A Fish with its Mouth Closed Never Gets Caught

Open wide!

As anglers one aspect of a fish’s anatomy is probably more important than any other in our pursuit to catch our finny adversaries. Without this feature we would not be able to do what we do. As a matter of fact, the fish would not be able to do what it does either. The morphological characteristic that I am referring to is the mouth of course. Whether or not we are conscious of it, we are rather obsessed with the oral cavity of fish. With pretty good reason too! To legally catch a fish a fisherman needs to have the fish pick up the hook (lure, fly, bait, etc) in its mouth where we do all we can to make sure that hook gets a good hold so we can bring the fish to hand (alright, there are a couple of exceptions like "fishing" for paddlefish). I bet you never thought of fishing as a fish mouth fixation before!

yes, it is real, now don't ask that again!

But what does a fish’s mouth tell us about the fish? And how does that help an angler catch more fish? Well, I am glad you asked! In a lot of ways the mouth tells us the primary occupation of that fish. It tells us where the fish prefers to feed which in explains what it likes to feed on. When we know this information we can use it to our advantage. 

I dare you to put your fingers in there!

There are three basic mouth locations in fish. Yea, I know what you are thinking: they are all at the head of the fish. True enough. But the placement of the mouth on the head of the fish is what I am talking about. If the mouth is pointing up it is called a superior mouth, right at the end of the fish it is called a terminal mouth, and if it is on the bottom of the head pointing down it is an inferior mouth. This tells us the preferred method of feeding. 

Silver Arowana

Tarpon

African Butterfly

A superior mouth generally points upward and indicates a fish that feeds mostly off the surface, especially on things like insects. In Vermont, we really don’t have a lot of really good examples of this although the banded killifish (Fundulus diaphanus) is pretty good, but not familiar to a lot of people (this is a mid-sized baitfish that is common along Lake Champlain and some other areas of the state). Some of you trout guys might question that trout often feed on top (especially the dry fly nuts), but let’s face it, trout don’t spend all that much time feeding off the surface of the water in all reality. Compared to some tropical fish like the arowana or the African butterfly fish and of course the tarpon, which have very good examples of superior mouths, trout are definitely not surface feeding specialists. Take a look at the photos for comparison. Sorry hatch matchers!

Sucka!

 An inferior mouth is not one that doesn’t work well. Yes, a bad joke, but I did have to go there. It just means that the mouth is partly or totally at the bottom of the head. We have some great examples in this area in the Catastomidae- the suckers. I suspect that almost everyone has seen these fish before and probably caught them too- mostly by accident, but a few of us (myself and JP “Roughfisher” Lipton in particular) really love to fly fish for them. The suckers, like their name suggests, suck food off the bottom of the river. The common carp is also another good example of this. Some fish with inferior mouths are very suck-sess-full. (groan) The white sucker (Catostomus commersoni) is the most widely distributed fish in the state of Vermont. That does say a lot doesn’t it? There are others that have not done quite as well, like the lake sturgeon (Acipenser fulvescens). Unfortunately that is more of a function of human activity rather than a function of their mouth’s location. Shameless plug here- get rid of the stupid #@$%ing dam in Swanton already!

Even a hybrid can exhibit a terminal mouth....

How about the terminal mouth? That is a “typical” fish mouth. The mouth is right in the middle of the head pointing forward just like you see in most fish. Bass, sunfish, perch, trout, and fallfish all fall into this category. A mouth like this allows a fish to have a wide range of options in its diet. They can feed all over the water column with little issue. Pretty darned handy! Which also explains the success of these fishes… one moment the bass nabs a little crawfish on between a couple of rocks on the bottom, then darts up and grabs a damselfly on the water’s surface, then chases down a minnow that is straggling behind its school. Not many worries about locating food huh? Fish with a terminal mouth are less likely to specialize and generalists seem to always do well.

Just because you are specialized doesn't mean I can't catch ya!

There is one general category of fish mouth that I have not mentioned yet, and these are specialized mouths. Fish like this have a mouth that is dedicated to a specific type of food item. In Lake Champlain an excellent example of a very specialized mouth is found in the longnose gar. This primitive predator has a very long, slender, bony mouth loaded with lots of needle sharp teeth. The gar’s mouth allows it to slash rapidly to the side to grab onto baitfish. Once the gar grabs the fish it repositions it in its jaws to swallow it headfirst. This specialized mouth structure is a very common specialization found in fishes (and even a couple of species of crocodilians- the gharial and false gharial) to be able to prey on smaller baitfishes. 

There's a little convergent evolution for ya folks!

It seems like I have fish geeked out enough for a while now. Next time I talk about the fish mouth I will tell you how this information relates to fishing. And it does…. Oh yes indeedy do!