By Koaw - December 2020

MERISTICS INTRODUCTION:

Counting the soft rays and spines in the fins of lepomids is a very useful diagnostic ability. In ichthyology, or the field of biology that studies fishes, characteristics on a fish that are countable are called meristic characteristics, such as the spines in the dorsal fin or lateral line scales. Commonly this method of counting characteristics is called meristics.

Morphometric characteristics are features that are measured and/or proportionally analyzed against other characteristics, such as the total length and largest dorsal spine length vs. head length.

The adjacent video shows how to count the spines and rays in the fins of lepomids and is hosted on the KN Fishing Smarts YouTube channel.

UNDERSTANDING MERISTIC COUNTS IN KOAW’S GUIDE

Any species of lepomid will show variance in meristic characteristics. In this guide, you might see on the green sunfish page: “Typically 3 anal spines, 9 (8) anal rays and 13-14 pectoral rays, 10 dorsal spines and 10-11 dorsal rays.”

If a number before a characteristic is only a single number, such as the 3 above, then that means the characteristic rarely provides a count of anything different on that species. It is extremely rare to find any lepomid without 3 anal spines. For the dorsal spines, it is less rare but still uncommon to find a green sunfish with more or less than 10 dorsal spines.

If you see two numbers with a hyphen between them, such as the 13-14 above, then both of those counts are the most common and appear with somewhat similar frequency.

If you see a number in parenthesis, such as the 9 (8) above, the first number is the usually count on that species while the number in parenthesis appears much less but with enough regularity to be considered.

It is possible to encounter specimens that will have a count for a meristic characteristic that does not fit into the suggested ranges listed in my guide. These outliers are considered in the statistical analyses but not mentioned in the species description as they are far too uncommon. I based the the meristics offered in this guide from a combination of studies, field guides as well as my own data gathered on lepomids.

Below I’ve provided supplementary graphics and descriptions for how to count all the fin spines and rays for the 1st and 2nd dorsal fins, the anal fin and a pectoral fin. I will use photos from a beautiful green sunfish I caught in Missouri.

This counting method is fairly standard in ichthyology; I’ll be adhering to the described methods from Page & Burr (2011) & Hubbs & Lagler (2004); both references have similar methods for meristics. This method is applicable to all sunfishes as well as many other groups of fishes—but not all.

COUNTING FIN SPINES & RAYS WALK-THROUGH

DORSAL SPINES - Lepomids have a fused dorsal fin where the first dorsal fin (closer to the head) is composed of hard, thick spines and the second dorsal fin is composed of soft rays. All spines are counted. Counting spines is relatively easy if the fish is being physically analyzed as these spines are noticeably sharper and denser than soft rays. If you plan on doing your counts when you get home or to your lab then I suggest you double check to make sure you captured photos with high enough quality of all the fins spread out, of which, may require taking a few separate photos.

DORSAL SOFT RAYS - The soft rays are trickier to count. These are thinner and flexible compared to the spines. Counting the posterior rays, or the last rays, can be a headache sometimes.

Firstly, count at the base. These soft rays will branch off distally, or away from the body. It’s important to count at the bases so as to not overdo the meristic count.

Secondly, and this is where it gets tricky, the last two rays coming from the body are typically going to be counted as one ray because they actually sprout from a single place under the surface. Depending on the specimen, this may be obvious or it may not be. Basically, if the branching of the last ray appears to happen at or near surface then count the ray as one because it probably is connected beneath.

PECTORAL RAYS - Pectoral rays are in each of the two pectoral fins, one on each lateral side. There are no spines in the pectoral fin, only soft rays. All pectoral rays are counted, even if they are small. Count at the base of the rays as they will branch distally.

Often a magnifying glass is needed to examine the rays properly in the field. If a photo is taken, make sure the fin is spread out, there is no blur in the photo and the highest quality photo setting is set on the camera. If possible, count the pectoral rays on both the left and right pectoral fin. It does happen where these counts are different on the same fish.

ANAL SPINES – The anal spines are the first anterior extensions (closer to the head) coming from the anal fin. These spines are very similar to the dorsal spines as they are sharp, hard, and thick. If the meristic count for anal spines is not 3 then consider yourself lucky to have found such an oddity!

ANAL RAYS – The anal rays are posterior to the anal spines. Again, just like with the dorsal rays, these rays may present difficulty for counting.

Counting anal rays is the same routine discussed for dorsal rays. Count at the bases as these rays branch distally. The last two rays are typically going to be counted as one ray. Spreading out the fin is really necessary for this count. Sometimes it’s quite obvious what constitutes as the last two rays and sometimes you’ll have to make a judgment call. If it seems like the last rays coming out the body probably connect under the surface, then count those as one—they’ll usually be touching or nearly touching at the dermal layer and branched underneath.

Alright, so it looks like this green sunfish has 3 anal spines, 9 anal rays, 10 dorsal spines, 11 dorsal rays and 14 pectoral rays, all of which, fall into the expected counts for this species.

I hope this extra add-on to the guide has helped you out. Cheers! -K

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REFERENCES:

1. C. L. Hubbs and K. F. Lagler, FISHES of the Great Lakes Region: Revised Edition/ Revised by Gerald R. Smith, The University of Michigan Press, 2004.

2. L. M. Page and B. M. Burr, Peterson Field Guide to Freshwater Fishes, Houghton Mifflin Harcourt Publishing Company, 2011.