Pufferfishes can inflate themselves by
swallowing water (never allow a pufferfish
to inflate with air!), which is when their
spines become most prominent. This
inflation is made possible by the presence
of a bulging sack in the intestine with very
thin and elastic sides. There are freshwater,
brackish, and fully marine species of puffers,
all sharing this ability to inflate and thus
make themselves look larger as a defense
mechanism when they feel threatened.
Another characteristic trait of pufferfish
are their large, protruding, mobile eyes.
Each eye can move independently of the
other, which allows the fish to monitor its
African elephantfishes and South American
knifefishes share the ability to generate
a weak electric current that helps them
navigate waters with poor visibility, find
food, and communicate with conspecifics.
The elephantfishes are intriguing and
definitely strange-looking fish from Africa,
with “trunks” protruding from their nose
area that inspired their common name. All
over the body, and especially around the
head and along the back, are a few hundred
electroreceptors, and electric organs located
at the caudal peduncle are capable of
generating electricity. These organs help
the fish navigate in darkness as they look
for food hidden in the muddy bottom and
also allow for intraspecific communication.
Elephantfish have poor eyesight, so they
forage mostly at night using electrolocation.
Knifefishes, such as South America’s black
ghost knifefish (Apteronotus albifrons) and
green knifefish (Eigenmannia virescens),
also possess multiple electric organs created
from transformed nerve tissue. They
generate a weak electric field that they use
in electronavigation and to look for prey
in water with poor visibility. All over the
body surface, from head to tail, there are
scattered many very sensitive, specialized
electroreceptors of two types: one type
detects changes in the high-frequency
electric field generated by the animal’s own
electric organs, while the other picks up
low-frequency signals generated by other
organisms in the water.
The world of aquarium fish holds a
dizzying variety of shapes, sizes, and colors,
and the specialized biological adaptations
many fish species have developed over time
just make them that much more fascinating
to watch and interact with through the
glass panes that are our windows into their
worlds. For whatever reason each arose,
these specializations contribute to making
fishkeeping a strange, wonderful, and ever-entertaining hobby. D
74 www.tfhmagazine.com Sep/Oct 2017
Carinotetraodon travancoricus, the Malabar pufferfish, may inflate its stomach with
water to appear larger when threatened.
The black ghost knifefish (Apteronotus albifrons) generates an electric field it uses to navigate
turbid waters and locate prey.