Different species saltwater requirements

Post by **JediMasterThrash** » Fri Jul 11, 2008 1:39 am

I still sometimes hear many times the blanket statement "all crabs require saltwater". While of course good advice, I'd still like to provide some specific information regarding the topic. Clypeatus and Brevimanus penetrate inland and survive off freshwater and brackish streams. Compressus and Rugosus (suspect Violascens) go between the beach and inland, and require brackish or weak saltwater, but can subsist on freshwater for periods. Perlatus, spinosus, variabilis, and cavipes (suspect Purpureus) are restricted to beaches and require full saltwater. All species still use a concentration of saltwater for their shellwater (isotonic with their body fluids), but additional necessary salt is obtained from foods/diet, not water. Crabs that have evolved to live on fresh water have different concentrations of salt ions in their blood and urine to compensate (hypotonic vs. hypertonic relative to sea water). Crabs that live primarily on the beach haven't evolved to compensate and still require brackish or full saltwater. For the purposes of drinking water and shellwater, note that "salt" does not equal just sodium chloride. Saltwater is a mixture of half a dozen different salts, and the relative ratios are important. A high concentration of only one salt can be detrimental, while the proper mixture benefits molting and vitality. Finally, salts in their internal water create the hydrostatic pressure that breaks the exo. That's why crabs fill their molt-sac with water prior to burying, and why their burrow needs to be moist. But the salt concentrations are created by osmoregulation so that the crab's body reaches homeostasis. Salt is mostly lost due to evaporation and excretion, which is why in a humid environment salt doesn't need to be replenished as quickly, and the crabs will reingest urine or pass it through their bronchial chambers to recover the lost ions. Capabilities and body fluid requirements again vary between those species evolved to subsist on dilute saltwater versus those that require full saltwater.All that said, all crabs still benefit from having saltwater available, since it gives them the most tools to regulate their shellwater and blood ion concentrations (in lieu of missing dietary needs). And all crabs seem to enjoy a drink or bath occasionally.Reference:"JMT's Crab Species Evaluation" http://landhermitcrabs.com/eve/forums/a ... reenaway's "Terrestrial Adaptations in Anomura"http://www.bees.unsw.edu.au/school/staf ... %20MMV.pdf

Guest · Post by **Guest** » Fri Jul 11, 2008 1:44 pm

Hi JMT, Very interesting thread and I am so glad you posted the links!I was under the impression that saltwater is what helped the crab crack his/her exo during the molting process. In addition, I thought I had solved the mystery of my PP "Sunset" passing(it was going to be her 3rd moult)....that my saltwater was not salty enough.I am glad to learn that it is just water pressure.May I ask what you use for your saltwater and drinking water and how you store it? I look forward to your answers and greatly appreciate it.

Post by **JediMasterThrash** » Fri Jul 11, 2008 3:36 pm

I believe carol of crabworks did not use saltwater for her PPs for the first 30 years of their life (no 1st hand source on that, could be mistaken)I have used Red Sea Salt in the past, but now I use Instant Ocean. I mix 3/4 cup with 1 gallon, add water conditioner. I make 1 gallon of the saltwater and freshwater at a time and use it up for 1 or 2 weeks until I have to make a new batch.My saltwater is overconcentrated because it ensures the Strawberries get enough. And all the species of crabs are capable of osmoregulation so they can self-regulate their salinity by taking water from both the salt and fresh water pools. So they have access to full salt and full fresh and they can make whatever inbetween they like.

Margaret · Post by **Margaret** » Wed Jul 16, 2008 7:10 am

quote:but additional necessary salt is obtained from foods/diet This would fall short, though, with crabs that are too lethargic to eat or are suffering in some other way. I wish that in addition to a salt water dish, we could find a safe way to provide weak and troubled crabs with a chitin/calcium/protein/cellulose/etc. water dish!I know you've got your ear to the ground on these things, JMT, so... is anyone working on "vitamin water" for crabs, or do certain kinds of sea salt mixes already provide some of those other essentials?

Post by **JediMasterThrash** » Wed Jul 16, 2008 1:36 pm

Some minerals come from the saltwater mixes, and some minerals and vitamins come from the food. I think that if I crab is too weak to get to the food bowl, they'll be too weak to get to the water bowl too. In these cases, crabbers usually hand feed the proper foods to the crabs, or place them in ISO where they can always be in close proximity to their food and water. I haven't heard of any vitamin water, but not to say someone hasn't thought of it.

Post by **JediMasterThrash** » Thu Jul 17, 2008 1:38 pm

I recommend giving full (package) strength salt water for PPs and Es. It's just easier and safer to let the crabs pick and choose their own amounts of salt and fresh water to equalize it to their liking, than to rely on us to give them the perfect ratio.Sea salt should be mixed with water. Don't just give them salt in a food dish. The actual amount of salt they consume a day is probably less than mg, a very tiny amount. so letting them eat a salt pile could give them too much. Plus all the trace minerals and ions which are beneficial may have special properties dissolved in water.If you have strawberries, then I recommend the oversaturated saltwater.