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Old 09/28/2000, 10:29 AM   #1
Biogeek
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Someone just asked me about these guys again on Aqualink, and I couldn't find my detailed response from the past in the archives of either board, so I thought I'd post it again in the hopes that I'll never have to type this out again Unfortunately the software still seems to have a couple of bugs and won't let me add certain links to the post no matter how I try, so I'll have to skip them...

I'm going to guess from your description here that you are talking about one of the "flame” or “flashing scallops” Lima spp. Although these animals are called "scallops" they are not related to scallops by anything other than appearance, and are really file clams (scallops swim "forwards" while clams swim "backwards"). Flame and flashing "scallops" have a very poor survival record in aquaria, and the typical pattern of the animals hiding, and slowly wasting away (over a few to about 6 months) is the norm for these animals. The single most common cause for their demise in aquaria, I would guess, is starvation. Although I should also point out that these animals are pretty short-lived (estimates usually run about 3 years), and with the gaining popularity of feeding reef aquaria phytoplankton, I have now heard a couple of reports of the animals living for a year or so in captivity.

Another factor to consider is that these animals are protandrous hermaphrodites, and small individuals (~2.5-5 cm shell height) being predominantly male, and large individuals (~5-7.5 cm shell height) being predominantly female, so if you have any intent to try to breed them, you’ll need a range of sizes, and it is worth keeping in mind that getting a male will mean that you’ll have a chance of keeping the animal alive for a few years...

These animals are specialist filter feeders that require a *lot* of planktonic food. These animals feed entirely on phytoplankton and tiny zooplankton (<1/10th of a mm -- much smaller than newly hatched brine shrimp), and without heavy supplements, no reef tank produces enough of these foods to support a decent-sized filter feeder like this. The majority of their food by number is usually phytoplankton in the 5-40 micrometer (um) range (1/25 to 1/200th of a millimeter), but invertebrate larvae (up to a maximum size of 200 um -- 1/5th of a millimeter) are preferred if the animals are offered a choice, and these tiny zooplankton are likely the primary source of energy intake for the clams in the wild.

In most filter-feeding species, the addition of phytoplankton along with the presence of the tiny zooplankton (the primary zooplankton in this size range are rotifers, and invertebrate larvae) increases the rate of feeding (although this does not seem to be the case with Lima, which I’ll explain below), so it is almost always a good idea to feed both phytoplankton and tiny zooplankton (like rotifers) to the tank at the same time if you plan to keep any filter-feeding animals. At least some clams and oysters actually seem capable of selecting particles directly by their surface flavor (which is probably why pea flour and yeast-based aquarium products fail so often at keeping these animals live), and flame “scallops” seem to be among them, rejecting the majority of food typically offered in an aquarium, as many people have observed.

In laboratory feeding experiments, researchers found that inert plastic beads of the size of phytoplankton (5-40 um) were ingested at the same rate as the phytoplankton themselves, suggesting that the animals are incapable of excluding tiny particles regardless of taste. However, inert beads the size of invertebrates larvae (100-200 um) were rejected by the clams, and given that it has traditionally been difficult to obtain food even this small, it is not surprising that success rates with these animals has been so low. Unlike most studies of invertebrate filter-feeding, addition of phytoplankton to the medium did not affect the ingestion rate of the larger (100-200 um), and in this case, the animals actually seem capable of selecting particles directly by their surface flavor; this is probably why pea flour and yeast-based aquarium products fail at keeping these animals alive, and we have actually done demonstrations for students in our Invertebrate Zoology classes here of the animals rejecting pea flour and yeast-based invertebrate foods. The primary prey of the animals were invertebrate larvae, and ~75% of larvae on average were consumed by a clam in a given feeding trial (because they become so dilute in the culture jars after that point that the clams can’t pump enough water to catch the last few).

In any case, a good diet of mixed phytoplankton and enriched rotifers ought to be appropriate for keeping these animals, but I would suggest staying away from the typical rack of bottled "invert foods" at the local petshops, which typically contain high concentrations of dissolved organics, and rarely contain particles of the correct size and ‘flavor’ (for lack of a better word) that would be acceptable to Lima.

If you are not feeding a lot of phytoplankton and rotifers on a regular (at least every second day) basis, your clam is going to starve to death, and no matter how cool you think the animal is, you should not add one to your aquarium. If you are willing to start feeding phytoplankton (which has recently become readily available through vendors such as DT’s, BSD, LiquidLife, etc...) and could be convinced to start culturing rotifers to feed as well (e.g., I have an article on the biology and culture of rotifers in the Aquarium.Net archives that the system refuses to link to normally for some reason -- the url is http://www.aquarium.net/0397/0397_5.shtml), then it may be possible for you to keep one of these clams in an aquarium. The availability and ease of feeding Rotifer Pearls may also increase chances of survival of these animals, but I have not personally tried to feed with them, and simply do not know whether or not the clams will readily accept these as surrogate invertebrate larvae...

Another important consideration is that flame "scallops" are pretty reclusive by nature, and part of the reason I think so many people fail with them (aside from the diet issue above) is that they force the animals to stay where they are visible (or keep moving them back to the front where they are "supposed to be"). The clams prefer a deep crevice in which they can hide and gain some measure of protection from predators, against which they have very few defenses. Most bivalves escape predation by having tightly closing valves and a special type of muscle that allows them to "lock" the valves closed. Lima lacks those adaptations, and is easily preyed upon by "wimpy" stars that would not be able to eat a green mussel of equivalent size, so predation is more of an issue for these clams than for most bivalves. Many people have reported that some sea star in their tank has eaten their scallop, and that is why I think that, in general, keeping stars out of a tank with these clams is a good idea, but I suspect that the stress of keeping the clams out in the open takes it's toll on most of them, and the stars simply move in to finish off an easy meal when the clams stop resisting. My guess is that this problem derives from the stress caused by placing these animals out in the open for easy viewing. Because they are easy prey, and prefer deep crevices into which they can retreat, they will continue to move away from an easily accessible and viewable spot (much to the chagrin of the aquarist), and that takes a lot of energy from the animals (they are not all that motile to start with). If they are getting limited or insufficient food in the first place, and then placed into a stressful situation in which they continually have to expend an enormous amount of energy, it is not at all surprising that the animals frequently die...

All of these factors need to be taken into consideration if you plan to add a “flame or flashing scallop” to your tank, and if you are not prepared to feed them properly and allow them to crawl back into the rock-work to a place that makes them difficult to view, but where they will feel comfortable and remain for the long-term, then you should certainly not consider purchasing one of these animals...

Rob


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Old 09/28/2000, 10:32 AM   #2
Steve Richardson
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Arrow

Thanks Rob, appreciate you detailing it again.

We will archive it this time.

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-S


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Old 09/29/2000, 10:50 AM   #3
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Rob,
I have been posting on several boards a very condensed version of your spill above when the topic comes up on a monthly basis. Basically I tell them that these guys are 100% filter feeders and without extensive feeding of phytoplankton and zooplankton they will starve and they hang out way back in the rockwork so I may be the only one who knows I have a flame scallop in my tank anyway.

I don't have any scientific equipment or really much scientific knowledge, but am currently attempting to see if the heavy feeding of phytoplankton (tahitian blend cryopaste - 1ml twice a day in a 120 gallon tank) and feeding cluster and rotifer sizes of golden pearls will enable a simple hobbyist to actually keep these guys.

I have had mine for 6 months and have been trying to find out how long they live normally to determine success or failure in my trial. You mention the possiblility of keeping a male alive longer than a female. Do males typically live longer in the wild, or is it due to their smaller size that you feel they would be easier to keep alive. I did not know there were even males and females to begin with let alone any clue on how to sex them, so I am afraid that I probably have a female as the shell height on mine is probably around 3" or maybe even 3.5".

As far as actually trying to breed these in captivity with a male and female, how does the reproductive cycle work for them?

I will just stick to my current plan of trying to keep this one alive for > 1 year and see how that goes. I also had a couple of pics of mine hanging from a large thread or foot of some kind that I found very interesting. Pic of Hanging Flame Scallop.
There is another pic of the scallop before it and a pic of an oyster after it, you can go to those pics by going to the bottom of the page and clicking on the thumbnails. In the preceeding pic of the scallop I just noticed a mini starfish (down and right from the scallop) with 7 legs. My pic might be to poor to make it out though. I don't know if those stars are predatory or not, they seem so small they couldn't be very predatory.

Oh well, I would appreciate any additional info you might be able to give on these creatures. In retrospect I could have weighed it when I purchased it and then weighed it quarterly to see if it was gaining or losing weight, but didn't, and it would be hard to get it out from it's current location and probably stress it out. My research or lack thereof on this creature also is evident in that fact that I have a green brittle star (predatory I know) and a brown serpent star in the tank. So far they seem fat and happy and haven't bothered anything else in the tank or the scallop.

Quote from Biogeek:
we have actually done demonstrations for students in our Invertebrate Zoology classes here of the animals rejecting pea flour and yeast-based invertebrate foods. The primary prey of the animals were invertebrate larvae, and ~75% of larvae on average were consumed by a clam in a given feeding trial (because they become so dilute in the culture jars after that point that the clams can’t pump enough water to catch the last few).

I would be very interested in testing to see if they will eat golden pearls but would not have the setup to do this. Maybe the next time you do a demonstration for the students in your class you could try this with the cluster (60-100 micron size) and rotifer (100-200 micron size) golden pearls.

Thanks for any additional information you might be able to give, especially on lifespans of male vs. female scallops and the possiblility of testing to see if they will readily consume golden pearls. Also if you have any comments on the thead that the scallop is hanging from in the pic that would be great. My scallop seems to be able to attach itself to the rock somehow and release the attachment and then reattach.

Thanks, Nathan


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Old 09/30/2000, 07:10 PM   #4
Biogeek
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Glad to hear that yours seems to be doing so well, Nathan. Given it's current size, I wouldn't expect it to grow much, so it'll be hard to tell visually if it has grown at all or not. The weight idea is a good one, but then again (like repositioning the scallop for easy viewing), the stress of removing and weighing it regularly might be a bad thing to do for the long-term health of the animal anyways

The reason that males typically live longer is that these animals are sequential hermaphrodites, with the small animals being males that grow and go through a sex change as they become larger females. A small (young) flame scallop is likely to be a male, while a large (older) animal is likely to be a female -- it doesn't really have anything to do with the sex of the animal, just the size and age. The basic idea is that sperm are cheap to produce, so when you are a small animal and don't have as much energy to spare, sperm is a better investment than eggs in terms of reproductive "bang for the buck" -- when the animals reach a size that allows them a better chance for greater reproductive success by producing eggs, they switch sex to become a female...

These guys free spawn their gametes, with both sperm and eggs being broadcast into the water around them, and fertilization occuring if males and females happen to be close enough (< 1m on average for maximal fertilization rate) that the sperm and egss are not diluted too much. In the wild, these animals typically mass-spawn once (Oct-Dec)or twice (Oct-Dec & another small spawn in June-July) a year when water temperature drops due to the onset of upwelling -- it should be quite simple to induce spawning in the aquarium by simply dropping the temp by a couple of degrees (which frequently happens during water changes and induces spawning in animals like urchins that people observe all the time). The timing of mass-spawnings follows the phytoplankton bloom maximum, and studies of gonad development and maturation suggest that it is the high phytoplankton content of the water that is responsible for animals coming into breeding condition -- in fact, the presence or absence of the second mass-spawning in mid-summer is correlated with ambient phytoplankton production and concentration. Obviously, these animals rely heavily on phytoplankton for reproductive efforts...

The hanging position of your animal is not usual, but not overly surprising, either. As I said, although they are called 'scallops' they are not, and file clams actually have a byssal gland and attach themselves to the substrate with byssal threads like a mussel. Like true mussels, these byssal threads may be released if the animal wants to move or is otherwise unhappy. I wouldn't worry about the brittle star -- even large predatory species like your green brittle star Ophiarachna incrassata are not very good at prying things open, and I don't know of any ophiuroid off-hand that should be able to get into the shell of a healthy clam.

I'll have to see whether or not these guys will take the golden pearls when Invertebrate Zoology is taught again in the spring...

Rob





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Old 10/01/2000, 12:31 AM   #5
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Excellent Post Biogeek

I kinda figured the starvation thing out after about 6 attempts to keep one. I had the tank in prefect perameters.
I even resorted to removing them and putting them in prepared and homespun versions of invert foods and one thing that was helping a bit was Boyds vitamins but they eventually expired. I knew the vitamins were helping for the red seemed a bit more pronounced. But in the end I just chocked it up that they could not be kept. My trial and error assumption has been confirmed.


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Old 10/01/2000, 01:05 AM   #6
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Rob, let me know what links you want to add and I'll take care of it.


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Old 10/01/2000, 03:36 PM   #7
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Thanks Rob,
Hopefully I will be able to keep this one alive for a while longer. I didn't realize the naturally short life span when I picked it out (I got the biggest one for my $5).
These guys must be good breeders based on the price of them in the aquarium and shell trade. Hopefully we will figure them out and be able to sustain them in captivity.

Thanks again, Nathan


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Old 10/01/2000, 05:25 PM   #8
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Boring Bivalve

Rob,
While this is not a flame scallop, could you identify this boring bivalve?

I have 4 that must have come as hitchikers in the live rock. I have not added any live rock in over 12 months, so I have to assume they are doing well.

They range from 2cm to 5cm and are the same basic shape as a mussel. When the mantle is bright red. When disturbed the shell closes, however, it ether never closes fully or the halves don't fit together as there is always a small gap. (As they came as hitchhikers, I assume they must be able to close fully as they would have dried out in shipping.)

3 of them live in holes in the live rock and only move in and out of their holes. The fourth is living in the corner of the tank and appears to move around a little more.


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Old 10/01/2000, 05:51 PM   #9
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It's impossible to tell without seeing the complete shell removed from the rockwork, but given the color, shape and habit of the critter, I would guess one of the Spondylus species (perhaps S. varians?) as the most likely candidate. I'd link you to a picture to compare if I could find one, but all I can locate are links to shell-collectors and shops - no live animal photos...

In any case, this is one of the most common thorny oysters in the IndoPacific, and are common imports on live rock, where they are often so encrusted that they are not noticed by many reefers who ask questions about "what moves my rocks?"

Rob



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Old 10/01/2000, 06:12 PM   #10
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Rob,
Thanks for the quick response.

It does look much like the picture of Spondylus varians in Gosliner (1996), but wasn't sure how many other Spondylus sp. there were. Also, shell of the one in Gosliner is fairly encrusted so I can't make out any pattern. Mine seem to have ridges and grooves on the shell like a cockle.

I assume these are filter feeders.


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