Fishes Phylum Chordata

1. FishesPhylum Chordata Chapter 24

2. Class Myxini • Common name: Hagfish • Lack jaws • Entirely marine • Scavenger & Predators- feed on annelids, mollusks, crustaceans, and dead/dying fish • About 65 species • Best known in North America

3. Hagfish • Most are completely blind • Attracted to food by keen sense of smell and touch • Enters a dead or dying animal an orifice or by digging inside

4. Hagfish feeding • Using 2 toothed plates on its tongue that fold together in a pincer-like action, the hagfish rasps ways bits of flesh from its prey

5. Hagfish feeding • For extra leverage, the hagfish often ties a knot in its tail, then passes the knot forward along its body until it is pressed securely against the side of its prey

6. Hagfish defense • Renowned for their ability to generate enormous amounts of slime • Exudes a milky fluid from special glands along its body • On contact with seawater, the fluid forms a slime so slippery that its almost impossible to grasp

7. Class Cephalaspidomorphi • Common name: lampreys • Has a habit of grasping a stone with its mouth to hold position in a current • Some are parasitic • All lampreys ascend freshwater streams to breed • Marine forms are anadromous-they leave the sea where they spend their adult lives to swim up streams to spawn

8. Lampreys • Sea lamprey, feeding on body fluids of a dying fish

9. Lamprey reproduction • In NA, spawning is in winter or spring • Males begin nest building and are joined by females later • Using their oral discs to lift stones and pebbles and body vibrations to sweep debris away to form a depression • At spawning, with the female attached to a rock to maintain her position over the nest, the male attaches to the dorsal side of her head • As eggs are shed into the nest, they are fertilized by the male • The sticky eggs adhere to pebbles in the nest and quickly become covered with sand • The adults die soon after spawning

10. Lamprey reproduction • Eggs hatch in about 2 weeks, releasing small larvae called ammocoetes • Larvae looks very similar to amphioxus

11. Parasitic Lampreys • Attach themselves to a fish by their sucker-like mouth to a fish, and with teeth, rasp away the flesh and suck out body fluids • To promote blood flow, the lamprey injects an anticoagulant into the wound • When gorged, the lamprey releases its hold but leaves the fish with a large, gaping wound which is sometimes fatal

12. Questions? • What is the freshwater larval stage of a lamprey? • Hagfishes A. An entirely freshwater animals B. Are parasitic C. Generate enormous quantities of slime if disturbed D. Have massive jaws

13. Class Chondrichthyes (Cartilaginous Fish)

14. Subclass Elasmobranchii • Sharks, Skates, and Rays

15. Form and Function • Median anal fin is present (clasper) used for copulation • Lateral eyes are lidless, and behind each eye a spiracle (remnant of the first gill slit) is usually present • 5 gill slits are found anterior to each pectoral fin

16. Shark body • Tough, leathery skin is covered with tooth-like, dermal placoid scales arranged to reduce the turbulence of water flowing along the body surface during swimming • Can detect prey from a kilometer or more away with large olfactory organs capable of detecting chemicals as low as I part per 10 billion

17. Shark body • Prey are also detected by sensing low frequency vibrations with receptors in the lateral-line system • In final stage of attack, sharks are guided to prey by the bioelectric fields that surround all animals with ampullae of Lorenzini

18. Shark body • Front row of functional teeth on the edge of the jaw is backed by rows of developing teeth that replace worn teeth throughout their life • All have internal fertilization, but maternal support varies • Oviparous sharks (lay eggs immediately after fetilization) deposit eggs in a horny capsule called a “mermaid’s purse” • Many retain embryos in reproductive tract for a loing time (ovoviviparous) • Some have true viviparous reproduction (like humans)

19. Rays • Include skates, electric rays, stingrays, manta rays • Specialized for bottom dwelling and greatly enlarged pectoral fins fused to head used like wings in swimming • Gill openings are on the underside of the head, but have large spiracles on top • Water for breathing is taken in through spiracles to prevent clogging the gills, for the mouth is often buried in the sand • Teeth are adapted for crushing mollusks, crustaceans, and some small fish Clearnose skate

20. Rays • Stingrays have a slender, whip-like tail armed with one or more saw-edged spines with venom glands at the base • Electric rays are sluggish fish with large electric organs on each side of their head • High-amp current is produced that flows out into the surrounding water (almost 1 kilowatt) stunning prey or discouraging predators Southern stingray

21. Electric ray anatomy

22. Questions? • Sharks, skates, and rays belong to what class? • Which organism have lateral expansion of the pectoral fins that resemble wing-like appendages? • Sharks are unique in all of the following EXCEPT • Being able to detect bioelectric fields • Having a cartilaginous skeleton • Having external fertilization • Having placoid scales

23. Questions? • What is the function of the large spiracles on top of the head of skates and rays?

24. Class Osteichthyes (Bony Fish) • Class Actinopterygii- ray-finned fish • Class Sarcopterygii- lobe-finned fish • Adaptations: • Operculum: gill cover • Swim bladder: buoyancy

25. Class Actinopterygii • More than 23,600 species • Represented by freshwater and anadromous sturgeons, paddlefishes, and bichirs

26. Teleosts (modern bony fish) A. Bowfin B. Longnose Gar

27. Class Sarcopterygii • Includes lungfish

28. Adaptations • Myomeres: locomotory musculature in zigzag bands Most fish can swim about 10 body lengths per second

29. Adaptations • Lateral Line: senses vibrations and water currents for schooling • Buoyancy • All fish are slightly heavier than water because of skeleton • Squalene: fatty hydrocarbon allowing sharks to stay buoyant (produced by liver) • Swim bladder: gas filled organ that expands with gas when in shallower water because of reduced pressure (and vice versa)

30. Swim Bladder

31. Osmoregulation • Saltwater fish- Hypoosmotic regulators: have much lower blood salt concentration than seawater around them • Risk is drying out- loss of water and taking on of salt • Freshwater fish-hyperosmotic regulators • Risk taking on too much water