Fishes: external structure, skeleton, swim bladder
Fishes are aquatic chordates: the body has scales, they breathe with gills, the heart has two chambers, and they have three unpaired fins (dorsal, tail, anal) and two paired fins (pectoral, pelvic). The common carp lives in all water bodies except mountain rivers, reaches 1 m and 8–16 kg. Its streamlined body flattened from the sides overcomes water resistance for fast swimming; the head is fixed to the body. The tail fin drives swimming; paired fins give balance, turning and stopping. The skin is covered with scales and mucus: mucus reduces friction and rings on scales show the fish’s age. A dark back and pale belly give protective colouring. The skeleton has a vertebral column of 39–42 vertebrae, ribs, a skull (braincase, jaws, gill covers) and fin skeletons. Strong muscles are in the back and tail. The swim bladder lies above the gut and is filled with gas; changing its volume makes the fish rise or sink, and it also amplifies sound.
On the board draw a carp, label the 5 fins by name and write their functions. Safety: be with adults at the water’s edge when fishing; beware of fish bones; do not eat raw fish.