It is hard to imagine what senses fish have without already knowing. Being mammals ourselves, we have the idea that all mammals have the same senses as us; sound, sight, smell, touch, and taste.
Fish have the same five senses that land mammals do: sight, smell, touch, taste, and hearing. Another sense fish have is called the lateral line which allows them to detect water vibrations and therefore movement around them. Some can also detect electrical fields.
With birds, we know that they can see, make sound, and therefore can hear. However, with fish they are almost alien to us. Living below the water, they are completely different from mammals that live on land.
Fish generally have large, bulging eyes that lack eyelids like a mammal. Fish are vertebrates, and as with all other animals with a backbone their eyes are similar. The eye is sphere-shaped with a protective cover. Fish have an iris that surrounds the hard lens of the eye. The retina of the eye is at the back, made up of light-sensitive nerve cells.
Whereas the human lens is oval shaped, the lens of a fish is a sphere. The lens is clear and positioned closely to the outer of the eye. This allows the fish to send undistorted images to the retina.
Fish can’t see particularly long distances, but if it needs to see something close up then they can move the lens within the eye by using special muscle. This allows them to see in focus close up.
As with many other animals, the retina is full of cells called cones. The cones are used to see bright lights and colors. Due to the presence of cones in the retina, fish are believed to be able to see in color.
However, this is not true for all fish, as deep-sea fish or nocturnal fish do not need to see in color. This is especially true for fish that stick to the bottom of the ocean.
Fish can also see in different directions using each eye. A trout can catch an insect while on the surface while looking out for predators with the other eye.
Smell and Taste
Unlike mammals, fish have four nostrils on each side of their head. Fish do not breathe in the same way as mammals and the nostrils are not used to breathe.
The two pairs of nostrils on each side of the nose lead to nasal sacs which are filled with sensory organs. Fish have an excellent sense of smell, with some detecting one thousandth of a gram of crushed worm in 58 million gallons of water.
The sense of taste in fish comes from cells that are found on the lips, the mouth, the barbels and on some fishes, the lower head and fins.
Some fish such as carp taste their food by touching it with its barbels, and doesn’t even need to put the food into its mouth to know if it is edible.
The sense of taste plays a huge part in finding food. By using their barbels and fins, many fish brush the sand constantly searching for food.
Although we think of the sea as quiet, it rarely is. Although we do not hear fish, they do use sound. Some grind their teeth to communicate or blow bubbles from their bladder. Some even make grunting or groaning noises using their swim bladders. These sounds are amplified using special muscles.
Carp can amplify their hearing by using a bony connection between their inner ear and their swim bladders. This helps them to hear better. As there can be hundreds or thousands of fish, they are surrounded by sound as they move. This is caused by the movement of the fish, moving their muscles and fins.
Some fish such as haddock make noise as they move around in a school on the sea bed. Haddock make grumbling and drumming noises as they move around.
Schools are able to keep together using sound even if they cannot see. In dark parts of the sea, schools can still swim together using their hearing and can communicate to each other about predators or food.
Fish have a line of pores that open onto the scales on the side of the body. This is called the lateral line and is seen in most species of fish. The lateral line is a sophisticated sense that is difficult for us to understand.
The lines that we see on the fish’s side have openings. These lead into a canal which has sensory cells that can detect changes in water pressure. The pressure changes can be detected when a school changes their direction, caused by the change of shape in their bodies.
When the school reaches an obstruction or a predator the pressure changes, allowing the school to change direction as if as one fish. The lateral line can be thought of as a radar system as it alerts the fish to movements around it in its immediate surroundings.
Some species of fish such as shark can detect the electrical charge made by the muscles of other fish. By using a system of pores on their undersides, sharks and some other fish such as skate, can detect tiny electrical fields. This helps them to hunt other fish or animals.
Skate also produce their own electrical field and can use this to recognize others of their own species. Some species such as electric eels or rays can use these electrical charges to also stun prey.