Chapter 10 Marine Fishes Vertebrate Jawless vertebrates jawless

Chapter 10 Marine Fishes

• Vertebrate – Jawless vertebrates – jawless fish – Jawed vertebrates – Fish » Chondrichtyes » Osteichtheyes – Amphibians – Reptiles – Birds – Mammals

• First we’ll talk about fish: • Jawless fish • Jawed fish – Cartilaginous fish – Class Chondrichthyes » Chimeras and ratfish » Elasmobranchs – sharks, skates and rays – Class Osteichthyes » Lobed fin fish » Ray finned fish

Fishes • Fishes are vertebrates—animals that possess vertebrae, a series of bones or cartilages that surround the spinal cord and help support the body • Primitive fishes lacked paired fins and jaws • Adaptation of jaws and paired fins allowed fish to more efficiently obtain food ultimately replacing all but a few jawless forms.

Jawless Fishes • • Hagfish and Lampreys Lack both jaws and paired appendages Have skeletons of cartilage (no bone) Lack scales • Hagfish also lack vertebrae (some scientists consider them invertebrates), recent DNA evidence indicates that they are most closely related to lampreys

Hagfishes • Bottom dwelling “slime eels” • Skins are used to make leather goods • Slime glands produce abundant milky, gelatinous fluid for protection if hagfish is disturbed

Lampreys • Have oral disk and rasping tongue covered with horny dentacles to grasp prey, rasp hole in the body and suck out tissue and fluid.

Cartilaginous Fishes • Class Chondrichthyes – sharks, skates, rays, chimaeras – Skeleton of cartilage – Possess jaws and paired fins – Placoid scales cover skin • 2 major groups: – chimaeras or ratfish – elasmobranchs • 2 body forms: streamlined, e. g. , sharks or dorsoventrally flattened, e. g. , skates and rays)

Sharks - Elasmobranchs • Top predators of ocean’s food webs • 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

Dorsal fin Kidney Rectal Spine Stomach Testis Gill slits gland Spleen Caudal fin Mouth Clasper Heart Pharynx Pelvic Intestine Pancreas fin Liver Pectoral Cloaca fin Placoid scales Stepped Art Fig. 10 -3, p. 266

Sharks • Found in all oceans with the greatest numbers in temperate and tropical waters • Humans exploit shark populations for fins, meat, oil, leather, cartilage and sport

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 • Eyes and spiracles (openings for the passage of water) on top of the head • Gill slits on the ventral side • Lack anal fin • Specialized pavement-like teeth are used to crush prey (e. g. benthic invertebrates)

Skates and Rays • 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 • Fished commercially for food, many are considered threatened

Differences between Skates and Rays: swim by moving fins up and down streamlined tails with venomous barbs or spines larger size Skates: create a wave from the forward to backward fin edges fleshier tails with small fins and no spines smaller size Ovoviviparous – young mostly oviparous – egg born live but no placental laying connection

Chimaeras • ratfish, rabbitfish, spookfish • Large pointed heads and long, slender tails • Gills covered by operculum; water inhaled through the nostrils rather than mouth • Have flat plates for crushing prey instead of teeth • Males have claspers on their heads and pelvic fins

Chimaeras • Oviparous – produce large eggs in a leathery case • Generally bottom dwellers • Little commercial value

Lobefins • Coelacanths – classified as lobefins due to presence of rod-shaped bones surrounded by thick muscle in the pelvic and pectoral fins • Only known as fossils until discovery of living specimen in 1938

Lobefins • Live in Indian Ocean at depths of 150 to 250 meters • Skeleton made of bone and cartilage (vertebral column is cartilage) • Rostral organ in head detects weak electrical currents, may aid in prey detection • Life span is 60 years, reach sexual maturity at ~ 20 years, produce 5 to 26 live young • Considered to be in danger of extinction

Ray-Finned Fishes • Ray-finned fish are named so because of the rays seen in their fins • Most dominate group of vertebrates in ocean • homocercal tails: tails with dorsal and ventral flanges nearly equal in size; vertebral column usually does not continue into the tail • scales that are thinner and more flexible; less cumbersome for active swimmers

Ray-Finned Fishes • dorsal fins, caudal fin, and 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

The Biology of Fishes: Body Shape • Shape of body determined by characteristics of habitat • Fusiform body shape: streamlined shape with a very high and narrow tail – efficient movement for active swimmers

Body Shape • Laterally compressed or deep body – allows navigation through complex habitat, e. g. , grass or corals

Body Shape • Depressed or flattened bodies – bottom-dwelling fishes

Body Shape • Globular bodies, enlarged pectoral fins – appropriate for sedentary lifestyle

Body Shape • Long, snake-like bodies, absent or reduced pelvic and pectoral fins – useful for burrowing, living in tight spaces

Fish Coloration and Patterning • Countershading is seen in open ocean fish – obliterative countershading—coloration in which the back (dorsum) is dark colored, and graduates on the sides to the belly’s pure white – when viewed from above, dark color blends in with surrounding water; when viewed from below, white belly blends in with lit surface waters • Disruptive coloration—background color of the body is usually interrupted by vertical lines; may be a dark dot (“eyespot”) present in tail area – more difficult for predators to see the fish

Fish Coloration and Patterning • 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

Fish Coloration and Patterning • Cryptic coloration: coloration which blends with the environment – used for camouflage

Locomotion • In swimming, the trunk muscles propel the fish through the water – trunk muscles are arranged in a series of muscle bands – muscles contract alternately from one side of the body to the other – contractions originate at the anterior end and move toward the tail, flexing the body and pushing against the water

Locomotion • Fish with different body forms swim in different ways – elongate fish undulate the entire body – swift swimmers flex only the posterior portion of the body – other fish are somewhere in between – fish with a dermal skeleton can only flex the area before the caudal fin – some fish swim using their fins alone without body flexure

Buoyancy Regulation • Maintaining buoyancy – sharks sink if they stop swimming – large livers produce squalene—an oily material with a density less than seawater

Buoyancy Regulation • Most fish use a swim bladder—a gas-filled 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

The Biology of Fishes 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 • Parrotfish secrete a mucus cocoon • Surgeonfish are armed with razor-sharp spines

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

Reproduction • Three reproductive modes: • Oviparity – eggs are shed into the water column and embryo develops outside the mother’s body – common in ray-finned fishes • Ovoviviparity – fertilization is internal and eggs hatch within mother’s uterus, where they are nourished by yolk stored in egg – common in sharks • Viviparity – young attach directly to mother’s uterine wall or uterus produces “uterine milk” that is absorbed by embryo – occurs in some sharks and some ray-finned fishes

The Biology of Fishes: Schooling • School of fish = group of individuals that operates in a polarized, synchronized fashion • Reasons for schooling: - more eyes increases food finding abilities and predator avoidance - predators can’t focus on an individual