Anatomy and Life Functions

Sharks are considered fish 10,000 species of fish exist Fish have an internal air pouch called a swim bladder Most bony fish are herbivores Seahorses do not have a stomach Many fish use a type of “mating dance” to attract mates Sex reversal is common in many fish

What are Fishes? Fishes are vertebrates, which is any organism that has a spine and a backbone Fishes can be categorized into three groups Jawless Fish Bony Fish Cartilaginous Fish (Sharks)

Jawless Fish Jawless fish are also known as agnathans They are the most primitive fishes! Two major types are hagfishes and lampreys Characteristics include: No Jaws, feed through suction Slender, elongated, eel-like bodies Skeletons made of cartilage Bodies not covered in scales

Lampreys Parasitic Fish- feed off of host fish Mouth is an oral sucker- contains sharp teeth that cut the host’s flesh and then suck the blood Paddlefish Parasites

Hagfish Scavenger of the sea- it feeds on dead or dying fish Also called a slime eel Uses their tongues to bore into prey and eat them from the inside out Produces a slime that covers its skin and makes it hard to catch

Bony Fish The majority of fish species are called bony fish, or osteichthyes (os-tee-ik-thee-eez) Over 30,000 species of bony fish exist

Bony Fish External Anatomy

External Anatomy- Fins Fins- most consist of thin membranes that are supported by bony spines Most fish have two dorsal fins, two pelvic fins, two pectoral fins, an anal fin and a caudal fin (tail) The caudal fin is considered to homocercal, or the same length on both the top and bottom

Types of Fins Dorsal Fins- prevents rolling and aids balance Pectoral and Pelvis Fins- used for turning, steering, and moving up and down Anal Fin- stabilizes fish when swimming and aids balance Caudal Fin- used for propulsion (pushes water)

Specialized Pectoral Fins: Flying Fish Blue Planet- Flying Fish

External Anatomy Lateral Line- sense organ lined with sensory cells that detects vibrations in the water Enables fish to avoid obstacles, find prey, orient water currents, and keep their position in a school Peduncle- narrow part of the fish’s body where the caudal fin attaches Vent- external opening to digestive, urinary, and reproductive tracts

Types of Scales Cycloid Ctenoid Form an overlapping covering Similar to roof shingles Thin, flexible Allows good mobility Ex: Salmon Very similar to cycloid scales Also overlap and look similar to shingles Square in shape Found on spiny rayed fish Ex: Mackerel

Bony Fish Internal Anatomy

Buoyancy Control Uses a structure called a swim bladder to adjust their density in water It allows them to stay at a certain depth without effort Can fill or empty it with gas and adjusts to pressure changes Swimming speed depends on ability to control swim bladder

Buoyancy Control

Feeding Patterns Most bony fish are carnivores, but many species also feed on plants and algae Bony fish have various different types of mouths and jaws that are adapted to the food they eat Most swallow their prey whole, while some use their teeth to tear prey

GrazersFilter Feeders Feed primarily on seaweeds, plants, and algae Many have beak-like jaws Ex: Parrotfish Strain food by swimming with their large mouths open Filter plankton through gill rakers Ex: Herrings, Whales

Bottom Feeders Have a downward oriented mouth adapted to suck food from the bottom

Digestion Pathway of food: Mouth  Esophagus  Stomach  Intestines Specialized organ called the pyloric caeca which secretes digestive enzymes Some bony fish lack a stomach Ex: Seahorses

Circulation Fish have a closed circulatory system- blood is contained in veins, arteries, and capillaries Two chambered heart Blood is pumped from heart to gills to pick up oxygen, then travels to all parts of the body Fish are cold blooded- their body temperature is the same as the water temperature

Respiration Oxygen is obtained from water through gills Water passes over the gills, and oxygen dissolved in the water enters the capillaries via diffusion Gills are supported by bony structures called gill arches Each gill arch has two rows of fleshy projections called gill filaments, which are surrounded by capillaries

Coloration Varies with fish, species, and sex Some are vibrant colors, some are camouflaged Color is due to special cells in the skin called chromatophores Some fish can expand and contract the pigment in their chromatophores to rapidly change colors Cells called iridocytes (pigment cells that contain reflective granules) work like small mirrors

Outrageous Acts of Science- Octopus Camouflage

Vibrant Colors

Camouflage Fish Camouflage

Disruptive Coloration

Countershading Top of fish is dark in color, and bottom is light Helps conceal fish from predators both above and below

Reproduction Tremendous variation among fish! Males- testes present, produce sperm (called milt) Females- ovaries present, produce eggs (called roe) Some fish are hermaphrodites- can produce both eggs and sperm (hamlets, lancetfish) Common in the deep sea! Sex reversal is not uncommon (sea bass, groupers)

Breeding and Courtship Most breeding occurs at a specific time of year and at a specific location Some fish species have elaborate mating rituals, such as swimming upside down, postures that display certain colors, and “dances” The sockeye salmon changes color from silver to red, and the jaw of the males grows into a hook Seahorse Mating Dance

Fertilization Usually external (spawning) Fertilized egg develops into an embryo, then a larva, then adult fish Produce numbers of eggs and sperm in the millions to ensure fertilization happens Few use internal fertilization ex. sharks

Development Embryo begins to develop inside egg, gets nourishment from yolk of egg Eggs are usually adrift or attached to something Many develop in a nest built by one or both parents

Paternal Care In some fish species, the males keep the fertilized eggs inside them until they hatch! Ex: Seahorses, Pipefish