The Fish BodySection 33.1

Modern Fish Key Characteristics:

1. Gills – function to remove oxygen from water; have a large surface area and rich supply of blood

2. Single-loop blood circulation – blood moves from heart gills body heart

3. Vertebral column – internal skeleton made of either cartilage or bone

Gills

Gills

Made of gill filaments – projections which increase the surface area and are rich in blood

Water is drawn into the mouth and then forced over the gills and out the gill slits

Water flows in one direction and the blood flows in the opposite direction – countercurrent

This means that diffusion happens all along the gill length

Flow through the gills

Circulation

Chamber-pump heart with four chambers in a row:

1. Sinus venosus – collection chamber2. Atrium – thin, muscular walls to hold

blood3. Ventricle – thick-walled, muscular

chamber to contract and push blood to gills and the rest of the body

4. Conus arteriosus – a second pump to add more force

Circulation of blood

Kidneys

Salt water fish lose water from their bodies

Freshwater fish gain water Kidneys help maintain proper

water concentration Contain nephrons – tubes that

regulate salt and water content and remove wastes from the blood

Kidneys produce urine – salt water fish excrete small amounts; freshwater fish large amounts

Internal anatomy

Reproduction

Sexes are separate Fertilization occurs externally –

spawning Eggs and sperm are released near

each other in the water Eggs contain a yolk sac with

nutrients for the developing young Some species of sharks have internal

fertilization of the eggs within the female’s body

Fish embryo with yolk sac

Shark Egg