Fish BiologyOceans 11 – May 2012

Fish DistributionMost 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.

Fish Anatomy 1. 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

AppendagesFish 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

External Anatomy Cont’dPaired fins :

pectoral fins = “arms/legs” of a fish

Pelvic/ventral fin = maneuverability

External Anatomy: ScalesScales 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 roofMosaic = fitting closely together

Four types of scales:PlacoidCosmoidGanoidLeptoid – found on bony fishes – like our perch!

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

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.

The Swim (or gas) BladderReduces 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:1. Swallowing air when surfacing

2. Transferring gas from the blood stream to the swim bladder when at great depths.

The Lateral Line• Sensitive to

differences in water pressure nearby

• Neuromast = bundle of sensory cells = what makes the lateral line sensitive

Fish ReproductionMost fish lay eggs

Three methods of reproduction:

1. Heterosexual – male/female mating

2. 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

3. Parthenogenetic – unfertilized eggs develop into embryos