A stingray is depicted with his shark friend from Little Ray & Shark Patch Things Up and displayed at 50% of viewport width.
July 2020 by Terry Verduin

FISHY FISH: WHAT ARE CARTILAGINOUS FISH?

Sometimes when we trip or fumble,
teamwork may just stop our stumble.
That's why we must always show respect
to help that comes as we least expect.
(Little Ray & Shark Patch Things Up)

Fishy Fish Differences

Fishy Fish? Discover differences between stingrays, manta rays and sharks. Chondrichthyes, or cartilaginous fish, have no bones, have no swim bladders and may have no scales or teeth. They are fish, but quite unlike other fish.

Stingrays & Manta Rays & Sharks

Amazing Powers? The speed, abilities and traits of fish motivated scientists and engineers to develop submarines, robots and water-proof equipment. Tapping into mind-blowing fish abilities benefits all human beings.


Cartilaginous Fish? The Elasmobranchii subclass of Chondrichthyes made of cartilage includes rays, sharks, skates and sawfish. Human babies begin life with more cartilage than adults. Bone will replace much of it.


From the Same Cloth? Cartilage shapes Elasmobranchs. They have no bones to provide form. Cartilage breaks and wears out. It may not repair. Distinguishing features of each Pancake Shark make them seem unrelated.

Vertebrates

Backbone? Although their skeletal system is made of cartilage rather than bone, sharks and rays are classified as vertebrates. They have spinal columns and spinal cords. They have no rib cages.


Ancient Times? Elasmobranchs date back hundreds of millions of years. Their cartilaginous endoskeletons do not fossilize like bones. Findings of fossilized teeth show small evolutionary changes across the ages.


Jaw-less fish? Lampreys and hagfish have no jaws, no fins, no scales and no stomachs. Hagfish are not a true vertebrate. They have a skull but no spine. Both of these primitive fish have muscular mouths and rows of teeth.

Aging

Age scales? Some bony fish develop yearly scale rings, like tree trunks. Counts give rough age estimates. NOAA SWFSC researchers age Elasmobranchs by counting concentric calcified bands in the vertebra.


Earrings? Elasmobranchs have no otoliths. Bony fish have these ring-like inner ear bones. The ring development matches seasonal changes. Like tree-ring dating, scientists can examine and count the rings to determine age.


Stunted Growth? Unless water conditions and food supply are poor, fish continue growing until they die. After the age of sexual maturity, this growth slows. It is difficult to age fish by size, due to differences between species.

Long History

Dating Game? Scientists use radiocarbon dating to estimate the age of organic matter. It measures the remaining Carbon-14, or radiocarbon, a naturally-occurring radioactive isotope. Accuracy can be within decades.


Eyeballing It? The carbon level of eye lenses does not break down over time. The accuracy of age calculations improves when carbon measures of this organ are taken from dead or fatally-injured by-catch after euthanasia.


Stretching It? Revisions of the calibration curve associating radiocarbon years to calendar years estimate the actual age of an organism. Whatever its age, the Greenland Shark likely remains the longest-lived vertebrate.

Scales

In Full Bloom? Many Elasmobranch species sport denticles, classed as placoid scales. This tooth material with enamel coating, extends from the dermal, or middle skin layer. Electric rays and manta rays have no scales.


It All Stacks Up? Denticles differ among Elasmobranchs. Fish scales grow with the fish. Denticles stop growing. At a certain size, new ones fill the empty spaces. The pattern is regular in sharks, but irregular in stingrays.


Right Confections? Sharklet Technologies, Inc. invented denticle-like plastic medical wraps to repel germs. The CDC warns about water contamination and waterborne illness in Healthy Pets, Healthy People.

Respiration

Back from the Future? Fish largely breathe with gills. Gill arches hold them in place. Human embryos have gill-like parts. Amphibians, crustaceans and mollusks have gills. Land or water insects and spiders also have them.


Ancestral Lungs? Like lung air sacs, gills provide an interface between the oxygen and blood. It is unknown if fish gills evolved from ancient lungs, or if they evolved into lungs used for breathing air. Early fish had both.


Operculum? Elasmobranchii lack this hard, plate-like, bony gill covering. It protects the gills of bony fish and helps them pump water over their gills for respiration. Mollusks and snails also may have opercula, or operculums.

Auto-Pilot

One-Way? Water exits, but it cannot enter gills. Oxygen enters the bloodstream via capillaries. Sharks, stingrays and manta rays breathe unlike the fish majority. Fishy fish can pull water by mouth over their gill slits.


Trademark? The large number of gill slit openings in cartilaginous fish is unique. Five to seven pairs of gill slits are on both sides of their heads. From four embryonic gill slits, bony fish develop a single gill opening on each side.


Gas Exchange? Few fish need to think to breathe. Gas exchange occurs passively and automatically as they swim. Their gill muscles power oxygen intake. Gases pass into the blood stream. Carbon dioxide seeps out.

Deep Breath

Oxygen Boost? Bottom sharks, stingrays and electric rays have supplemental spiracle breathing holes. These external openings bypass mouth-to-gill respiratory flow when obstructions are present or while they are eating.


True Gills? These external organs are on the heads, behind the eyes of most fish and sharks. Gills are under the heads of stingrays, rays and some sharks. Gills have gill filaments for breathing capacity.


Spiracular Valve? Hinged-like valves on the skull roof efficiently open and close the spiracles. They only remain open briefly during aspiration. Spiracle breathing may have been an evolutionary breakthrough for transition to land.

Blow Hard

Diaphragm? Pushing and pulling of the diaphragm muscle make lungs work. Fish have no diaphragm or true lungs. Ventilatory muscles or spiracles push water over their gills. No diaphragm also means no hiccups.


Windpipe? There is no windpipe, or trachea, between the mouth and gills of fish. The lungfish has a unique gill bypass mechanism to the lungs. Spiracle openings have a short tracheal system. Since it doesn't block, fish don't choke.


Sorbet Style? Spiders and insects have spiracles. On the heads of whales and dolphins, they are called “blow holes”. They also assist the breathing of stationary rays, except mantas. In manta rays the spiracles are nonfunctional.

Taste

On the Block? Most fish have tongue-like parts, called basihyals. Small basihyals made of cartilage are on the mouth floors of stingrays and sharks. Osteichthyes, or bony fish, have bony basihyals on the floors of their mouths.


Fringe Art? Basihyals serve no purpose in most fish. These largely immobile structures have few muscles and no taste buds. Basihyals add suction to the deep bites of cookiecutter sharks, making them an exception.


Good Taste? All fish can taste. Taste is sensed by the body surface of some fish. Catfish and nurse sharks sense prey with whiskers, called “barbels”. Stingrays and sharks have taste buds lining their mouths and throats.

Smell

The sense of smell triggers the eating behavior of most animals, including people. Taste and smell work together to determine the nature and identity of potential food. Fish can smell food over long distances.


Extension? Fish nose holes are called nares. They provide the sense of smell. The nares of cartilaginous fish are under their bodies. Fish nares are not connected to their mouths or throats. They play no role in breathing.


The sense of smell for fish is enhanced by the rapid movement of water over these sensory nares. Fish can navigate by smell. Fish swim to the source of the oder, then taste-test for edibility.

Extrasensory

Sharp Note? Internal hearing parts have no outside openings. Ear-like parts or lateral lines sense sound vibrations. Like sonar domes on vessels, echolocation or bio sonar locates and sizes up obstacles or targets.


Doubling Down? Some land and aquatic mammals echo locate. They emit sound waves to sense objects in their environment. Waves bounce back indicating relative locations. Studies show humans can learn echolocation.


Loud and Clear? Other fish scan and navigate their environment with ultrasound. These species hear at high frequencies and over great distances. Learn scientific details about What sounds can animals hear? from DOSIT.

Jaws

Food Capture? The jaw structure, with or without teeth, enables biting, suction or filtering for food. This starts the digestive process of drawing food into the body, absorbing nutrients and extracting wastes for healthy survival.


Bony Fish? Bony fish usually have two sets of jaws. Oral jaws open and close the mouth to capture, bite and crush prey. Pharyngeal jaws in the back of the throat move food from the mouth to the stomach. Elasmobranchs have one set.


Effective Weapon? Sharks have unique jaw structures. The upper jaw sits below the skull. It detaches to open wide when sharks attack prey. Sharks bite first with the lower jaw, then with the upper jaw. They have no pharyngeal jaws.

Teeth

Big Bites. Shark teeth vary with dietary and feeding habits. Fish-eating species have pointed teeth. Shellfish and crab-eating species have flat crushing teeth. Species that eat seals and sea lions have razor sharp teeth.


Family Matters? During mating season, some male stingrays develop triangular points on their normally dull, flat teeth. This helps them grasp the female. Shark's teeth vary with dietary types. Manta rays have no teeth.


Scheduled Maintenance? Tooth replacement distinguishes Elasmobranchs. Sharks shed and replace tens of thousands of teeth over long lifetimes. Divers and beachcombers often find them. Stingray tooth findings are rare.

Dentistry

Yottabyte? Cookiecutter sharks simultaneously replace rows of teeth. In most sharks, new teeth move forward to fill individual gaps. Stingray teeth also push forth in bands, individually replacing problem spots from behind.


Cavity-Proof? German researchers found the teeth of some Shark species contain natural fluorinated calcium phosphate. This is a main ingredient in most toothpastes. It makes teeth less prone to decay.


Hope for Humans? Doctors at the Department of Animal and Plant Sciences of the University of Sheffield in England identified genes for tooth development and lifelong regeneration in sharks. Humans have these genes.

Gill Rakers

Food Traps? These bony or cartilaginous structures are present in most fish. Their mucus-secreting cells help to prevent food particles from exiting the gill arches. Unlike gill filaments, they have no role in respiration.


Water World? Gill rakers act like sieves. They keep large debris from entering the gills. They are particularly important for filter-feeding fish, like mantas and whale sharks. They trap food suspended in exiting water.


Variability? Fish with many long rakers are filter feeders. Those with a few, short rakers are omnivores or carnivores. These findings were made by Gordon E.E. Moodie, 1985 and Mummert & Drenner, 1986.

Digestive Organs

Screen Test? Animals have different digestive systems with different parts. Most digestive organs are hollow, like mouths, esophagi, stomachs, intestines. The tongue and teeth are accessory structures of the mouth.


Esophagus? In fish, the esophagus typically is short. In sharks and rays, the esophageal lining has cilia. These hair-like structures beat in rhythmic waves to facilitate food transport through the digestive tract.


Stomach? Many fish, like goldfish and carp, have no stomach. Digestion, nutrient absorption, fluid and electrolyte balance, within these fish take place in the intestine, which can measure double the body length.

Accessories to Digestion

Vital roles? The liver, pancreas, and gallbladder have critical roles in digestion. Livers, gall bladders and pancreases are solid. The gall bladder stores bile from the liver. When needed, it helps break down fat.


Stepping it Up? The liver breaks down fats, removes toxins and stores some vitamins and minerals. It is the largest and most sensitive internal organ. Pancreas enzymes help break down proteins, fats and carbohydrates.


Gall Bladder? Some fish have no gall bladder. The presence may matter to human diners. The Indian Journal of Nephrology gives an example of Acute renal failure following consumption of fish gall bladder.

Food Processing

Gizzards complete the “chewing” process for birds, reptiles, earthworms, mollusks, insects and some fish. It replaces teeth in these animals. The mullet and the mud shad have gizzards to grind up plant material for digestion.


Short-changed? Most fish have small and large intestines to regulate digestive hormones, boost metabolism and aid immunity. Sharks, rays, sturgeons, and lungfish have no small intestine.


Intestines? Fish intestines are long, allowing them to slowly absorb nutrients. Sharks are among those fish with single spiral intestines between the stomach and the anal opening. Intestines are of one dimension, not large and small.

Elimination

Holding Forth? Stingrays and sharks neither drink nor leak water. This vital liquid comes from their food. Cartilaginous fish, mammals and amphibians convert ammonia to urea in their livers. All fish have kidneys to filter wastes.


Acid Wash? Elasmobranchs have unique urinary systems. Rays and sharks store urea. It moistens their skin. Kidneys process urea into urine. It exits through the skin. Urea makes the meat smell like ammonia, which is a base.


Beginning and End? Not all fish have an anal pore. Amphibians, reptiles, birds, Elasmobranch fish and monotremes have a single opening called the cloaca for the passage of offspring, feces and urine. It is not present in most fish.

Swim Bladder

Clean Break? Sharks, skates, rays, guitarfish, sawfish and chimeras have no swim bladders. These gas or air-filled sacs are associated with the digestive system of most bony fishes. They help with buoyancy, not digestion.


Stop and Sink? Manta rays, Great White, Hammerhead, Mako and Whale Sharks must keep moving to avoid floating to the surface or sinking while in water. Like flounder, cobia and mackerel, they lack swim bladders.


Kitchen Secrets? Sharks store fats and oils in their livers. These do not solidify at ocean depths. Other deep-sea fish have piezolytes instead of swim bladders. These newly-discovered molecules protect against crushing water pressure.

Seeing Is Believing

View Finder? Manta rays and most sharks have side-facing eyes. Hammerheads have eyes at each end of their heads. Those of angel sharks and most rays are on top of their heads. Sight requires light. Acuity varies. Some fish are blind.


Blind Spots? Whether eyes are front-mounted, top-mounted or side-mounted, most animals have blind spots. Cuttlefish, squid, and octopus are rare exceptions. These cephalopod class members can see in all directions.


Fish-Eye Lens? The retina belongs to the central nervous system. This light-sensitive lining behind the eye converts light from the lens to nerve signals that it sends to the brain for vision. Fish lenses move back and forth to focus.

Studio Sessions

Glow-Getters? Bioluminescent and biofluorescent sharks glow to attract mates or give warning. Bioluminescent animals emit light of their own making. Biofluorescent animals absorb light to cast green, red, orange or blue glows.


Bioluminescence? Deep-sea viper dogfish, lantern sharks and cookiecutter sharks are marine vertebrate examples. Fireflies and fungi are examples of this chemical process on land. Insects are invertebrates. Fungus are neither.


Biofluorescence? These animals absorb sunlight, then emit it as another color with a longer wavelength. Catsharks and swell sharks emit green light. Visibility is not self-powered, presents with low energy and produces no heat.