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man looking into fish mouth

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

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 diagram
External fish anatomy (smallmouth bass)

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.



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.



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.

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.

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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.

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.

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.



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

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.



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.



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.



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.



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, 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

east tennessee fly fishing pic

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.



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.



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.



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.



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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palomar knot bass pic

Fishing Tip | How to tie the palomar knot (and double palomar knot)

Simple and strong.

That’s how you could describe the palomar knot. Who doesn’t like simple and strong.

So, let’s show you how to tie the palomar knot as well as the double palomar knot.

Looking for a really strong fishing knot that’s simple to tie? In this illustration, we’ll show you step-by-step how to tie the palomar knot (you can also view instructional videos further down the page).

Time needed: 1 minute.

Step-by-step instructions for tying the palomar knot:

  1. Thread fishing line through the eyelet of the hook.

    threading line through hook eyelet for palomar knot

  2. Thread tag end of line back through the hook eyelet.

    threading line back through hook eyelet for palomar knot

  3. With loop end and other end, tie a simple overhand knot, but be sure to keep it very loose and large (you’ll need that loop in the next step!)

    tying overhand knot for palomar knot

  4. Now, take the hook and insert it through the loop end of the line…

    inserting hook through loop for palomar knot

  5. Grab the hook in one hand and the line strands in the other and pull slowly. The knot will begin to cinch. (Be sure that the loop cinches above the eyelet of the hook!)

    pulling line and hook for palomar knot

  6. Trim the tag end of the line and you’ve completed the palomar knot!

    trimming the tag end of line on palomar knot

Want more instruction? View video below on how to tie the palomar knot!



Check out these other related articles on N1 Outdoors!


(How to tie the palomar fishing knot video transcript)


Video #1: Learn to tie the Palomar Knot step-by-step

Learn a fishing knot that’s simple and strong. Stick with us for the N1 Outdoors N1 Minute.

Hey everyone. Today I’m going to show you how to tie the palomar knot. It’s my favorite fishing knot. It’s one I learned many years ago. And, I like it because it’s very strong and easy to tie. Whether you’re fishing for crappie, bass, or even ice fishing, it’s a great, strong knot for all-things fishing.

Step 1. Thread the hook

Ok, we’re going to show you how to tie the palomar knot. We’re just using 10 lb. test mono line. Now, this knot works very well with braided lines, and I’ll show you why it’s a little easier with braided line in just a minute. 

But, basically, we’re going to have to take this line and double it over… about eight inches or so. We need to get this end – the double end – through the eye of the hook. So, we’ll try to press down… now, this is where it gets a little tricky with mono. So, to get this through the eye of this hook, and you can tell it’s a little bit difficult to do that. Sometimes, you’ve actually got to crimp this line. That’s not a good thing for line strength, so, I’m going to show you another way in just a minute. But, we slip that through the eye of the hook… it should look like this.

Now, there’s another way we can do this without having to crimp that line. We can just take this line and thread it through the eye of the hook. Now, we’ll just take this line and thread it right back through the way we came. Like I said, about eight inches or so should do the trick. This is what it will look like. Now, we’ve kept from having to crimp the line. This is a much better option. 



Step 2. Tie a simple overhand knot

Now, we’re just going to tie a simple overhand knot, like you’re going to start tying your shoes. Just a simple overhand knot. It’s going to look just like this. 

Step 3. Drop the hook through the loop

Before you cinch that knot all the way tight, you want to take this hook and drop it through the loop right here. So we’re going to take it and drop it through the loop. We’re going to begin to pull both ends of the line tight. 

Now, sometimes when you begin to pull this knot, this loop is going to try to get stuck under the eyelet of the hook. You just need to make sure it gets over the top of the hook before you pull tight.

Step 4. Pull tightly and trim

We’re going to take the ends and pull tightly. 

I’m going to take my clips and snip the tag end here, just to give you and idea of what it looks like. That’s what it’s going to look like when you’re finished. It’s a very, very strong knot. You can also moisten this before you pull tight. It reduces the friction and helps the knot cinch down tighter.

My Dad, when I was a kid… one of the first knots he showed me was the clinch knot. I used that for years. And then I came across the palomar knot. It’s the go-to knot for me. It’s very strong and it’s very easy to tie. And, hopefully, this is a knot you can use when you fish. And, we hope you put a hook N1.

Thanks for joining us for this edition of the N1 Outdoors N1 Minute. We want to remind you to come by and visit N1outdoors.com and join our new N1 Outdoors forums. We’ve got hunting, fishing and outdoors topics, wild game recipes, the whole deal, but we need your help to grow this. So, come visit and join in the conversation.

We hope you have a great week, and remember, where the moments happen… we’ll meet you there. We’ll see you next time.

In this next video, learn how to tie the DOUBLE palomar fishing knot.

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(How to tie the double palomar knot video transcript)



Video #2: How to tie the double palomar knot

Hey everyone. You may have joined us earlier for the instructional video on how to tie the palomar knot.

In this video, we’re going to show you how to tie the double palomar knot. It’s great for braided line and for when you’re fishing heavy, thick cover. It’s just extremely strong and it’s only one extra step from the standard palomar knot. 

Step 1. Thread the eye of the lure

In this example, we’re going to use an actual lure. It’s a little bit easier to see the eye of the lure, as opposed to the smaller eye of a hook. So, we’re going to use this and just like with the standard palomar knot, we’re going to pass our line through the eye. And, then we’re going to take the end of this line and go back through the eye of the hook like this.

Step 2. Tie an overhand knot with two passes

And, tie a standard overhand knot, just like we did with the palomar knot, except when we do that this time, we’re going to actually make two loops through here. Through this loop, we’re going to go one loop, two loops. A standard overhand knot… two passes.

Step 3. Drop the lure through the loop

Pull it down a little bit so that your loop end is large enough for the lure to go through. And, then we’re going to take the lure and just drop it through the loop.

Step 4. Pull tightly and trim

At this point, it’s great if you can moisten that knot. It will pull tighter a lot easier. You’ll pull on both ends and then each end individually. Just pull tightly, and you see, that’s what we have. Now we’ll take our snips and clip that tag end. And there you have an extremely strong, double palomar knot. 

Thanks for joining us. If you’d like to see other hunting and fishing tips videos, simply visit N1outdoors.com and click on the videos section and the whole library is there. Thanks for watching. We hope you enjoyed this double palomar knot illustration.

Be sure to watch some of our incredibly entertaining fishing videos, as well as other fishing rig tips. And, read the details behind our apparel designs.



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