man looking into fish mouth

The Anatomy Of A Fish | An Inside (And Outside) Look

Written by N1 Outdoors on . Posted in Blog, Fishing

It’s hard to beat the feeling (and the smiles that follow) when you put a hook N1. After all, who doesn’t love catching fish? But, when it comes to fish anatomy, they are as equally fascinating as they are to catch.

There are thousands of fish species all over the world. Fish are cold-blooded animals, which means that in most cases, their body temperature can change to mirror the temperature of the water they live in.  

A Fish’s anatomy can be divided into external and internal. Let’s start by examining the external anatomy of a fish.

External Fish Anatomy

The external anatomy of a fish includes the fins, scales, gills, eyes, nares, mouth, lateral lines and vents. Let’s take a look at each.

External fish anatomy (smallmouth bass)

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Fins

The fins of a fish are appendages used to move, steer, stop or position. The fins also give the fish balance in the water.

The fins could be single fins (such as the anal fin, the back or dorsal fin, and the caudal or tail fin) or paired fins (they include pelvic or hip fins and pectoral or chest fins) along the centerline of the fish.

Certain fish, such as the catfish, have an adipose fin which is behind the dorsal fin. The purpose of the anal fin and dorsal fin is to help the fish conveniently roll over to their sides.

The caudal fin, on the other hand, allows for propulsion as the fish moves forward. Lastly, the paired fins allow the fish to steer, stop, and hover around.

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A lot of freshwater fish have spines that support their fins. These rigid spines can be very sharp, thus playing a defensive role in protecting the fish from danger. The catfish, for example, has sharp fins in the dorsal and pectoral area and anglers should be aware and careful when handling these fish.

In some species, the number of spines in the dorsal fin actually helps differentiate between two species, as is the case with white crappie and black crappie. 

Dorsal fins and caudal fins, on the other hand, have rays which are frequently branched and are less rigid.

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Scales

Most bony fish have scales that are either cycloid or ctenoid, except for a few such as the catfish, which doesn’t have a scale, or the gar which possesses ganoid scales.

Cycloid scales have edges which are smooth and rounded while ctenoid scales have edges which are jagged.

To prevent infection, most of the fish have a mucus layer which covers the body. It is important that anglers who intend to return a fish to the water, be very careful with the way they handle the fish, so they don’t mistakenly rub off this mucus layer from the fish. Wetting your hands before handling the fish can help reduce the likelihood of damage to the mucous layer.

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Lateral Line

The lateral line in the fish is a group of organs that helps the fish sense the pressure of currents and movement in the water. It consists of a “line” of sacs filled with fluids.

These sacs have sensory apparatus which open to the water by means of pores which creates a line along the side of the fish. The lateral line helps the fish sense other fish as well as prey.

fish lateral line

The lateral lines of a fish serve to help them sense other fish… predators as well as prey.

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Gills

Fish gills are very delicate and sensitive structures that allow fishes to breathe while they are underwater. The fish gills have a bright, red color because they are highly vascularized.

The gills are protected by a gill cover (operculum) which is a flexible, bony plate.

To breathe, the fish takes in water through the mouth, which passes through the gills and is removed from beneath the operculum. 

operculum of a smallmouth bass

The operculum serves as a protective covering for a fish’s gills. (photo credit: Brad Alan)

Eyes

Fish have well-developed eyes to detect varying colors. While mammals achieve focus by the changing shape of the eye lens, fish achieve focus in the water by the in-and-out movement of the lens.

Learn the differences between smallmouth and largemouth bass HERE

Nares

The nares are a pair of nostrils which the fish uses to detect odors in the water. These nares are very sensitive. Fish like catfish and eels have a sense of smell that is well developed.

Fish that live in water that is dark or murky, tend to rely on smell more heavily than fish in clearer aquatic habitat.

Fish can also use their sense of smell to detect chemicals in the water, which may indicate predators or even help a fish to locate a mate.

fish nares

Fish use their nares (or nostrils) to sense odors from predators and prey alike.

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Mouth

The shape of a fish’s mouth can dictate the kind of food the fish eats. For example a fish with a larger mouth will tend to have larger prey.

Fish have a good sense of taste, and in some cases, they can taste their prey even before they swallow it. Some fish are omnivores, like many freshwater fish in Florida. Other fish are mainly piscivorous, which means they feed mainly on other fish.

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There are also some fish, such as grass carp, that are herbivores, eating plant life. Depending on the species of fish, some may have teeth while others don’t.

Some fish, such as the gar or chain pickerel, have canine-shaped teeth. Others, however, like the catfish have cardiform teeth, which feel like a rough area in the mouth.

Keep learning! Check out info on deer anatomy!

Some have vomerine teeth, which are like tiny patches of teeth in the roof of the fish’s mouth. Others, such as the grass carp have pharyngeal teeth which are located in the throat.

The anatomy of a fish’s mouth can affect what type of hook to tie in fishing for particular species of fish.

Vent

In most fishes, the vent is in front of the anal fin. The vents are external openings which open to the reproductive and digestive tracts of the fish. During spawning, the vent serves as an outlet for eggs and sperm.

The vent is also the site where waste is excreted from the body of the fish.

Internal Fish Anatomy

Internal fish anatomy consists of the brain, spine, spinal cord, swim bladder, kidney, stomach and intestines, vent, liver, heart, gonads/eggs, muscles and pyloric caeca. Let’s take a look at each below.

internal fish anatomy diagram
Internal fish anatomy diagram
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Spine

The spine serves as the primary structural framework of the fish. The fish anatomy as a whole is built upon the spine. The spine also connects to the tail of the fish at the rear and the skull of the fish at the front. Numerous hollow vertebra helps to house and protect the spine of the fish.

The skeleton of the fish can be made of either bones or cartilages.

fish skeleton

The fish skeleton is the framework for the entire fish.

Spinal Cord

The spinal cord of the fish is connected to the brain of the fish as well as to the rest of the fish’s body. It carries sensory information from the body to the brain and also relays instructions from the brain to the rest of the body.

Brain

It is in the brain that sensory information is processed. This is the center of control in a fish. In the brain, automatic functions such as respiration as well as other behaviors are controlled.

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Swim Or Air Bladder

The swim bladder is a hollow organ which the fish uses to conserve energy. The swim bladder functions much like a human lung. The fish draws oxygen into the bladder that has been drawn from the water by way of the fish’s gills. The more oxygen the sac holds, the more buoyant the fish becomes.

Conversely, when the bladder releases oxygen, the fish becomes less buoyant, which allows it to sink to deeper water.

The fish can use the swim bladder to to suspend itself in the water, thus saving energy.

Because of atmospheric pressure difference between the water surface and deep water, fish which were caught from deep waters will need to have some air released from their body before they can return to the deep water.

Some species of fishes, however, do not have swim bladders and because of this, they can sink if they stop swimming.

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Kidney

The kidney is a part of the fish anatomy that aids a fish in discharging waste from the body. Waste materials in the blood are filtered by the kidney and then removed from the body. The kidneys also help to regulate the concentration of water and salt in the body of the fish. 

Stomach And Intestines

The stomach and intestines of a fish play an important part in the fish’s survival. They help to break down ingested food and to absorb the nutrients. Some fish have short intestines because the food they take is easy to digest. Other fish, such as the herbivores, have longer intestines that help them break down the food they eat.

Pyloric Caeca

The pylori caecum is situated at the junction of the intestine and stomach. It has finger-like projections. Although the function of this organ is not completely understood, the organ has been known to secrete enzymes that help in digestion.

Muscles

The muscles of the fish help the fish to move in the water. The fillet of the fish, which is generally the part of the fish that is eaten, is comprised primarily of muscle.

Anyone who has ever caught a fish and had it flip out of your hand has experienced how powerful a fish’s muscles can be.

fish muscle filet photo

The fish muscles are the powerful force behind a fish’s ability to swim quickly… and also what make them a tasty meal.

Liver

The liver is another important organ with various functions. The liver supports digestion by means of secreted enzymes which break down fats. It also helps to store carbohydrates and fats in the body of the fish.

Old blood cells are destroyed by the liver to maintain the blood chemistry of the fish and the liver also helps in the excretion of nitrogen or waste.

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Heart

The heart of the fish helps in blood circulation. Through the blood, various cells and organs of the fish receive digested nutrients and oxygen.

Waste products are also transported by the blood to organs such as the kidney and liver for removal. This function is made possible by the heart.

Gonads

The gonads are the reproductive organs of the fish. They produce sex cells in the fish. Female fish produce eggs by means of paired ovaries while male fish produce sperm by means of paired testes.

The gonads of the fish are located in the same general location. The eggs of some fish are considered a delicacy in certain parts of the world.

Parts of a Fish Conclusion

Whether you eat the fish you catch or practice catch and release, we hope you have learned a lot from this article about fish anatomy and the various parts of a fish. And, of course, we hope you put a hook N1! You can also view fishing tips videos and read our articles on all types of fishing topics.

And, if you love reading about anatomy of wild game, be sure to check out our article on deer anatomy. 

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deer hoof print next to mans hand

Deer Hooves… More Than Meets The Eye

As a hunter, it’s always nice to see deer tracks.

At least you know you have deer in the area. But deer hooves do much more than just leave a “deer was here” signature in the dirt.

Hooves make just about everything a deer does possible and easier.

Deer hooves are made up of keratin, which is the same thing human finger nails are made of.

deer hoof print and dew claw

Deer front hoof and dew claws

The hooves consist of two divided, or cloven, elongated toes.

Each deer hoof has two “dew claws” (see picture), located above and behind it.

Mammals such as gazelles, sheep, hogs, cattle and goats also have cloven hooves.

A deer’s dew claws typically will not show as part of its track, unless the deer is travelling through mud or snow.

In these conditions, the dew claws give the deer’s foot a larger and wider platform with which to move about.

Hooves are one of the most important parts of deer’s body and are useful for many purposes. So, let’s take a look at 5 ways in which deer use their hooves…

A deer’s hooves are cloven, or split, and are made up of keratin, much like human fingernails.

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Deer will use their hooves for:

Running And Jumping

Deer obviously run and jump using their legs. But, while powerful hind leg muscles account for much of a deer’s ability to run and jump, hooves play a vital role as well.

A deer’s front cloven hoof helps it to turn sharply and push off when jumping.

So, whether deer are running up to 40 miles per hour to evade predators, chasing during the rut, or jumping in excess of eight feet in the air, they couldn’t do it without their hooves.

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The keratin in deer hooves is sheeted and runs in all directions.

This results in hooves that are stronger, harder and more crack resistant than bone, making them durable enough to support the animal’s weight, even when it is running or jumping with force.

When deer run, the toenails on the front of the hooves allow it to reduce the area of the foot that touches the ground, resulting in a longer stride that allows it to cover more ground.

Hoof Stamping (Stomping)

If you’re a hunter, you have probably experienced the ‘ole “foot stomp.” It usually goes something like this… You’re watching from a tree stand or a permanent blind when a deer sees your shape or movement, or gets wind of your scent. It senses the danger and stops abruptly, curls up a front leg and starts stamping its hoof.

Deer do this to either confirm the apparent danger or become comfortable that there is actually no threat. Sometimes the deer will flee, but hopefully for the hunter, the animal will eventually settle down and continue browsing or travelling in a manner that allows an ethical shot.

deer stomping foof

Deer will stomp their hooves to try and cause movement from perceived danger.

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Defense

It’s not uncommon, especially in suburban areas, for people to mistake deer for defenseless animals. But don’t let their majestic appearance and graceful movements fool you.

In addition to hunters, deer have other natural predators. These can include wolves, coyotes bobcats, and sometimes even bears and alligators.

When a predator threatens or attacks, a deer can either run or fight. Bucks often use their antlers to defend themselves, but just like does, can rise up on their hind legs, using their hooves to strike predators. They can also kick from behind, using the hind legs and hooves, if necessary.

Deer hooves do more than just leave tracks. They can be used by a deer to help defend itself against predators and perceived danger.

Deer Scraping

For hunters, the rut is a magical time of year. It’s that time when many hunters dream about that deer of a lifetime walking into view. Bucks are rubbing trees, using licking branches, and making “scrapes.”

In addition to hooves giving a buck the ability to chase does back and forth at high speeds, they also play a key part in the deer scraping activities.

Bucks and does alike will visit and use scrapes, but during the rut, bucks scrape more aggressively and will use the scrapes to announce their presence in the area as well as to tell other bucks to stay out of it.

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Bucks will make “scrape lines” along travel routes and as they move through their territory. These can show up along field edges, fence lines and between feeding and bedding areas.

Bucks will paw and clear (scrape) an area to be free of leaves and debris. They will urinate in the scrape to leave their scent, effectively marking their territory. In addition, they will lick and chew overhanging branches, leaving forehead scent as well.

Does will also visit and use these scrapes, allowing bucks, upon a revisiting of the scrape, to know if a doe is ready to be bred.

As you can see in this video (sound up), whitetail bucks will make “scrapes” on the ground with their hooves and urinate in them. They will typically make these scrapes under a “licking branch,” where they will chew and rub their forehead, leaving scent.

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Interdigital Scent

Deer have interdigital scent glands in between the two hooves on each leg and one of the most important glands the animals have. Deer use the scent dispersed from these glands to track one another.

The interdigital glands are small, sparsely-haired sac located between the hooves on each foot. The sacs contain a yellowish material called sebum. The scent is left in a deer’s track every time it takes a step.

fawn hoof print next to human finger

Fawn tracks are much smaller than full-grown deer tracks. The size of a fawn hoof print compared to human thumb

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Whitetail Deer Hooves Vs. Mule Deer Hooves

Whitetail deer and mule deer have many discernable differences in appearance and movement. Both have a unique antler structure.

Mule deer utilize a bouncing gait, known as a pronk or stot. The whitetail do not utilize this type of gait, but rather tend to run and leap when fleeing danger.

While whitetails and muleys may have their differences, hoof structure and tracks are nearly impossible to differentiate. Both whitetail and mule deer have two hooves that form and upside-down heart-shape on the ground with the rounded bottom.

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The side of the hooves are convex, while the tips of its hooves are located towards the inside of the track. The outside of the toe is usually slightly larger than the inside toe while the hind feet are smaller than the front feet.

Without other non-hoof signs, distinguishing between whitetail deer and mule deer is nearly impossible.

mule deer with white face
Photography by Matt Hartsky
whitetail deer grayer color in fall
Photography by Matt Hartsky
The tracks of mule deer (left) and whitetail deer (right) are indestinguishable.
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Hunt The Deer Tracks?

Hopefully, we’ve been able to provide you with a useful overview of how deer use their hooves. Here’s one final thought… those deer tracks you find will only tell you where the deer have been. Here’s to hoping you find out where they end! Happy hunting!

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East Tennessee Fly Fishing Surprise

The following is how my wife turned her pick-pocket skills into an East Tennessee fly fishing surprise and an N1 Moment for me.

Fly Fishing experience?

I had dabbled in fly fishing while in college, but I hadn’t done it in years and would still be considered very much a rookie fly fisherman.

Then, in 2013, while on a family vacation to Sevierville, Tennessee, my wife surprised me with a guided fly fishing trip. She had arranged for me to go on an all-day, smallmouth bass fishing float with Frontier Anglers TN.

Smallmouth bass fishing is fun. They are very aggressive fish and are a blast to catch. But, when you put a hook N1 with a fly rod, the experience goes to another level.

Frontier Anglers TN owner, Josh Pfeiffer, was my guide on this extremely hot July day. But, although the weather was sweltering hot, the fishing was hot as well.

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Unfortunately, in addition to hooking several nice smallmouth, I also hooked Josh’s hat 3 consecutive casts (I told you I was a fly fishing rookie, remember?)

Thank goodness for patient fishing guides.

I tucked that trip away in the unforgettable outdoor moments files, but didn’t fish the area again… until 2018. And, this trip was as much of a surprise as the last one!

East Tennessee Fly Fishing Surprise

It was Father’s Day, 2018. My wife and two daughters gave me a few gifts like they do every year. The last gift was an envelope. I opened it up, and inside was a gift certificate for… you guessed it, a fly fishing trip with Josh Pfeiffer. And while I was certainly excited about getting to go fly fishing again with Josh, there was more to the story…

About a month prior to receiving this gift, I thought it would be great to contact Josh and see if we could set up a time to do a little fly fishing and film some instructional fishing videos.

Even after 5 years, I still had his business card in my wallet. So, I emailed him to see what he thought of my idea. He emailed me back and said he might be interested in working something out. But, I got sidetracked and never closed the deal.

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My pick-pocket wife

My wife, who had no idea I had been communicating with Josh, thought that sending me fishing for the weekend would be a great Father’s Day idea. But, she couldn’t remember anything about who had taken me five years earlier. So what did she do? She went through my wallet, of course!

She found Josh’s business card and called him to book the trip. I later asked Josh if he thought it was strange that both my wife and myself were separately contacting him. He said he wasn’t really sure what to think, so he didn’t say anything to my wife. Smart man.

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Fly Fishing with an old friend

So, a few weeks later, I was back on the water with Josh, five years removed from my last fly fishing trip with him. On this second trip, we fished for trout. And just like the previous trip, Josh’s knowledge of East Tennessee fly fishing didn’t disappoint. Over a two day span, I caught close to 30 rainbow trout. And while I love to put a hook N1, that was only part of what made the trip so special.

I wanted to go fly fishing again with Josh. My wife wanted me to go fly fishing with Josh. But, neither of us knew what the other was thinking. What resulted was a great surprise, a few laughs, and some great fishing.

Fish anatomy diagram here

I thought to myself, you know, this is what we always say at N1 Outdoors. It’s not the size of the fish or the wild game. It’s the unforgettable moments and memories that are made outdoors with friends and family. That’s what we love to celebrate. This trip was no different.

I’ll do some East Tennessee fly fishing again… and this time it will be a lot sooner than five years! Can’t wait to get that trout fishing line back in that Tennessee water!

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