FISH
COELACANTH
The coelacanth (Latimeria chalumnae Smith,
1939) is one of the famous marine fish on Earth. Coelacanths are classic
examples of “living fossils” - organisms known initially as fossils, then
afterward discovered still living today. The first living coelacanth was
caught in 1938 offshore from southeastern Africa. Two modern species have
been described. Coelacanths were once hypothesized to be the fish group
transitional to the first tetrapods, but this is now known not to be the case.
Classification: Animalia, Chordata, Vertebrata, Sarcopterygii,
Coelacanthiformes, Coelacanthidae
Latimeria chalumnae (above & below) - the coelacanth (models).
Known distribution of the genus: Indian Ocean from South Africa to Indonesia.
Above:
CMC public display (Cincinnati Museum of Natural History and Science;
Cincinnati, Ohio, USA)
Below:
CMNH public display (CMNH, Cleveland Museum of Natural History, Cleveland,
Ohio, USA)
FRESHWATER ANGELFISH
This is not the “angelfish” that most people have
heard about. Most angelfish (or angels) are marine fish related to &
in the same family as the butterfly fish (Family Chaetodontidae). The
freshwater angelfish shown below is somewhat similar to the overall body form
of marine
angelfish.
This is Pterophyllum scalare, a cichlid fish
(Family Cichlidae). Cichlids are quite variable in body form, but Pterophyllum
is unusual even for a cichlid. Garden-variety fish have an elongated,
fusiform body (for example, tuna).
Pterophyllum has a laterally compressed and anteriorly-posteriorly
truncated body. Marine angelfish also have laterally compressed bodies,
but are less truncated. The body form of Pterophyllum is often
seen in fish inhabiting low-energy freshwater settings having moderately thick
aquatic vegetation.
Classification: Animalia, Chordata, Vertebrata, Osteichthyes,
Actinopterygii, Teleostei, Perciformes, Labroidei, Cichlidae
Pterophyllum scalare (Lichtenstein, 1823) (captives) from the Rio Negro
drainage basin, northern Brazil.
Some info. from Lagler et al. (1962) and Herald
(1962).
ARCHERFISH
The mostly brackish-water archerfish is famous
for its ability to shoot narrow streams of water from its mouth (see photo).
Archerfish do this to knock down potential prey (typically insects) from above
the air-water interface.
Classification: Animalia, Chordata, Vertebrata, Actinopterygii,
Neopterygii, Perciformes, Percoidei, Toxotidae
Toxotes jaculatrix (Pallas, 1767) (above & below) - the banded
archerfish (captives). Brackish water to freshwater to marine. Natural
distribution: SE Asia & Australia.
LARGESCALE FOUR-EYED FISH
Four-eyed fish (Anableps anableps) are some of
the more bizarre fish on Earth. This species inhabits freshwater to brackish
water settings in coastal northeastern South America. It typically hangs
out just below the air-water interface. While at the surface, its eyes
protrude from the water. Four-eyed fish eyes have pear-shaped lenses
& each eye is divided into two parts by a thin band of horizontal tissue
(each eye has two corneas and two retinas). The dorsal portion of each
eye can focus on & image objects in air (using the lower retina), while at
the same time the ventral portion of each eye can focus on & image objects
in the water (using the upper retina).
Four-eyed fish are live-bearers - they do not lay
eggs. External reproductive structures in male & female four-eyed
fish are remarkable for being asymmetrically directed. So, “left-handed
males” can only mate with “right-handed females” and vice-versa.
Published observations indicate that dextral males, dextral females, sinistral
males, and sinistral females are roughly evenly distributed in natural
populations.
Classification: Animalia, Chordata, Vertebrata, Osteichthyes,
Actinopterygii, Cyprinodontiformes, Cyprinodontoidei, Anablepidae
Anableps anableps (Linnaeus, 1758) (above & below) - largescale
four-eyed fish (captives) from the Paria Peninsula of coastal Venezuela.
Most info. from Herald (1962) & Lagler et al.
(1962) & the Newport Aquarium.
MEXICAN BLIND CAVEFISH
Many caves are known to have blind fish in
subterranean bodies of water. Members of several unrelated families have
become blind cavefish. Here’s the Mexican blind cavefish, Astyanax
fasciatus (sensu lato), which has been recorded from throughout
Central America. It completely lacks eyes (eyes are useless in a
permanently dark environment) and also has no pigmentation (hence the pinkish
color from blood). However, this species does still possess the genes for
eyes. Why? It’s ancestors did have eyes - they’ve been lost
through evolution. This is the ultimate fate for all vestigial
organs. However, the genes for lost structures are often retained for
long geologic intervals of time (for example, chickens still have genes that
code for teeth, despite the lack of teeth in chicken beaks).
New info. - recent published research has determined that young cavefish of this
species do have functioning eyes and have a light-sensitive area in
their brains. The eyes degenerate with ontogeny, as does the
light-sensitive area in the brain. The adults have zero light sensing
ability.
Classification: Animalia, Chordata, Vertebrata, Actinopterygii,
Cypriniformes, Characoidei, Characidae
Astyanax fasciatus (Cuvier, 1819) (or Astyanax mexicanus
(De Filippi, 1853), depending on one's taxonomic preferences) - the Mexican
blind cavefish (captives) from southern Mexico.
