Stickleback Fish- JG

Background
Gasterosteus Aculeatus, otherwise known as the Stickleback fish, is a type of vertebrate with a developed circulatory system and a big brain. They are migratory fish and are of 4-6cm in size. Marine Sticklebacks live in salt water environments, such as the Pacific and Atlantic Oceans, where they hide in marine vegetation to escape predation. Freshwater Sticklebacks live in freshwater lakes. Marine Sticklebacks spend much of their lives in salt water environments but migrate to freshwater environments to breed. Freshwater Sticklebacks spend their entire lives in a freshwater environment. The Stickleback use their bone structure as a way of defence; parts of it's skeleton, such as the pelvis, have become larger over time which makes them more difficult to swallow by predators.

Gas Exchange
Oxygen diffuses into the fish from the surrounding water and CO2 diffuses outundefinedinto the water- gas exchange is made more efficient due to the counter-current flow of blood.

Homeostasis
Sticklebacks maintain homeostasis by using negative feedback to return the levels of salt and water to what they should be. The Stickleback has a two-chamber heart: the blood travels throughout the circulatory system in a single circuit, from the heart to the gills, and then loops through the rest of the body to get back to the heart.

Thermoregulation
The stickleback fish maintains it's body temperature through the countercurrent flow of blood. Blood vessels carry blood in opposite directions, allowing for heat transfer so the internal body temperature is higher than that of the surrounding water.