Shrimp molt

[kreblak]

How long should it take for a candy striped cleaner shrimp's shell to harden after a molt? Yesterday my cleaner shrimp looked completely normal, nothing out of the ordinary. Today, he looks the same, except his colors are a little brighter, and his antennae are longer. Strangely, there is a shrimp shell on the tank floor. Is it possible for a shrimp to molt and harden within 14 hours? (the approximate time between viewings)

I was under the impression that the hardening process took a couple of days. Also, is it strange that my shrimp and my hermits are molting as fast as they can? All 6 of my scarlett hermit crabs have molted within the last months, one of them twice. The cleaner shrimp has been in the tank a week, and has now molted. What gives?

[VoodooChild]

I'm sure they can do it that quickly if they can, though a few days is the norm. You may want to check your iodine levels. If these are high they'll molt as much as they can, which may explain why you're having such frequent molts.

[mogurnda]

It's pretty dependent on growth. Sounds like they are growing and molting, which is pretty normal. Scarlet cleaners will molt about every 2 weeks, for example.

While there seems to be a requirement for iodine for general crustacean health, the requirement for molting is dubious. Although it resides in reefkeeping lore, I have found nothing in the scientific literature that implies a link between iodine and crustacean molting.

BTW, the cuticle will harden in about a day.

[kreblak]

Every two weeks? Wow, I thought molting was more like a once every six months sort of thing. My hermits went for five months without molting (or I just didn't notice) and now it seems like every time I look in the tank I see an old shell.

Could it have anything to do with the food I am putting in the tank? I have recently (within the last month) begun using frozen food consisting of formula one, formula two, spiriluna, brine, mysid, and various other goodies. The fish seem to like it well enough, but my hermits go bananas when the chunks hit the substrate! The shrimp is all about it, too. He will travel the length of the tank at warp speed for meaty piece.

[Boogiechillin]

Two weeks is pretty standard for most common aquarium shrimp species, and it does occur more or less overnight. Many crustacean species will hide the following day while their cuticle/exoskeleton hardens, but cleaner shrimp are (mostly) "off-limits" to predators...since they aren't as worried about being eaten, cleaners are usually willing to walk around out in the open immediately after a molt.

Don't worry about dosing iodine for crustaceans; your salt mix contains all the trace elements needed.

[mogurnda]

My hermits went for five months without molting (or I just didn't notice) I bet it's the latter. Let's face it, how carefully do most of us watch our hermits? But they may molt less often than shrimp. More calcified cuticles take longer to prepare for a molt, and longer to build.
I agree with boogiechillin about dosing iodine. It's not only in the salt mix, but there's lots in the food.

[VoodooChild]

Well there we. I stand corrected:) So is it important though to molting?

[mogurnda]

I would say no, but just because I can't find a reference doesn't mean it isn't important. I have done searches on several major databases and have found nothing. Plus, part of my professional life is insect endocrinology, which is very similar to that in crustaceans. None of the hormonal steps involves iodine (their molting hormones are all steroids and peptides, nothing like thyroxine) in either insects or crustaceans.
However, there is a pervasive belief that iodine is important in crustacean molting on these boards, so I find it hard to believe that it's based on nothing.

[kreblak]

Mogurnda,
I'm willing to bet that I simply didn't notice the molts. The first time I saw a molt, it was right up on top of my largest piece of live rock, sitting in plain view. Now I see them all the time, but I'm pretty certain it's because I'm actually looking for them now.

I have read that iodine is important to crustaceans, though I don't know for what reason. I have done some work with insects as well, mostly involving cholinesterase inhibitors. I have also looked at the effects of insecticide runoff on ocean crustaceans, and I can't remember anything about iodine being essential to them. However, I am certain that somewhere along the line I have read that iodine is important. This is going to bug me, I'll have to consult some old textbooks...

[mogurnda]

If you find a reference for the role of iodine in the molt, you'll get 10 bucks!

[VoodooChild]

Another quick thing Kreblak, depending on just how many things you have in your tank, molts usually are quickly consumed. A molt in my tank may last two days. If you have enough inverts, it'll be gone before you notice it.

[kreblak]

I have looked at five seperate books on marine animal anatomy and physiology, and have been able to produce a single reference on iodine importance in the molting process. I quote,

"There seems to be a high mortality rate among shrimp that have recently molted, as they molt the entirety of their gills along with the exoskeleton... A stress free environment facilitates higher survival rates for the shrimp. An abundance of hiding places are necessary for the shrimp as it waits for its new exoskeleton to harden. Nutrition is also of the utmost importance, of which Iodine is thought to play a vital role."

That is as specific as I was able to get. The best minds out there "think" iodine plays a vital role, but no one wants to come right out and say how.

I am thinking that it plays an important role in osmoregulation, like it does in human thyroids. Just my hypothesis. Is that worth $10?

[mogurnda]

Well, it was worth a good chuckle. If that was all it took, then I'd owe VoodooChild $10 too. Just once, I'd love to see one of those "great minds" present a teensy bit of experimental evidence. BTW, if you are interested, the most complete, if somewhat dated reference I have read is Dorothy Skinner's chapter in vol 9 of "The Biology of Crustacea." There are newer reviews, but they don't add much, as far as I can tell.

[OrionGirl]

Not a great mind by any stretch, but some hypothetical proof for the importance of iodine (and where it entered the realm of thought)--brackish crabs being maintained in FW environments seldom molt successfully. While there are an abundance of other differences between the FW and B/SW chemistry, iodine could be one of the key differences that results in molting failure in those crustaceans kept in FW.

There is a lot of information indicating that crustaceans contain a higher level of iodine than other critters--this is one of the reasons many people are allergic to iodine.

[mogurnda]

There is a lot of information indicating that crustaceans contain a higher level of iodine than other critters-- That's true. But there's a lot of debate as to whether the iodine needs to be there, or is precipitated as a byproduct of the tanning process in the cuticle.

[kreblak]

I have consulted yet another stack of books on crustaceans, and I still cannot find one single line that reads anything like "Iodine is crucial to the molting process because..."

Everything just alludes to iodine being important nutritionally and as an element in the water. This lack of an answer really bugs me...

[mogurnda]

This lack of an answer really bugs me... Tell me about it. I have been ranting on Reef Central for months, even posted a thread offering the same $10, and have received no info.

I guess it doesn't hurt anybody. But it would feel great to finally know how the whole thing started.

[Boogiechillin]

Mogurnda,
In between drifting off for naps in college zoology, I think that I remember a reference that iodine can be used to stimulate premature crustacean molts in laboratory settings. My guess is that this would actually be detrimental since it probably rushes proecdysis and results in the critter salvaging less of the mineral content from the old exoskeleton. I don't have the reference for this, but it's not much of a leap to go from the use of iodine to forcefully stimulate a molt to a popular belief that iodine is *necessary* for a molt.

Anecdotally, when my tanks were soft coral dominated, I dosed iodine more frequently to stimulate their growth. Granted, this is retrospective, but I seem to recall the shrimp molting more frequently and leaving less-transparent exoskeletons behind, several of which scared me as they were colored enough to look like a dead shrimp. More recent molts that I saw after shifting away from softies and iodine are more translucent.

Definitely not my field, but this is an interesting topic!

[kreblak]

If dosing iodine into a tank (or labratory setting) can induce a crustacean to molt, then isn't it logical to conclude that iodine is a sort of "trigger" for the crustacean? If the iodine levels in seawater are constant (I think they are) then the crustacean will take in iodine on a regular basis. When enough has accumulated in it's system, it is time for a molt. (in theory) I don't think its much of a stretch to conclude that evolution has built into crustaceans a timing mechanism for their molts based on a constant.

Of course, this assumes that the iodine content of seawater is constant. If it isn't then my theory is shot to *&%$.:rolleyes: Also, it assumes that the molt isn't triggered by growth or some other variable. All in all it isn't a very good hypothesis, but its the best I can come up with right now....I want that $10!;)

[mogurnda]

isn't it logical to conclude that iodine is a sort of "trigger" for the crustacean? Not really. We can get lots of things to happen in the lab using artificial methods, but they don't necessarily indicate the way things work normally.
Under normal circumstances, the molt is controlled by a hormone called ecdysone, or for the type A people out there, a derivative called 20-hydroxyecdysone. The secretion of this hormone is in turn controlled by peptides such as molt inhibiting hormone. Outside factors such as stress boost the secretion of MIH, keeping the animal from molting until the right time.
If, for example, iodine were to inhibit the secretion or function of MIH, it could induce a premature molt.
What I would really, really, really like to see is the reference BogieChillin mentioned about iodine inducing molting. People quote it, but I would love to read it.

[kreblak]

Has anybody else noticed how intellectual this thread has become? I haven't done this much homework reading since college. I feel like I ought to receive an honorary Ph.D. in marine biology.

Anyway, I have access to one more database. I'm going to check for a solid reference. One worthy of citation in a bibliography. If this is unable to yield any solid results, I may just have to give up. What are the odds of someone out there doing a study on the role of iodine in crustacean molting? Better yet, what are the odds of us finding it?

[mogurnda]

I figured the aquaculture guys would really want to know this, because it affects their income, but I sifted through the aquaculture databases and came up with zip.

Dangit, were zooming around on the Information Superhighway! Where's the information?
I feel like I ought to receive an honorary Ph.D. in marine biology. First you need to be stressed and drink a lot for 5-7 years.

[Boogiechillin]

Originally posted by mogurnda
First you need to be stressed and drink a lot for 5-7 years.

LOL...I'm in Year 2 of that process. Not marine bio, but I definitely concur.

I'm venturing dangerously close to a chemistry discussion here, but should we be thinking more broadly? Maybe it's not iodine specifically that causes the (hypothetical) molt, but some characteristic of iodine. What naturally triggers B-ecdysone release?

[Boogiechillin]

Hmm...just thought of something else. Iodine CAN be used to force molting...of feathers on poultry. Wouldn't that be a hoot if that was what kicked off this whole idea?

[mogurnda]

What naturally triggers B-ecdysone release? I can tell you off the top of my head for insects, but not crustacea. I'll read some this weekend.

That's been bounced around before. Habib from salifert sent me a whole bunch of references about molting, including chickens, when I whined before. For some reason, I found it hilarious. I just think chickens are funny.

Signing off for now.

[kreblak]

Chickens are funny. Naked chickens are funnier still. So far the best study I have been able to come up with is "The Bacterial Expression of the Shrimp Molt-inhibiting Hormone (MIH): antibody production, immunocytochemical study and biological assay" by Pei-Li Gu, Ka Hou Chu, and Siu-Ming Chan at the University of Hong Kong. They don't get into the specifics of iodine's role, but they do come very close. It deals mainly with supressing the molt with neuropeptides from the CHH/MIH/GIH family.

Boogie, ecdysone is secreted by the Y-organ, but I don't know the specific mechanism that causes the Y-organ to release it.

I'm not sure what's scarier, the fact that there are people actively studying crustacean hyperglycemic hormone, or the fact that we're interested in it. The database is not yet exhausted, the search continues...

[kreblak]

Mogurnda and Boogiechillin, I think you both will like what I have found. Your original thoughts about iodine NOT being necessary for a molt may just be right after all. The following is a quote from the book "Without a Backbone" by Ronald Shimak, Ph.D.

"There is a persistent myth in the reef aquarium hobby that iodine is necessary for crustacean molting. This is definitely not the case. In fact, iodine may stimulate molting by acting as a poison that short-circuits part of the molt cycle. Healthy small crustaceans, such as cleaner shrimp, will shed an exuvium that is almost transparent and colorless. The molting process influenced by excess iodine results in a less transparent, often colored, molt or exuvium. This indicates that the animal was not able to salvage all of the necessary material from the cuticle and after the molting has occurred may be at a nutritional disadvantage."

This is probably the reason no one can find anything about iodine as a chemical used in stimulation of ecdysis.... because it isn't! If this guy is correct, then iodine in excessive quantities is a poison, and the molt stimulated by it is simply the crustaceans reaction to the poison. Almost like losing a leg I suppose.

[Boogiechillin]

But, there is still a definitive lack of research out there showing that ANYTHING can jumpstart a molt, let alone iodine. It's all fine and well for Shimek to say it's bad, but we can't find any REAL research showing that iodine can be used to initiate molting. Much as I like and respect Ron Shimek's work in aquarium literature, he really hasn't done a whole lot in terms of scientific publications...he's got about a half dozen cites in BIOSIS and he teaches marine bio in the middle of Montana. He's a great guy, knows a lot about captive systems and sand bed infauna, but experimentally, as a grad student who is very familiar with evaluating research, I wouldn't pin a whole lot on his findings...

[mogurnda]

Boogiechillin,
You took the words right out of my mouth! I think RS is great for invertebrate ID, but he doesn't have a track record as an experimental biologist. In his articles he tends to generalize from a small observation, and then the Ron-keteers regurgitate it as gospel.
I have been too busy to do any reading this weekend, and I shouldn't even be logged on right now, but I have a stack of papers that describe the hormonal events that lead to a molt. I don't think they've figured out the physiological link between body size and molting, but this is a good excuse to sit with some papers.

Kreblack,
That helped. Did the good Dr mention his source for the molt info? By the way, I certainly didn't mean you in my diatribe about the ronketeers.

[kreblak]

The entire discourse presented by Dr. Shimak contains not a single footnote or bibliographical reference. I therefore thought he was expounding on his own research. I was unaware that Dr. Shimak had such notariety. I didn't take it personally, Mogurnda, this is my first foray into his works. He certainly does write as if he is THE authority on crustacea. He had me convinced, anyway.

[Boogiechillin]

Most of Shimek's research is on various marine snail species, especially parastic species, and in that arena I would consider him to be a strong researcher. He has also done some work with sandbed infauna, like copepods. But, for most of his articles he just summarizes and accumulates material from grad-level marine invertebrate textbooks. This is a great service for a lot of people as it brings information that isn't available to most hobbyists to those who need it, but doing a book report on Moby **** doesn't make you Herman Melville, ya know? ;)

Even still, I wouldn't mind if Shimek allowed open discussion of the experiments that he does on aquarium-related topics. He gets really defensive if anyone questions his methods or conclusions. For example, there's a recent thread over in his forum on RC where someone was smacked down right quick for displaying a lack of total confidence in his salt mix study. I don't get that response...what makes a strong research finding is the ability to respond to criticisms!

[kreblak]

I found this in a round about fashion. Its a cancer study from the university of Shandong that I stumbled upon as a reference in another article I was reading.

"a. Molting Hormone

The clearest and most direct evidence reflecting the regulation of genetic expression at the level of transcription is the formation of "dilated vesicles " seen in the chromosomes of the salivary glands of the larvae of fruit flies and other dipterous insects. These vesicles appear one after another along with the development of the insects (The genetic transcription in the dilated vesicle zone is going on). Therefore, the "dilated vesicles" of polytenic chromosomes are regarded as the morphologic expression of essential molecules and development process---activation of specialized genes. Molting hormone can bring about the orderly emergence of the dilated vesicles of the chromosomes of the salivary glands of the larvae of fruit flies [4]. The cicada slough in traditional Chinese medicine is the skin of Gryptotympana atrata and it should contain molting hormone after ecdysis several times and eclosion. The experiment made by Sato proves the inhibition rate of cicada slough on the cancer cells cultivated extrinsically is 100% [3].

b. Thyroid Hormone

After an injection of thyroid hormone into an animal the increase of some RNA will be observed before that of the activity of the polymerase of RNA and that of a series of enzymes [9]. Although little is known about the mechanism of the compounding of RNA and proteins promoted by the thyroid hormone, it has been discovered that the thyroid hormone can combine itself with mitochondiae rapidly in cells to promote their biological oxidation. It can then change the functions of chromatins and intensify the compounding of RNA and various sorts of zymoproteins [9]. Indeed, the thyroid hormone can stimulate metamorphoses like rapid development and differentiation in animals [3]. Many facts have proved thyroid hormone deficiency has something to do with cancer. For instance, iodine deficiency is positively correlated with the incidence of mammary gland cancer in statistics [3]. c. Thyroid-Stimulating Hormone (TSH)

TSH comes from peptide hormone of the lobus anterior hypophyseos. Experiments on animals show when TSH is added to thin thyroid slices or whole animals, the absorption of iodine by thyroid cells can be stimulated by 500 times [10]. Besides, TSH can activate the adenylate cyclase on cellular membranes, so it quickens the formation of cAMP and increase cellular concentration of cAMP, which is one of the best inducers of the cellular differentiation of neuroblastoma [8]. d. Estrin"


The full text is available online at www.eciwo.sdu.edu.cn/medicine/f06.html

I'm not sure how much it helps, but it's an attempt at correlating iodine to the molting process.

[VoodooChild]

I just wanted to run on the side of Boogie as far as Ron goes. Too often, IMHO, people praise his name. While he is a very intelligent man, his works often contain citings by papers that aren't peer reviewed. If 4 people write a paper on the feeding habits of so and so, it doesn't make them right just because there's 4 reports (on the other hand, peer reviewing by a scientific counsel doesn't always make it right either). I just feel that he throws his stuff out there too often without accepting the paper's limitations or is willing to admit that he was wrong. I read is I.O. paper too, and while it's information may have been correct, it had way to much of a "my tank crashed because of this, and yours will too" theme going for it.

[mogurnda]

Agreed. But wrt the original topic, I did a little reading last night. I had a chance to do some searching on all the databases that the Marine Biological Laboratory at Woods Hole has when i was there for a party, I mean meeting, in March. I skimmed it, then got busy. What I learned can be summarized as:
1) Much crustacean endocrinology is published in journals so obscure that even MBL doesn't get them.
2) Entry into the molt is controlled by 20E (20-hydroxyecdysone), under the control of MIH (molt-inhibiting hormone), and maybe methylfarnesoate (which I am ignoring because it isn't very clear). The molt starts when the old cuticle separates from the epidermal cells, and the cells begin to secrete a new cuticle. Once the new cuticle is complete enough, and a lot of the proteins and stuff from the old one are reabsorbed, the animal sheds the cuticle in a process called ecdysis. In most species, they then eat the molted cuticle to get the rest of the nummy goodness out of it. The molt is triggered when MIH stops being secreted, which causes a peak of 20E. It looks like there has to be both a rise and a fall in 20E levels for molting to happen normally, because 20E will inhibit ecdysis when injected during a molt.
What started people thinking about the existence of MIH was the fact that removal of the eyestalks, induces molting. Kids, don't do this at home, because it's abnormal, and they usually die. Anyway, this led to the discovery of the X organ, which is a neuosecretory thingy connected to the brain that resides in the eyestalks. It got its name because the discoverer marked it with an "X" on a figure.
Another way of inducing a precocious molt is to remove a few legs. This gets the molting system moving, and gets the guys new legs through regeneration. What the Skinner review said was that more legs off=faster molt.
Another interesting factoid is that serotonin inhibits 20E secretion, possibly by stimulating secretion of MIH. Stress also inhibits 20E secretion, maybe via the same pathway.
There's a lot of complexity, and many things are stage and species specific, but this is the general outline as I understand it. For example, adult lobsters molt annually, so there is a seasonal component to regulation, while shrimp that molt every 2 weeks will presumably have different triggers.
I left the papers at home, so let me know if you want the references.
Kreblak, I still like your theory that the iodine idea came about because someone equated shrimp with chickens.
If anyone wants to discuss the above, I am afraid that I, Dr Dave, will become combative and ban you from my forum. Oh, yeah, it's not my forum. Careful, I may still become difficult.

[VoodooChild]

I just wanted to say that that was very interesting. Good searching. Can you list the database where you found it?

[mogurnda]

At my home base, I used Pubmed and Web of Science. At MBL I went through AFSA (aquatic science and fisheries abstracts), BIOSIS, and Zoological record. The searches were crustacea AND iodine, crustacea AND molt, crustacea and ecdysone, iodine AND molt, and probably a few other permutations. Plus generous use of wildcards. Most searches involving iodine came up with nil.
The papers I got the info from were:
Skinner, DM (1985) Molting and regeneration. In DM Bliss and LH Mantel (Eds) The Biology of Crustacea v9, 43-146. Academic press.
-Most complete, if old
Chang et al., (1993) Regulation of crustacean molting: a multi-hormonal system. Amer Zool 33:324-329
Huberman (1990) Hormonal control of molting in crustacea. Prog Comp Endocrinol [vol?] 205-210
-There's a more recent (2002?) Huberman review that came up in Web of Science, but I haven't put my hands on it yet.
They are all reviews, sorry. A lot of the original literature was not even available at MBL. Not that any of it looked like it dealt with the iodine issue based on titles and abstracts. Apologies for typos. I'm beat.