Fishes

DBS 402B.2Presidency University, 2016

Classification

Phylogeny

# of species

Mammals:5,490 (8.6% of all living vertebrates)Birds:9,998 (15.7%)Reptiles:9,084 (14.2%)Amphibians:6,433 (10.1%)Fishes:32,776 (51.4%)____________________________________Vertebrates:63,781 (100%)

Within fishes Hagfishes (Myxini): 76Lampreys (Cephalaspidomorphi): 46Cartilaginous fishes (Chondrichthyes): 1,223 (about 3.7% of all fishes)Bony fishes (Actinopterygii): 31,423 (about 95.9% of all fishes)Coelacanths (Coelacanthimorphi): 2Lungfishes (Dipnoi): 6_______________________________________TOTAL: approximately 32,776

Trivia •

The 32,776 living species of fishes are distributed among approximately 63 orders, 553 families,and

5,093 genera. •

Of the approximate 1,223 living species of Chondrichthyes

(sharks, skates, rays, and chimaeras), more than half (655 or about 54%) are rays.

•

Actinopterygians

or bony fishes constitute about 96% of all living fish species, and all but 51 species or about 96.4% belong to a group

called the Teleostei.

•

Of the 553 fish families, the nine largest contain about 9,600 or 30% of all species. These families are Cyprinidae

(about 220 genera and 2,420 species), Gobiidae

(about 210 genera, more than 1,950 species), Cichlidae

(about 112 genera and 1,350 species), Characidae

(about 165 genera and 962 species), Loricariidae

(about 92 genera and 684 species), Balitoridae

(about 59 genera and 590 species), Serranidae

(about 64 genera and 475 species), Labridae

(about 68 genera and 453 species), and Scorpaenidae

(about 56 genera and 418 species).

•

Sixty-four families are monotypic; that is, they contain only a single species. Sixty-seven families contain 100 species or more, of which three contain more than 1,000. The average number of species per family is 54;

the median number is 12.

Scales 1 1.

Placoid

Scales

1.

Placoid

scales, the most primitive form of scales, are found in sharks. These scales do not grow in size as the fish size increases. Instead, more scales are added. Placoid

scales

have 3 layers. The first is the pulpy vascular core. Secondly, a layer of dentine comprises the middle layer. Finally, the outside layer is made of hard vitrodentine.

Scales 2Ganoid

Scales

Ganoid

scales, found in gar, are slightly less primitive than placoid

scales. These scales grow in size as the fish ages.

Ganoid

scales are diamond shaped. These scales are hard and thick. The scale is formed from ganoine.

Scales 3Cycloid ScalesCycloid scales are the less advanced of the advanced scale types. An example of a fish with cycloid scales is minnows. Cycloid scales increase in size as the fish ages. The growth can be seen in rings on the scale. These rings can be related to the age of the fish. Cycloid scales are thin, circular scales covered by a thin layer of epidermis and mucus. This gives the fish a slimy feel.

Scales 4Ctenoid

Scales

Ctenoid

scales are the most advanced of all the scale forms. Sunfish and drum are fish with ctenoid

scales. These

scales also increase in size as the fish grows, producing rings. Ctenoid

scale structure

is similar to cycloid scales with the exception of tiny comblike

protrusions on the posterior of the scale. These projections allow the fish to swim faster.

Scales 5

Scales 6

Scales 7

Tails

Pectoral girdles

Shark

Gill function

Bony fish

Gill function

Digestive system -

shark

Digestive system -

perch

Development of aortic arches

Heart

Nephron development

Kidney organization

Kidney organization •

Pronephron:–

Tubules form at the anterior part of nephric

ridge

–

Tubules fuse and open into cloaca–

Glomeruli

make direct contact with tubules

•

Mesonephron:–

Tubules form at the middle of nephric

ridge

–

Tubules then fuse with the pronephric

duct but are called mesonephric

duct

•

Generally are functional in embryo, in adult it generally incorporated posterior tubules (metanephron) and are called opisthonephron

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