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Fishes I
Fishes I Chordate taxonomy Dichotomous keys Fins and scales Hagfishes Lampreys Sharks, skates and rays Chimaeras Sturgeons Gars and Bowfins Chordate Taxonomy Phylum Chordata (Subphylum Cephalochordata - lancelets: 0 in BC) Subphylum Urochordata - tunicates Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fish Class Actinopterygii – ray-finned fishes (Class Sarcopterygii – lobe-finned fishes:0 in BC) Class Amphibia - amphibians Class Reptilia - reptiles Class Aves - birds Class Mammalia - mammals Subphylum Cephalochordata: the lancelet Branchiostoma Dorsal nerve cord Notochord Brain Gill slits Post-anal Tail Chordate Taxonomy Phylum Chordata Subphylum Cephalochordata (lancelets) Subphylum Urochordata (tunicates) Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fish Class Actinopterygii - ray finned fishes Class Amphibia - amphibians Class Reptilia - reptiles Class Aves - birds Class Mammalia - mammals Subphylum Urochordata: tunicates Adult “sea squirts” are sessile filter feeders Chordate Taxonomy Phylum Chordata Subphylum Cephalochordata (lancelets) Subphylum Urochordata (tunicates) Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fish Class Actinopterygii - ray finned fishes Class Amphibia - amphibians Class Reptilia - reptiles Class Aves - birds Class Mammalia - mammals Characteristics of Subphylum Vertebrata 1. Chordate characteristics - notochord, dorsal nerve cord, pharyngeal pouches, post-anal tail. 2. Cartilaginous or bony endoskeleton with a backbone and vertebrae (except hagfish). 3. Pronounced cephalization: well-developed nervous system with anterior brain and specialized receptors (nose, eyes, ears). 4. Closed circulatory system with 2 to 4 chambered heart and blood with hemoglobin. 5. Excretory system of paired kidneys 6. Endocrine system of ductless glands (adrenal, pituitary, thyroid…) Fish Taxonomy Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fishes Subclass Elasmobranchii – sharks and rays Subclass Holocephali – chimaeras (ratfish) Class Actinopterygii – ray-finned fishes Subclass Chrondrostei – sturgeons, paddlefish Subclass Neopterygii – modern bony fishes (Class Sarcopterygii – lobe-finned fishes) Actinopterygii and Sarcopterygii are sometimes referred to collectively as Osteichthyes – bony fishes Fish Taxonomy Subphylum Vertebrata Superclass Gnathostomata Class Chondrichthyes - cartilaginous fishes (850 species – 24 in BC) Class Actinopterygii – ray-finned fishes (~25,000 species ~500 in BC) Class Sarcopterygii – lobe-finned fishes (7 species – 0 in BC) DICHOTOMOUS KEYS, e.g. Key to Families of Freshwater Fishes in Canada 1a. Mouth without true jaws ........…..LAMPREYS 1b. Mouth with true jaws ....................................2 2a. homocercal tail .............................................3 2b. heterocercal tail .......................STURGEONS 3a. Large bony plate between lower jaws ... BOWFINS 3a. Soft between lower jaws and bony plate not present ...............................................................4 Key to Families of Freshwater Fishes in Canada 4a. Pelvic fins present ..................................5 4b. Pelvic fins absent .......................... EELS 5a. Adipose fin absent ................................. 6 5b. Adipose fin present ..............................11 Key to Families of Freshwater Fishes in Canada 11a. Lack scales, barbels present ... CATFISHES 11b. Scaled, barbels absent .......................... ...12 12a. Scales ctenoid .................................. PERCH 12b. Scales cycloid ........................................... 13 13a. Mouth not extending beyond eye ........... 14 13b. Mouth extends beyond eye…SALMONIDAE Fin types 1st dorsal 2nd dorsal adipose pectoral anal pelvic caudal Types of caudal fins Diphycercal (coelocanth) Homocercal (perch) Heterocercal (shark) Types of fish scales 1. Placoid – sharks and rays spine pulp basal plate Placoid scales = “denticles” Types of fish scales 1. Placoid – sharks and rays 2. Cosmoid – lung fish Similar to placoid scales and probably evolved from the fusion of placoid scales Types of fish scales 1. Placoid – sharks and rays 2. Cosmoid – lung fish 3. Ganoid – sturgeon, bowfins, gars, etc. gar Modified cosmoid scales with pegs and sockets Types of fish scales 1. Placoid – sharks and rays 2. Cosmoid – lung fish 3. Ganoid – sturgeon, bowfins, gars, etc. 4. Leptoid – most fish - cycloid trout herring Smooth posterior margin Types of fish scales 1. Placoid – sharks and rays 2. Cosmoid – lung fish 3. Ganoid – sturgeon, bowfins, gars, etc. 4. Leptoid – most fish - cycloid - ctenoid ctenii on posterior margin perch snapper Most fishes have scales … but some lack scales swordfish mackerel ratfish catfish eel … and some that appear to lack scales have a complete coating of deeply embedded scales Blue-fin tuna ENVR 242 Taxonomy for BC Subphylum Vertebrata Superclass Agnatha - fish without jaws Class Myxini (hagfish) Order Myxiniformes Family Myxinidae (1 genus, 2 species) Pacific hagfish Eptatretus stouti Hagfish no paired fins caudal fin only Hagfish slime glands no eyes Cartilaginous skeleton: notochord persists in adult as cartilage rod no vertebrae Hagfish Hagfish Hagfish Hagfish mouth barbels two rows of teeth on tongue Class Myxini • 30 species (2 sp. in BC: Pacific Hagfish and Black Hagfish) • all marine • mouth modified for sucking – jawless with two rows of teeth and barbels • no eyes • no paired fins (caudal fin only) • cartilaginous skeleton • notochord extends the length of the body as cartilaginous rod (no vertebrae) • slime glands • predators and scavengers on invertebrates and dead and dying fish ENVR 242 Taxonomy for BC Subphylum Vertebrata Superclass Agnatha - fish without jaws Class Petromyzontida (lampreys) Order Petromyzoniformes Family Petromyzontidae (1 genus, 2 species) tooth at top of mouth with 3 points prominent eyes Pacific Lamprey (Lampetra tridentata) Maximum size: 76 cm Lamprey dorsal fins prominent eyes gill pores Lampreys oral disc has numerous teeth (no jaws!) dorsal fins gill pores no barbels Cartilagineous skeleton: Notochord persists in adult, surrounded by cartilage pipe with rudimentary vertebrates Sea lamprey Lamprey - Life history migrate to lakes or ocean adults reproduce in streams and die parasitic adult anadromous - spend all or part of their adult life in salt water and return to freshwater streams and rivers to spawn. (larvae) Lampreys • 35 species (2 in BC: Pacific Lamprey and River Lamprey) • notochord – surrounded by a cartilaginous pipe with rudimentary vertebrae • parasites on fish • jawless, sucking disc with many teeth, no barbels • prominent eyes • dorsal fins (and caudal fins) ENVR 242 Taxonomy for BC Subphylum Vertebrata Superclass Gnathostomata - jawed vertebrates Class Chondrichthyes - cartilaginous fish Subclass Elasmobranchii (sharks, skates, rays) Order Lamniformes (regular sharks) Order Squaliformes (dogfish & sleeper sharks) Order Rajiformes (skates & rays) Subclass Holocephali (ratfish=chimaeras) Subclass Elasmobranchii (sharks, skates, rays) shark shark ray skate Sharks 460+ species (12 in B.C.) Streamlined body Cartilaginous skeleton Oil in Liver Must swim continuously Sharks Paired pectoral and pelvic fins Two dorsal fins caudal fin Shark picture heterocercal tail caudal fin water enters spiracles and/or mouth… Shark picture heterocercal tail … and exits through 5 to 7 pairs of gill slits How sharks (almost) achieve neutral buoyancy • Cartilaginous skeleton (bone is dense) • Pectoral fins, surface of the head and heterocercal tail provide lift • Large livers with large quantities of lipids (sp. gr.= 0.90-0.92) and squalene (sp. gr. = 0.86). (Specific gravity of seawater = 1.026.) … but are still negatively buoyant and must swim continuously Shark picture teeth are shed and replaced Most sharks are predators with large teeth … … but the largest sharks filter plankton (free floating, mostly microscopic organisms) maximum length: 15.2 m ... but most <10 m Basking shark Cetorhinus maximus Temperate zone oceans of the world; In BC: Strait of Georgia, Queen Charlotte Sound, Prince Rupert The whale shark filters plankton not in BC The world’s largest fish – maximum length: 18 m Sharks’ teeth are modified placoid scales sensitive to water pressure and vibration sensitive to weak electric fields (and possibly temperature, water pressure and salinity) Sharks have relatively short digestive tracts … …but the spiral valve increases surface area. The blood of sharks is isosmotic to sea water and contains high concentrations of urea and trimethylamine oxide (TMAO – from ammonia) and low concentrations of NaCl (about 1/3 that of seawater). kidney rectal gland excretes NaCl Internal fertilization ! Claspers (in males) = modified inner edges of pelvic fins: inserted into female cloaca for sperm transfer oviparous – eggs laid outside the mother’s body ovoviviparous – mother retains eggs in uterus; embryo nourished by egg yolk; young born alive viviparous – embryos develop in the uterus nourished by the mother’s blood through a placenta Most sharks are viviparous! In viviparous sharks, the embryo receives nutrients from its mother via a yolk sac placenta embryo yolk sac placenta yolk stalk uterus Shark egg case (“mermaid’s purse”) embryo yolk egg case (keratin) Direct development: a shark pup emerges from its egg. Class Chondrichthyes Skates and rays: cartilaginous fish collectively known as “batoids” What is the difference between skates and rays? Rays have 1-lobed pelvic fins and stream-lined tails without fins (may have spines) Sting rays, Galapagos Sting ray with spine (modified placoid scale) with venom gland at base. Manta ray: a plankton feeder 6m Skates have 2-lobed pelvic fins and fleshy tails with small dorsal fins (and sometimes thorns) Clearnose Skate thorns skate Mermaid’s purse (skates) All skates lay eggs; rays are ovoviviparous! Rays • fewer species • long, thin tail without fins • stingray tail armed with spines • ovoviviparous • 1-lobed pelvic fins Skates • more species • thicker tail with fins • thorns on tail • oviparous •2-lobed pelvic fins Class Chondrichthyes – cartilagenous fishes Subclass Elasmobranchii - sharks, skates and rays • cartilaginous endoskeleton • placoid scales • 5 to 7 pairs of gills and gill slits • no swim bladder • heterocercal tail (sharks) • spiral valve in intestine • urea in muscle tissue – blood isosmotic to seawater • direct development • internal fertilization • oviparous, ovoviviparous, or viviparous • senses of smell, vibration sensation (lateral line system) , and electroreception (ampullary organs of Lorenzini) welldeveloped ENVR 242 Taxonomy for BC Subphylum Vertebrata Superclass Gnathostomata - jawed vertebrates Class Chondrichthyes - cartilaginous fish Subclass Elasmobranchii (sharks, skates, rays) Subclass Holocephali (ratfish) Spotted ratfish Hydrolagus colliei = only ratfish sp. in B.C. Spotted ratfish - Hydrolagus colliei spine long thin tail large pectoral fins Skeleton of cartilage Spotted ratfish - Hydrolagus colliei upper jaw fused to the skull teeth are large plates bottom feeders on mollusks and other invertebrates Spotted ratfish - Hydrolagus colliei male, identifiable by the paired pelvic claspers and the cephalic clasper Spotted ratfish Hydrolagus colliei male, identifiable by the paired pelvic claspers and the cephalic clasper Spotted ratfish egg capsule - Hydrolagus colliei Subclass Holocephali • 30 species (1 species in BC) • cartilaginous skeleton • lack scales • males possess pelvic and cephalic claspers • upper jaw fused to skull, mouth ventral ENVR 242 Taxonomy Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fishes Subclass Elasmobranchii – sharks and rays/skates Subclass Holocephali – chimaeras (ratfish) Class Actinopterygii – ray-finned fishes Subclass Chrondrostei – sturgeons, paddlefish Subclass Neopterygii – modern bony fishes Class Actinopterygii – ray-finned fishes Subclass Chrondrostei – sturgeon Sturgeon (Acipenser) barbels Sturgeon 2 species in BC: • Green Sturgeon (Acipenser medirostris) • White Sturgeon (Acipenser transmontanus) Green: marine White: freshwater Sturgeon 2 species in BC: • Green Sturgeon (Acipenser medirostris) • White Sturgeon (Acipenser transmontanus) Sturgeons are the largest fish found in freshwater. White Sturgeon (Acipenser transmontanus) Columbia and Fraser Rivers up to 6.1 m and 816 kg Sturgeon • cartilaginous skeleton • heterocercal tail • head covered with bony plates • 5 rows of bony scutes (remnant ganoid scales) • no teeth and 4 barbels • prey on benthic invertebrates and fish ENVR 242 Taxonomy Subphylum Vertebrata Superclass Agnatha Class Myxini (hagfish) Class Petromyzontida (lampreys) Superclass Gnathostomata Class Chondrichthyes - cartilaginous fishes Subclass Elasmobranchii – sharks and rays Subclass Holocephali – chimaeras (ratfish) Class Actinopterygii – ray-finned fishes Subclass Chrondrostei – sturgeons, paddlefish Subclass Neopterygii – modern bony fishes (Infraclass Holostei – gars and bowfin: 0 in BC) Infraclass Teleostei – majority of modern bony fish: >20,000 extant species globally Bowfin (Amia) Gar Pike (Lepisosteus) Infraclass Teleostei majority of modern bony fish: > 20,000 extant species globally e.g. salmon, herring, rockfish, groundfish…etc…etc.
