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Class Osteichthyes Bony Fish General Characteristics of Class • internal skeleton ossified (turned to bone) • Paired fins made of rays and spines, or lobed fins • swim bladder or lung present • bony scales (ganoid, cycloid, ctenoid) • gill slits covered by an operculum (single external gill opening) • 2 chambered heart Actinopterygii VS Sarcopterygii • Ray-finned • fins with multiple parallel supports • fins controlled by muscles in body wall • Lobe-finned – Have lungs as well as gills – Can live periods outside of water • Ex: lung-fish coelacanth Modern Fishes • Great Diversity – 27,000 species – Representing 96% of all living fishes or about ½ the vertebrates – Thought to be 5-10,000 undescribed species • Diverse Habitat – Highest mountains to 8,000m below surface – Hot springs (44ºC) to polar seas (-2ºC) – Freshwater to extreme salt concentrations The Aquatic Environment: Life in the Water • Water has a high specific heat – Endothermy is not needed • Less O2 in water – efficient gills required • Water is dense – bony skeleton not needed (but Osteichthyes does) • Water will conduct electricity, air does not – Can use this to help detect predators or prey • Water is more viscous than air – Develop methods to propel self Ectothermy vs. Endothermy • Ectotherms– Low metabolic rates – Little insulation – Rapid heat exchange F I S H • Endotherms– High metabolic rate – Insulation (large quantities) hair/feathers – Minimize heat exchange Modern Fish: Agnatha: Jawless fish (primitive) ex: Lamprey and Hagfish Chondrichthyes: cartilaginous fish ex: Sharks Osteichthyes: bony fish ex: Perch, salmon … External Anatomy Operculum Dorsal Fins Caudal Fin Pectoral Fin Pelvic fin Anal fin SCALES Figure 24.18 Tale of Tails • A) - Heterocercal, (B) - Protocercal, (C) - Homocercal, (D) - Diphycercal Sharks Lungfish Coelacanth Perch Swim Bladder • Arose from the paired lungs • Needed to achieve neutral buoyancy • Secreting gas into the bladder as it swims up, and removing gas as it swims down. Types of gas bladders • 1. Physostomous Fish • Pneumatic duct connect swim bladder to esophagus used for air removal • 2. Physoclistous Fish • No tube - gas in blood used to fill bladder How Swim Bladder Works Physoclistous Fish • Ovale – a vascularized area of the swim bladder – Used to get air out of the swim bladder • Rete mirabile – moves gas from the blood into the swim bladder Flow of water is opposite the flow of blood Maximal Oxygen uptake This is called: Counter-current Exchange System Ventilation in Fish: The Gill • Gills: – thin filaments/ covered epidermal membrane • These membranes fold into lamellae. – Richly supplied with blood – Covered by operculum • (protection and pumping system) • Mouth gills out operculum Osmotic Regulation • Freshwater (fish are hyperosmotic regulators) – Low salt – so water tends to enter the bodies osmotically and salt is lost by diffusion outward. – Body has mucous covering to try to prevent this, but most exchange occurs in the gills • Defense against this – Excess water pumped out by kidneys which create very dilute urine – Salt absorbing cells – move salt from water to blood. Osmotic Regulation • Marine (fish are hyposmotic regulators) – High salt – so fish need to lose water and gain salt. (risk: fish can dry-out) – To compensate for water loss – a marine fish drinks seawater. • Salt is carried by the blood to the gills where they are secreted by salt-secretory cells. Integument • Live cells next to environment • Mucous layer (to get rid of bacteria?) • Scales evolved from armor for protection: – A. Cycloid (perfectly smooth) – B. Ctenoid (comb-like) Pigment cells-Under Neural Control • 1. Chromatophores-contain true pigments – A. carotenoids – B. erythrophores – C. melanocytes • 2. Iridocytes-contain waste products (guanin) helps to reflect light Digestion • Buccal cavity esphogusstomachintestines • Some species don’t have a stomach (minnows) possess a pyloric caecae Food swallowed whole Primitive teeth Gill rakers and gill filaments screen objects exchange air Generalized feeders Pharyngeal teeth: last arch in back, help to tear