own species, it’s recommended that only
one toadfish be kept to each aquarium.
In large aquariums, or those that provide
a very high number of hiding places and
visual barriers, more than one toadfish can
usually be kept together.
Toadfishes tend to ignore tankmates that
are too large to swallow. However, several
keepers have reported that their toadfish’s
aggressiveness increased as the specimens
got older and larger. As male toadfishes
become sexually mature, their interests can
shift from food to finding a mate, possibly
resulting in a heightened aggression level.
This may become more evident on a
Typical aggression maneuvers employed
by toadfishes may include a gaping mouth
that is occasionally snapped shut, flattening
of the head, full fin extension, shuddering,
and even a full-force ramming with their
mouths open to intruders. Contact is
usually not made, but when it is, the
resulting bite may be very dangerous to
the victim, and in some cases may result in
their death. To be on the safe side, utilize
tankmates that are more prone to stay in
the open and not battle for bottom space
with a toadfish.
The leopard toadfish Opsanus pardus.
Aside from their good looks, toadfishes
have a fantastic ability to tolerate horribly
polluted waters that many other fishes
could not survive in. Obviously then, water
quality is not very much of an issue.
While doing research on striped bass
Morone saxatilis in Delaware Bay, New
Jersey, I observed oyster toadfish O. tau in
some of the muddiest and most inhospitable
waters of the area. They seem to thrive in
and around docks and marinas, sewage
pipes, runoff areas from highways, and
other areas that you would not think to
find fishes—let alone want to wade around
looking for them!
The oyster toadfish Opsanus tau is the largest-growing member of the genus, as well as one
of the most aggressive.
indiscriminate with respect to what it
zaps. Good, bad, ugly, indifferent…it kills
it all. Newly set-up aquaria need to become
stable before UV sterilizers are used.
Regarding medication and toadfishes,
consult a veterinarian or experienced
marine aquarist, since that topic is beyond
the scope of this brief overview.
The best disease treatment is simple:
prevention. While opsanus generally are not
bothered by nasty water conditions, they
can fall victim surprisingly fast to a host
of external parasitic diseases. Marine ich,
more appropriately called Cryptocaryon,
is a killer to toadfishes, as is dwarf ich
Oodinium. These parasites usually attack
the fins first, then the body, and finally
the gills, which is where the bulk of the
damage is done. To further complicate
matters, toadfishes are very sensitive to
strong medications for such ailments.
This is perhaps where nature has
intervened, however, as one method stands
above all others in preventing and treating
parasitic infestations on toadfishes—
In aquariums containing a single
opsanus, or even a group of them, the
salinity can be altered 5 or 6 ppm in either
direction with each water change, which
should be weekly or bi-weekly (at the
very least) since these fishes tend to be
messy eaters and can foul their water very
quickly. With salinity alteration I have had
good success in keeping parasites from
taking hold of the fish. Unlike fishes, with
their highly adaptive capabilities, parasites
need a more stable environment in which
In aquariums that are more traditional
communities, salinity alteration is less
likely to be an option, especially if there
are reef species incorporated into the mix.
Reef fishes tend to do poorly in fluctuating
environments, and therefore salinity
alteration becomes more problematic for
other tank inhabitants.
In this case, the use of a good ultraviolet
sterilizer in combination with a generally
low specific gravity ( 1.020, for example)
seems to work well. Understand that
UV sterilization is best utilized on
mature, “balanced” aquariums, as it’s
Catalog of Species
Currently there are six valid species of
Opsanus. None are considered common
in the aquarium trade. This is true for
various reasons. First, opsanus are not the
most colorful fishes. Second, they tend to
be a bit on the feisty side—but they don’t
usually harass tankmates too much, unless
they try to steal the toadfish’s hiding spot.