A stingray is depicted with his shark friend from Little Ray & Shark Patch Things Up and displayed at 50% of viewport width.
July 2021 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 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 replaces much of it.


From the Same Cloth? Cartilage shapes Elasmobranchs. Bones do not give them 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. These primitive fish have muscular mouths and rows of teeth. Hagfish are not true vertebrates. They have a skull but no spine.

Aging

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


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


Stunted Growth? With good water conditions and food supply, fish continue growing until death. After the age of sexual maturity, their 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 remaining Carbon-14, or radiocarbon, a natural radioactive isotope. The accuracy is within decades.


Eyeballing It? The carbon level of eye lenses doesn't break down over time. Age-calculation accuracy improves when eye lens carbon measures are taken from dead or fatally-injured by-catch after euthanasia.


Stretching It? The calibration curve associating radiocarbon years to calendar years approximates the age of an organism. Whatever its age, the Greenland Shark likely is the longest-lived vertebrate.

Scales

In Full Bloom? Many Elasmobranch species sport denticles, or 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. Unlike bony fish scales, denticles stop growing. At a certain size, new ones fill in empty spaces. The pattern is regular in sharks, but irregular in stingrays.


Right Confections? The CDC discusses how to avoid waterborne illness in Healthy Pets, Healthy People. To repel tough germs, Sharklet Technologies, Inc. designed denticle-like plastic medical wraps.

Respiration

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


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


Operculum? Elasmobranchs 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 may have operculums.

Auto-Pilot

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


Trademark? The number of gill openings in cartilaginous fish is unique. Five to seven pairs of gill slits are on each side of their heads. From four embryonic gill slits, bony fish develop one 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 faced with obstructions or while 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 to add capacity.


Spiracular Valve? Hinged-like valves on the skull roof efficiently open and close the spiracles. They remain open briefly to take breaths. Spiracle breathing may have evolved for transition to land.

Blow Hard

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


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


Sorbet Style? On the heads of whales and dolphins, spiracles are called “blow holes”. Spiracles do not assist the breathing of manta rays. 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. Bony fish, have bony basihyals on the floors of their mouths.


Fringe Art? Basihyals serve no purpose in most fish. Largely immobile, they 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”. Taste buds line the mouths and throats of stingrays and sharks.

Smell

Triggers? The sense of smell sparks eating behavior for most animals, including people. Taste and smell work together to identify potential food. Fish can smell food over long distances.


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


New Order? Fishes' sense of smell is enhanced by water movement over their nares. Fish identify and locate predators, mates and food by smell. Fish swim to the source of an oder, then taste-test it.

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 water mammals echo locate. They emit sound waves to sense objects in their environment. Waves bouncing back give relative locations. Studies show humans can learn echolocation.


Loud and Clear? Other fish scan and navigate 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 survival.


Bony Fish? Most bony fish have two sets of jaws. Oral jaws open and close the mouth to capture, bite and crush prey. Pharyngeal jaws in 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 for large 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 diet 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. 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 push forward in bands to individually replace problem spots.


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 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 very 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 and 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 of these fish take place in the intestine, which can measure twice 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. Bile helps break down fats.


Stepping it Up? The liver breaks down fats, removes toxins and stores some vitamins and minerals. It is the largest and most delicate 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

Gizzard? It replaces teeth to complete the “chewing” process for birds, reptiles, earthworms, mollusks, insects and some fish. Mullet and mud shad have gizzards to grind up plant material for digestion.


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


Intestines? Fish intestines are long, allowing them to absorb nutrients. Large prey and plants are slow to digest. Sharks have single, spiral intestines between the stomach and the anal opening to improve absorption.

Elimination

Holding Forth? Rays and sharks neither drink nor leak water. This vital fluid 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 to moisten their skin. Kidneys process urea into urine. It exits through the skin. Urea makes the meat smell like ammonia.


Beginning and End? Not all fish have an anal pore. Amphibians, reptiles, birds, Elasmobranchs and monotremes have an 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 too deep. 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 molecules protect against crushing water pressure.

Seeing Is Believing

View Finder? Manta rays and most sharks, including hammerheads, have side-facing eyes. 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 cephalopods can see in all directions.


Fish-Eye Lens? The retina belongs to the central nervous system. This light-sensitive eye lining converts light from the lens into nerve signals, then sends them to the brain for sight. Fish lenses move back and forth to focus.

Studio Sessions

Glow-Getters? Bioluminescent and biofluorescent animals glow to attract mates or give warning. Bioluminescent glows are self-powered. Biofluorescent green, red, orange or blue glows require absorbed light.


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


Biofluorescence? These animals absorb sunlight to emit it in another color of a longer wavelength. Catsharks and swell sharks emit green light. The chemical glow shines with low energy and produces no heat.