Amberjack Identification

Introduction

Today I wanted to touch on amberjack identification, specifically, how to properly ID them. Amberjack identification is not the easiest task in the fish world, but with a little practice you shouldn’t have any problems. This is a question we see on a regular basis, and one even experienced captains get wrong repeatedly. I was recently approached by some mates from a local charter boat who were asking how to correctly ID these fishes, and I found it difficult to explain without pictures, so this is my attempt. The fishes we will be referring to as “amberjacks” from here on out include: the Greater Amberjack, Seriola dumerili, the Almaco Jack, Seriola rivoliana, the Banded Rudderfish, Seriola zonata, and the Lesser Amberjack, Seriola fasciata. Although there are 9 fishes in the genus Seriola, these four fishes are the only resident amberjacks present along the eastern coast of the US.

Why does amberjack Identification matter?

Amberjack identification may not matter to you at all, however if you are a fisherman, many states have regulations that cover greater amberjack differently from almaco, lesser and banded rudderfish. You better hope you can tell them apart before you put one in your cooler!

The basics

With very few exceptions, most bony fishes respire though organs called gills, and most of these gills share the same general structure presented below.

Amberjack Identification
A Gill Arch. Rakers are the white projections, filaments the red.

Without going into too much detail, the red string-like structures in this image are known as filaments, and the white protrusions are known as gill rakers. The structure as a whole is known as a gill arch, and many gill arches together make up the gills. The number of rakers on the first gill arch is what we are going to use to ultimately help us identify the differences between the amberjacks.

Size

Before you have to start counting gill rakers, let’s cover the obvious external characteristics. First of all, large adult greater amberjack are easy to identify on their size alone. None of the other amberjacks reach as large of a size as the greaters. Although the almaco jack comes close, its body shape is completely different, and is easily differentiated.

Common Name Max reported Size Common Size
Greater Amberjack 190 cm (74.8 Inches) 100 cm (39.4 Inches)
Almaco Jack 160 cm (62.9 Inches) 90 cm (35.4 Inches)
Banded Rudderfish 75 cm (29.5 Inches) 50 cm (19.6 Inches)
Lesser Amberjack 67.5 cm (26.5 Inches) 50 cm (19.6 Inches)

 Other Characteristics

Almaco jack can further be differentiated by their darker color and their second dorsal fin being much higher than the other amberjacks.

Amberjack Identification
Here you can clearly see that the almaco jack’s second dorsal fin is higher. The first dorsal is not visible in either fish. Almaco jack on top, greater amberjack on the bottom.

Juvenile almaco jacks do not look like other juvenile amberjacks or very much like adults:

Amberjack Identification
Juvenile Almaco jack. Bars are present when fresh. The exposure was lightened on the dorsal fins Intentionally.

Banded rudderfish are slimmer, with a less deep body than other amberjacks.

Amberjack Identification
Greater Amberjack on top has a deeper body. The Banded Rudderfish below, has remnants of bars, and a shallower body.

They are also much smaller, and tend to have a blue sheen in my experience. Up until about 14 inches, they also have either black bars, or the remnants thereof. Please note that pilot fish, Naucrates ductor is another jack that looks superficially similar to juvenile banded rudderfish. The easiest way to tell them apart is to look for the presence of 2 dorsal fins. Pilot fish have lost the first dorsal fin, although rudimentary spines may still be present.

Amberjack Identification
A banded rudderfish with bars fading.
Amberjack Identification
An adult banded rudderfish. Notice the blue sheen, and the lack of bars.

 

Maxilla Comparisons

 

Amberjack Identification
Maxilla and supramaxilla

Lastly, there are two bones on the jaw of the amberjacks, called the maxilla and supramaxilla, that are often cited during identification. For ease of reading, we will refer to both these bones combined as the maxilla, as they are not easily separated visually. The shape of this bone can be used as a method of preliminary identification, but shouldn’t be the only factor used. The greater amberjack’s maxilla is very rounded, with a “boot” protrusion on its dorsal surface. The banded rudderfish’s maxilla is pretty flat across the top, and drops with little curve in what is almost a 90 degree angle. The lesser amberjack’s maxilla does have a bit of curve to it, but no “boot” projection. The almaco’s maxilla is sort of a cross between the lesser and the rudderfish. I seem to be out of adjectives at the moment, but look at the pictures, they say it all.

It is also important to note the position of the maxilla with respect to the eye. Notice how in the greater amberjack, the maxilla reaches to at least the midline of the eye, while the rudderfish and the lesser do not.  The almaco’s maxilla barely meets the front of the eye. Please note that this can vary, especially with younger fish, and should not be the sole factor in determining the species.

It is also important to note the line running through the eye of the fish, towards its first dorsal fin. Known as the “nuchal bar”, when present, it will flow from the eye to well in front of the first dorsal fin in lesser amberjack, and from the eye to the first dorsal fin origin in greater amberjack, almaco jack, and banded rudderfish. This bar can fade with age.

Gill Raker Counts

Gill Arch
Gill Arch Diagram

When external morphologies fail to ID the fish, we must resort to counting gill rakers on the first gill arch. You can do this by simply lifting the operculum (“gill flap”), and start counting all the rakers on both the upper and lower limbs of the first gill arch.

Amberjack Identification
The gill arch of an almaco jack

Once you have counted a few times, and are sure of your count, you can consult this table to help Id your fish:

Common Name Fish Length Gill Raker Count Fish Length Gill Raker Count
Greater Amberjack < 20 cm FL 18-24 >20 cm FL 11-19
Lesser Amberjack < 10 cm FL 23-26 >20 cm FL 23-26
Almaco Jack < 10 cm FL 24-29 >20 cm FL 18-25
Banded Rudderfish < 10 cm FL 20-25 >20 cm FL 12-17

 

The number of gill rakers in the greater, almaco, and banded rudderfish slowly decrease in number between 10 cm and 20 cm. Note that 20 cm is 7.87 inches. The gill rakers in the lesser amberjack remain constant.

As you can see, the greater amberjack, and the banded rudderfish counts can potentially overlap, as can the lesser and the almaco jack.  This is where you will start comparing the other characteristics, in conjunction with the raker counts, to make a positive ID. The hardest fishes to differentiate are the greater and lesser amberjacks, and this chart of raker counts will simplify that for you.

It may help to just check if the rakers extend all the way to the point where the gill arch connects to the fish. In greaters and banded, there will be a space between the last gill raker, and the point of connection, where in the remaining two, the rakers will continue along the arch up until the connection point.

Amberjack Identification
Notice how the rakers extend most of the way to the end of the gill arch. Almaco Jack.
Gill Arch
Notice how the rakers stop well before the end of the gill arch. Greater Amberjack.

 

My methodologies

When I come across one of these fishes, the first thing I do is to check if it is larger than 20 cm. Then I check to see if it is an almaco jack. Remember to look for the high second dorsal fin, the size of the fish, the darker olive coloration, and the maxilla without a boot. If it doesn’t meet any of those prerequisites, then I move on and try to eliminate a banded rudderfish as a possibility. What does the maxilla look like, what is the size of the fish, is there a nuchal bar present, is there a blue sheen? Usually you can knock out both banded rudderfish and almaco jacks without ever lifting the operculum. At this point, you have narrowed it down to either a lesser or a greater amberjack, and it’s time to check the gill rakers. If the raker count is 11 – 19 then the fish is a greater amberjack, if it is 23 – 26, then it’s a lesser. On a side note, the lesser amberjack is a much less common fish, and I have only ever seen a handful.

So there you have it, amberjacks demystified. If you have any issues with your amberjacks, or any other fish for that matter, don’t hesitate to post a question or send an email under the contact us page.

Further Reading:

Greater Amberjack 

Lesser Amberjack

Banded Rudderfish

Almaco Jack

 

SOURCES:

Banded Rudderfish

Robins, C.R. and G.C. Ray, 1986. A field guide to Atlantic coast fishes of North America. Houghton Mifflin Company, Boston, U.S.A. 354 p.

Almaco Jack

Myers, R.F., 1991. Micronesian reef fishes. Second Ed. Coral Graphics, Barrigada, Guam. 298 p.

Lesser Amberjack

Smith-Vaniz, W.F., J.-C. Quéro and M. Desoutter, 1990. Carangidae. p. 729-755. In J.C. Quero, J.C. Hureau, C. Karrer, A. Post and L. Saldanha (eds.) Check-list of the fishes of the eastern tropical Atlantic (CLOFETA). JNICT, Lisbon; SEI, Paris; and UNESCO, Paris. Vol. 2.

Greater Amberjack

Paxton, J.R., D.F. Hoese, G.R. Allen and J.E. Hanley, 1989. Pisces. Petromyzontidae to Carangidae. Zoological Catalogue of Australia, Vol. 7. Australian Government Publishing Service, Canberra, 665 p.

FAO. 2002. THE LIVING MARINE RESOURCES OF THE WESTERN CENTRAL ATLANTIC.
Volume 3, Pages 1434-1435.  8 July 2014.

 

 

 

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Blue Marlin Sampling

A Blue Marlin
A composite shot of a Blue Marlin

 

Ever wonder what becomes of a blue marlin after all of the photographs, interviews, and fanfare of a fishing tournament? How exactly do you dispose of a 900 pound fish?

Blue Marlin
A blue marlin on display.

In order to answer that, I took a camera along to document the process! After all the crowds disperse, the fish is loaded onto a flatbed truck, and moved to a suitable location on the water for biological sampling. Unfortunately this takes a lot of brute force, and there was no time for photographs.

After the fish is removed from the truck, which is by no means an easy feat, sampling can begin.

Blue Marlin Sampling
A blue marlin ready for sampling.

Blue Marlin Sampling:

The goal of this whole project was to harvest tissue samples for various laboratories. These include liver samples, stomach contents, age structures, and muscle samples. Different labs will use these tissues to determine things such as diet, age, and mercury content. In order to access these tissues, the fish must be cut up! Although that may seem obvious, there is a right and a wrong way to achieve this. Cut up incorrectly, you risk damaging the tissues to be sampled,  or, you risk floating 900 pounds of stinking fish into some poor fools backyard who happens to live down current.

Here you can see some organs, including the bubbly swim bladder, which we will discuss later on.

Blue Marlin abdominal cavity
A Blue Marlin’s abdominal cavity

I have no photos of the actual samples being taken, as I couldn’t sample and photograph at the same time. Essentially, they are cut out, and unceremoniously placed into plastic bags, which are then placed into a cooler to be frozen afterwards. The samples will be sent to the various labs after they are frozen for a day.

At this point, the sampling is finished.

Blue marlin Sampling
A Blue marlin after having its organs harvested

Disposal: 

Now we move on to disposal! The fish must be chopped into smaller pieces so that the local sharks and other fishes can finish the job for us. We had to ensure that the swim bladder was completely popped to prevent any of the pieces floating away, and as I said earlier, ending up in someones back yard. This apparently was not always the procedure, however, after a few complaints and phone calls, is now on the books.

 

After this, there is a lot of hosing blood over the side of the dock, and throwing of 15 pound hunks of meat into the sound. The bill and head were collected the next day by the angler so that he could get a mount created. A fair question that I hear from people regarding this process has to do with why we throw away so much meat. On the surface, that is a great question, and although there are some people who love to smoke marlin, they are generally regarded as not safe to eat. This does depend on locality and species, and I have heard that Hawaiian anglers often eat their billfishes. In the eastern US however, the mercury content is deemed too high for safe consumption. In fact, as of writing this, the EPA recommends less than one serving per month for men and 0 servings for both women and children. Then why kill it at all? That is another discussion for another day.

Further reading on methylmercury contamination:

US EPA Page on Methylmercury bioaccumulation

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Parasitic Isopod

I was lucky enough to catch a ride on a commercial gill net boat recently, and while the fishermen were targeting spot (Leiostomus xanthurus), I was hoping to add some species and photographs to our collection. The trip was your typical Core Sound gill net trip, with a few hundred pounds of spot, butterfish (Peprilus triacanthus), kingfish (Menticirrhus spp.), cobia (Rachycentron canadum), spotted sea trout (Cynoscion nebulosus), and what I believe to be a live sharksucker (Echeneis naucrates). Unfortunately the condition of the fish, after 12 hours in the net, made it more difficult to identify than I had hoped. Nonetheless, I thought I would take a side by side shot of a small cobia next to the sharksucker as a way of showing the differences between these two often confused fishes.

 

Sharksucker on top, cobia on the bottom
Sharksucker on top, cobia on the bottom

Turns out that the condition of both fishes was too poor to really help with teaching identification, but while preparing for the shot, I noticed another interesting animal:

 

This is a species of parasitic isopod (think rolly-polly), and although I haven’t the slightest clue as to which species, I can tell you that it plays an identical role to another similar isopod, Cymothoa excis. For the uninitiated, this is a parasitic isopod that attaches itself to the base of the tongue, and then sucks blood from the tongue causing it to atrophy. Once the tongue is out of the way, the isopod then sets up shop, attaches to the stub, and replaces the tongue. From this point onward, the fish will use the isopod as it would its own tongue.

ssmouthside
Parasitic Isopod trying to escape

In the south eastern US, some anglers refer to Atlantic Menhaden (Brevoortia tyrannus) as “bug mouths,” as they are often infected with a similar parasitic isopod.

This particular isopod survived the death of the fish, and attempted to escape. Whether or not it is capable of surviving on its own, I don’t know. However, in case you ever come across one and have the crazy idea to handle it, be prepared, they are not only very quick to latch on, but very capable of biting you too! It doesn’t tickle.

 

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