1. Fish Biology
Oceans 11 – May 2012

2. Fish Distribution
Most of the world’s fishes are continental – they live either as part of the freshwater systems on land or as sea-dwellers staying near the coastal environment.
Why?
Rich source of nutrients due to discharge by rivers, upwelling from the ocean, aeration due to surf/tide/waves and penetration of sunlight.
Upwelling = winds push surface water offshore, which is then replaced by nutrient-rich deep waters.

3. Fish Anatomy Exterior Anatomy:
Agnatha – backbone is called a notochord, which is a rod- like structure made up of special notochordal tissue.
Chondrichthyes – backbone is a notochord surrounded by rings of cartilage, known as the vertebrae. Sometimes this cartilage calcifies and becomes hardened like bone.
Osteichthyes – have bony vertebrae that are united to form the backbone; the notochord is no longer present

4. Appendages Fish have fins as their appendages
Fins can be median (alone) or paired (in pairs).
Median fins are located along the centerline of the body (top, bottom and end)
Top fin = dorsal = acts as a “keel” to keep fish stable during quick turns
Fleshy fin = adipose fin = stability
Bottom fin = anal fin = stability; can be used to slow down
End fin = tail or caudal fin = propulsion

5. External Anatomy Cont’d
Paired fins :
pectoral fins = “arms/legs” of a fish
Pelvic/ventral fin = maneuverability

6. External Anatomy: Scales
Scales are colorless. Fish usually get their color from various structures underneath the scales.
Scales can be arranged two ways:
Imbricate = overlapping like shingles on a roof
Mosaic = fitting closely together
Four types of scales:
Placoid
Cosmoid
Ganoid
Leptoid – found on bony fishes – like our perch!

7. Internal Anatomy – Circulation, Respiration, Temperature
Blood transports oxygen, nutrients and waste
Single circuit circulation – heart-gills-body-heart
Two-chambered heart with upper atrium and lower ventricle (in contrast to our 4-chambered heart)
Fish get oxygen from water via their gills, which requires a huge amount of energy
Therefore gills must be efficient. They are made efficient in the following ways: large surface area, short diffusion, water flows one way over the gills, use of countercurrent circulation

8. Continued…
Fish are cold-blooded – their body temperature varies with the surrounding environment
Some fish have evolved to be warm-bodied (tuna)
By “locking in” their body heat, they are able to contract their muscles 3 times as fast as a cold-bodied fish, giving them more power and more speed.

9. The Swim (or gas) Bladder
Reduces the density of a fish so that it can float
Sea water is the most dense type of water, therefore salt water fish need smaller swim bladders than fresh water fish
Fish get gas for their swim bladder in a few ways:
Swallowing air when surfacing
Transferring gas from the blood stream to the swim bladder when at great depths.

10. The Lateral Line Sensitive to differences in water pressure nearby
Neuromast = bundle of sensory cells = what makes the lateral line sensitive

11. Fish Reproduction Most fish lay eggs Three methods of reproduction:
Heterosexual – male/female mating
Hermaphroditic – a single fish is both male and female, producing both egg and sperm. Some of these fish undergo fertilization with similar hermaphroditic fish, and others self-fertilize
Parthenogenetic – unfertilized eggs develop into embryos