What the Fish? Episode 7: We Found Nemo

We Found Nemo and Friends... in the Field Museum Fishes Collection!

For ichthyologists and fish enthusiasts everywhere, Disney-Pixar's Finding Nemo is one of those rare pieces of art and cinema that captures the essence of being a fish from a dazzling number of perspectives. It is clear from the very first frame that great care and attention to detail was taken with each marine species and their oceanic habitats. Sure there are the occasional liberties taken, such as the bizarre combination of different deep-sea fish species to form the mutant anglerfish that terrorizes Marlin and Dory.  But overall the attention to detail in this movie is spectacular from a fishy point of view. Scales shimmer and reflect light, movement is superb, and more often than not each fish is recognizable down to an exact species. For this episode we recorded a commentary track that can be played alongside the movie where we discuss our favorite scenes, the science behind the fishy stars, the plausability of plot points from a biological point of view, and just some plain old fashioned yammering.

Can you name all these Finding Nemo species housed in our very own Field Museum zoological collections?

Link to the picture of our friend Grant Galland surrounded by a school of fish that we talked about in the podcast.

What the Fish? Episode 4: Sneaker Males Are my Anemone

To milt or not to milt?

For most fishes, reproduction involves eggs and milting, which is like crop-dusting with sex cells (aka gametes). The vast majority of fishes are oviparous, which means they lay eggs that are fertilized and develop outside the mother's body. In these situations, males typically milt, which is the release and spreading of their gametes, onto the eggs that have been deposited in the environment. In ovoviviparous fishes, the eggs develop inside the body of the mother, and male gametes have to be passed into the females’ body through specialized structures, such as claspers (modified pelvic fins) in sharks or gonopodiums (modified anal fins) in guppies. Live birth (viviparity) has also evolved in a number of lineages of fishes, including sharks, guppies, and rockfishes. In viviparous fishes, the young develop within the mothers’ body.

 

Male, female, or both?

While most fishes have separate sexes, a number of lineages are simultaneous or sex-switching hermaphrodites. Some fishes, such as clownfishes, can change their sex once during their lifetimes either from female to male, or male to female depending on environmental and/or behavior scenarios. A small number of fish species are simultaneous hermaphrodites capable of producing both male and female gametes at the same time (e.g., lancetfish, some species of moray eels as seen above). Scientific studies have identified that at least some of these species (e.g., the mangrove killifish Kryptolebias marmoratus) are capable of self-fertilization!


What the Fish? Episode 3: You Light Up my Life

How does a fish make light?

Bioluminescence, the production and emission of light from a living creature, is widespread among different groups of marine fishes (e.g., anglerfishes, flashlight fishes, dragonfishes). Most organisms produce light through a chemical reaction between luciferin (a small molecule) and oxygen. The enzyme luciferase speeds up this reaction, resulting in the production of light. But unlike the incandescent lightbulbs in your home, this light gives off almost no heat. Some fish species have the ability to produce the chemical compounds necessary for bioluminescence themselves (such as lanternfishes), while others rely on symbiotic bacteria to create and generate light (including the beloved anglerfish in our logo).

 

Why would a fish want to make light?

The majority of bioluminescent fishes are found in the deep sea. Below 1,000 meters there is no visible sunlight in the ocean. As a result, many organisms that live below this depth have evolved bioluminescent structures, and fishes use this light in a variety of ways. Some fishes use light for camouflage, specifically counterillumination.  This is where the fish emits light around its belly to match any light coming from overhead, making it invisible to predators looking upwards for shadows in the water column. Others use light to attract and catch prey, such as the beckoning luminescent lure of the anglerfish. Fishes will even use light for communication in order to recognize each other in the darkness of the deep or to communicate with potential breeding partners.

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? Episode 1: You Are All Fishes

What is a fish?

When most people hear the word fish, they think of Nemo (clownfish), tunas, cichlids, and sharks. Everyone knows what a fish “is”, but why? It turns out that identifying the characteristics that define fishes is a daunting task, and with good reason! Fishes, as we think of them, are actually a paraphyletic or "unnatural" group. When scientists say “fishes”, they are discussing a group of organisms that includes all the descendants from a common ancestor.  So, the correct grouping of fishes includes us, the tetrapods (amphibians, turtles, crocodiles, birds, squamates, mammals, and countless extinct forms).

Yes, you are a fish. Now that your view of the world has been forever altered, let us explain. In general, there are three main groups of fishes still living today; the cartilaginous fishes (e.g., sharks, rays, skates, chimeras), the ray-finned fishes (e.g., goldfish, tuna, cichlids, clownfish, and our beloved anglerfish from the logo), and the lobe-finned fishes (e.g., coelacanths, lungfishes, frogs, birds, humans).  While terrestrial (or land) vertebrates such as frogs, dogs, and humans are classified as tetrapods within the lobe-finned fishes evolutionary lineage, we owe our earliest vertebrate origins to an aquatic environment. In short, just as humans are mammals, mammals are tetrapods, and tetrapods are all fishes. Welcome to the club!

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So…what the fish?

As ichthyologists, scientists, and researchers that study fishes, we primarily study the cartilaginous fishes (greater than 1,000 species), the aquatic lobe-finned fishes (e.g., lungfishes, coelacanths, eight living species), and the ray-finned fishes (greater than 35,000 species). This podcast series will predominantly focus on fishy issues related to these evolutionary lineages. Fishes have thrived in aquatic environments that vary from the rivers and streams near your backyard to the deepest recesses of the ocean. The evolutionary history, biology, and ecology of fishes are as diverse as they are fascinating, and we look forward to discussing the vast biodiversity of fishes with you. Thanks for listening, and enjoy this ongoing podcast series!

University of Kansas, Biodiversity Institute, 1345 Jayhawk Blvd., Lawrence, KS 66045; 785.864.6874 ©2016 W.L. Smith