What is Fish?
Fish are water living vertebrates of which there are some 25,000 different species. These species are divided into three groups: jawless fish; cartilaginous fish, which include sharks and rays; and bony fish, by far the largest group, which include eels, swordfish, and trout.
The goldfish’s brain control all its body activities. It does this by sending messages along its spinal cord which run protected inside the backbone. It’s heart pumps blood around the body and its kidney remove waste products from its blood. Like most fish, a goldfish has a streamlined body covered with slimy scales. Fish has gills which they use breathe to in water to extract oxygen from water flowing over them. The swim bladder is a bag of gas that helps the fish to rising and not sinking involuntarily.
How fish breathe? With its two operculum close, the fish open its mouth to suck in water. It then closes its mouth, and uses muscles to force water over the gill and out through each operculum. As water passes each operculum, oxygen is extracted. By opening and closing its mouth, an operculum in its coordinated matter, the fish maintain a constant flow of water over its gill.
How fish swim? A fish propels itself through the water by moving the rear portion of its body, Muscles running down both sides of the fish’s backbone control the movement of the tail. A fish contracts these muscles first on one side and then on the other, sweeping its tail from side to side, to swim forward. Fish use their fins to steer to the left or to the right and up or down.
Fish use their pectoral and pelvic fins to rise, stay level, or dive down. Water pressure keeps the dogfish from swinging sideways, and transfer the side to side movement of its tail into forward motion.