Chapter 10: Fishes

Fishes Vertebrates: presence of a backbone 1st fishes lacked paired fins and jaws Evolved 425 million years ago

Jawless Fishes No jaws or paired appendages Skeletons composed of cartilage Bodies lack scales

Hagfish Lack vertebrae Called “slime eels” Bottom-dwelling Act as scavengers or feed on live prey Eat carcass from inside out Slime glands provide physical protection Normally separate sexes

Lampreys Freshwater and saltwater Larvae are filter feeders

Cartilaginous Fishes (Chondrichthyes) Skeletons made of cartilage Jaws and paired fins Skin is covered by placoid scales Teeth are modified placoid scales

Sharks Streamlined bodies (excellent swimmers) Swim with sideways tail sweeps (caudal fin) Slightly denser than water Will sink if they stop swimming Large livers Produces squalene (oily secretion)

Sensory systems Eyes Eyes lack eyelids Clear nictitating membrane to protect eye Can perceive color Well-developed olfactory receptors Helps find prey

Lateral line system Canals along length of animal’s body and over the head Neuromasts can detect vibrations in fluid that fills the canals Used to locate predators and prey

Teeth continually lost and replaced Food swallowed whole Osmoregulation Retain large amounts of nitrogenous wastes Can enter freshwater by reducing levels of nitrogenous wastes in body fluids Digestion Teeth continually lost and replaced Food swallowed whole

Sperm produced in paired testes Reproduction Sperm produced in paired testes Transferred to female through groove in claspers Paired ovaries and oviducts Carries eggs to oviducts Internal fertilization

Eggs hatch within mother’s uterus Oviparity Eggs laid outside the body Embryos develop in protective case Attach to hard surfaces on seafloor Ovoviviparity Eggs hatch within mother’s uterus No placental connection is formed

Viviparity Young directly attach to mother’s uterine wall Mother’s uterus produces milk that is absorbed by

Skates and Rays Flattened bodies Enlarged pectoral fins that attach to the head Reduced dorsal and caudal fins Eyes on top of head Spiracles: openings for passage of water Gill slits on ventral side Lack anal fin Pavement-like teeth used for crushing prey 500 species

Rays Swim by moving fins up and down Tails are streamlined Contain venomous barbs or spines Some species grow large Ovoviviparous

Skates Swim by creating a wave, resulting in a glide Tails have small fins Lack venomous spines Fleshier Oviparous Release eggs in leathery rectangular egg case called a mermaid’s purse

Electric organs in head that can deliver 220 volts (ex: electric rays) Defense mechanisms: Electric organs in head that can deliver 220 volts (ex: electric rays) Can be used to navigate and stun prey Stingrays have hollow barbs connected to poison glands Can inject venom

Chimaeras Ex: ratfish, rabbitfish, and spookfish Large pointed heads Long, slender tails Gills covered with an operculum Water taken in through nostrils Oviparous Flat plates used to crush prey Bottom dwellers 35 species

Bony Fishes (Osteichthyes) 25,000 species Has swim bladder (lungs) Bones Bony scales Fin rays 95% of all species of fishes

Coelacanths Lobed, paired fins 150-250m deep; rocky areas Skeletons made of bone; vertebral column made of cartilage Ovoviviparous Keep high concentration of urea in blood to remain isotonic to seawater

Ray-Finned Fishes Dominant vertebrates in ocean Fins attached to body by fin rays Fish scales: Ganoid, Cycloid, and Ctenoid Body shape determined by characteristics of its habitat

Coloration: Vision used as primary sense in finding food and communicating Pigments Colored compounds found in chromatophores Can alter color by moving pigments Structured colors Produced by light reflecting from crystals located in specialized chromatophores (iridophores) Colorless Immobile

Countershading Back colored dark colors Shades graduate on the sides to belly which is white Can camouflage fish Disruptive coloration Background color usually interrupted by vertical lines Makes it difficult for predators to see fish

Used to blend with their environment Poster colors Bright, showy color patterns May advertise territorial ownership, aid foraging individuals to keep in contact Can be warning coloration Cryptic coloration Used to blend with their environment

Locomotion: Drifting with the current Burrowing Crawling on the bottom Gliding Swimming

Respiration and Osmoregulation: Use gills to extract oxygen from water, get rid of carbon dioxide, and aid in maintaining proper salt balance

Nervous system: Olfactory receptors in olfactory pits Taste receptors located on surface of head, jaws, tongue, mouth, and barbels Vision Eyes lack eyelids Sides on head

Feeding Carnivores Herbivores Filter-feeders Adaptations to avoid predation: Can swallow large amounts of air or water to inflate their bodies Can leap out of water Some secrete a mucous cocoon at night

Reproduction Most are oviparous Gonads are paired and suspended from roof of body cavity by membranes called mesenteries Development of eggs and sperm is seasonal

Pelagic spawners Release a lot of eggs into water Males fertilize eggs Fertilized eggs drift with the current No parental care Advantages: offspring widely dispersed Disadvantages: high mortality

Benthic spawners Live closer to shore Produce eggs that are larger with more yolk Nonbuoyant eggs Spread over vegetation Large numbers produced No parental care

Brood hiders Guarders Bearers Hides its eggs No parental care Care for offspring until they hatch Can defend territory if needed Bearers Females lay eggs in male’s mouth or abdomen Incubates in mouth or abdomen until they hatch

Hermaphrodites Both testes and ovaries In 14 families of fish Synchronous Has functional gonads of both sexes at one time Sequential Changes from one sex to another Can change from females to males (protogyny) or males to females (protandry)

Fish Migrations Common May occur daily or seasonally Seasonal association with spawning, changing temperatures, or feeding Daily associations with feeding and avoiding predators

Salt  freshwater to spawn Can move between freshwater and saltwater Fresh saltwater to spawn Called catadromous Ex: freshwater eels Salt  freshwater to spawn Called anadromous Ex: salmon