Download Marine and Reef Janitors - Kieron Dodds

Cleanup In Aisle Three – Marine and Reef Janitors Part 1
There was a time when we could barely keep fish alive in
marine aquariums. And, even then, these were only a few “bulletproof” species like the various damselfishes. At that time, you could
find the occasional octopus offered for sale, or perhaps a sea star
species or two. In today’s hobby, the story is a much different one.
While available fish species certainly outnumber the available motile
invertebrates regularly offered for sale, there are still dozens of
invertebrates to choose from. Unfortunately, care information and
species descriptions can be lacking at points of purchase. And, to
make matters worse, many sellers of such animals will recommend
inordinately large numbers of these organisms. Of course, we’re not
discussing anemones, corals, or ornamental crustaceans. What we
are talking about are organisms that are used to lessen the aquarists’
burden, those used to “clean” the tank. These can be consumers of
all forms of detritus, from uneaten food to fish waste to the exudates
of other organisms, or algae grazers, or even some of the few
organisms that are known to consume cyanobacteria.
These organisms are collectively lumped into a group of very
dissimilar families, genera and species and called “Reef Janitors”,
“Clean-up Crews” or any of a few other variations on “cutesy” names.
As you will see, the “cutesy” aspect detracts from the organisms as a
whole and can even create problems, and unnecessary expense,
financial, physical and mental, for the aquarist. First, I believe it is
important to establish what it is we actually expect these creatures to
do, and how we expect them to further our enjoyment of the hobby.
After all, if they just take away from our enjoyment, directly or
indirectly, why would we want to include them in our aquaria? That’s
a very good question, and one you will hopefully find the answers to
in this article.
There is a tendency within our hobby to lump these organisms
together based on what they are believed to consume. Sometimes
you will see “packages” of such organisms offered for sale as
“detritus packs” or “algae packs”. That’s a fair enough distinction, if
the animals sold in the packages do actually consume that which they
are advertised to consume. Sometimes this is the case and
sometimes it isn’t. The beginning of our understanding then needs to
address why and what we need to control, how it gets there, why it
continues to be a “problem” and what the possible solutions are.
These things may be easy to understand, but they’re not always easy
to accept. Without nutrients available for their growth, nuisance
organisms, like other organisms, will not survive. Removing detritus
in some way, before it is available to these nuisance organisms,
which are most often algae and cyanobacteria, is one approach to
controlling or eliminating those organisms. However, and this can not
be stressed enough, the nutrients that are consumed by detritus
feeders are not removed from the environment. They are
sequestered in the biomass of the detritivorous organisms, or
excreted in the waste products of those organisms. For all intents
and purposes, when using detritivorous organisms, detritus is never
really removed from the aquarium, just converted into other forms.
So, there are still some nutrients available, and the detritivorous
organisms won’t live forever either so the nutrients sequestered by
them will become once again available at some point in time. This
nutrient availability can still fuel algae and cyanobacteria “blooms”.
Controlling these nuisance organisms through direct predation is
another tool used by aquarists. However, some of these organisms
are not consumed by predators, at least not predators we keep or can
keep. Furthermore, they often grow faster and spread more rapidly
than mostly invertebrate predators can consume them.
Assuming that the “detritus packs” and “algae packs” you
purchase are collections of organisms that do consume what they are
advertised to consume, you may still even find that the problem is not
being brought under control, either with rapidity (which is neither
normal nor indicative of success) or at all. The tendency would then
be, if utilizing these organisms, to purchase more of them in the
attempt to bring the problem under control. However, there are a lot
of discrepancies in this line of thought, enough, in fact, to fill many
pages. Let’s leave it to a few simple ones. For example, often turbo
and Astrea snails (Astrea spp.) are purchased with the intent of
controlling algae. However, they really only consume algae films,
and mostly only very little and in a line to wherever they may be
traveling. The practical result is that mats of hair algae like Derbesia
spp. and Bryopsis spp. are not brought under control by these snails.
Further, if the intent is to keep the walls of the aquarium clear the
aquarist will discover that scraping the remainder of the aquarium
wall that has been half cleared of algae by these snails will still
involve covering the same surface area, saving the aquarist no work
at all, really. Hermit crabs, reported to consume hair algae, will
mostly eat everything else but hair algae. As a last resort, some will
consume hair algae, as will some true crabs like Mithrax spp. and
smaller Percnon spp. individuals. Still, these algae eating organisms
are quite small, with quite low metabolisms, and often can not keep
up with algae growth and spread. And, even if they can, if enough
have been added to eradicate the nuisance algae, many are
dependent on certain specific types of algae to survive.
The recommendations for huge numbers of snails and hermit
crabs to be added to an aquarium will sometimes help control a
problem, at first. But what happens, as stated above, when the
problem is brought under control? When there are no longer copious
amounts of various algae species growing out of control, these
“cleaners” will have nothing left to clean, no food to sustain them, and
they’ll begin to die off. Or, in the case of hermit crabs and true crabs,
the “cleaners” may be resilient enough to find their food sources
elsewhere. Unfortunately, this usually results in their preying upon
other organisms within the aquarium, including other hermits and
crabs and snails.
Before discussing specific species, it is this author’s assertion
that including these organisms within a marine or reef tank is mostly
beneficial if their numbers are kept very low. “Packs” offered for sale
at recommended volumes are often offered with five, ten, or twenty
times the organisms that that particular volume might be expected to
be able to reasonably sustain long term. Keeping this in mind, the
recommendations for numbers of individual species per gallon that
will follow are guided by the premise that diversity with minimal
contradiction is a good thing. Therefore, numbers of organisms
recommended take into account that other, different organisms will be
present within the aquarium in question. These recommendations
are not intended as hard and fast rules, but more as guides to help
the aquarist more reasonably stock an aquarium with motile
invertebrates.
Snails
Almost every discussion of “cleaner” organisms will begin with
snails. And any discussion on snails will usually begin with the
herbivorous - or thought to be – grazing snails. Of these, the most
popular snails are the Turbo spp., and Astrea spp. snails.
Representatives of these genera, in the United States at least, are
usually species that come from the Gulf of Mexico or Caribbean and
they are usually fairly intolerant of extended periods of higher reef
tank temperatures (80-84ºF). As such, great numbers are often
introduced to the new aquarium in the hopes of avoiding nuisance
algae blooms, only to be found dead in almost equally huge numbers
within days or weeks of introduction. If the tank in question if kept a
little lower in temperature (76-80ºF), these mortalities will be usually
be lessened significantly, provided that there is food availability.
Better choices in herbivorous film grazers are available, both animals
that tolerate tropical reef temperatures better, and that live longer.
Trochus spp. and Tectus spp. are readily available and, while they
may not ship as well, leading to higher initial mortalities, they tend to
live quite a bit longer than Turbo spp. and Astrea spp. in our aquaria.
Currently, I have no less than a dozen of these snails in a 450 gallon
aquarium that were transferred over from a 180 gallon aquarium and
have been in my care for 7 years. That’s quite a long time
considering that some aquarists seem to need to “re-stock” their
snails every years or so. There are a few other snails that, while
infrequently available, are very good choices. Haliotis spp.,
commonly known as abalones, are herbivorous grazers on films and
diatoms. Initial acclimation can be a problem, they do require full
strength salt water, and they are infrequently available and
expensive. Certain cowries (Cypraea spp.) are excellent choices not
only for film algae control, but for filamentous (hair) algae control as
well. Certain prejudices do exist when it comes to cowries, however,
and it is important to note here that there are many cowry species
that are not obligate herbivores, but corallivores, and will consume
corals. Of the cowry species that are desirable, the most commonly
available are the tiger cowry (C. tigris) and a handful of species
collectively called money cowries. There is one last commonly
available species, or collection of species, that are worthy of
discussing here and these are the bumble bee snails. It is reported
that these snails are algae consumers, and there may very well be
some species for which this is true. However, they are all black
shelled with yellow bands and virtually impossible for the lay aquarist
to identify down to a species level. The bumble bee snail collection of
species definitely contains organisms that are predatory upon other
snails and other invertebrates. Because it really is impossible for the
aquarist to tell the bad from what might be potentially good, or at least
not directly harmful, these animals should not be considered.
There are dozens of other snail species available as well, some
commonly available and some not, and some that aren’t available for
sale at all but may make it into your aquarium on live rock. Some are
not even suitable for reef aquaria at all, for varying reasons.
Taking on an algae problem directly with a biological agent
alone, particularly an invertebrate that can not consume much, is
often a futile effort. However, there are other ways to combat nutrient
accumulation and the availability of those nutrients to nuisance
organisms. There are several snail species kept specifically for this
ability. They are detritus consumers and their performance as
cleaners will go a long way towards preventing the accumulation of
detritus and nutrients in the aquarium. Cerithium spp., commonly
sold as cerith snails are one of the best choices in this respect. While
they will spend much of their time in or near the sand bed consuming
detritus, bacterial and algae films, they will occasionally graze algae
off of aquarium walls as well. These snails will also readily reproduce
in the aquarium. Nassarius spp. and Ilyanassa spp., collectively
referred to as Nassarius snails will also remain in the sand most of
the time. However, like little zombies, once dead flesh hits the water
(hopefully in the form of food) they will almost literally explode from
the sand bed en masse, track down and consume any leftover foods.
The Nassarius snails will not consume detritus directly, but will
consume introduced foods before they become detritus. Other sand
dwelling species also serve to keep a sand bed clean, and turned,
like the algae grazing conchs (Strombus spp.). The queen conch,
Strombus gigas, gets far too large for most marine aquaria. But, its
smaller cousins, the fighting conchs, Strombus alatus and Strombus
gibberulus are excellent algae grazers and sand turners and remain
fairly small at around four inches.
Of those snails that are predominantly introduced to our tanks
as “hitchhikers” on live rock, Collonista spp. are probably one of the
most frequent. Commonly called “mini” or “baby” turbos, these snails
are herbivores and consume algal films and diatoms like their
namesakes.
Stocking subtropical and temperate invertebrates in a reef tank
that is not also dedicated to organisms from these areas, which most
reef tank are not, can be a huge and costly mistake. Not only do
these organisms invariably die off, sometimes slowly and sometimes
quickly, but the potential for fouling the water when these animals are
purchased in “recommended” numbers is very great. One of the
biggest sellers in this respect is the margarita snail, Tegula funebralis,
often sold in huge numbers in “algae packages”. Less frequently,
although still commonly, available is the red-footed moon snail,
Norrisia norrisii, another subtropical snail that will suffer the same fate
as the Margarita snail in tropical aquaria. But simply sticking to
tropical species does not guarantee that they are appropriate either.
For instance, the Nerites spp. snails are tropical, commonly available,
and do quite well – if you can keep them in the water. These snails
are tide pool and tide line animals that, in the wild, congregate in
huge numbers on pier pilings and rocky surfaces near the shore. As
such, they spend a good deal of time out of the water and will
eventually attempt to do the same in your aquarium, spending the
day time at, near, or above the waterline. All individuals, some five
dozen or so, I have kept have eventually “gone overboard”.
Cleanup In Aisle Three – Marine and Reef Janitors Part 2
Snails are not, by far, the only organisms used to “clean” our
aquaria. While snails are the predominant creatures used for this
task, there are many other organisms that will consume algae and
detritus. Some of them are cryptic and not usually introduced
voluntarily, others are prized and eagerly sought out, and still others
cause more problems than they could ever possibly resolve. So,
when you’re offered a mixed bag of species as a tank cleaning
package, how comfortable are you that all of the species offered are
compatible not only with each other, but with your long term goals for
your aquarium. In the case of many such packages, you should not
be comfortable at all. It is hoped that once you’ve read the
descriptions – and warnings – of the most commonly available
species listed below you should be able to approach your choices
more wisely.
Hermit Crabs
Hermit crabs are probably, after snails, the most commonly
utilized and sold cleaner creatures. While the minute hermits sold in
these packages are scavengers, they are not above preying upon
smaller organisms or raiding cnidarian polyps for food if detritus is in
short supply. This should definitely be kept in mind when stocking
these and other creatures mentioned here. It can not be emphasized
enough that the sheer number of individuals sold and recommended
for a particular tank size is ridiculously large in most cases. The most
commonly sold hermits are of the genera Paguristes, Clibanarius,
and Calcinus. Each “species” has its own mixed reputation amongst
aquarists and it’s probably prudent to assume all accounts are true.
Hermits will, sometimes, attack and kill crustaceans, other hermits,
and most particularly snails. With this in mind, any of the minute
species offered are as good – or bad, depending on your
interpretation – as any other. If you do, however, keep their individual
numbers low, they can make interesting, and entertaining, inhabitants
of your reef tank. Personally, I would recommend no more than one
or two hermit crabs per 25 gallons.
True Crabs
Also staples in some cleaner packages, Mithrax sculptus, the
emerald crab, is almost completely herbivorous. Reported to
consume the bubble algae Valonia spp. and Ventricaria spp., I have
seen no evidence of the emerald crab’s ability to consume, much less
control, either. Still, they will consume film, tuft and turf algae, as well
as, sometimes, hair algae. They are also excellent at picking detritus
from the interstices in our rockwork. Both the sally lightfoot crabs
(Percnon spp.) and arrow crabs (Stenorhynchus spp.) are sometimes
sold in packages as well. It is important to point out that, while
smaller individuals of the Percnon spp. will consume some algae,
larger individuals will, like most crabs, take their food where they can
get it. Larger individuals are predatory and will consume whatever
they can catch and hold, including small fish. The danger to healthy
fish, particularly larger species is very slim, and as such the sally
lightfoot crab can make an interesting addition to the reef tank.
However, it can and will consume other crustaceans, molluscs,
worms, pods, and anything else it can catch. Arrow crabs, on the
other hand, have a distinct and nasty reputation for preying upon
more beneficial organisms like bristleworms. In fact, they are often
sold – correctly – for exactly this purpose. The problem with this is
that the worms are actually more beneficial and efficient detritus
consumers and the arrow crab will also prey upon other crustaceans,
molluscs, and most other living organisms smaller than itself.
Worms
Creepy, disgusting, ugly, and unsightly, these are all very
common description applied to worms. Perhaps you’re not aware of
those worms that remain more out of sight, those you rarely see, or
perhaps have mistaken for something else. There are two families of
worms that are commonly available, although usually most individuals
are brought in to our aquariums as hitchhikers, which fit the latter
description perfectly. The Terebellid, or spaghetti, worms are rock
and sand dwellers that are almost never seen in whole. They extend
their tentacles out across the substrate and consume particulate
organic matter, detritus. Cirratulid, or hair, worms are often mistaken
for Terebellids. The Cirratulids will mostly remain in sediment, almost
never venturing out of the sand, and filter organic particles within the
sand bed, passing them up, insuring that a sand bed stays turned.
And then it starts to get “creepy”. Amphinomid polychaetes,
what we aquarists refer to in the vernacular as bristleworms, are
perhaps the single best all around organisms in terms of keeping your
tank free of detritus, decaying matter, and leftover food. These
animals don’t discriminate. If it’s dead or dying, they’ll consume it.
Better yet, they’ll breed quite readily and maintain populations easily,
which will naturally wax and wane according to food availability. The
larvae, in turn, are also a rich protein source for fishes, which will
consume them. Yet, because of one, possibly two, species that will
potentially consume healthy corals, and possibly simply because of
their “ugliness”, this most desirable of reef scavengers is hunted,
trapped, and destroyed routinely. Many thousands of aquarists,
including myself, actually seek out and purchase these organisms
when we start a new tank. Consider wisely before you disregard their
inclusion in your reef aquarium. If a large fish should die while you
are away for the weekend, their presence may mean the life or death
of an entire tank.
The “Pods”
Collectively referred to as “pods”, minute crustaceans like
amphipods, copepods, Mysid shrimp and the like make up a
collective of detritus, algae, and excess consumers. They do more
than that for our reef aquaria, though. These organisms readily
reproduce in captivity and will make up the bulk of the naturally
occurring zooplankton in our tanks. For zooplankton feeders and
obligate grazers upon these crustaceans, like Mandarin dragonets,
their presence is beneficial to mandatory. Usually not available for
purchase in your local fish store, there are several sources online that
make these organisms available in “detritivores kits”. While they may
not accomplish as much as bristleworms in terms of keeping the tank
free of detritus, they benefits of a naturally occurring diet in the tank
can not be overlooked.
Shrimp
Sold in some packages, there are several shrimp commonly
available, none of which are very effective in a “janitorial” capacity.
However, there are some that are beneficial in other ways, and others
that can be harmful, so I have chosen to include them here. It would
probably be best to start with the cleaner shrimp of the genus
Lysmata. Found in tropical waters across the globe, the group of
species referred to as “skunk” or “striped” cleaner shrimp do serve as
cleaners, just not in the capacity to which this article refers. These
shrimp remove dead skin and scales and parasites from fishes and
are beneficial to the reef tank in this respect. The Stenopus spp. will
also perform this service, although not as readily, and will consume
detritus. However, the Stenopus spp. can be aggressive towards
other shrimp and crustaceans and will resort to predation upon other
beneficial organisms in the aquarium like the worms and “pods”
mentioned above. The peppermint shrimp species of the genus
Lysmata are also prized by many aquarists for their reported
consumption of the Aiptasia spp. pest anemones. My personal
experience with them in this respect is that their performance is
spotty at best. Peppermint shrimp have also been known to pick
apart cnidarian polyps to get at food, and I personally witnessed their
attacking and consuming healthy urchins and small sea stars. The
aquarist should be aware that there are other species sometimes sold
as, or in with the Lysmata spp. peppermint shrimp. These are the
hinge-backed or camel back shrimp of the genus Rhynchocinetes.
These shrimp are coral/polyp predators and can not be considered to
be even remotely reef safe.
Echinoderms
Popular for their behaviors and appearance, echinoderms are
collected and imported in massive numbers for use as cleaners, sand
turners, and ornamentals. More often than not, with the ornamental
species, like Linckia spp. and Fromia spp. sea stars, their dietary
needs are not met, not known, or not capable of being met. Any
Echinoderm additions should be considered wisely. Even if their
needs can be met, there are a variety of reasons why the aquarist
might want to exclude them.
Ubiquitous and, to some, pests, the Asterina spp. stars and
there like make their way into almost all of our tanks. Most species
seem to be detritivorous, thus beneficial. However, I have had
problems with them in the past. Because they are impossible to
identify down to a species level without DNA testing, they should be
watched closely. In my case, I have dozens, if not hundreds, in my
450 gallon reef that will make a bee-line for any Zoanthids, Acropora
spp., or Montipora spp. introduced. Although authorities on the
matter have insisted that such stars would be predatory on very
specific corals and die off outside the presence of the corals, I can
verify that this is not the case. This tank has been set up, in one form
or another, for over six years. The corals introduced are healthy at
the time of introduction, and the sea stars immediately head for them
within minutes of introduction.
Of the dozens of traditional sea star species that might be
considered, only one species can be maintained for reasonable
periods of time in our aquaria, Linckia multiflora. Although its dietary
needs are unknown, individuals can live for many years in captivity.
However, there is no basis or evidence to suggest that this species is
an adequate “cleaner”. It is important to mention two other collectives
here. The first, the sand-sifting stars, Astropecten spp. and Luidia
spp. are often sold for the purpose of keeping the sand bed clean.
Nothing could be further from the truth. These sea stars actually prey
upon the organisms that do keep sand beds cleared of detritus, and
they can quickly wipe out all such organisms in a sand bed. Of
course, without a food source, the sand-sifting sea stars then
eventually starve. The second, the Protoreaster spp., are possible to
maintain for long periods of time. Possibly well suited to fish only
tanks, they are not suitable for reef tanks where they have been
known to consume sessile invertebrates like corals and clams.
The brittle and serpent stars (vernacular designations only)
offer some more promising prospects in terms of keeping our tanks
clean. Again, the smaller species, those less than six inches in
diameter, will make their ways into our tanks at one point or another.
These “mini” brittle stars are mostly beneficial detritivores that will
readily reproduce, making them excellent animals to include. The
larger brittle star species should be included with caution. For the
most part, those with longer spines (Ophiarachna spp., Ophiocoma
spp.) are facultative predators and will catch and consume
crustaceans, and sometimes even fish, if there is not enough food
available – and sometimes even if there is enough food. Those brittle
stars with shorter spines, however, are mostly quite safe and
excellent detritivorous animals. These stars (Ophiolepis spp.,
Ophioderma spp.) are generally referred to as serpent stars.
While none of the aforementioned Echinoderms will graze
algae with any regularity, their cousins, the sea urchins, are mostly
herbivorous and excellent algae grazers. In fact, they are such
effective grazers that in recent years the decimation of urchin
populations in the Caribbean has been recently proven to have been
one of the primary causes, if not the primary cause, of algal
overgrowth on Caribbean reefs. There are some concerns when
keeping urchins, however. The first, and most obvious, is that they
are spiny, and that the aquarist must, therefore, use care and caution
when performing any maintenance in the tank. Because they are
relatively sedentary, the second concern may not be so obvious.
Urchins are not delicate or graceful movers by any means, but they
do move, and frequently. They are also quite strong and persistent in
their movements. I have had a one inch urchin, for instance, knock a
securely place spherical four inch rock off of the rock structure in the
tank. Care should be taken, when including urchins, to secure rocks
and corals. Of the urchins available, the long spined Diadema spp.
seem to be the most effective algae grazers. Some sea urchins are
potentially lethal to the aquarist. It is therefore suggested that only
the commonly available long-spined, pencil, and tuxedo urchins be
used and that the prettier and more ornamental urchins be avoided.
The last group of Echinoderms that many aquarists consider is
the sea cucumbers. It must be pointed out, before anything else is
said about them, that sea cucumbers have the potential to wipe out
an entire tank of fish. When stressed, for whatever reason, sea
cucumbers can, and do, eviscerate themselves in our aquaria. The
sand dwelling species such as the tiger tail sea cucumber (Holothuria
thomasi) and the common sea cucumber (Holothuria edulis) are
somewhat useful for keeping a sand bed stirred and clean. Ask
yourself this question first, though: Is there inclusion in your tank
important enough to risk the potential lethality to your fish?
Mixed Bag
There are several other odd species routinely available that
may serve as detritus and/or algae consumers in our aquaria. The
Enoplometopus spp. reef lobsters, while appearing dangerous, are
generally quite safe with other organisms in our aquaria as long as
there is enough food to meet their scavenging tendencies. Smaller
tanks, therefore, are not suited to housing this species in a mixed,
community environment.
Enticing in their oddity, horseshoe crabs lure many aquarists
into purchasing them. They are, however, exceedingly poor
candidates for our aquaria. The various genera and species all
consume living organisms in deep sand beds. A single individual
horseshoe crab can strip an entire sand bed of all life in a matter of
days, at which point it will slowly begin to starve to death. Many
species sold are not tropical, but subtropical, or even temperate.
And, while some tropical species do remain relatively small, most
species exceed a foot in length, some reaching or exceeding two
feet.
More closely related to snails than to the organisms mentioned
directly above, sea slugs deserve a separate discussion because
they are often just as misunderstood as the above creatures. The
primary problem with keeping sea slugs, including the drop-dead
gorgeous nudibranchs, is that each species consumes only one
particular type of food, for the most part. Several brightly colored
slugs are sold as “algae eaters”, including the flatworm predator
Chelidonura varians sea slug and the – mostly – spongivorous
Chromodorid spp. nudibranchs. Only the Elysia spp. sea slugs,
commonly sold as lettuce slugs, will consume algae, and this is
mostly limited to hair algae like Bryopsis spp. and Derbesia spp.
These slugs do not consume the algae fronds themselves, but suck
the contents from the algae. As with all other species we use to keep
our reefs “clean”, they will starve once a food source has run out.
Unlike other organisms, however, they are obligate feeders and, as
such, will not resort to consuming other foods. Be that as it may,
there is usually enough algae in a large tank, that does not contain
other consumers, to support a small number of individual Elysia spp.
I have even had the breed for three generations before the
introduction of a rabbitfish (Siganus unimaculatus) eliminated all food
sources. Other than the Elysia spp., the only suitable slugs for
marine aquaria are the sea hares. Mostly from the genus Aplysia,
these animals will consume most non-calcerous macroalgae with the
possible exception of Caulerpa spp. They are not truly reef
creatures, however, and the flow rates of reef tanks can be
detrimental to them. Additionally, their soft, fleshy bodies are often
irresistible to fishes and predatory crustaceans. The remaining sea
slugs feed upon organisms it is impossible for us to provide in
quantities sufficient to keep them alive (bryozoans, sponges, worms)
or consume organisms we would rather not have them consume.
Many sea slug species are obligate corallivores. One Cnidarian
consumer is gaining in popularity, however. This is Berghia
verrucicornis, an obligate predator of the pest anemones Aiptasia
spp. These tiny slugs will eliminate colonies of Aiptasia spp. fairly
quickly and, like their brethren, will starve once food sources become
low. As such, many aquarists intentionally culture Aiptasia spp. in
separate tanks for the express purpose of feeding Berghia
verrucicornis.