L20 - Sharks and Rays Flashcards
What are the subclass of the class chondrichthyes?
Elasmobranchii, Holocephali
What is the sub-class elasmobranchii?
1,268 extant spp, can be broadly divided into sharks and rays. Subdivision Batoidea (rays, skates and sawfish), subdivision selachii (sharks)
What is the sub-class Holocephali?
55 extant spp, Chimaeras
What do all batoids share?
All batoids share a stereotypical bodyform. Enlarged pectoral fins fused to a flattened body, gill slits on ventral surface, pair of spiracles on dorsal surface.
What are the 4 orders of batoids?
Rhinopristiformes (guitarfishes, sawfishes)
Torpediniformes (electric rays)
Rajiformes (skates)
Myliobatiformes (sting rays, eagle rays)
What is the shark subdivision Selachii?
8 pristiophoriformes (sawsharks)
6 hexanchiformes (cow and frill sharks)
9 heterodontiformes (bullhead sharks)
24 squantiniformes (angel sharks)
45 orectolobiformes (carpet sharks)
135 Squaliformes (sleeper sharks, dogfish sharks)
16 Lamniformes (mackerel sharks)
286 carcharhiniformes (requiem sharks)
Elasmobranch and Teleosts?
Both have pairs of filaments. Teleosts (bony fish) have gills hidden.
Teleosts fins?
Paired fins, very flexible, retractable fins supported by soft and spiny rays in bony fishes.
elasmobranch fins?
Rigid, inflexible, non-retractable fin of present day elasmobranchs
Heterocercal tail?
Different tail, upper and lower lobes different. True heterocercal - sharks, abbreviated heterocercal - sturgeon, bowfin
Homocercal tail?
Same tail, externally symmetrical. Most bony fish virtually all lower lobe
Buoyancy?
Elasmobranchs do not possess swim bladders. Mainly rely on dynamic lift to maintain position in the water column, some also use static lift from lipids.
Dynamic lift?
W = submerged weight of fish
B = hydrodynamic lift from pectoral fins
C = lift from caudal fin
If W = B + C, neutral buoyancy
If W > B + C, negative buoyancy = sink
I.e. if fish stops forward movement it will sink
What are the disadvantages of static lift from lipids?
- lipid only slightly less dense than water. So need a lot : more bulk = more drag.
- quantity of lipid cannot be adjusted quickly. So no ability to compensate for short-term changes
Where do elasmobranchs store lipids?
In their livers, liver can exceed 20% of body weight, whereas teleost liver is 1-2% of body weight.
What is the density of some elasmobranchs?
Benthic (dogfish/rays) 1.075 (g ml-1)
Fast swimmers (blue) 1.051 (g ml-1)
Very slow sharks (basking/whale) 1.030 (g ml-1)
Deep sea squaloid sharks 1.026 (g ml-1)
Squaloid sharls may be neutrally buoyant but have huge liver stuffed with squalene of relative density 0.86. This gives 50% greater buoyancy than normal fish oil. But makes them very fat and sluggish, with relatively tiny pectorals as no need for them.
Advantage of dynamic lift?
More economical at high speed
Advantage of static lift?
More economical at low speed, opportunistic prey encounter.
What are all elasmobranchs?
Predatory (except for 13 species of filter feeders)
How do they detect the location of prey?
Usually involves a mix of visual (10s m) and non-visual (olfaction, lateral line (~100m), electric fields, touch) senses.
Thresher shark tail adaptation reason?
To shock prey
What are the ampullae of lorenzini?
Found in all elasmobranchs and some teleosts (some catfish, sturgeons, paddle fish, lungfish). Sensory cells sensitive to electrical stimulus of low frequency 0.05 - 8Hz, as well as mechanical stimulation and changes the salinity and temperature.
What are the reproductive strategies?
Most actinoptryginians, large no of eggs with little provision and no aftercare e.g. cod. Chondrichthyans: very few offspring with lots of provision and aftercare e.g. most sharks
How do chondrichthyans show mating?
All show mating with internal fertilisation, intromittent organs: claspers formed from the posterior portions of pelvic fins
What is elasmobranch reproduction?
Oviparity, few large eggs are laid individually with large yolk reserves and tough egg case. Development time is considerable (5-12 months, typically). Newly hatched juveniles are totally independent e.g. skates, catsharks.
What is ovoviviparity?
Aplacental, many elasmobranchs, eggs retained in body after internal fertilisation, if eggs hatch substantially before birth, the young will require further nutrition:
Uterine oophagy: consumed unfertilised eggs produced for this purpose. Sandtiger sharks show uterine cannibalism: the largest foetuses consume the smaller ones until only a single pup is present in both of the uteruses. Some rays produce a fat and protein-rich uterine ‘milk’
What is true viviparity?
Viviparity (placental), Carcharhiniformes, developing embryo is nourished via a placenta. The empty yolk sac attaches to the uterine wall to form a yolk-sac placenta. Nutrients and oxygen pass from mother to foetus through an umbilical cord derived from the yolk sac stalk, waste passes the other way. E.g. in smoothounds the embryo is nourished from a yolk sac for 3 months then via a placenta for 7-8 months.
How many sharks are killed for their fins?
An estimated 100 million sharks
What are chondrichthyes generally?
Cartilagenous, 1,334 extant spp, no bone, spiracle, no operculum opening, no swim bladder, ampullae of lorenzini, internal fertilisation.
What are osteichthyes generally?
Bony fish, 34,045 extant spp, true bony skeleton, no spiracle, operculum covers gills, swim bladder, usually no electroreceptors, mostly broadcast spawners.
