Marine Fishes- Basics of Ichthyology Chapter 8

How are Humans and Sea Squirts related?

Subphylum urochordata- sea squirts.

Phylum Chordata Not all Chordates are vertebrates! Characteristics of Chordates: 1.) Dorsal nerve cord 2.) Notochord 3.) Gill slits 4.) Post-anal Tail The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc.

Basic Chordate plan

Lancelets- Simple Chordates

Subphylum vertebrata Have the 4 major characteristics of chordates. Also have vertebrae that protect the dorsal nerve cord (spinal cord). Bilateral symmetry Fish-oldest vertebrates found in the fossil record.

Figure 8.01

Class Agnatha- jawless fish Have no jaws- feed by suction of round mouth. Long, slender body (like an eel) Lack paired fins and scales. Hagfishes- feed on dead or dying fish. Sometimes bore into their prey and eat from the inside out. Lampreys- mostly freshwater- parasitic feeders.

Pacific hagfish

Pacific hagfish

Lampreys

Class Chondrichthyes- cartilaginous fish Sharks, rays, skates and ratfishes. Cartilage skeletons- lighter and more flexible than bone. Placoid scales- have a pointed, sometimes sharp tip. Caudal fin (tail fin)- top lobe is larger than the bottom lobe. This is called a heterocercal fin. Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.

Class Chondrichthyes- (cont’d) Most cartilaginous fish have two dorsal fins. Large, pointed, fleshy pectoral fins. Five to seven gill slits on each side. Many rows of triangular teeth. As teeth are lost, a tooth from the row behind it moves forward.

External anatomy of a shark Spiracles are found in some sharks and all rays. They are a pair of openings just behind the fish's eyes that allow it to draw oxygenated water in from above. The spiracles aid the fish in breathing even when it is lying on the ocean bottom or buried in the sand.

Figure 8.04

Galapagos Hammerhead

Great White Shark

Great White Sharks

Bull Shark

Bull Shark

White tip reef shark

Skates and rays 450-550 Species Mostly demersal- live on the bottom. Rays have their gill slits on their ventral side. Pectoral fins are very large and flat, like bat wings. Spiracles aid in gill irrigation.

Rays- (cont’d) Stingrays- Whip-like tail with stinging spines for defense. Poison gland produces the venom. Bury themselves in the sand and feed upon molluscs and crustaceans. Have specialized teeth for grinding shells of prey.

Manta Ray and Diver

Spotted Eagle Ray

Blue Spotted Stingray

Southern Stingray

Class Osteichthyes- bony fish The majority of fishes- 96%. Almost half of all vertebrates are bony fishes. Have cycloid, or ctenoid scales- thin, flexible and overlapping. They are smooth to the touch. Operculum- a flap of bony plates and tissue that cover the gills. Fins- thin membranes instead supported by bony spines, or fin rays.

Class Osteichthyes- cont’d Mouth is usually terminal (at the end of its head) Caudal fin is usually homocercal- both lobes the same size. Swim bladder- gas filled sac above the stomach. Helps with buoyancy.

External anatomy of a bony fish

Body shape of fishes Related to its lifestyle Streamlined for constant swimming- ex tuna and mackerel. Laterally compressed- maneuverability- around reefs ex- damselfish, (our fish) Flattened- good for demersal fish and rays. Eel-shaped – good for living around rocks and for quick propulsion. Irregular shapes aid in camouflage

Streamlined shape

Yellowfin tuna

Flattened shape

Japanese Flounder

Leafy Sea Dragon

Damselfish and Tangs- Laterally compresed

Eel shaped

European eel

Coloration Chromatophores- special cells in the skin that contain pigments. Irregular in shape with branches Some fish can contract and expand the pigment to rapidly change color Iridiophores- special chromatophores that contain reflective crystals.

Winter Flounder on a checkerboard background

Coloration (cont’d) Warning coloration- indicates toxins or danger. Cryptic coloration- blending in with the environment to avoid predation Disruptive coloration- colored bars, stripes or spots that break up the outline of a fish. Intended to confuse predators. Countershading- found in open water fish- dark on dorsal side, silvery on ventral side.

Warning coloration

Cryptic coloration- flounder

Disruptive Coloration- Four-Eye Butterfly fish and Ornate Cowfish

Locomotion Swim with a side to side S-shaped motion using muscles called myomeres. Pectoral fins- provide lift in sharks, not in bony fish (why?) Dorsal and anal fins- used as rudders Pelvic fins- help turn, balance, and “brake” Flexibility of fins allow some bony fish to use other methods of swimming.

Undulating “S-shaped” swimming- gives the ability to maneuver rocky habitats

Tuna swim fast by flexing their caudal fins.

Many reef fish use movement of fins to move precisely in feeding habitats

This trunkfish can only swim slowly by moving only the end of the caudal fin.

Locomotion in cartilaginous fish

Locomotion in bony fish

Feeding- mouth adaptations Sharks- mostly carnivores- often feed on prey larger than themselves. Some are filter feeders- whale shark, megamouth shark, manta rays. Carnivorous fish-well-developed teeth for catching and holding prey. Grazer- feed primarily on seaweeds Plankton feeders- filter plankton over structures called gill-rakers.

Mouth adapted for taking bites out of large prey

Butterfly fish eat very small prey

Parrotfish have a beak-like mouth for scraping algae and corals

Herring have large mouth for filtering plankton

Circulation All fishes have a two-chambered heart, located below the gills. The first chamber collects deoxygenated blood from the body. The second chamber pumps this blood to the gills for gas exchange. Fish have a closed circulatory system of arteries, veins and capillaries. Sharks- have low blood pressure and use muscle contraction to aid in circulation.

Figure 8.15

Respiration- irrigation of the gills Sharks- most take in water through the mouth AND the Spiracles. Skates and rays-spiracles on the dorsal side take in water when on the bottom. Bony fish- draw water in by opening and closing the operculum and by the expansion and contraction of the pharynx.

Figure 8.16b

Countercurrent system Oxygen enters blood by diffusion. There must be a lower concentration of oxygen in the blood in order for diffusion to occur. The blood in the gills flows opposite to the direction of the water. This makes respiration by diffusion more efficient.

Figure 8.17d

Figure 8.17e

Nervous systems All fish have a central nervous system. Highly developed sense of smell- olfactory sacs on both sides of the head. Taste buds- some have them on the fins and skin. Bottom dwellers have ‘whiskers’. Lateral line system- allows fish to detect vibrations in the water. Chondrichthyes- ampullae of Lorenzini- can detect weak electrical fields for locating prey.

Lateral Line system

Behavior Territoriality- when an animal establishes and defends a particular area. Territories can be: Only during reproduction. Permanent- for feeding and shelter. Most common in crowded environments. Ex.- Damselfish.

Aggressive behavior Used to defend territories or mating rights. Fighting is rare, bluffing is common. Open mouths, raised fins, rapidly darting at another. Some use sounds, like rubbing bones or fin spines together.

Schooling- herring, sardines, mackerel, few sharks and rays. Well coordinated, but have no clear leaders. Use vision, lateral line, olifaction, and sound to remain in perfect unison. Why do fish school? Confuse predators by circling or dividing. Increase swimming efficiency. Advantages in feeding and mating.

Traveling schooling pattern

Plankton feeding- schooling pattern

Encirclement of predator- schooling pattern

Streaming- schooling pattern to avoid predation

Migration- mass movements from one place to another. Migration can be daily, yearly, or once in a lifetime. Migration can be from offshore to intertidal, up and down the water column, to transoceanic. Mostly related to feeding and reproduction. Ex.- Open water fish like tuna migrate for feeding purposes.

Migration for reproduction Anadromous fishes- Spend adult lives at sea, but migrate to fresh water for spawning. Salmon- once entering streams to reproduce, they do not feed, and their kidneys must adjust to fresh water. Homing behavior- salmon use chemical memory of their home stream and the streams they pass to find their spawning ground.

Figure 8.22

Migration for reproduction (cont’d) Catadromous fishes- Live in fresh water and return to sea for breeding. Freshwater eels- live in freshwater and migrate to the Sargasso Sea to spawn. Their larvae drift for a year before metamorphosis into adults. Possibly use magnetic field and currents for locating spawning grounds.

Figure 8.24

Reproduction Sexes are usually separate. (not always) Hermaphrodism-most common in deep-sea fishes that rarely encounter another of their own species. Sex reversal- Begin life as one sex but change during life cycle. ex- sea basses, groupers, parrotfishes Anemonefish- all begin as males, one female develops. If she dies, the next largest male becomes female.

Reproductive behavior Migration to breeding grounds. Color changes in bony fishes- salmon eyes turn bright red. Changes in chromatophores can cause skin changes. Behaviors- Postures, fin displays and swimming pattern to attract mates.

Fertilization External fertilization- (broadcast spawning). Many eggs are produced, can float as plankton or be deposited on the bottom. Most do not survive. Internal fertilization- used mainly by cartilaginous fish. Oviparous- Egg-laying. Most fishes. Ovoviviparous- eggs held within the mothers body until hatching- mostly cartilaginous fish. Viviparous- birth to live young that are nourished by the mother- a few sharks.

Figure 8.28