Reptile & Amphibian Forums

Does anyone know whether crayfish are normally cannibalistic? I know lobsters and crabs are, but some things tell me cray fish aren't.

For example, I once saw a pet shop with crayfish of varied sizes in a small (ten-gal) aquarium. No aggression was seen. In a creek near where I live, I saw a large dead crayfish that had been there for a while, but nothing had touched it. Shouldn't the crayfish come out at night the way crabs do and scavenge?

I caught two crayfish and am keeping them together as an experiment, but does anyone here have any experience with this? One is 45 mm the other is 25 mm. Despite what I've seen, crayfish should cannibalize, like all their relatives, right?

The crayfish I caught (and the dead one I saw) were O. rusticus, a highly successful invasive species in North America -- maybe a reluctance to cannibalize is why populations of this species out-compete native crayfish so quickly and over populate, decimating stream plant life?

Any experience with social behavior among crayfish in aquarium settings?

O. rusticus is an aggressive species. It removes the native crayfish from their burrows by crayfish to crayfish competition, and increased predation. "O. rusticus have been shown to reduce aquatic plant abundance and species diversity which can be especially damaging in areas that are relatively unproductive such as the northern lakes. These aquatic plants are important for habitat for invertebrates, food for fish and ducks, shelter for young game fish, pinfish, or forage species of fish, nesting substrate for fish, and erosion control (by minimizing waves). Although other crayfish eat aquatic plants, O. rusticus eat even more because they have a higher metabolic rate and appetite." (from http://www.issg.org/database/species/ecology.asp?si=217 the invasive species database).

They are cannibalistic (and I have a link to a very ecological paper of a study done on the cannibalism rates in juveniles if you'd like to read it). Even though the link below says O. propinquus, it does mention O. rusticus.

Perhaps the events you noticed were during the peak predation time (in the case of the dead crayfish), and the crayfish at the pet store were probably getting along at the time you were there(that's my guess anyways). I wouldn't use that experience at the pet store as a given for the species. That is one instance (and an unnatural one at that).

O. rusticus does not appear to me to be a scavenger, but it looks like they are nocturnal. The reason why they are "successful" invasives are listed above. I don't like the term successful and invasive in the same sentence. It's just not right.

I have no experience with crayfish, but I did research all your questions. All but the invasive species database were from journal articles (science based- experience). Hope this helps.
The Effects of Gender and Density on the Rate of Cannibalism in Orconectes Propinquus

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Phishie
Site Coordinator

"An ounce of prevention is worth a pound of cure."

Thanks, phishie.

What I've found with my two is very odd. The larger one seems to have earned the cave as his territory, but when the small crayfish enters and the larger one isn't inside, the larger one doesn't return. Never are the two in the cave together, but encounters do not appear aggressive. When the cave and plastic plant are removed, leaving a bare cage, the two quickly move to opposite corners or sides.

The crayfish seem to have equal fear of each other, even though one is the larger. It's almost as if the larger one can smell that another crayfish is nearby, but has no way of knowing that the other one could be potential prey. The paper of course indicates that cannibalism is common, so perhaps the fact that these crayfish are never forced to contact each other is why there have been no incidents. At night (foraging time) they never leave their usual hides, so perhaps cannibalism is brought on only in high density populations.

I keep the crayfish fed with earthworms, but I don't let them gorge themselves. Since I have no experience in aquarium maintenance, I just keep them in a plastic tub with a few inches of water, which I change every day or so. They're fascinating creatures to observe, if you ever get the opportunity to keep one.

Thanks a bunch for the help, phishie. I looked at past postings and you seem to be answering more of the questions. I can't help because I have no aquarium experience but I know some people who are into this subject. Would you like me to enlist them?

crocacutus

Your welcome.
Your two do seem to not fit the norm, but that could just be for the moment. Nature is funny sometimes... and most of the time when we make observations and then rules, the animal kingdom changes their ways. I always find that fascinating. That's why I will never know everything about everything.

I would like to make a suggestion. I would recommend keeping your crayfish in a bigger enclosure (maybe a 10 gallon?) because the smaller the enclosure, the more drastic the water parameters are. Crustaceans need very good water quality or they could encounter molting issues and die. It's easier to manage the water quality in bigger enclosures. And with a 10 gallon you would only need to do a 10% water change a week or 20% every two weeks.

I just may own one some day, you never know.

It is my job to try to answer every question asked. Although, sometimes I can't find the answer, then I rely on people with the experience with the particular organism. Luckily, for your question there is a lot of information out there. I do tend to stick to scientific facts or experiments, but sometimes that's not possible.

You can feel free to invite whomever you like to check out our site. Just be sure they read the TOS so they know the rules.

Good luck with your little ones.
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Phishie
Site Coordinator

"An ounce of prevention is worth a pound of cure."