WFSC 448 – Fish Ecophysiology
(Week 8 – 21 Oct 2015)
Major point: Physical and chemical properties of water dominate lives of
aquatic organisms in ways largely alien to terrestrial vertebrates
Imagine for terrestrial vertebrates all the feeding modes of which you can think.
List them:
Suction, raptorial, spearing, crevice invaders, blood feeding, winnowing,
echolocation…
Which work or don’t work in the aquatic environment? Are constraints in each
case due to environment per se (lack of functionally equivalent niche), lack of preadaptations in fish, or the physical properties of water?
What is missing from the list (i.e. what do fish do that terrestrial mammals don’t?)
Examine diversity in a fairly conserved family (Cichlidae):
http://malawicichlids.com/mw01100.htm
Examine diversity (and convergences) in distantly related (evolutionarily less
constrained) taxa:
http://www.dep.state.fl.us/secretary/ed/life/apalachicola/files/fish_adaptations_boat.pdf (last page)
Questions to ask—how is the mouth powered internally and how does it work—
protrusible lips, suction gap fillers, fleshy or bony lips, mouth size, what integration
is evident with rest of body (e.g. eyes, gut, locomotory apparatuses), etc.
This type of exercise is useful in any field (car mechanic, human health, etc.).
Four-bar linkages –engineering bliss
http://en.wikipedia.org/wiki/Four-bar_linkage
Here is a vid of the SA cichlid Petenia splendida: Link
Jaw anatomy and function is well understood in fish feeding, but this is only the
entry point of food. There is a whole train of organs after that whose functions are
both mechanical and physiological per se.
Keep in mind we typically speak in general terms regarding fish eco-phys and ecomorph. Much important detail exists but may be poorly understood, even for
critically important things like ontogenetic development and niche shifts, breadth
and constraints of inducibility, etc.
Here is my adaptation of information from an educational website (Earthlife.net),
following the food path in order:
Mouth  Pharynx  Esophagus  [Gizzard]  [Stomach]  Intestines  Rectum
Many Cyprinids and Cyprinidonts lack a stomach, while gizzards are found in relatively few
species (e.g. mullet, gizzard shad)
The Mouth
Four bar linkages aside, note that the mouth can process food and secrete
lubricatory mucous (no saliva glands). Food processing is done with teeth. Fish
who capture large elusive prey on the run often have needle-like teeth on
elongate jaws (barracuda, gar) for grasping prey. Fish who bite food off larger
structures have teeth that are knife-like (shark, piranha) or chisel-like (triggerfish).
Biofilm scrapers have villose “lips” (e.g. mollies, plecostomus). Detritivores often
have fleshy lips. Some fish have molar-like teeth or bony/toothy plates in their
palate area (drums, many African cichlids, sheepshead) for crushing hard prey.
The tongue of fish is generally simple as food movement
is mostly a matter of moving with water passed through
the oral cavity. An exception is that the Agnatha have
toothy keratinized tongues used to rasp flesh from living
or dead prey.
Directly from Earthnet:
“The teeth of Elasmobranchs are simply embedded in the gum, and not attached to
the cartilage that supports the jaw. In fish there is a continuum stretching from the
Paddlefish Polyodon spathula where the teeth are embedded in the gums and not
connected to the jaw bones at all through a few species like the Pike (Esox lucius)
wherein the teeth are loosely attached to the jaws by means of fibrous ligaments to
the majority of fish which have the teeth ankylosed, or tightly and immovably
bound by fibrous tissue, to the bones of the jaws etc. In a few species of the
Characidae the teeth are implanted in special sockets of the jaw bones.”
Belonesox © Thomas J. DeWitt
Pharynx
The pharynx is the entry to the esophagus and contains the gills, which open to the
exterior surface. Gills we discussed regarding respiration but they have been
coopted for several feeding functions. Gill filaments often serve to filter small
plankton like pelagic alga from the water passing (e.g. crappie, shad). Or the bony
arches may have projections called rakers used for filtering generally larger
plankton like zooplankton (bluegill) or winnowing invertebrates from sediment
(geophagus ciclids). Often raker projectsions are modified into teeth, creating a
pharyngeal mill (redear sunfish). Finally sometimes the jaw is “build backwards) in
that a vertical pharyngeal mill (like our mouth) is present backwards in the back of
the throat (many african cichlids; see x-ray of Astatoreochromis alluaudi.
Astatoreochromis alluaudi © Thomas J. DeWitt
Some species of fish fold gill rakers down to allow large prey to pass and then back
to imprison the prey.
Esophagus
The esophagus is a muscular tube that passes food to the gizzard, if there is one, or
the stomach, if there is one, else to the intestines. Muscular contraction and
mucous secretion keep food moving.
Gizzard
The gizzard is a highly muscular modification of the first part of the stomach. It
grinds coarse food into smaller pieces which due to increased surface area per
mass facilitates enzymatic and ehcmical breakdown in the stomach and intestines.
The gizzard begins secretion of digestive enzymes into the food.
The Stomach
Fish stomachs are often not well defined (compared to ours, for example) and in
some cases are so poorly delineated we consider it absent. A stomach is where
bulky items are held, above the pyloric valve, to be broken down with localized
heavy muscular, enzymatic and acid activity. Small particulate food is generally
digested in the intestinal run. Herbivores tend to have reduced stomachs and very
long intestines, often several times the length of the body (stonerollers),
sometimes arranged as a spiral (paddlefish, lungfish, lamprey). Many fish
(perches, mackerel) also have pyloric caeca which are finger-like projections at the
rear of the stomach that increase surface area for nutrient absorption.
Rectum
In some ancient fishes (lungfish, sharks) the rectum opens into a cloaca which also
receives wastes (urine) from the kidneys and reproductive cells and secretions. In
bony fish the rectum leads to the anus, which normally occurs just anterior to the
urinary and reproductive openings. In some fish the anus evolved an anterior
location (electric eel, pirate perch). Sidebar: Although in mammals urogenital
openings pass nitrogenous wastes harvested by the kidneys, fish usually convert
nitrogenous wastes into ammonia, 80-90 % of which is dealt with by ion exchange
in the gills. Many herbivorous and omnivorous fish derive nutrients from the
activity of gut microbes such as single-celled archaea, bacteria and fungi that feed
on cellulose and other plant products difficult for animal digestion to deal with.
Enzyme organs (pancreas, liver, gall bladder)
The pancreas is well developed in lungfish, sharks and rays and most juvenile fish.
In teleosts, typically, the organ becomes reduced and diffuse during ontogeny. In
sharks and rays it is distinct from the liver, but in those teleosts wherein it is found
it is often partially embedded in the liver. The pancreas secretes enzymes such as
trypsin (attacks proteins), amylases (attack carbohydrates) and lipases (attack fats)
into the intestines either through sharing one of the hepatic ducts (those
belonging to the liver), or through its own pancreatic duct.
The liver is a large organ that play various roles in the fishes body. Relevant to the
current discussion it produces enzymes that aid digestion. The gall bladder is
usually found somewhere within the liver, it secretes substances that attack fats
and help them to be broken down. The liver always has at least one, and
sometimes as many as eight ducts leading into the first part of the intestines. In
many cases the pancreas will share one of these ducts.
Reading for Wednesday: http://www.biomedcentral.com/content/pdf/1471-214813-277.pdf
Creativity exercises…
Morrison & co. show that anthropogenic noise reduces nesting success in chirpetty
chirpescent warblers. Why?
Imagine something like that in fish… discuss
Plants produce chemicals toxic to other species of plant. Why?
Imagine something like that in fish… discuss
Chimps eat fuzzy leaves when their stomachs are upset. Why?
Brits drink tea like fish drink water. Hmmm…
Female fish often prefer to mate with males who have eggs already. How can
males evolve to take advantage of this fact? Keep going until you have something
really worthy.
Try one of your own—transfer concepts from radically different concept—can be
anything—I tend to draw mine from other domains in biology, but you can take
anthropomophic interpretations from daily activities and turn it into something
cool and likely to exist in fish ecology.
Consider our local shad species, which often co-occur.
(image from source)
Why would you expect two closely related congeners to not co-occur? How might
these fish do it?