The baby whale Pollimyrus isidori is actually a mormyrid, one of a
group of nocturnal African fishes that are known for generating weak
electrical fields in their immediate vicinity.
The baby whale you saw for sale was most likely a
Pollimyrus species, possibly Pollimyrus isidori. This
genus is part of the family Mormyridae, which also
includes the elephantnose fishes, Gnathonemus and
Campylomormyrus spp. In fact, for all intents and purposes, P.
isidori and other members of its genus look like elephantnoses, minus
the long snout.
Pollimyrus spp. are collected from turbid African rivers and, in common
with other mormyrids, produce a weak electrical field that allows them
to sense their environment, locate food, and communicate with others
of their kind in murky waters. They are nocturnal fishes, and their diet
consists primarily of small aquatic invertebrates and insect larvae.
In the aquarium, Pollimyrus spp. prefer subdued lighting and ample
hiding places. Heavy plantings and a tangle of driftwood would make
an excellent choice for aquascaping. These fishes tend to root around
the river bottom in search of food, so a sandy substrate is best. Water
chemistry should be neutral to slightly acidic, with low to medium
hardness. They’re not especially demanding in this regard, provided that
extremes are avoided. However, they will not tolerate a high level of
Though these mormyrids tend to school in nature, they are best kept one
to a tank in a single-species aquarium in order to prevent squabbling. A
good minimum tank size for a single specimen is in the range of 20 to 30
gallons. In very large systems, it is possible to keep a small group of them.
It is sometimes challenging to wean Pollimyrus spp. off live foods,
but they can usually be taught to accept thawed frozen items, such as
mysid shrimp and bloodworms. Offer foods just after lights-out in the
vicinity of the specimen’s usual hiding place.
Cleaning Aquarium Gravel
I’m brand new to the aquarium hobby, so you’ll have
to forgive me if this sounds like a silly question. My
20-gallon tank has been running for about three
months now, and I’m starting to see quite a buildup of gunk in the
gravel. How do I eliminate this? Do you recommend pulling out the
gravel and rinsing it under tap water to prevent this buildup?
Bismarck, North Dakota
Welcome to the hobby, and please don’t feel silly for asking
an honest question! No doubt other newcomers have the
same question on their minds but are afraid to ask. I
would not advise rinsing your gravel under tap water, as
doing so would wipe out many of the beneficial bacteria that make up
your aquarium’s biological filter. Remember, you need thriving colonies
of so-called nitrifying bacteria in your aquarium to convert ammonia
to nitrite and then convert the nitrite to nitrate. If large numbers of
these bacteria are suddenly removed, your system will experience a
major ammonia spike, which will prove deadly to your fish.
To eliminate the buildup of gunk—more accurately, detritus—from
your substrate, you should vacuum the gravel during each water
change. A gravel vacuum, essentially a narrow, flexible siphon tube
with a wider, rigid tube at the end of it, can be purchased for a very
modest price at any aquarium store and is very easy to use. All you
have to do is start the water flowing through the siphon tube and then
insert the wider vacuum end into the gravel bed at different points to
suck out the detritus.
Oh, and please don’t suck on the end of the tube to get the siphon
started. Not only is that unsanitary, but it’s also completely unnecessary.
Instead, position the vacuum over the aquarium with the open end
facing up. Place the narrow end of the siphon tube in a bucket below the
level of the tank. Next, lower the vacuum into the aquarium and allow it
to fill with water. Then, raise the vacuum (with the open end still facing
up) above the water surface and allow the water to just begin flowing
down into the bucket. Before all of the water drains from the vacuum
end, lower it back into the water. This will create a continuous siphon,
and you can then start vacuuming the gravel. It may take a few tries at
first, but you’ll soon get the hang of this technique.
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