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Chapter 18 The Fishes Zoology Mrs. Fleming Evolutionary perspective • Water covers over 70% of the earth. • It is believed by some that life began in the water. • Water is an essential element to all life, land and water life. • Fish dominate the watery environments and are the ancestors of all other members of the subphylum Vertebrata. Relationships • Fish belong along with the chordates in the group called the Craniata. The name describes the skull that surrounds the brain, organs, eyes, and inner ear. • It is believed that fish started out in the marine environments (salt water) and then adapted to the freshwater environments. Subphylum Vertebrata • Breaks down into 6 categories (classes) • Class Cephalospidomophi • Class Gnathostomata • Class Placoderm • Class Chondrichthyes • Subclass Actinopterygii • Subclass Sarcopterygii • The tetrapods The placoderms were small fish, usually only a few inches long. The mouth of these fish was interesting because as the lower jaw moved down the head shield moved up, thus giving a wide gape. They had no teeth, instead using a bony plate as a biting surface. Fish Body Parts Fish Fins Start of day 2 Locomotion page 285 • Swimming is less energetic that humans running. • Fish are streamlined shaped and have mucoid secretions that lubricate its body surface to reduce friction between the fish and the water. Locomotion continued • Fish move through the water • using their fins and body wall to push against the surrounding water. Muscles are arranged in a side ways W pattern. Because they extend posteriorly and anteriorly in a zigzag fashion the contraction of each muscle bundle can affect a large portion of the body wall. Body wall on both sides of the fish. Nutrition and Digestive System • The first fish were probably filter feeders and scavengers. However fish nutrition dramatically changed with the evolution of jaws. • Most modern fish are predators and spend most of their time searching for food. • Prey varies greatly. Nutrition and Digestive System • Some feed on vertebrates, larva, • • plankton, other fish. Teeth capture and hold prey, some teeth are modified for crushing the shells of mollusks or the exoskeletons of arthropods. Another method of eating is by using gill rakers that trap plankton while the fish swim. Basically they swim with their mouth open and everything goes through their gills. Teeth Digestive system • Similar to other vertebrates. • Has a stomach that stores meals • Small intestine is primary site for enzyme secretions and food digestions. Some have a spiral valve in their intestine and others have out pockets of the intestine called pyloric ceca, both of these parts increase absorption and secretory substances. Digestive System Circulation and Gas Exchange • All vertebrates have a closed circulatory system where the heart pumps blood with red blood cells containing hemoglobin through a series of arteries, capillaries, and veins. • The typical fish's circulation is a single circuit: heart-gillsbody-heart Circulation and Gas Exchange • The fish heart proper is two-chambered, • • • consisting of an upper atrium and a lower ventricle. Amphibians, basically, have a three-chambered heart, two atria and one ventricle; Reptiles have a three- or four-chambered heart; and Mammals and birds have a four-chambered heart consisting of two atria and two ventricles. Comparison • Amphibian Heart Mammal Heart Comparison Circulation and Gas Exchange • The fish heart, however, has two accessory • • • chambers, and all four chambers are contained within a single pericardial sac. One accessory chamber is the thin-walled sinus venosus, which collects blood and leads into the atrium; the other accessory chamber is the conus arteriosus, an enlargement of the main artery leading out of the ventricle. In some fishes, such as sharks, the conus arteriosus is muscular and pumps blood in the manner of the ventricle. Start of Day 3: Reproduction • • • • Most fishes are egg-layers, but many bear living young. Live-bearing fishes may be ovoviviparous, in which the eggs essentially simply hatch within the female, or viviparous, in which the unborn young are supplied nourishment through the mother's tissues. In some ovulation (or release of the egg) and birth occur at the same time. In some viviparous fishes the walls of the egg follicle are in intimate contact with the embryo, supplying it with nourishment. In the viviparous sharks, a part of the oviduct, or egg channel, is developed into a uterus, where the modified yolk sacs of the young are closely joined to pockets within the uterus. Fish Eggs Reproduction • In live-bearing fishes and in some egg- • layers, fertilization occurs internally, and methods have been evolved for introducing the sperm into the female's body. In sharks the pelvic fins of the male are modified into intromittent organs called myxoptergia, and in the male topminnows the anal fin is modified into a similarfunctioning intromittent organ called the gonopodium. Know that fins are used in the deliverance of sperm into the female fish. Stopped here on April 24 Reproduction • At least three modes of reproduction-• • heterosexual, hermaphroditic, and parthenogenetic--are found in fishes. In the most common form, heterosexual reproduction, there are separate male and female parents, but even here there is considerable variation. In some live-bearing fishes, the female is able to store sperm for up to 8 or even 10 months, and this sperm is used to fertilize new batches of eggs as they develop. In some cases, a female may carry sperm from several males at once. • In hermaphroditic reproduction, a single fish is both male and female, produces both eggs and sperm (either at the same time or at different times), and mates with other similar hermaphroditic fishes. External self-fertilization occurs in one hermaphroditic fish, which sheds egg and sperm simultaneously. In another, internal self-fertilization may occur. In certain fishes there is a time sequence of hermaphroditism, young fishes reversing their sex as they grow older. Reproduction • In parthenogenetic reproduction, unfertilized eggs develop into embryos. This is known to exist in at least one fish species, Poecilia formosa, of the Amazon River; however, even though development proceeds without fertilization in some of these females, mating with a male is still required to stimulate egg development. • Parental care also shows great diversity. • Some fishes, like the Atlantic herring, form huge schools of males and females and freely shed their eggs and sperm (milt), and then abandon the eggs. • Other fishes build nests and care for both the eggs and newly hatched young. Others have evolved methods of carrying the eggs with them, commonly in their mouths, but also in gill cavities or in special pouches on the body. Mutton Snapper Plankton Bay anchovie Silver Perch Diseases Signs of Disease • Clamped fins (fins are held abnormally close to body) • The fish refuses its usual food for more than 2 days. • There are visible spots, lesions, or white patches on the • • • • • • • fish. The fish gasps at the surface of the water. The fish floats, sinks, whirls, or swims sideways. The fish shimmies (moves from side to side without going forward). A normally active fish is still. A normally still fish is very active. The fish suddenly bloats up, and it's not due to eggs or young. The fish is scratching against tank decorations. Live Birth of a Killer Whale Another live birth Baby is alive and well. Swim Bladders and Lungs • Do fish have lungs? Sort of??? • The Indian climbing fish is an example of a fish that has • • • • pneumatic sacs. These are ducts that connect to the esophagus or antoher part of the digestive tract. They swallow air and it gets trapped in these sacs. Then gas excahnage occurs across the vascular surfaces. So the climbing fish that spends most of its time on land can still breath so to speak with a strange form of lung. Buoyancy Regulation • • • • Buoyancy= how things can or do stay a float. Humans can because of their lungs and body makeup. Fish do this in one of four ways. 1. incorporate low density compounds into their tissues livers are saturated with buoyant oils • 2. use fins for lift • 3. reduction of heavy tissues, bones are less dense and cartilage is only slightly heavier than water • 4. use of a swim bladder Swim Bladder • A fish regulates buoyancy by controlling the volume of gas in its swim bladder. • Fish gulp in air at the waters surface and forces air into their swim bladder. • The blood also can exchange gas into the swim bladder and out of it to help maintain buoyancy. Nervous System • Consists of the brain and spinal column. • Have sensory receptors for touch, temperature, • • • hearing, vision, olfaction, balance, equilibrium, detecting water movements. Fish have no eye lids Lenses are round which means that they must move them backwards and forwards to focus. Receptors for equilibrium, balance, and hearing are in the inner ear. Nervous System • How do fish hear? • They have no middle or outer ear, so they hear from vibrations in the water that strike the fish and are amplified by the swim bladder and sent to the skull. • The lateral-line system is in the epidermis and it is a series of canals with sensory receptors. Electric Fish • All organisms produce a weak electrical field from the activities of nerves and muscles. • Electroreception: is the detection of the electrical fields that a fish generates. • Over 500 species of fish can do this. • Some fish can also generate electrical current. Electric Fish • Muscles near the caudal fin are modified into • • • • organs that produce a continuous electrical discharge. Current spreads between the head and the tail. The most well known is the electric eel. The organs for producing the electric current are in the trunk. They can produce in excess of 500 volts. Can stun or kill prey. Stop here • Main Types of Litter • Type of Litter Percentage • Fast Food Waste(33%) • Paper(29%) • Aluminum(28%) • Glass(6%) • Plastic(2%) • Other(2%) • Source: Missouri Department of Transportation (MoDOT) survey of AdoptA-Highway volunteers - 1994 • • • • • • • • • • • How long does it take to decompose? ObjectDecomposition Time Styrofoam container> 1 million years Plastic jug1 million years Aluminum can200-500 years Disposable diaper550 years Tinned can90 years Leather shoe45 years Wool sock1 year Paper bag1 month Banana peel3-4 weeks