External Anatomy + Physiology

6 Types of Fish Body Plans

1. compressed

2. globiform

3. anguilliform

4. depressed

5. sagittiform

6. fusiform

Fish shape: Compressed

• squished on the sides; tall + thin

• short bursts of speed + navigating tight spaces

Fish shape: Globiform

• GLOBE

• slow swimmers that often rely on specialized defense

Fish shape: Anguilliform

• eel-like (long + cylindrical)

• efficient swimmers, lower speeds, tight spaces + crevices

Fish shape: Depressed

• pancaked

• typoical of bottom-dwellers + good ocean floor camoflage

Fish shape: Sagittiform

• elongated, arrow-like, pointed head

• rapid acceleration + ambush attacks

Fish shape: Fusiform

• sleek, tapered at both ends (torpedo/bullet-like)

• fast swimmers, typically pelagic fish

• most common fish shape

3 Types of Fish Mouths

1. inferior

2. superior

3. terminal

Mouth Type: Inferior

downward-pointing; typical in bottom-dwellers

Mouth Type: Superior

upward-pointing; typical in surface oriented fish

Mouth Type: Terminal

mouth at the end of snout (most common)

5 Main Fin Types

1. pectoral

2. pelvic

3. dorsal and anal

4. caudal

5. adipose

Which fins are paired?

pectoral and pelvic

Which fins are unpaired?

dorsal and anal, caudal, and adipose

Lobe fins

fleshy + muscular like a tetrapod’s

Ray fins

webbed skin supported by needle-like bones

Spines

bony, stiff, round, sharp and unsegmented

Rays

soft, flexible, segmented, and may be branched

3 Types of Rays

1. soft

2. spiny

3. branchiostegal

Soft rays

• most flexible ray

• propulsion, steering, maneuverability

Spiny rays

• most rigid ray

• stabilization, scaffolding for fish, defense

Branchiostegal rays

• flexible BUT structural

• help pump water across the gills

Pectoral fins function

variable:

• steering/maneuverability

• braking

• hovering

• stabilizing (prevent tipping forward/back)

What’s different about shark pectoral fins?

• rigid + wing-like; can be moved but NOT collapsed

• operate as stabilizers to steer up and down

• normally at an elevated angle to generate lift for head

Pelvic fins function

• Stability

• Steering

• Braking

Dorsal and anal fins function

• stability especially when turning

• prevent turning belly-up and minimize head jostling

• can reduce drag

Caudal fin function

propulsion + braking → shape related to swimming speed

Caudal Fin Shapes

rounded vs lunate + homocercal vs heterocercal

Adipose Fin

• fleshy, rayless fin dense w/ nerve endings

• proposed sensory function

What are scales?

calcified hard material

4 Main Types of Fish Scales

1. placoid

2. ganoid

3. cycloid

4. ctenoid

Scales: placoid

• tiny + tooth-like

• in Chondricthyes

• sandpaper-y

Scales: ganoid

• thick, tough, usually diamond-shaped

• peg and socket joints NOT “layered“

• in ancient Actinopterygiians

Scales: Cycloid

• flat, circular

• smooth

• annual rings

• thought to be inner layer of ganoid scales

Scales: Ctenoid

• “toothed” or spiny edge

• rough

• annual rings

• on most Acanthopterygian fishes

Cosmoid scales

• RARE; only in Sarcoptergiian

• 3 layers

• extant have thinner + lighter versions that are similar to cycloid scales

Lateral Line

sensory system that detects movements, vibrations, and pressure changes in the water

What’s special about Teleost jaws?

• premaxilla is moveable

• allows for jaw protrustion = improved suction feeding