isotope ratio mass spectrometer available for use.
The original project was advertised as a study of cannibalism in wild populations. Again, I'm not sure if the student will have time to conduct a study to calibrate the appearance of carapace fragments in the stomach, as well as then using the calibration. I agree though that these would be very interesting things to study. The only way I can think of doing it though is with live crayfish being given smaller conspecifics to eat at known times and then dissecting them at different time intervals after consumption. We do not have the licenses required to keep the animals in captivity unfortunatley.
Is it easy to tell apart different tissue types, e.g. leaf detritus and wood detitus or invertebrate parts? Are there stains that could help discern between food types?
Feeding studies take guts – critical review and ...
https://onlinelibrary.wiley.com › doi › jfb
by PA Amundsen · 2019 · Cited by 65 — The methods that are used for stomach-content analysis of fish comprise three main approaches: presence–absence, numerical and bulk,
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