Fish

Ho Suet Ying

6S (8)

General features• any gill-bearing aquatic vertebrate (or craniate) animal which lacks limbs with digits

•most fish are ectothermic (Tuna, swordfish, and some species of shark are homoiothermic)

•has a streamlined body

• has gills or an accessory breathing organ

•has two sets of paired fins

•has skin that is usually covered with scales

Fishes are divided into two main classes: chondrichthyes(fishes

with cartilaginous skeletons) and osteichthyes(bony fishes)

Fish

Chondrichthyes Osteichthyes

Elasmobranchii

Holocephali

Sarcopterygii

Actinopterygii

Chondrichthyes (Cartilaginous fishes)

•jawed fish with paired fins

• paired nares

• scales

•two-chambered hearts

•skeletons made of cartilage rather than bone

•large, oily liver for buoyancy

•swim bladder and lungs are absent

•forward swimming only

•2 subclasses -Elasmobranchii (includes sharks , rays and skates) -Holocephali.

(A) Skeleton

•cartilaginous (cartilage is often partly calcified )• notochord •lack ribs• do not have bone marrow (red blood cells -> spleen , epigonal organ , Leydig’s organ

(B) Scales (placoid scales or dermal denticles)

•covered with dermal teeth

•toothlike ( feel like sandpaper)

•protection

•in most cases streamlining

(C) Respiration

•breathe through 5-7 gills

(D)Excretion•excrete urea as nitrogen waste (they are ureotelic, like adult amphibians and mammals).

Tuna gills

(E) Reproduction (Three types)

•OVIPAROUSlike fish-- external fertilization of egg

•OVOVIVIPAROUS-embryos develop inside eggs - no placental connection

•VIVIPAROUS - oppose to laying eggs

Catfish and its egg

Bullhead and its egg

Osteichthyes (Bony fish)

•head and pectoral girdles are covered with large dermal bone

•eyeball is supported by a sclerotic ring of four small bones

•a lung or swim bladder

•Gas-filled swim bladder for buoyancy

•no fin spines (has lepidotrichia)

•an operculum

•bones are much heavier and less flexible than cartilage

•both forward and backward swimming

•2 subclasses -Sarcopterygii -Actinopterygii

(A) Scales ( 2 types )1 . Ganoid scales

•covered by enamel like substance called ganoin•found in primitive bony fishes such as gars •diamond-shaped•thick•non-overlapping

2 . Leptoid scales

• found on higher-order bony fish•overlap in a head-to-tail direction•2 sub-groups - Cycloid scales -Ctenoid scales

*scaleless fish -sacrifice protection of scales presumably for added flexibility

2 subclasses : Sarcopterygii & Actinopterygii (A) Sarcopterygii (fleshy-finned fish)

• a clade (traditionally a class or subclass) of fleshy-finned or lobe-finned vertebrates.

•only eight living species

•lobed paired fins, joined to the body by a single bone

• two dorsal fins with separate bases.

• 3 subclasses - Coelacanthimorpha — Coelacanths - Dipnoi — Lungfishes

- Tetrapodomorpha — Tetrapods and their extinct relatives

A specimen of Latimeria Chalumnae

Queensland Lungfishes

(B) Actinopterygii ( ray-finned fish )• possess lepidotrichia or "fin rays"

•Considered more “advanced” than (A)Sarcopterygii

– increased caudal symmetry - trend toward homocercal tail– fin membranes with fewer rays– reduction in dermal armor– loosening of maxillary and premaxillary bones, leading to a rounded mouth

•2 subclasses - Chondrostei

- Neopterygii

Nile Bichir

(Chondrostei)

Gar Fish

(Neopterygii)

Excretion

•excrete nitrogen as ammonia, NH3, (they are ammoniotelic)

Reproduction

•generally is external •gametes are released in the water, where they can fecundate their counterpart and form the zygote.

Osteichthyes VS Chondrichthyes

Chondrychthyes Osteichthyes

Skeleton Cartilage only Cartilage and bones

Swimming Forward only Forward and backward

Buoyancy Large . oily liver Gas-filled swim bladder

Respiration Gills Lung or swim bladder

Reproduction Internal and externalfertilization

Eggs usually fertilizedexternally

Scales Rough , sand-paper likeplacoid scales

Smooth , overlapping scales

Sources

http://en.wikipedia.org/wiki/Osteichthyes

http://en.wikipedia.org/wiki/Chondrichthyes

http://en.wikipedia.org/wiki/Fish

http://www.biology-questions-and-answers.com/fish-facts.html