The document describes several key characteristics of milkfish: - They are ray-finned fish with gill slits covered by an operculum and may possess an air sac. - Their scales and skeletons have evolved over time from large ganoid scales to thinner, more flexible scales in modern teleosts. - Modern teleosts have movable jaws/palates and pelvic fins farther forward compared to earlier fish.

1. Milkfish
Chanos chanos

2.  Actinopterygii (Ray-finned fishes)
 Sarcopterygii (Lobe-finned fishes)

3.  Membranous fins are supported by slender fin rays
radiating from basal skeletal elements within the body
wall
 Gill slits covered by a bony operculum
 Air sac is usually present
 Internal nares are lacking
 Basal Actinopterygians
 Neopterygians

4.  Paleoniscoids
 Large ganoid scales
 Well-ossified endoskeleton
 Air sacs are connected to the pharynx by an air duct that
enebles aerial respiration
 Sturgeons and paddlefishes
 Have endoskeleton is largely cartilaginous
 Scales lack ganion
 Skin of paddle-fishes is naked exept for small bony
scales on tail

5.  Gras and bowfins
 Trunk and tail of gars are covered with ganoid scales; trunk
and tail of Amia have modern fish scales
 Endoskeleton is ossified
 Brainacase (neurocranium) remains largely cartilaginous
 Teleosts
 “modern”
 Scales are in the dermis, very thin and flexible
 Dermal bones of the skull are thinner and more numerous
 Jaws and palate are more independently maneuverable
 Pelvic fins are far forward

6. - Fleshy lobe at the base of their paired fins
- Have internal nares that open into the oropharyngeal
cavity and retain a gas-filled air
- Gill slits are covered by a bony opercullum that grows
caudad from the second pharyngeal arch
- Actinistia
- coelacanths
- Rhipidistia
- Dipnoans

7. Lateral View

8. Tail fin (caudal fin)
2 types of tail fin
* Homocercal- Top and bottom
halves the same size.
* Heterocercal- Top half different
size than bottom half.

10. LATERAL LINE
a. A system of canals on the sides of fishes that helps fish
detect changes in pressure, vibrations and currents.
b. This incredible sense organ helps fishes to detect prey,
adjust their position to the currents, and keep in position in a
school.
c. They pick up vibrations from the swimming of other
animals and water disturbed by sound waves, which cause
changes in pressure.
d. The longer the fish’s body the longer is the lateral line
and the more sensitive to the environment. The canals are not
only in the skin but also in the bone or cartilage of the head.

11.  Found on non-teleost
bony fishes
 Usually diamond
shaped bony scales
 “Heavy armor”

12.  Found on teleost
fishes
 Light, thin, & flexible

13.  Teleost fishes
 Have comblike ridges
along the exposed
edge to reduce
friction (drag)

17. a. Closed circulatory system
i. The blood is always kept in vessels
b. Heart
i. Only has two chambers
ii. Blood goes from heart to gills to
the rest of the body
iii. Mammals blood goes; heart,
lungs, heart, rest of body