Diversity Of Fishes Week 4

Taxonomic rank

 7 main ranks

 Many additional ones usually by adding ‘sub’, ‘infra’, ‘super’

 New findings changes things often

 When a previously assigned rank proved to be paraphyletic (not a clade) the previously assigned rank (e.g. class) is often replaced with ‘grade’

Traditional classification of vertebrates (outdated)

 Subphylum Vertebrata

 Class Agnatha (jawless fishes)

 Class Chondrichthyes (cartilaginous fishes)

 Class Osteichthyes (bony fishes)

 Class Amphibia (amphibians)

 Class Reptilia (reptiles)

 Class Aves (birds)

 Class Mammalia (mammals)

Monophyletic or paraphyletic?

Amphioxiformes (lancelets)

 Sister group to vertebrates with a common ancestor

 Differ from conventional fishes by lacking most parts of the head, vertebrae, scales, genital ducts, a heart, red blood cells, hemoglobin, specialized respiratory structures, and having only one cell layer in the epidermis

 Have up to 25 pairs of gonads

 Live in sandy bottoms up to 7 years, have pelagic larvae

Myxiniformes (hagfishes)

 Hagfishes are a primitive non-vertebrate group in their own superclass (myxinomorphi) constituting the sister group of vertebrates and the basal craniate taxon

 Produce copious amounts of slime

 Slime has various functions but can also clog their own gills

 Can get rid of slime by tying themselves in a knot (has other functions as well)

Hagfish characteristics

 They posses four rudimentary hearts:

 A primary three-chambered branchial or systemic heart

 Three auxiliary single-chambered hearts

 Hagfish blood is isosmotic-same salinity as surrounding-, which makes them stenohaline- having a narrow range of salinity tolerance

 Respiratory system:

 Oxygen uptake occurs both at the gills (water uptake through nostrils) and capillary beds at the skin (handy when its head is buried in a carcass)

 Low oxygen consumption and metabolic rates (handy for when buried in mud and when prey encounter rate is low)

Hagfish characteristics cont.

 Digestive system:

 Lack true stomach

 Immune system:

 No antibody production (as all gnathostomes do have) but production of proteins called variable lymphocyte receptors to respond to infectious agents

 Sensory system:

 Lack complete eyes, but have photosensitive receptors

 derived characteristic: visual sensory input has been lost over time in the deep, dark habitats that hagfishes occupy

 Food is found through smell and touch by their barbels

 Spawn repeatedly during their lives and produce a few large eggs each time

Petromyzontiformes (lampreys)

 The notochord in lampreys is supported by primitive vertebrae made of cartilage

 Many lampreys are parasitic on other vertebrates, and have circumferential teeth on the oral disk that aid in grasping live prey

 Lampreys have the largest diploid chromosome number of any vertebrate, between 140-170

Lamprey reproduction

 Produce many small eggs and adults die after spawning

 Larvae are known as ammocoetes who may live and filter- feed up to 7 years

 Adults life span:

 in non-parasitic species about 6 months during which no feeding occurs

 In parasitic species about 1-3 years during which they live off blood, body fluids or flesh of their host

 All non-parasitic species are freshwater, some parasitic species are anadromous (all spawn in freshwater)

Chimaeras

 Also know as ratfishes or rabbitfishes

 Share with sharks: cartilaginous skeleton, ceratotrichial fins, spiral valve intestine, lack gas bladder, using an oil filled liver for buoyancy, no larval stage

 Different from sharks: upper jaws are immovably attached to the braincase (their name, Holocephali – ‘whole head’, refers to this fusion)

 Teeth are continually growing tooth plates instead of replaceable dentition

Chimeras cont.

 Geographically widespread, mostly found below 80 m to as much as 2600 m

 Lack scales except for small denticles along the midline on the back

 A single gill flap covers four internal gill openings (as in bony fish) instead of having five or more external gill slits (like sharks)

 Poison-laden spine in first dorsal fin

 Extant chimaeras represent a small fraction of a previously successful and diverse group

Modern elasmobranchs

 Highly derived from the abundant, diverse elasmobranchs of the Mesozoic

 Characterizing traits that have remained the same: cartilaginous skeleton, placoid scales, internal fertilization, replacement dentition, multiple gill slits

 Other characters: Upper jaw free from braincase, making it protrusible during feeding, fin rays are soft, unsegmented ceratotrichia, lack gas bladder, use large livers for buoyancy, have spiral valve intestine

Elasmobranch Reproduction

 Males possess pelvic fin-derived intromittent organs (myxopterygia or claspers)

 Most sharks mature in 6-18 years, older ages are not uncommon

 Females either lay eggs (oviparity) or nourish embryos internally for several months before giving birth (viviparity)

Elasmobranch Habitat

 Most inhabit marine waters on the continental shelf

 Only about 5% dwell in the open ocean, and 5% in freshwater

 Seldom occur in deeper water than 3000 m

 Mostly occur in coastal areas, and 170 species are capable of entering estuaries

 This puts sharks close to people, and at risk of human impact

Elasmobranch movement

 The evolutionary history is characterized by the development of traits that favor movement at the lowest possible energetic cost

 The placoid scales serve a streamlining function

 Sharks keep their buoyancy by:

 reduced skeletal weight (cartilage has 55% the specific gravity of bone)

 Low density substances, like large oil-rich liver

 Oil-rich liver instead of gas bladder advantages:

 ability to change depth quickly

 Energy reserve (liver 90% oil) when food is scarce

 Sharks can move extensive distances

Elasmobranch Metabolism

 Emphasis on efficient energy use: low metabolic rates

 Reduced energy need as compared to bony fish

 Some lamnid sharks can conserve heat generated in the active swimming muscles, maintaining elevated body temperatures

 Slow metabolism linked to slow growth and long life spans

 Linked to old age of maturation, slow turn-over rate, and higher sensitivity to overfishing

Elasmobranch Feeding Habits

 Apex predators, but also filter feeders (basking shark, megamouth shark, whale shark, manta ray), and benthic invertebrates feeders (most skates and rays)

 One ectoparasitic elasmobranch: Cookie Cutter Shark

 Dentition morphology correlates strongly with food type

Elasmobranch Sensory Physiology

 Olfactory sensitivity (smell) is strong

 Vision is good as well

 Acoustic sensitivity and sound localization is well developed

 Very high electrical sensitivity

 Experiments have shown that predatory sharks use weak electrical cues, and ignore strong olfactory cues, to home in on prey

 Prey detection with sensors in saw of sawfish is relative recent discovery

 The relatively large brain of sharks is to allow for the integration of all this information in the central nervous system

Subdivision Selachii (sharks) vs. subdivision Batoidea (skates and rays)

Order Heterodontiformes

 Bullhead Sharks or Horn Sharks

 Have two types of teeth; sharp front teeth and flat rounded back teeth

 Small (up to 150 cm) bottom dwellers

 Oviparous

 Spine in fontal dorsal fin

 Anal fin present

 8 species, marine

Order Orectolobiformes

 Carpet, blind, bamboo, zebra, nurse, whale sharks and wobbegongs

 Two dorsal fins, without spines

 Many have barbels

 Small gill slits with fifth overlapping the fourth

Order Lamniformes

 Mackerel sharks; Well-known group of large sharks (e.g. Great white, Basking, Mako, Megamouth, Goblin, Thresher)

 Large mouth, jaws extending far back

 Mostly large predators except for basking shark and megamouth shark

 Ovoviviparous: eggs are fertilized and hatched internally

 Display oophagy; first hatched eats others

 Two dorsal fins, no spines

 Anal fin present

 15 species, marine

Order Carcharhiniformes

 Ground sharks make up more than half the shark species

 224 species, mostly marine

 Enter freshwater periodically, with the bull shark as a notable example (e.g. Amazon, Mississippi River, Potomac River)

 Mostly viviparous

Order Hexanchiformes

 Frilled sharks and cow sharks

 Most primitive sharks

 One dorsal fin

 Six or seven gill slits

 ovoviviparous

 Five species, marine

 Deepwater -dwelling

 Rare and near-threatened

Order Echinorhiniformes

 Bramble sharks

 Two small dorsal fins

 No anal fin

 Large dermal denticles on body

 Ovoviviparous

 Two species, marine

Order Squaliformes

 Dogfish, gulper, lantern, sleeper, rough and kitefin sharks

 97 species, marine

 Two dorsal fins, no anal fin

 Five gill slits

 Especially dogfish sharks know for their slow maturation

 Dogfish liver contains squalamine which is antibacterial and, also used in anti cancer drugs (now being synthesized)

Order Squantiformes

 Angel sharks

 15 species, marine

 Flattened bodies; pectoral and pelvic fins held horizontally

 No anal fin, and lower lobe of caudal fin is larger than upper

 ovoviviparous

Order Pristiophoriformes

 Sawsharks (not the same as sawfish, see later slide)

 Blade-like snout edged with teeth

 Two dorsal fins, lack anal fin

 Five-six gill slits depending on species

 Five species, marine

 barbels

Order Torpediniformes

 Electric rays and numbfishes

 59 species, marine

 Capable of producing electric discharge from 8-220 volts depending on species

Order pristiformes

 7 species, marine and freshwater

 Sawfishes

 Sawlike rostrum with electrosensitive pores

 Breath with two large spiracles and have ventral gills (characteristic for Batoidea)

 Ovoviviparous; live pups rostral blades are soft and teeth are covered

 No barbels

Order Rajiformes

 285 species, marine

 Bowmouth guitarfishes, guitarfishes, wedgefishes, and skates

 Large pectoral fins, up to two dorsal fins, no anal fin

Order Myliobatiformes

 Stingrays, butterfly rays and eagle rays

 183 species, marine and freshwater

 Formerly included in the Rajiformes, but studies have shown it is a more derived monophyletic group

 ovoviviparous

The living coelacanths

 Once thought extinct, a living specimen of Latimeria chalumnae was trawled up in 1938

 Characteristics:

 thin bony layer vertebral spines and fin rays

 Unconstricted and unossified modified notochord

 Fleshy, lobed pectoral, pelvic, anal, and second dorsal fins

 A symmetrical three-lobed diphycercal tail (vertebrae extend to the tip of the tail)

 Large thick bony scales

 Numerous osteological features

Order Coelacanthiformes

 No lungs, but fat-filled gas bladder for buoyancy (other characteristics also point out it is not ancestral to tetrapods)

 Highly electrosensitive

 Ovoviviparous

 Small clutch size and late maturation

 2 species, marine

Subclass Dipnoi; Order Ceratodontiformes

 Lungfishes (lungs, gills)

 Two methods of breathing

 All extant lungfishes occupy freshwater

 Have toothplates: teeth are not attached to the jaw margin but only occur on interior bones

 Some are obligatory, some are facultative air breathers

 6 species

Lungfish characteristics

 Best known for their ability to survive desiccation of their habitat

 This estivation – state of dormancy during the summer – involves construction of a subterranean mud cocoon

 Dormant period lasts 7-8 months

 Rely entirely on air breathing

 Heart rate drops

 body proteins metabolized

 Weight loss

 When rain returns they emerge and cannibalize on smaller lungfish

Class Actinopterygii, Subclass Cladistia

• Bichirs and Reedfish

• Was taxonomically controversial:

  • lobelike fins (sarcopterygian trait)

  • ganoid scales (like gars)

  • gular plates (like coelacanths)

  • spiracles like sturgeons

  • external gills when young and double ventral lung (like some lungfishes)

  • Modified heterocercal tail (as in gars and bowfins)

  • Spiral valve intestine (shared by all major groups)

• However, they have a high number of autapomorphic characters that are analogous to traits in others

Order Polypteriformes: Bichirs and Reedfishes

• 16 species, freshwater

• Bichirs:

  • 5-18 dorsal finlets consisting of spine with vertical rays

  • Pectoral fin lobe-shaped in a unique way

  • Relative few and small chromosomes

  • Only four gill arches

• DNA research settled the current phylogenetic placement of this group

Order Acipenseriformes Subclass Chondrostei

 Sturgeons and paddlefish

 25 species of sturgeons, all in one family (Acipenseridae), coastal and freshwater

 All species spawn in freshwater, some are migratory or anadromous

 Four barbels

 Five rows of scutes

 Heterocercal tail, One dorsal fin

 Largely cartilaginous skeleton

 Unrestricted notochord

 Exceptionally long-lived, few spawning events

 Commercially valuable (caviar), overexploited

 These two factors plus habitat destruction endanger the sturgeon

Order Acipenseriformes Subclass Chondrostei Freshwater Paddlefish

(Family Polyodontidae)

 Larvae similar to those of sturgeon

 Heterocercal tail

 Unrestricted notochord

 Largely cartilaginous skeleton

 Two small barbels

 No scutes or scales except for few minute scales

 Not benthic swimmers but pelagic zooplankton and fish eaters

 Rostral paddle contains electroreceptors; used to detect prey

 Same problems as sturgeons with regards to conservation

Order Lepisosteiformes Subclass Neopterygii

 Gars

 Seven species, fresh and brackish water

 Entirely ossified skeleton

 Diamond ganoid scales

 Abbreviated heterocercal tail

 Eggs are toxic

 No electroreception

Order Amiiformes Subclass Neopterygii

 Bowfin

 Two species, freshwater

 More derived than gars

 Primitive features: abbreviate heterocercal tail and rudimentary spiral valve intestine

 More derived: vertebrae, cycloid scales

 Gular plate on the underside of the head

 One long dorsal fin; swims through undulation of this fin

 No electroreception