Fishes Lesson 4

-Aquatic vertebrates (they have backbones) -Most have paired fins, scales on some parts of the body, and gills. -Fins are for movement -Scales provide protection from environment and predators -Gills aid in gas exchange with the environment (O2, CO2,etc.) -Lateral line system: can help fish to sense the motion of other organisms -air bladder prevents fish from sinking in the water

- Heart and closed circulatory system (blood stays in arteries and veins ) - 2-chambered heart pumps blood in single loop: heart to gills, gills to rest of body, then back to heart - Nervous system: includes brain, cerebrum, cerebellum, medulla oblongata - cerebrum primarily regulates sense of smell in fishes -cerebellum regulates body movements -medulla oblongata controls most internal organs

Reproduction: can be internal or external (3 types) -oviparous (egg-laying– released into water- egg yolk for nourishment) -ovoviparous (embryos remain inside female, but feed on egg yolk) -viviparous (parasites– nourishment from female instead of egg yolk) Most oviparous fishes do not care for their young, but there are exceptions:

Bettas and bubble nest Male seahorse and young Stickleback male guarding nestFemale cichlid mouth-brooding

Jawless fishes: lampreys and hagfish - Fibrous skeletons, no true jaws or teeth -Parasitic as adults -Most of lamprey’s head is a sucking disc with a round mouth in the center -Attaches to other fish, bores a hole and sucks out host’s tissues and fluids -Hagfish: no eyes, 4-6 tentacles on mouth, thick slime layer to protect against predators -Eats dead or dying fish, can also absorb nutrients through skin and gills like invertebrates -Could be transitional species -Lampreys decimated Great Lakes fish populations

Hagfish slime! Dr. Gene S. Helfman

Cartilaginous fishes: sharks, rays and skates - skeleton is cartilage; most sharks have tooth like scales on skin, rough as sandpaper -sharks have streamlined bodies, a large, curved tail, a pointed snout, and thousands of teeth in rows. -New teeth replace the old– up to 20,000 teeth in a lifetime! -Sharks eat fishes, including other sharks, marine mammals, birds, and invertebrates. -A few are filter feeders, like most rays and skates. -Most sharks, rays and skates are oviparous (egg cases laid– enough food for 2 months in yolk sac) -Some sharks bear live young– sandtiger shark pups survive by eating their siblings and even unfertilized eggs inside the mother!

Bony fishes - Skeleton of true bone -Incredible diversity, from flying fish to flounders, some can breathe air (e.g.,lungfish, tarpon) -Some are vegetarians, some omnivores and some are strictly carnivorous -Most live in either fresh water or the ocean -However, some species, like salmon, can move from freshwater to saltwater ecosystems and vice versa. Granddad

Salmon begin life in freshwater rivers and streams, but eventually migrate to the oceans years later, they return to their birthplace to breed -Trip can take several months and almost 2,000 miles! -Salmon recognize their home streams using their sense of smell

Of course, not all make it back home, and not all the eggs hatch, but salmon, like other fishes, are an important part of the food web