Chapter 6. Osteichthyes Originated in late Silurian Radiated in Devonian (with other fish groups) Sister taxon to acanthodians Derived Traits (synapomorphies) Lateral line canals Opercular and pectoral dermal bones Fin webs supported by rays Endochondral bone Two lineages: Sarcopterygians lobe-finned fish Actinopterygians ray-finned fish Sarcopterygii Extant forms lungfish (Dipnoi) and Coelacanth (Actinista) Dipnoans Upper jaw fused to cranium (autostyly) Durophagous Early forms marine, living forms freshwater Median fins fused around posterior 1/3 of body Australian lungfish (Neoceratodus) 1sp uses gills to breathe (lungs for stressed periods) Large scales, conspicuous lobed fins South American lungfish (Lepidosiren) 1 sp (little known) African Lungfish (Protopterus)- 4 sp closely related to S.A. form Gills used for eliminating CO 2 ; Lungs for breathing Aestivation in dry periods (6 months to 4 years) Sarcopterygii (cont.) Actinista Coelacanths (Latimeria) Symmetrical 3-lobed tail Fossils from up to Cretaceous rediscovered in 1938 then 1952 Off Madagascar (in 1998 second group in Indonesia) Up to 2 m long, fat-filled, ossified swim bladder Electroreceptive organ in head Livebearers Move fins like legs as swim Sister taxon to dipnoi + tetrapods
Actinopterygii Evolutionary trends Increasing mobility and specialization of jaws Protrusible maxilla and premaxilla Allows suction Pharyngeal jaws and teeth Reduction in armor Increasing mobility of fins and locomotor ability 27,000 species (most of any vertebrate) Several lineages Primitive forms: Polypteriformes bichirs 11 sp. Most primitive lineage Heavily armored, well ossified skeletons Larvae have external gills (perhaps ancestral?) Heterocercal tails Primitive Forms (cont.) Acipenseriformes Sturgeons 24 species Strongly heterocercal tail Armor plates Benthic Anadromous or freshwater Source of caviar heavily impacted Paddlefish 2 species One in Mississippi R., one in China Heterocercal tails Rostrum with electroreceptive function Filter feeders Slightly more derived groups Lepisosteiformes gars 7 sp. North American Elongate predators Heavily armored Amiiformes 1 species (Amia) bowfin Advanced jaws (suction) and loss of armor Heterocercal tail
Modern fishes Teleostei 4 clades: Osteoglossomorpha (Bony tongues) 220 species tropical freshwaters Arawana, Mormyrus Elopomorpha 800 sp. Most are eels Leptocephalous larvae (small headed) Drift with currents Includes tarpon, bonefish, and eels American eel catadromous life history Breeds in ocean (sargasso sea) Enter rivers to live to maturity Teleostei (cont.) Clupeomorpha 360 sp. Herring, shad, anchovies, sardines Filter feeders (ram ventilation, strain water with gill rakers) Some are anadromous (american shad) Euteleostei most modern fish Basal groups: Ostariophysi Euteleostei 25-30% of living fishes, 80% of freshwater forms Highly diverse but two unifying characteristics Weberian apparatus» Bones connect swim bladder to inner ear» Helps with hearing Fright chemicals in skin» Released by damage changes behavior of others Characins, carps and minnows, catfishes, knifefishes Euteleostei (cont.) Esocidae (pikes) and Salmonidae (trout and salmon) Pectorals low and pelvics well back Derived euteleosts Acanthopterygii Spiny finned fishes 13,500 sp Marine and freshwater habitats Silversides, grunions, flying fishes, cyprinodonts (killifishes and livebearers) Perciformes largest order of fishes 9300 sp. Perch, bass, darters, billfish, tuna, cichlids, most coral reef fish
Fish Locomotion 3 general types: Anguilliform, eel-like swimming Carangiform, undulations limited to caudal 1/3 (most fishes) Ostraciiform, only caudal fin moves (boxfishes) Other types too - e.g. rajiform (skates/rays) Fish Locomotion (cont.) Must overcome gravity and drag Gravity - produce lift (swim bladders) Drag produce thrust Advanced in groups like tunas Thin caudal peduncle, expanded tail fin Minimizing drag Fusiform shape (inertial drag), smooth skin (viscous drag) Reproduction and Conservation Great diversity among actinopterygians Most produce eggs Some with elaborate parental care Nests, mouth brooders, pouch brooders etc. Freshwater teleosts Generally, small number of large eggs Demersal (attached) Conservation concerns- highly threatened Large human impact In U.S. 160 of 800 native species threatened (20%) Reproduction and Conservation (cont.) Marine Teleosts reproduction Often pelagic eggs that hatch into larvae Larvae float and feed on plankton Reduces competition with adults Removes eggs from predators Allows larvae to forage in most rich zone Increases chances of colonization Conservation issues Good vs. bad years for reproduction (weather) Means, current stock bad predictor of future stock Makes management difficult (overfishing is the result)
Deep Sea Fishes Diversity, size, and abundance decreases with depth All greater under productive regions Mesopelagic fishes (to 1000m) Migrate vertically with low light Move into higher productivity for feeding Deep Sea Fishes Bathypelagic fishes (1000-5000m) No vertical migration generally lower activity rate Large eyes, mouth, stomach, teeth Low prey availability eat whatever comes along Light organs prey attraction, communication Ceratioid anglerfishes parasitic males Coral Reef Fishes Acanthopterygian teleosts Two shifts Diurnal brightly colored, feed and hide in crevices Nocturnal dull colored, feed on surface of reef Hide during day Conservation issues Collecting (cyanide poisoning) Global warming (2 months of heat killed 95% of Belize s coral) Bleaching??