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.

Stingrays and Manta Rays and Sharks

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.


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.


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.

Long History

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.


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

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.


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.


Deep Breath? 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 cartilaginous fish gill slit openings is unique. Five to seven pairs of gill slits are on both sides of their heads. Bony fish typically sport just four gills on each side.

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.


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 do have a tracheal system.


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.


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.

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.


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.

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 identify objects with ultrasound. These species hear at higher frequencies and over greater distances than people. Learn scientific details about What sounds can animals hear? from DOSIT.


Hidden Assets? Ultrasound enables bats and dolphins to scan and navigate their environment. It also is used to create images for medical testing. With Sonography, high-frequency sound waves depict organs within bodies.

Jaws

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.


Cartilaginous Fish? Elasmobranch jaws detach from the skull. They have one set of oral jaws. They have no pharyngeal jaws. In most fish the lower jaw moves freely but the upper jaw is attached to the skull.


Effective Weapon? Sharks have a unique jaw structure. Their upper jaw sits below the skull. It detaches to open wide when the shark attacks its prey. A shark bites first with the lower jaw, then with the upper jaw.


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.

Teeth

Family Matters? During mating season, some male stingrays develop points on their normally dull, flat teeth. 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.


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.


Food Capture? Jaw and tooth structures enable 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.

Gill Rakers

Food Traps? These bony or cartilaginous structures are present in most fish. Unlike gill filaments, they are not involved in respiration. They prevent food particles from exiting between the gill arches.


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.


Defense mechanism? Mucus-secreting cells are attached to the gill rakers. Mucus may help regulate water losses between the rakers and the arches and speed the transport of food particles away from the arches.

Accessories to Digestion

Vital roles? The liver, pancreas, and gallbladder are considered accessory digestive organs. Their roles in the digestive system are critical. Livers, gall bladders and pancreases are solid.


Stepping it Up? The liver breaks down fats, removes toxins and stores some vitamins and minerals from food. It is the largest organ and most sensitive internal organ in humans and fishy-fish.


Companion Parts? Pancreas enzymes help break down proteins, fats and carbohydrates. The gall bladder stores the bile that is produced by the liver. When needed, bile helps break down fat.


Pancreas? Dr. Erika M. Plisetskaya, revolutionary in the Physiology of fish endocrine pancreas, stated “Fish have become the most widely used model for studies of biosynthesis and processing of the pancreatic hormones.”

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.


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.


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.

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? Amphibians, reptiles, birds, Elasmobranch fish and monotremes have a single opening called the cloaca for the passage of offspring, feces and urine.


Anus? Not all fish have an anal pore. In pearlfish the anus is near the throat. In cartilaginous fish, the cloaca opening also serves in mating. This singular, multi-purpose organ is 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? If deep sea fish had these air sacs in their bodies, they would get crushed by the water pressure. Deep sea creatures have piezolytes. These newly-discovered molecules protect against water pressure.


Cold Storage? To make up for the absence of swim bladders, some sharks store unsaturated fats and oils in their livers. These do not solidify at cold ocean depths. Membranes must stay flowing to function.

Seeing is Believing

View Finder? Manta rays, whale sharks and most sharks have side-facing eyes. Sphyrnid Sharks, or hammerheads, have eyes at each end of hammer-shaped heads. Those of angel sharks and most rays are on top of their heads.


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.


Love Hue? Sight requires light. Acuity varies by species and specimen. Some fish need periods of light and dark. Others live in darkness. Some are blind. Some glow to attract mates or give warning, not for lighting.

Studio Sessions

Glow-Getters? Bioluminescent and biofluorescent sharks glow in the dark. Bioluminescent animals emit light of their own making. Biofluorescent animals absorb light waves to cast green, red, orange or blue glows.


Bioluminescence occurs widely in marine vertebrates and invertebrates. Deep-sea viper dogfish, lantern sharks and cookiecutter sharks are marine examples. Fireflies and fungi are examples of this chemical process on land.


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


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.