The Fish Body Section 33.1

Modern Fish Key Characteristics: Gills – function to remove oxygen from water; have a large surface area and rich supply of blood Single-loop blood circulation – blood moves from heart  gills  body  heart 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: Sinus venosus – collection chamber Atrium – thin, muscular walls to hold blood Ventricle – thick-walled, muscular chamber to contract and push blood to gills and the rest of the body 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