Osteichthyes

Osteichthyes Means fish with bony skeletons There are over 20,000 species of bony fish

Where Do Most Fish Live? Most fish live in the epipelagic zone

Types of Fins Tail Fin (CAUDAL FIN) Paired Fins (PECTORAL and PELVIC FINS) Medial Fins (DORSAL and ANAL FINS)

Rayed Fins Ray-finned fish have fins supported by a fan-shaped array of bones Makes the fin light, collapsible, and easy to move Ray-finned fishes are the most diverse group of living vertebrates, making up nearly half of all vertebrate species.

External Anatomy of a Fish

External Anatomy

Caudal Fins Caudal fins have different shapes 1.  Homocercal --> Top and bottom halves the same size a.      Rounded (Low A.R.) b.      Truncate (Intermediate A.R.) c.      Forked (Intermediate A.R.) d.      Lunate (High A.R.) 2. Heterocercal --> Top half different size than bottom half

Types of Caudal Fins

Types of Caudal Fins Heterocercal – often found on sharks

Nervous System Most fish have a complex sense of smell Used to detect prey, mates and predators Smell is detected in the nares (nostrils) Fish also have taste buds Found in the mouth, fins and skin Catfish have taste buds on barbels (whiskers) Rely on vision Eyes focus by moving closer or further from the object they wish to view Covered by a nictitating membrane – clear membrane that allows the fish to see while protecting the eye

Fish Senses Sight – some fish can see color and can see in very dim light Hearing – fish can hear Smell – fish have nostrils used for smelling Touch – fish can feel objects against their skin Lateral line- A system of canals on the sides of fishes that helps fish detect changes in pressure, vibrations and currents

Lateral Line Fish “hear” via their lateral lines, a line of pressure sensors running along each side of the fish that pick up pressure waves (= sound) in water. When someone pounds on an aquarium, that creates waves of pressure in the water that, to the fish, would be analogous to cupping your hands and pounding on your ears--NEVER POUND ON A FISH TANK!

Functions of the Lateral Line Detect changes in pressure and vibrations and currents Detect prey Swim together in a school Detect predators on the side or behind them Pick up vibrations from the swimming together of other animals

Lateral Line

Movement Most fish swim with an S motion A rhythmic side to side moving from the head to the tail Controlled by bands of muscle called myomeres Run parallel along the sides of the fish Visible in fish you eat Makes up 75% of the fishes weight White muscle is used for bursts of speed Red muscle is used for constant locomotion The fins are used like rudders to change direction in the water Some fish move by moving only their fins and not their body

Myomeres

BUOYANCY

Maintaining Buoyancy To maintain buoyancy the fish will either: Adjust the density of its body by using a SWIM BLADDER They will adjust the density of the components of their insides (they will consume lighter weight ions and leave the heavier ones in the surrounding water)

SWIM BLADDERS A swim bladder is a balloon-like structure that is: inflated to make the fish rise higher in the water or deflated to make the fish sink lower

No Swim Bladder Some fish like Tuna do not have a swim bladder and must swim fast to prevent sinking Some fish like catfish do not have a swim bladder and spend their life on the bottom

Respiration Fish use gills to absorb oxygen from the surrounding water

Parts of a Gill Gill Arch - stiff structure that supports the gill filaments and the gill rakers Gill Rakers – prevent food from clogging up the gill filaments Gill Filaments – fingerlike projections where oxygen is absorbed and carbon dioxide is removed

Parts of a Gill

Excretion and Osmoregulation Marine fishes Drink constantly Less blood is filtered Water is reabsorbed Freshwater fishes never drink Lots of nephrons Ions are reabsorbed

Fish Reproduction Most fish have internal sex organs that we cannot see. fish gonads (sex organs) produce gametes (sex cells) only at certain times. These times must be the same for both males and females and must be timed to the most favorable conditions.

Fish Reproduction Fish may only reproduce when there: 1. Is enough of the right kind of food 2.There are enough hours of light each day 3. The water is the right temperature

Fish Reproduction Includes: Courtship: a series of behaviors designed to attract mates Spawning: a release of gametes into the water Copulation: a direct transfer of sperm into a females body

Fish Reproduction Most fish reproduce by spawning. This is when the female swims and lays eggs on plants or sand in the water The male fish swims behind her depositing sperm into the water where some of it may land on and fertilize the eggs

Fish Reproduction Some fishes are hermaphrodites. They have both male and female gonads Hermaphrodism is more common among the deep-water fishes. (Gourami)

Fish Reproduction Sex Reversal Males may change to females or females to males (ex. Clownfish)

Sex Reversal Among some species of anemone fishes a single large female who mates only with a single large dominant male inhabits each sea anemone. All others are small non-breeding males. If the female disappears her mate changes into a female and the largest of the non-breeding males becomes the new dominant male. The new female can start spawning as soon as 26 days after her sex change.

Feeding Fish can be either carnivorous or herbivorous (mostly carnivorous) The teeth will tell you what they eat Used for grasping and holding the prey Prey is usually swallowed whole Usually have one preferred food source A type of fish, anemone, urchin, etc. Fish that feed on algae are called grazers

Behavior Territoriality An established area that the fish protects against invaders Some are only territorial during mating period others are for life Thought this helps ensure there is enough food for the fish Defended by aggressive behavior like making themselves appear larger or by chasing other fish Fights are rare

Behavior Schooling 4000 species of fish school at some point in their lives Can provide protection against predators Can cause confusion Less likely to be the one eaten if there are thousands of other fish around you Can increase swimming efficiency by reducing the drag of the water Can be advantageous for mating or feeding

Class Osteichthyes Characterized by having: Bone in their skeleton An operculum covering the gill openings A swimbladder or lungs True scales Paired fins Homocercal tail (Exception lungfish – diphycercal) Mouth terminal Two chambered heart Sexes separate (Sex reversal in some) Fertilization external for most Excrete ammonia

Class Osteichthyes The bony fishes are the most diverse class of fish. ~24,000 species Osteichthyes are divided into two subclasses The lobe-finned fish (Sarcopterygians) The ray-finned fish (Actinopterygians). *Most modern fish are members of the ray-finned, Teleost subdivision.

Sarcopterygians Sarcopterygians are the fish most closely related to modern amphibians, reptiles, birds, and mammals = terrestrial vertebrates This subclass includes the lungfish and coelacanth. Coelacanth were thought to have become extinct at about the same time as the dinosaurs, until a live specimen was found in 1938

Sarcopterygians Characteristics: Muscular lobe associated with fins Have lungs for gas exchange Live in areas with seasonal droughts Can breathe air if water stagnates Can withstand desiccation Burrow in the mud Have enamel on the teeth

Sarcopterygians Can survive drought by remaining in aestivation for 6 months or more Aestivation = dormant state After rain fills the lake or riverbed Lungfish emerge from their burrows to feed & reproduce

Lungfish - Found in Australia & Madagascar

Australian Lungfish

African Lungfish

Lungfish scales Cosmoid scales

Lungfish Circulation

Coelacanth                                                             

Actinopterygians Ray-finned fish (Fins lack muscular lobes) Have swimbladders to regulate buoyancy ~23,900 species

Chondrosteans (Fresh water fish) Include sturgeons and paddlefish Sturgeon eggs make caviar

Caviar = Sturgeon eggs

Paddlefish

Subdivisions of Teleostei Superorder Ostariophysi Order Cypriniformes (minnows, carps) Order Siluriformes (catfish) Superorder Protacanthopterygii Order Esociformes (pikes) Order Osmeriformes (smelts) Order Salmoniformes (salmon, trout, whitefish) Superorder Paracanthopterygii Order Gadiformes (cod, hakes, pollock) Superorder Acanthopterygii Order Percoidei (perches, snook, basses) Order Pleuronectiformes (flounders, soles) Order Perciformes (mackerel, tuna, swordfish)

Actinopterygians The Teleosts Teleosts are modern day ray-finned fish Use their fins and body wall to push against water for locomotion Some secrete mucus to reduce friction Most teleosts are carnivores swallowing prey whole Herring & paddlefish are filter feeders Teleosts have pyloric ceca (outpockets in the small intestine to increase absorption)

Ganoid Fish Scales Found on non-teleost bony fishes Usually diamond shaped bony scales “Heavy armor” Gars – Alligator Gar

Cycloid Fish scales Found on teleost fishes Light, thin, & flexible

Ctenoid Fish Scales Teleost fishes Have comblike ridges along the exposed edge to reduce friction (drag)