In this article I hope to refocus attention
on the Aeolid nudibranch Berghia as a species of interest
and value to the aquarium hobby. What little information exists
in popular hobby literature on the topic is indeed concise
and sufficient for guiding those intent on succeeding with
the culture of this organism. Yet, after more than 10 years
since its introduction to aquatic science, this utilitarian
sea slug eludes many willing commercial and private interests
of mariculture. I regard the still-diminished presence of
the animal in the trade to be an issue in need of address.
Among the traditionally difficult, if even possible to keep,
specialized members of the Aeolid nudibranchs, Berghia
are not only attractive, easy to keep, and easy to breed
but they also readily consume one of the most bothersome pest
organisms in marine aquaria: Aiptasia anemones (AKA
History and Overview
The genus Berghia is widely distributed
circumtropically in warm and temperate waters. The organism
that most people recognize and seek for Aiptasia control
is commonly identified as Berghia verrucicornis (A.
Costa, 1864). However, there seems to be some debate about
the number and name of species cited or held in regard under
this guise. Field pictures and observations of several specimens
called by this name throughout the Atlantic, Caribbean and
Mediterranean reflect not only variable color, but different
morphologies including contrasts between shapes of rhinophores
and cerata, the presence of tubercules and ridges or not,
and some differences seemingly in the structures of their
egg ribbons. It would not be surprising if more than one species
makes its way into the aquarium trade.
Another widely distributed Pacific Berghia,
B. major, also lives by the same modus operandi
of preying on Aiptasia. The most prevalent stock of
Aiptasia-eating nudibranchs in the American trade,
however, is heralded as having been collected from the Florida
Keys (east coast USA).
Berghia will often live closely associated with each
other and they
share meals quite peacefully.
Adult Berghia grow to about 1"
(25 mm), with some growing slightly larger. Their backs (dorsa)
are covered with handsome, colored, tassels known as cerata.
Cerata perform functions of respiration, digestion and defense.
Although this nudibranch consumes and utilizes the zooxanthellae
of its cnidarian prey, they cannot be sustained adequately
by the borrowed symbiosis with good lighting alone and they
must be fed Aiptasia several times weekly, if not daily
(adults can starve to death in mere days without Berghia).
With adequate supplies of anemones, however, Berghia
will be self-sustaining; that is to say, they will reproduce
and maintain a breeding colony. For their readiness to propagate,
inexhaustible demand from ongoing nuisance growths of Aiptasia
in overfed/overstocked aquaria, and their high dollar value
($10-$30 USD each), Berghia are highly desirable candidates
for the aquarium trade.
It is interesting and noteworthy to mention
that the reason Berghia are needed in the first place is both
ironic and avoidable. If aquarists would quarantine all new
livestock (not just fishes
but plants, algae, live rock,
sand, corals, etc.) and did not overstock or overfeed their
systems, then Aiptasia would be an almost unmentionable concern.
Nuisance anemones do not grow from thin air, or sterile water
as it were, but need food and nutrients to survive. When they
are not properly screened in quarantine, and then introduced
into a conducive aquarium system - only then do they proliferate.
The all-too- common realities of busy or neglectful aquarium
keepers are the things that Aiptasia thrive on: poor water
flow (less than 10-20X minimum turnover), which allows particulates
to accumulate and settle to feed anemones, overfeeding and/or
overstocking, poor lighting which allows pest Aiptasia to
outcompete more demanding and desirable organisms (like corals,
plants, macroalgae) for nutrients, and poor nutrient export
mechanisms (neglect of a well-tuned skimmer, weekly changes
of carbon/chemical filter media, frequent water exchanges,
etc.). Further compounding the problem, Aiptasia are naturally
prolific and successful in reproductive strategies. With adequate
light and food they multiply rapidly by budding and pedal
laceration. With inadequate light (even darkness!) they will
issue numerous asexual buds that drift with the purpose of
surviving elsewhere [note: imposing dark cycles is a way to
successfully exploit this anemone into producing smaller Aiptasia
to feed small Berghia in culture]. We may have to bow
with chagrin, but Aiptasia will continue to be an ever-present
inevitability in the aquarium trade, and Berghia are
direct solutions to this pest organism.
It is not uncommon to find Berghia patrolling the edges
of the water's surface.
Notice the very pale color of this Berghia that has
not fed on its favored
cnidarian prey in days. After a good meal, its cerata ripen
in size and
darken in color.
Right: The aftermath of a Berghia attack
is not pretty. Each Aiptasia preyed upon is usually
reduced in a matter of hours.
Left: Berghia become conspicuously stout
after a good meal with swollen cerata and a noticeably
inflated or elongated body. Although regarded as "photosynthetic"
for eating and utilizing the zooxanthellae of cnidarian
prey, Berghia cannot be sustained by illumination
alone. In culture, one must offer a regular, if not
continuous, supply of Aiptasia (several times
weekly, if not daily).
One of the biggest obstacles to the care
and culture of this sea slug has been their small adult size
and vulnerability to common aspects of aquarium filtration,
e.g. pumps, overflows, etc. Similarly, hatched juveniles cannot
be clearly seen with the unaided eye for many weeks' time
after hatching, perhaps up to two months. And subadults are
commonly shipped at ½" (12.5 mm) and are still
rather physically delicate to handle. For those receiving
shipped Berghia, please note that it is best to simply
sink the transport bag or cup into the new vessel for a gentle
acclimation of 15-20 minutes and then allow the sea slugs
to crawl out on their own volition. All of this is to be done
without illumination as a comfort to their nocturnal tendencies.
It should also go without saying that the
culturing vessels should be well-established with aged water
for some weeks in advance before seeking specimens. Newly
mixed seawater is harsh to many reef creatures
so to invertebrates. Also, do not underestimate the need to
have a significant supply of Aiptasia on hand; hundreds
of anemones will be needed to support a single pair of Berghia
for the first few months.
Any realistic plans for keeping Berghia
at any size will necessarily embrace a specialized system
at the start. I strongly recommend that all new Berghia
be acclimated in isolation. An appropriate home for them could
be as simple as a floating plastic cup or beaker, or something
as elaborate as a refugium. The pitfalls of the latter, however,
will likely include a pump or overflow at minimum. I recommend
glass beakers or plastic cups submerged partially in a temperature-controlled
aquarium. Note: it is critical to keep these containers tightly
covered to reduce evaporation, in which salinity can stray
quickly and fatally to the nudibranchs in such small volumes
Isolation gives these small creatures a
little bit of time to acclimate to the aquarist's water quality
and schedule of husbandry. Aquarists interested in culturing
Berghia must naturally engage this species in monospecific
culture. Others who seek only to reduce nuisance populations
of Aiptasia in another system or display will still want to
isolate new Berghia at first to give them a good start. Small
rocks covered with Aiptasia can be placed in the culturing
vessels for the first few weeks until Berghia become established.
Placing newly purchased Berghia directly into a
display tank is not recommended - they will almost certainly
die or be killed by any one of a number of pitfalls in the
aquarium before they completely eradicate plague Aiptasia
The bane of many aquarists: nuisance Aiptasia anemones,
which can reach plague proportions in aquaria.
Many common community fishes and invertebrates
will damage or eat small "nudis" out of curiosity
if they are simply dropped into an aquarium. There is also
the concern that they will fall to the perils of high water
flow, and the aforementioned pitfalls of pump intakes, overflows,
etc., before they can establish themselves and breed. Considering
how expensive they are to acquire, it only seems sensible
to provide them a good start in isolation; a mere matter of
days or couple of weeks is all that it takes to collect egg
masses from active breeders. A little patience with quarantined
Berghia in this case can easily translate into tens or hundreds
of propagated nudibranchs to fight the Aiptasia battle for
which they were purchased.
In light of all of this, the relationship
between Aiptasia and Berghia begs a question that Eric Borneman
(1998) and others have raised on the subject before, "Can
we expect Berghia to completely decimate populations of Aiptasia
in our aquariums and if so, what happens to the nudibranchs
when they do?" It's a matter of inverse predator-prey
relationship: Berghia flourish (population goes up) while
consuming Aiptasia (population goes down) and then high densities
of Berghia can no longer be supported and crash (population
goes down) while Aiptasia recover (population goes up). The
dynamic is played out in countless ways throughout the living
world between other organisms in predator-prey relationships.
Recent studies, for example, have claimed to dispel the remarkable
natural phenomenon of cyclical die-offs of rodent lemmings
by this "boom or bust" population rhythm. The sometimes-sudden
(100-1000-fold) expansions in lemming populations are intimately
linked to the numbers of four specific predators, one of which
(the stoat) is key as they prey upon the rodent to exclusion
among possible prey, like Berghia do upon Aiptasia.
An infinite supply of Berghia in any display
is not assured, or even likely, without assistance from the
keeper. A spike of prey, then spike of predator, then drop
in prey, and subsequently a drop in the numbers of predators
can be expected. Unlike wild habitats, however, the home aquarium
is not a balanced ecosystem and we cannot expect that some
Berghia will always weather the cycle. As such, I cannot repeat
and recommend strongly enough the importance of the need for
maintaining broodstock of Berghia even for aquarists that
merely wish to control Aiptasia in a display (versus culture
the nudibranchs). Neglect of this admonition would be a waste
of a living resource and, at best, require that the keeper
repeatedly buy Berghia with the "boom and bust"
cycles of prey over time to control their pest anemones.
A culturing system for Berghia is inexpensive and simple.
use beakers or floating plastic cups with gentle aeration
to keep adults.
Be mindful to control evaporation in these small vessels,
cups are uncovered in this picture, but must be tightly capped
prevent fatal salinity increases due to evaporation.
Most anyone with experience culturing Berghia
will recommend the same thing regarding housing: it's best
and easiest to grow these sea slugs in small cups or beakers
(250-1000 ml). The challenges of concentrating, feeding and
locating such tiny organisms in even the smallest aquaria
otherwise are daunting. Plastic cups floating in thermostatically
controlled aquariums seem to work very well for this purpose.
Rods, pipes, or lines can be used to cordon off the floating
vessels at the surface so that they don't bump around or capsize
in the display. All containers resting on a submerged PVC
"table" is better still. Water quality can be a
bit of a challenge in small cups due to evaporation, so its
important to mark the sides of the cups or beaker with a line
to indicate where to top off the vessel with distilled or
RO/DI water to compensate for evaporation. Keeping lids or
covers on culturing vessels will also be very helpful for
slowing evaporation and the resulting stress caused by fluctuating
salinities. Frequent water changes will also insure optimal
water quality (several times weekly for adults). The culture
of Berghia in this manner is really quite easy and straightforward,
but is admittedly tedious and indeed a part of the final price
of the creature for the inconvenience of husbandry. Small
lengths of flexible airline tubing and plastic or glass pipettes
are handy for conducting water exchanges, removing debris/feces,
and for transporting small Aiptasia between cups. In preparation
for the arrival of Berghia, place a couple of Aiptasia in
each of the cups that will hold the beloved Aeolid specimens.
Be warned though that it is quite possible to have too many
Aiptasia in a cup; they will compete for desirable elements
in the water, and they can slough copious amounts of slime
or mucus and degrade water quality. It's also best to let
Berghia prey on just one or two anemones at a time in small
cups or beakers for the obvious reasons (water quality).
Be mindful that vessels, instruments, hands
and anything else that comes into contact with live Berghia
are clean and free of contaminants. Nudibranchs, like many
invertebrates, can be very sensitive to small concentrations
of foreign substances and may suffer great morbidity or mortality
from exposure to these substances. It's easy to overlook potentially
fatal toxins like matter that might be under one's fingernails
or on the hands, adhesives on equipment (e.g., glue left behind
from the peeled price tag on a bit of submerged tubing), residues
from used cups, or residual cleaning products on towels used
near the culture system (transferred onto dried hands, or
dipped into the water by accident). Larvae are particularly
sensitive to these types of contamination. The rule here should
be to cleanse hands and objects of the system thoroughly in
pure freshwater only (de-ionized, if possible). Water changes
on vessels with adults can simply be done by wiping out the
walls of the containers and pouring off the old water before
gently tipping in seawater from the tank of healthy aquarium
water in which the culture cups float. After a pair spawns,
it's usually best to remove the breeders to a new cup and
leave the eggs undisturbed. Take note of the spawning date
to track the progress of the egg mass(es) for hatching predictions
Be very careful to use clean hands and clean instruments
when working with Berghia - this small invertebrate
in a small volume of water can be very sensitive to
contaminants like soap from hands and towels, or adhesives
from stickers or price tags on recently purchased equipment.
Culturing Aiptasia anemones?
it sounds as funny to me writing
it as it does to you reading it perhaps. But nonetheless,
culturing Berghia will require an address of producing a consistent
and adequate supply of food-Aiptasia. A novel way of producing
small Aiptasia is to keep a broodstock population of the pest
anemones in the dark for some weeks/months to produce tiny
asexual buds. Feeding the anemones during this time will be
necessary in the absence of light. Like many cnidarians, Aiptasia
can be maintained under inadequate illumination by compensating
with extra food. In overrun displays, it is this very thing
that is the catalyst for plague populations of the anemone:
excess nutrients. As many aquarists know, it does not take
much for illuminated and fed Aiptasia to proliferate. They
can also be propagated by way of simple division
rather, laceration. No doubt, they are challenging to eradicate
from display aquaria and attempts at scraping or rasping them
off the rocks has often met with dismal results as the effort
only increases the numbers of Aiptasia for the buds formed
by residual pedal tissue. Aquarists interested in culturing
Berghia will inevitably want to set up a tank for co-culturing
food -Aiptasia- for a controlled and reliable source of prey
Berghia reach sexual maturity early (at
approximately 12mm) - long before they achieve full adult
size. Eggs are laid in a characteristically spiral egg-casing
fashion. Spawns may be deposited on or underneath a rock,
if available, but can be found conspicuously on the aquarium
or container walls just the same. Occasionally, the egg masses
will be released in free-floating strands (often so, if they
are disturbed while egg-laying). Reproductive events can be
amazingly frequent at times with well-fed and well-conditioned
young adults, occurring at a frequency of one egg ribbon laid
every one to two days - per individual! Older specimens naturally
slow down and are less prolific. It is possible to start with
one pair of Berghia and have a couple hundred individuals
in just a month or two. As you can imagine, the need to provide
adequate supplies of Aiptasia to feed such colonies soon turns
your problem from an Aiptasia plague to a Berghia plague!
Fortunately, Berghia are so highly prized that it is not difficult
at all to find wanting and waiting homes for your surplus
juveniles through local channels or online. In kind, it is
not difficult to find fellow aquarists locally with Aiptasia
covered live rocks to share. Recruiting food for your Berghia
may be as simple as exchanging clean rocks for anemone covered
rocks pound for pound with other aquarists delighted to get
rid of their nuisance anemones. Nonetheless
of Aiptasia is still necessary as a more reliable means of
insuring adequate food supplies for the Aeolid.
A freshly laid Berghia spawn has a crisp and clean
with clearly distinguished tiny eggs within the strand.
Berghia are truly ideal and profitable
specimens for the cottage industry of reef invertebrate reproduction.
Which brings us to another wonderful aspect of this Aeolid's
anatomy - they are hermaphrodites, which spawn reciprocally
and take turns fertilizing each other eggs. (note:
self-fertilization and fission are rare by comparison). Courtship
is a conspicuous dance (OK
a slow dance) with two individuals
in a spiral "embrace." If you think it looks like
your mating pair are necking, you are not mistaken. The genital
openings on Berghia are on their right side (notice their
right-side aligned positions in the images) just behind the
rhinophores (dorsal tentacles). Their heads must be very close
together for the successful alignment of copulatory apparatus.
This series of three images shows the characteristic circular
courtship that leads to the (usually)
reciprocal genetic intromission of
gametes between Berghia. Genital openings are near
the head on the
right side of this
Aeolid, just behind the rhinophores/cephalic tentacles.
The larvae of B. verrucicornis are
metamorphosis occurs soon after hatching, which makes aquarium
culture much easier than species with extended larval stages.
In layman's terms: hatched larvae do not have a long or complicated
stage or series of stages of development as plankton, but
are non-feeding and settle out to the seafloor rather quickly
to begin feedings like adults, in a matter of days. As such,
the aquarist is spared the tedious co-culture of specific
larval foods like with so many other reef organisms that have
feeding planktonic stages. Very small Berghia simply eat very
small Aiptasia - or, at least, they will develop faster and
easier in captive culture if spared the monumental task of
wrestling large, oversized Aiptasia once they begin to feed.
Make no mistake, this predatory sea slug can, in fact, be
prey for Aiptasia in some circumstances such as poor acclimation
techniques where Berghia are poured into the aquarium and
dropped into the open and waiting tentacles of a hungry anemone!
Young Berghia forced to contend with oversized Aiptasia may
even be observed to pull back, as if rebuffed, on an approach
to the anemone and may consequently decline a feeding opportunity.
To the aquarist's further advantage, larval
Berghia hatched in un-aerated vessels may navigate
the planktonic stage and settle out faster to begin feeding
on anemones. My limited experience rearing hundreds of these
nudibranchs does not yet dispute this theory, and I'm eager
to examine the issue more closely in time. At least one reference
cites excessive aeration of egg-bearing containers as an impediment
to proper embryonic development. At any rate, rest assured
that adults and egg masses alike need little or no aeration
when water quality is kept well via regular water changes
and due diligence with evaporation compensation.
Berghia eggs begin to hatch after approximately 10-14
days. They take
on a milky or hazy appearance at that time which may be used
indicator for opportunities to artificially hatch them with
motion of a pipette.
Egg ribbons will hatch in 10-14 days depending
on temperature (a range of 76-79° F/ 24-26° C is recommended).
It will be some weeks before the juveniles can actually be
seen with the naked eye - about two months, in fact. Nonetheless,
keep small Aiptasia in the culturing vessel and observe
the decline of the hardy anemones as evidence of predation.
It may be helpful to artificially hatch the egg capsules by
"pumping" them into and out of a pipette repeatedly.
The rasping motion will rupture the casing and liberate the
larvae. It's difficult to say exactly when is best to conduct
an artificial hatch in this manner. After some time and experience
though, the aquarist will notice that after 9 or 10 days,
the egg's casing takes on a milky or hazy appearance with
embryonic development and growth (versus the crisp and clear
appearance on day-one with tiny "dots" in it).
A soft plastic pipette is indispensable for Berghia
culture. It is used to slurp detritus and debris from
inside a cup, rasp eggs for artificial hatching and
to conduct small water changes.
One of the biggest obstacles to rearing
Berghia, as mentioned before, is providing enough Aiptasia
of suitable size. The failure of juveniles to develop cerata
is often attributed to attempts to feed anemones that are
too large for juvenile Berghia to successfully attack. Lacerated
adult anemones may be helpful in the absence of an adequate
supply of small Aiptasia. Nicking, notching or shredding the
pedal base of feed-anemones opens the door, so to speak, for
tiny Berghia to begin feeding, as well as facilitates reproduction
by pedal laceration with any tissue left alone long enough
Note: it is a common and potentially fatal
error by breeders of Berghia to sell offspring that are too
young and too small. I have seen cultured specimens sold so
small that half a dozen could fit on the tip of a pencil eraser
some are even sold without well-developed cerata! This practice
is both poor business and poor husbandry. The aquarist is
advised to simply stall the launch of his sales/business/trade
in cultured Berghia by as many weeks as necessary for proffering
larger and more stable specimens. I recommend shipping at
10-12mm minimum size.
Please be sure to explore the references
listed in the bibliography of this article for further insight
and perspective on the genus Berghia for aquaria.
*Anthony Calfo is the author of
the "Book of Coral Propagation" (2001) and co-author
of the Natural Marine Aquarium series with Robert Fenner [vol.
1 - "Reef Invertebrates" (2003)]. He can be reached
daily at WetWebMedia.com
via the "Ask the Crew a Question" link, or by the
contacts listed on ReadingTrees.com
for book sales and information and also at the author's forum
for ReefKeeping e-zine at ReefCentral.com.