DEFINITIONS OF TERMS

I have also thrown together a video explaining all of these terms that is hosted on KN Fishing Smarts, Koaw Nature’s sister channel on YouTube.

BODY: All sunfishes have deep and compressed bodies. The descriptor “deep” refers to the body’s vertical height making up a large portion of the body’s horizontal length. The descriptor “compressed” refers to the fish having a laterally compressed body, that is, it looks very slender from a dorsal view, or a view from above. Some sunfishes have deep bodies that are more elongated, such as the green sunfish (Lepomis cyanellus) and the redbreast sunfish (Lepomis auritus), while some species have very deep bodies like that of the bluegill (Lepomis macrochirus).

FINS: Sunfishes have median fins and paired fins.

THE MEDIAN FINS OR UNPAIRED FINS: The dorsal fins, anal fin and caudal fin make up the median fins on lepomids.

DORSAL FINS: The first and second dorsal fins are fused, where the first dorsal fin is composed of spines and the second dorsal fin is composed of soft rays. Most all lepomids have 10 (9-11) dorsal spines. (The spines are very sharp so be careful holding sunfishes.)

NOTE: You may be wondering, “Wait…two dorsal fins?” Certain ichthyologists (biologists who study fishes) prefer to describe the dorsal fin region on centrarchids (fishes of the sunfish family) as a single entity when the spines and soft rays are fused and continuous along the dorsum. [1] [2] I have decided to follow the wording of ichthyologists opting to describe the fused spinous dorsal fin region and soft ray region as two separate entities while still recognizing these two entities are technically a single unit; [3] hence why I will describe the dorsal fin with soft rays with the descriptors “2d”, “2nd” or “second”. Though this may be illogical from some perspectives, I just prefer that greater precision offered from the semantics for guide purposes.

ANAL FIN: All sunfishes within Lepomis have a single anal fin that is posterior to the anus and urogenital opening. The most anterior part of the anal fin has three spines followed by soft rays.

CAUDAL FIN OR TAIL FIN: The caudal fin is indented, also known as concave or emarginated, where it may also be describe as shallowly forked. The caudal fin is composed entirely of soft rays.

PAIRED FINS: The paired fins are the pectoral fins and pelvic fins.

PECTORAL FINS: There are two pectoral fins, one on each lateral side, just posterior to the head and moderately ventral on the body. The pectoral fin is entirely made of soft rays with no spines. The length and shape of the pectoral fins are a great feature to analyze for lepomid identifications. (Click on the adjacent image to enlarge the pectoral fin on the longear sunfish.)

PELVIC FINS: The pelvic fins are both seated adjacent to one another ventrally and abdominally on the body. A large spine is anterior on each fin, followed by rays.

BREAST: The breast is the ventral region of a fish usually beginning at the isthmus (the ventral fleshy region of the throat that externally separates the two gill chambers), continuing below the pectoral fins and ending posteriorly at the anterior edge of the pelvic fins.

BELLY: The belly is a loosely defined common term for the exterior abdominal region. For lepomids, the belly may suitably be described as the ventral region of the body beginning at the pelvic fins and extending to the anus.

CAUDAL PEDUNCLE: The caudal peduncle is the posterior portion of the body that tapers off from the main body both dorsally and ventrally. Typically, the caudal peduncle begins behind the posterior edge of the anal fin (or sometimes dorsal fin) insertion (where the last ray leaves the body) extending to the caudal flexure (the posterior edge of the hypural plates, of which, is detectable by bending the caudal peduncle and seeing the indentation of the bones.)

CHEEK: The cheek is usually described as the region between the eye and the preopercle (the most anterior bone of the operculum, or gill plate.)

MOUTH: The mouth is the most anterior part of the fish. On lepomids, the mouth is slightly superior, or upturned, on most specimens, at times appearing terminal. (A superior mouth describes where the lower jaw extends farther forward than the upper jaw.) Sunfishes have moderately protrusible jaws, allowing the mouth to widen and extend forward to capture food sources. Mouth and jaw size are great features to examine when identifying sunfishes.

JAW: The upper and lower jaws are made up of a number of bones. For the purposes of this guide, the most posterior edge of the maxillary (marked by “2” in the adjacent photo) on a single lateral side is compared against the location of the eye, orbit and/or pupil.

The length of the upper jaw is taken by measuring from the most anterior edge of the premaxillary to the maxillary’s most posterior edge.

SNOUT: The snout is the region of the head in front of the eye. A snout length may be taken by measuring from the most anterior tip of the upper lip (premaxillary) to the most anterior edge of the orbit, or eye socket; though this is a horizontal measurement, not angling like the length of the upper jaw.

EYE: The eye rests in the orbit, or the eye socket. The eye has a dark pupil at its center that is mostly circular with a slightly tapered anterior edge. The iris surrounds the pupil and is often composed of different colors that may vary depending on the species, sex and season. E.g. – Male warmouth (Lepomis gulosus) get much brighter red irises in breeding seasons. (Often the term eye and orbit will be interchangeable for the purposes of this guide.)

Eye color may be quite variable within lepomids even within the same species in the same localized populations. I do not suggest depending on this feature for identifications with the exceptions of a few species such as the redspotted sunfish (Lepomis miniatus) and the spotted sunfish (Lepomis punctatus) where a conspicuous blue ‘bowl’ sits on the bottom of the eye in these two fishes.

GILL PLATE, GILL COVER OR OPERCULUM: The gill plate is posterior on the head and covers the gill arches. This gill plate is composed of four bones that collectively are called the operculum. The most anterior bone is the preopercle that rests above the interopercle. Posterior to the interopercle is the subopercle which rests under the largest bone of the operculum, the opercle.

GILL RAKERS: The gill rakers are boney extensions that exist on the gill arches and are primarily used for retaining food organisms when feeding. The arches are white and vary in size, shape and distribution along the arches. Different species may have very different sizes on the gill arches. These rakers may be very beneficial for analyzing during identifications, especially if hybridization is involved.

OPERCULAR FLAP OR “EAR FLAP”: Each species of lepomid has an opercular flap, or a fleshy extension atop the opercle. This flap is one of the best features to analyze for identifications of lepomids. Very colorful edgings may exist along this flap as well as colors existing on top of the flap. Some flaps grow to be very large such as on the longear sunfish (Lepomis megalotis) and the redbreast sunfish (Lepomis auritus).

NAPE: This is a dorsal region of a fish’s back typically starting behind the eye at the margin of the skull and extending to the anterior edge of the first dorsal fin. This term is somewhat loosely defined; some sources will suggest the nape begins on bony fishes where the dorsal portion of the head without scales meets the portion with scales then extending to the anterior edge of the dorsal fin.

LATERAL LINE: The trunk lateral line is usually easily visible on each lateral side of a sunfish. This is a part of the fish’s sensory systems for detecting vibrations formed by displaced water. The lateral line along the body begins behind the head usually just above the opercular flap and extends laterally all the way onto the caudal peduncle. The lateral line curves slightly both anteriorly and posteriorly along the body, sort of like a stretched out ‘S’ that is tilted and flipped. Each lepomid typically has a complete lateral line with the exception of the bantam sunfish (Lepomis symmetricus). A complete lateral line means that the pores running along the lateral line are visible (present) along its entirety.

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The Definition of Terms above has been created from the definitions provided in the following sources:

1. P. A. Hastings, H. J. Walker, Jr. and G. R. Galland, Fishes: A Guide to their Diversity, Oakland: University of California Press, 2014.

2. 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.

3. L. M. Page and B. M. Burr, Peterson Field Guide to Freshwater Fishes, Houghton Mifflin Harcourt Publishing Company, 2011, pp. 506-507.

4. FishBase, "FishBase - Glossary of Terms," 2020. [Online]. Available: www.fishbase.org. [Accessed November 2020].

5. G. S. Helfman, B. B. Collette, D. E. Facey and B. W. Bowen, The Diversity of Fishes: Biology, Evolution, and Ecology, 2nd Edition ed., Wiley-Blackwell, 2009.