Gag or Black Grouper?

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uconn fishhead
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Gag or Black Grouper?


     I decided to do a little policing of my own fish ID's. So, now I've confused myself about how much variation in color and pattern to expect between a Gag and Black Grouper.  I'm almost 100% certain the first photo here is a Gag, but is the 2nd a Gag or a Black?  The 2nd photo does not seem to have any kind of notch or spine on the edge of its cheek (which would be characteristic of a Gag).  Also, the 2nd photo has "chain-like patterns" (vs. "vermiculations") which is more like a Black.

    You guys who have seen a few:  What do you think?  Thanks

uconn fishhead
uconn fishhead's picture
Gag vs. Black Grouper Settled (Probably)

So after some research and asking around, I’ll respond to my own post.  Likely, the answer is that the first fish in my above photos is a Gag Grouper and the second a Black Grouper.

I messaged rc6750 and he sent the following response and helpful graphic:

     "Top one is a gag - bottom one is a baby black
They look very similar - good rule of thumb is gags never have squares on them. Check out this picture I made.of 2 black groupers - matched to yours and a gag for reference"

I also emailed three fisheries professors and attached the photos: 

     Dr. Deb Murie (Univ. of Florida) said the second photo was definitely a juvenile Black.

     Dr. Frank Jordan (Loyola Univ) said he's not initmately familiar with the groupers, but did an embarrassing (for me) amount of research to end up agreeing with Dr. Murie.

     Interestingly, Dr. Bart Henry (also from Loyola) thought both photos were probably Gags, although he didn’t sound certain.

     I guess this confirms that the two species can be easily confused, but most references claim that it is the juveniles (which these are) that are most similar. The most important characteristics separating them are:

Black:  Markings tend to form chain-like patterns (series of rectangles, often with a single horizontal line in the middle); edge of preopercle (cheek) is smooth; tend to be darker than Gags; either none or only a thin white margin on anal and tail fins; usually have a broad dark band on the outer 1/3 of the anal, soft dorsal and caudal fins. 88-89 lateral line scales.

Gag: Markings tend to be vermiculated (wavy) often with “kissing marks”; edge of preopercle is serrated (which is pronounced in adults, not well developed in juveniles); tend to be lighter colored; white or blue edge on anal and tail fins; dorsal, anal and caudal fins are more uniformly dark (without a dark band). 78-83 lateral line scales.

     In photos, it is typically difficult to see preopercular spines and the scales are too small to count, so we must rely mostly on the markings/coloration.

     Based the above characters, all the Gags and Blacks on Roughfish seem to be correct, except one:  wahdizzle’s Black Grouper appears (to me) to be a Gag.

NOAA has a helpful PDF that graphically compares similar Grouper species: