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Marine Fishes © 2006 Thomson-Brooks Cole Jawless Fishes • Class Agnatha • Lack both jaws and paired appendages • Have skeletons of cartilage (no bone) • Lack scales • Hagfish also lack vertebrae (some scientists consider them invertebrates) © 2006 Thomson-Brooks Cole Hagfishes • Bottom dwelling “slime eels” • Skins are used to make leather goods • Slime glands produce abundant milky, gelatinous fluid if hagfish is disturbed © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Lampreys • Have oral disk and rasping tongue covered with tooth-like keratin plates • Reproduction – males migrate up rivers and build nests – females arrive and they spawn; eggs attach to stones of the nest – larvae are benthic filter feeders – after 3-7 years, they metamorphose into adults and return to the sea © 2006 Thomson-Brooks Cole Lamprey Weir © 2006 Thomson-Brooks Cole Cartilaginous Fishes • Class Chondrichthyes – e.g. sharks, skates, rays, chimaeras • Skeleton of cartilage • Possess jaws and paired fins • Have placoid scales (denticles) © 2006 Thomson-Brooks Cole Sharks • Excellent swimmers with streamlined bodies – swim with powerful, sideways sweeps of the caudal fin (tail) – heterocercal tail—caudal fin in which the dorsal lobe is longer than the ventral • Males have claspers—modified pelvic fins which transfer sperm from the male to the female © 2006 Thomson-Brooks Cole Which is a male? © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Sharks • Maintaining buoyancy – sharks sink if they stop swimming – large livers produce squalene—an oily material with a density less than seawater – squalene offsets the shark’s higher density to help maintain buoyancy © 2006 Thomson-Brooks Cole Shark Sensory Systems • Vision – a clear nictitating membrane covers and protects each lidless eye – many species seem to have color vision • Olfaction – more important than vision – almost 2/3 of the shark’s brain cells are involved in processing olfactory information – sharks are sometimes referred to as “swimming noses” © 2006 Thomson-Brooks Cole Nictitating Membrane © 2006 Thomson-Brooks Cole Shark Sensory Systems • Lateral line system – consists of canals running the length of the animal’s body and over the head – neuromasts detect vibrations in the fluid which alert the shark to movements in the water, possibly made by prey animals © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Shark Sensory Systems • Ampullae of Lorenzini – organs scattered over the top and sides of the animal’s head – sense electrical currents in the water © 2006 Thomson-Brooks Cole Digestion in Sharks • Blade-like, triangular teeth in the mouth grasp prey and tear off chunks (in some species) • Food is swallowed whole (sharks cannot move their jaws back and forth to chew) © 2006 Thomson-Brooks Cole Shark teeth © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Osmoregulation in Sharks • Maintain an internal solute concentration > or = to the seawater – retain large amounts of nitrogenous wastes, mostly urea. • Gills work to excrete excess sodium chloride (salt) • Kidney excretes other salts © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Reproduction in Sharks • Males have claspers to hold females during copulation. © 2006 Thomson-Brooks Cole 3 Type of Reproduction in Sharks • Oviparity – most primitive mode – eggs are laid outside the body and the embryos develop in a protective case • e.g. whale sharks, bullhead sharks, skates © 2006 Thomson-Brooks Cole Oviparity © 2006 Thomson-Brooks Cole Reproduction in Sharks • Ovoviviparity – most common mode – eggs hatch within the mother’s uterus but no placental connection is formed • young are nourished by yolk from the egg – e.g. basking sharks, thresher sharks, saw sharks, sand tiger © 2006 Thomson-Brooks Cole Ovoviviparity © 2006 Thomson-Brooks Cole Reproduction in Sharks • Viviparity – most recent mode to evolve – either the young directly attach to the mother’s uterine wall or the mother’s uterus produces “uterine milk” that is absorbed by the embryo – e.g. requiem sharks, hammerhead sharks © 2006 Thomson-Brooks Cole Skates and Rays • Have flattened bodies adapted to a bottom existence • Greatly enlarged pectoral fins that attach to the head • Reduced dorsal and caudal fins © 2006 Thomson-Brooks Cole Skates and Rays • Eyes and spiracles (openings for the passage of water) on top of the head • Gill slits on the ventral side • Specialized pavement-like teeth are used to crush prey (e.g. invertebrates) © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Differences between Skates and Rays Rays: swim by moving Skates: create a wave fins up and down from the forward to backward fin edges streamlined tails with fleshier tails with small venomous barbs or fins and no spines spines larger size smaller size ovoviviparous mostly oviparous © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Defense Mechanisms • Electric rays have electric organs that can deliver up to 220 V • Stingrays have hollow barbs connected to poison glands – treatment for stingray wounds: submerge in hot water to break down protein toxin • Sawfishes and guitarfishes have a series of (non-venomous) barbs along their pointed rostrums © 2006 Thomson-Brooks Cole Sawfish © 2006 Thomson-Brooks Cole Chimaeras • Subclass Holocephali – e.g. ratfish, rabbitfish, spookfish • Large pointed heads and long, slender tails • Gills covered by operculum; water inhaled through the nostrils © 2006 Thomson-Brooks Cole Chimaeras • Oviparous – produce large eggs in a leathery case • Have flat plates for crushing prey instead of teeth • Generally bottom dwellers © 2006 Thomson-Brooks Cole Bony Fishes • Class Osteichthyes • Very diverse 25,000 species • Most forms have: swim bladder (or lung), bone, bony scales, and fin rays • 2 classes: lobed-fin fish and ray fin fish © 2006 Thomson-Brooks Cole Coelacanths • Characterized by lungs and lobed, paired fins • Known from fossils only before live specimen was discovered in 1938 • Fat-filled swim bladder for buoyancy • Nearly isotonic to seawater like sharks © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Ray-Finned Fishes © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Ray-Finned Fishes homocercal tails, cycloid or ctenoid scales, more maneuverable fins • homocercal tails—tails with dorsal and ventral flanges nearly equal in size; vertebral column usually does not continue into the tail • cycloid & ctenoid scales—scales that are thinner and more flexible; less cumbersome for active swimmers © 2006 Thomson-Brooks Cole Caudal Fin © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Ray-Finned Fishes • Possess paired fins, providing better control of movements • Median fins consist of 1 or more dorsal fins, caudal fin, and usually anal fin – help maintain stability while swimming • Paired fins consist of pectoral and pelvic fins – both used in steering – pectoral fins also help to stabilize the fish © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Body Shape • Fusiform body shape—streamlined shape with a very high and narrow tail – efficient movement for active swimmers © 2006 Thomson-Brooks Cole Body Shape • Laterally compressed or deep body – allows navigation through grass or corals © 2006 Thomson-Brooks Cole Body Shape • Depressed or flattened bodies – bottom-dwelling fishes © 2006 Thomson-Brooks Cole Body Shape • Globular bodies, enlarged pectoral fins – appropriate for sedentary lifestyle © 2006 Thomson-Brooks Cole Body Shape • Long, snake-like bodies, absent or reduced pelvic and pectoral fins – useful for burrowing, living in tight spaces © 2006 Thomson-Brooks Cole Fish Coloration © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Fish Coloration • Countershading is seen in open ocean fish • Disruptive coloration—background color of the body is usually interrupted by vertical lines; may be an eyespot – more difficult for predators to see the fish © 2006 Thomson-Brooks Cole Countershading © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Fish Coloration • Cryptic coloration—coloration which blends with the environment – used for camouflage © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Fish Coloration • Poster colors—bright, showy color patterns – may advertise territorial ownership, aid foraging individuals to keep in contact, or be important in sexual displays – aposematic (warning) coloration—bright coloration to warn predators that the fish is too venomous or spiny to eat © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Locomotion in Bony Fishes • In swimming, the trunk muscles propel the fish through the water © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Respiration and Osmoregulation • Gills often used to extract O2, eliminate CO2, and aid in salt balance – gill filaments—highly vascularized, rod-like structures which compose the gills – countercurrent multiplier system—blood flows in the opposite direction from the incoming water, maintaining a stable gradient that favors the diffusion of O2 in and CO2 out of the body © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Respiration and Osmoregulation • Water must be continuously moved past the gills to keep blood oxygenated – most bony fish ventilate gills by pumping water across them – very active fishes use ram ventilation— continuously swimming forward at high velocity with the mouth open © 2006 Thomson-Brooks Cole Respiration and Osmoregulation • Blood’s salt concentration is about 1/3 that of seawater, so water is lost • Fish drink seawater to compensate – chloride cells—specialized cells on the gills which eliminate most of the excess salt – kidneys and digestive tract remove other excess salt – marine fish excrete negligible amounts of urine in order to retain maximum water © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Cardiovascular System • Consists of heart, arteries, veins, and capillaries • Fish have a two chambered heart. © 2006 Thomson-Brooks Cole Cardiovascular System • Many active swimmers have a countercurrent arrangement of blood vessels – maintains body-core temperature at 2-10o C above seawater, increasing efficiency of swimming muscles © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Buoyancy Regulation • Most fish use a swim bladder—a gasfilled sac that helps offset the density of the body and regulates buoyancy – the fish can adjust the amount of gas in the swim bladder to maintain depth – gas is added as the fish descends and removed as it ascends © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Buoyancy Regulation • 2 methods for adjusting the amount of gas in the swim bladder – gulping air from the surface or spitting air out as needed – gas gland—a specialized gland which fills the swim bladder from gases dissolved in the blood • fish with a gas gland empty gas from the swim bladder through diffusion into the blood • Active swimmers do not have swim bladders, and must keep swimming © 2006 Thomson-Brooks Cole Nervous System and Senses • Taste and hearing – taste receptors may be located on the surface of the head, jaws, tongue, mouth and barbels (whisker-like processes about the mouth) – bony fishes have a lateral line system for detecting movement in the water – ears are internal © 2006 Thomson-Brooks Cole Nervous System and Senses • Vision – no eyelids – eyes are usually set on the sides of the head – shallow-water species can perceive color © 2006 Thomson-Brooks Cole Feeding Types • Carnivores (e.g. pufferfish, groupers) – most bony fishes are carnivores – prey are usually seized, swallowed whole • chewing would block water flow past gills • Herbivores (e.g. surgeonfish, parrotfish) – feed on a variety of plants and algae © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Feeding Types • Filter feeders (e.g. anchovies, larvae) – feed on plankton – typically use gill rakers—projections from the gill arches which filter phyto- and zooplankton from seawater – most travel in large schools, and are an important food source for larger carnivores © 2006 Thomson-Brooks Cole Adaptations to Avoid Predation • Many exhibit elaborate camouflage • Pufferfishes and porcupinefish inflate their bodies to deter predators • Flying fishes use enlarged pectoral fins to glide through the air and escape • Pearlfish hide in other organisms • Parrotfish secrete a mucus cocoon • Surgeonfish are armed with razorsharp spines © 2006 Thomson-Brooks Cole Adaptations to Avoid Predation • Clingfishes use a sucker to attach to rocks so predators can’t dislodge it • Triggerfish projects spines to deter predators or wedge itself into cracks • Scorpionfish and stonefish have venom glands for self-protection © 2006 Thomson-Brooks Cole Reproduction in Bony Fishes • Sperm and eggs pass to the outside through ducts, except in salmon • Egg and sperm development is usually seasonal © 2006 Thomson-Brooks Cole Reproduction in Bony Fishes • Pelagic spawners (e.g. tuna, wrasses) – release vast quantities of eggs into the water for fertilization by males – fertilized eggs drift with the currents – no parental care • Benthic spawners (e.g. smelt) – non-buoyant eggs with large yolks – no parental care – pelagic or benthic embryos/larvae © 2006 Thomson-Brooks Cole Reproduction in Bony Fishes • Brood hiders (e.g. grunion) – species that hide their eggs in some way but exhibit no parental care • Guarders (e.g. damselfish) – species that care for their offspring until they hatch and, frequently, through their larval stages • Bearers (e.g. jawfish, seahorses) – species that incubate their eggs until they hatch (in the mouth or a special pouch) © 2006 Thomson-Brooks Cole Reproduction in Bony Fishes © 2006 Thomson-Brooks Cole Reproduction in Bony Fishes © 2006 Thomson-Brooks Cole Fish Migrations • Migrations may occur within seawater or between seawater and fresh water (diadromous) – catadromous—fishes that move from fresh water to seawater to spawn – anadromous—fishes that move from seawater to fresh water to spawn © 2006 Thomson-Brooks Cole Fish Migrations • Freshwater eels – best-studied catadromous fishes – migrate down coastal rivers to the sea during the fall – adults spawn and then die – young hatch, develop into leaf-like leptocephalus larvae, and migrate back to rivers – after arrival, young metamorphose into juveniles (elvers) that migrate into streams and estuaries © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Fish Migrations • Salmon – Atlantic/Pacific species are anadromous – Pacific species return to spawning grounds once, reproduce, and die; Atlantic species may spawn more than once – lay eggs in a redd—a shallow depression in the gravel of a fresh water stream – salmon navigate upstream by the characteristic odor of the stream; there is not agreement on how they locate the correct river’s mouth from the open sea © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole