What the Fish? Episode 2: Smells Like Freshwater Eels
Fishes have the five major human senses
Fishes use the same five major senses that all humans have: hearing, sight, smell, taste, and touch. But for fishes, all of these senses differ somewhat from our normal day-to-day experience. Quite simply, living in a liquid environment is a very different thing than living in a gas (air) environment. Think about the difference between smell and taste. At some level tasting is like smelling wet things. How different are these senses when you are already wet or underwater? From an evolutionary or anatomical perspective, they do have fundamental, different origins and innervations, but because of their aquatic lifestyle these senses have more overlap in fishes when compared to humans. Given this similarity, one of the most striking differences is that fishes actually cover various parts of their bodies (ranging from their skin to specialized barbels, whiskers, or fin rays) with taste buds rather than just focusing on the tongue like we do. The whiskers of a catfish, like the one shown here, allow these fishes to taste the mud that they are digging around in. Would you want to drag your tongue around in the mud? We wouldn’t either.
Did you say seven senses?
Humans actually have more than five senses. For example, we have sensors for balance, temperature, and pain, but the five main senses dominate our daily lives and take up more relative sensory area in our brains. Fishes have two other major senses that are not found among the senses we experience: electroreception and mechanoreception (or distance touch). Electroreception is less common among fishes, but it is comparatively easy to grasp. This electro-sensitive system is much like a beach comber searching a sandy beach for valuable metals. Fishes use this system for a variety of reasons, but many fishes use this sense for hunting or gathering. A hammerhead shark or paddlefish will move the enlarged regions of their heads to search for small electrical signals in the water coming from animals respiring or moving. Specifically, fishes respiring underwater produce a small ionic charge that will stimulate electroreceptors, which allows a predator to find a sand dab or sea robin buried under the sand. Mechanoreception is the sensory system that allows fishes to school, fishes to measure the surrounding current to hold their position in a moving stream, and fishes in the dark (e.g., deep-sea or caves) to find cave walls or rocky outcroppings. This is carried out by particular hair cells that are housed in a series of tubed scales along the side of a fish, found on the surface “pit organs” that cover the skin of some fishes, and distributed within bony canals in the head of a fish. These specialized hair cells or neuromasts are stimulated (bent/displaced) by the change in motion of water over the structures. This bending of the hairs in particular directions tells the fish that their schooling partners are changing direction or that a shark is quickly approaching, hence its common name of distance touch. If you are like us, you wish that you had these other wonderful vertebrate senses; but alas, they only work when you live underwater…
What the Fish: Jaggedhead Gurnard (Gargariscus prionocephalus)
Distribution: Indo-West Pacific
Maximum Size: 30 cm
Fun Fact: All sea robins in the family Triglidae have finger-like, free, pectoral rays that allow the Jaggedhead Gurnard to drag his body along the sea floor like a legless zombie hunting for brains.
Encyclopedia of Life: Jaggedhead Gurnard
The sea robins comprise nearly 175 species that include both the traditional scaled species (Triglidae) as well as a completely armored subgroup that are occasionally treated as an independent Peristediidae. Species in this family are referred to as sea robins because many species have enormous pectoral-fin rays that are colorful and wing-like. Beyond these often characteristic wings, species in this family are just bizarrely shaped, so please download the associated surface scan to take a look at these species in three dimensions. Crazy!!
Sea robins have a lot of sensory specializations (production and reception). Although most of these species are drably colored, many species have bright pectoral fins that are believed to be rapidly opened to scare would-be predators. These species also have free pectoral-fin rays that are heavily covered with taste buds that they use to find food items buried in the mud and sand on the sea floor. They are omnivores that will eat just about anything that will fit in their mouths. Further, sea robins have drumming muscles associated with their gas bladders that allow them to make humming noises and grunts.Does it look like the Bat Symbol? Because of the unusual shape of these armored fishes, the What the Fish? crew had a disagreement about whether or not the Jaggedhead Gurnard looked like the Bat Symbol. Below, we provide a mirror-imaged dorsal silhouette of Gargariscus for our viewers to decide whether the species resembles this famous logo. Let us know your thoughts!
So long, and thanks for all the fish!