Diversity of Fishes

Question 1

Numbers

Answer 1

30,000 species, more than 50% of extant vertebrates.
Most diverse and abundant vertebrates.
Capture around 96 million tonnes of fish a year.
FIsheries management involves a complex interplay of population ecology, socioeconomics, and global politics.

Question 2

what is a fish

Answer 2

Fish is a paraphyletic taxon like reptile as it doesn’t include all descendants from common ancestor.

Question 3

Characteristics

Answer 3

Live in water
oxygen through gills
are ectothermic
have limbs in the form of fins
none are universal
Some fish can survive out of water, oxygen can be obtained by swallowing or diffusion, some species of shark and tuna maintain body temps above water, and many fish have reduced fins.

Question 4

Major fish groups

Answer 4

Agnathans, jawless. <100 species
Cartilaginous fishes (chondichthyes) ~1200 species.
Ray finned fishes (actinopterygii) >30000 species.
Lobe finned fishes (sarcopterygii) 8 species
Phylogenetic relationships are hard to establish.
Taxonomists often propose different hypotheses concerning fish systematics.
Scientists working on the fossil record may disagree on fish evolution from similarities between modern taxa

Question 5

Modern taxa

Answer 5

Chondrichthyes (sharks, rays, chimaera)
Percomorpharia, everything else
Ovalentariarae, like pleuronectiformes
Percomorphacae, >10,000 species, hard to determine
Scombriformes, high metabolic rate, fast hunters
Gobiomorpha, diverse chicilids and cardinals >5000 species.
Beryciformes, obscure mostly deep water taxa.
Gadiformes, cod, haddock, pollack, major commerical species for N hemi
Myctophiformes, small mesopelagic fish.
Protacanthopterygii, incl salmon and trout
Euteleosts, 17,500 extant species.
Ostariophysi, 70% of freshwater fishes.
Herrings
Eels
Sturgeons
Terapodomorpha

Question 6

Origin of fishes

Answer 6

Phylogeny for vertebrates:
Vertebratea, possess notochord, v-shaped muscle blocks ‘mylomeres’ and teeth
Actinopterygii, ray finned fish
Osteichthyes, ossified skeleton, includes sarcopterygiii, all tetrapods and ray finned fishes.
Gnathostamata, jawed fishes

Question 7

Chondrichthyes

Answer 7

Characteristcs:
-cartilaginous and variably mineralised skeletons
- distinct upper and lower jaws with teeth
- internal fertilisation
- neurocranium with no sutures.
- well-developed electroreceptive sensory organs
3 divisions, batiodia, holocephalii and selachii
Evolutionary relationships between elasmobranchs (sharks and rays) are obscure.
Fossil record of chondrichthyes is mostly based on teeth.

Question 8

Chondrichthyan anatomy

Answer 8

Vertebrea:
- of elasmobranchs are typically circular biconcave structures.
- discs may be mineralised for rigidity especially in fast swimmers where body needs to accommodate muscular force.
-mineralised vertebrae show growth bands.
Pectoral girdle and fin:
- attachments partially mineralised
- fin rays are usually unmineralized cartilage.
Gill arches:
- maintain structure and efficient water flow
Jaws:
- Most mineralised, for strength and anchor points for muscles.
Skull:
- single mineralised section of cartilage, seperated from jaws.

Question 9

Chondrichthyan Reproduction

Answer 9

Males have external claspers
Provide approximate estimations of maturitty in many sharks and rays

Question 10

Eggs and babies

Answer 10

Oviparity (egg laying) 40% of elasmobranchs, eggs laid in keratinous casting.
Viviparity, live birth, Ancestral and most common:
- yolk sac, embryo in sac throughout gestation.
-oophagy, embryo feeds on unfertilised eggs or other embyos.
- placental vivparity, yolk sacs with umbilical cord, transport nutrients and oxygen to embryo and waste to mum.