Chapter 10 Fishes Fishes Vertebrates presence of a

Chapter 10: Fishes

Fishes • Vertebrates: presence of a backbone • 1 st 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

• Digestion – 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

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

• 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

• 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 -250 m 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

• 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 – Hides its eggs – No parental care • Guarders – 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

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