Comprehensive DescriptionRead full entry
The snappers are a prominent family of predatory fishes found in all tropical waters and often associated with reef or mangrove habitats. The deeper-water species, in particular, are an important component of fisheries in the Caribbean and the Gulf of Mexico. There are numerous snapper species in the region and most of them can be found on or near coral reefs. The shallow-water snappers are almost all members of the large genus Lutjanus. The one exception, the Yellowtail Snapper Ocyurus chrysurus, falls well within the Lutjanus clade in phylogenetic studies. There are four additional deep-water lutjanid genera, three of which have only a single Caribbean representative.
Larval snappers exhibit the standard percoid characters shared to some degree by many other families: a wide body, large round eye, large terminal mouth, stout spines in the fins and a short anal fin with three spines. Later-stage lutjanid larvae are distinctive in having a large non-serrated spine at the angle of the preopercle. Fin-ray counts broadly overlap with two other common reef-fish families: the seabasses and groupers (Serranidae) and the grunts (Haemulidae). Separating larval snappers from serranids is not always easy and useful characters are discussed in detail below. Grunts are easy to distinguish since they have narrower bodies, short non-serrated dorsal-fin spines, two anal-fin spines (as larvae and small juveniles), and are typically much smaller at each stage of development.
Regional Species: There are at least ten Lutjanus species in the region. The shallow-water species include a pair of small snappers with a lateral spot: the Mahogany Snapper, L. mahogoni, and the Lane Snapper, L. synagris. This pair is distinct in having only twelve dorsal-fin soft rays (D-X,12); the remaining species in the genus have fourteen (D-X,14). The Mutton Snapper L. analis also has a lateral spot. The remaining shallow-water species have bars and/or a stripe through the eye and comprise the Schoolmaster Snapper, L. apodus, and the Dog Snapper, L. jocu, which appear similar and differ primarily in lateral-line scale counts and some markings. The Gray Snapper, L. griseus, and the Cubera Snapper, L. cyanopterus, also look similar, but Cubera Snappers grow to a much larger size, up to 125 pounds and over four feet in length. My mtDNA sequence analyses indicate that similarity in appearance does not always reflect relatedness: Gray Snappers are part of the Schoolmaster/Dog clade while the Cubera Snapper is well out on its own branch in the phylogenetic tree. The snappers with a lateral spot do all share a lineage, but the Yellowtail Snapper Ocyurus chrysurus, falls in the middle of that grouping, despite having no spot and a different morphology.
Three Lutjanus species are predominantly deep-water denizens, although juveniles occasionally occur in shallower reef areas: the Blackfin Snapper L. buccanella, the Silk Snapper L. vivanus, and the Red Snapper, L. campechanus. The Southern Red Snapper, L. purpureus, has recently been shown to have identical DNA sequences at multiple loci to the Red Snapper, L. campechanus, confirming that it represents the southern population of the Red Snapper (Gomes et al. 2008). L. campechanus from the Gulf of Mexico typically have nine anal-fin rays, but outside of the Gulf they mostly share the modal eight anal-fin rays of the other species in the genus. These deep-water Lutjanus have typical fin-ray counts for the genus (D-X,14 Pect-17) and, in genetic studies, fall within the same clade as the lateral-spot snappers. Interestingly, they also have lateral spots to some degree as juveniles.
There are four other lutjanid genera with a single Caribbean species each. The common Yellowtail Snapper Ocyurus chrysurus (D-X,13 A-III,9 Pect-15-16) forages in open water and thus has a more streamlined body form than other snappers but falls well within the Lutjanus clade. Three deep-water snapper genera have a single regional species each and comprise Apsilus dentatus (D-X,10 Pect-15-16), Etelis oculatus (D-X,11 Pect-15-16), and Rhomboplites aurorubens (D-XII,11 Pect-17-18). The remaining deep-water snapper genus has three species, all with the same fin-ray counts of D-X,11 Pect-15-16: i.e. Pristipomoides aquilonaris, P. freemani, and P. macrophthalmus.
Diagnostic Characters for Lutjanid Larvae:
Early-stage Larvae: Less-developed lutjanid larvae occasionally appear in collections made over the reef. They conform to many of the basic features of percoid larvae and have a large head, large round eye, large mouth with a prominent jaw angle, prominent preopercular spines, a wide body, continuous dorsal fins with stout spines, a short anal fin with three stout spines, and elongated and stout pelvic-fin spines. Features more specific to lutjanids, especially Lutjanus, are the moderately-serrated dorsal and pelvic-fin spines (these spines and the anal-fin spines often have anterior serrations as well), the first pelvic-fin ray longer than the spine, a non-serrated spine at the angle of the preopercle, and, most distinctive, a post-cleithral spine.
A number of families have similar-appearing early-stage larvae, fortunately few occur in the Atlantic. The most likely confusion in the region is with serranid larvae, especially since there is some overlap in fin-ray counts between Caribbean lutjanid and serranid species. In general, serranid species in the region have only seven (serranines) or nine or ten (epinephelines) anal-fin soft rays, while most lutjanids have eight, but this is a fine point for distinguishing larvae.
The most difficult to distinguish at early stages are the D-X,12 snappers and the Serranus species (the epinepheline serranids have more dorsal-fin soft rays). In this case, the early-stage larval snappers have mildly-serrated fin-ray spines while the Serranus have smooth spines. Interestingly, these two unrelated taxa can have quite similar basic melanophore patterns, however the Serranus all have a melanophore at the angle of the jaw and, if intact, obvious speckling of the pectoral fin-ray membranes.
There is a slight fin-ray-count difference between the D-X,14 snappers and the epinepheline serranids. Virtually all of the Caribbean epinephelines have either eight, nine, or eleven dorsal-fin spines and most have more than 14 dorsal-fin soft rays and nine or ten anal-fin soft rays, while lutjanids have ten dorsal-fin spines (one with 12), 14 or fewer dorsal-fin soft rays, and eight anal-fin soft rays (two with nine). In addition, the few overlapping epinephelines have 18 or more pectoral-fin rays (vs. 16-17 in the lutjanids).
The pretransitional larval epinephelines have markedly-serrated and extended dorsal and pelvic-fin spines, while the snappers do not. In addition, the second dorsal-fin spine is usually much longer than the third vs. slightly longer or similar in length in the late-stage larval snappers (this distinction may not apply to some deep-water snapper genera). The snapper preopercular spine is notably non-serrated, while that of the epinephelines is serrated, but that is not always obvious on initial inspection. In addition, lutjanids have the first pelvic-fin soft ray longer than the spine vs. distinctly shorter in epinephelines. Finally, there is a characteristic post-cleithral spine in lutjanid larvae that is not present in the serranids. (Note: special thanks to Jeff Leis and his books).
Late-Stage Larvae: Lutjanid larvae in general share a number of basic features, most particularly a long non-serrated preopercular spine. The spine decreases in length during transition and disappears in juveniles. There are also smaller spines lining the lower and posterior margins of the preopercle that similarly decrease in prominence during transition. Some pretransitional larvae can show a row of fine serrations along the supraorbital bony ridge (preopercular spine and supraorbital serrations visible at the top of the photograph below of a 12.2 mm SL Gray Snapper larva, L. griseus).
Marking patterns on the late larvae of most snappers can be quite similar, and comprise variations of the basic theme of mostly dorsal-facing melanophores. This suggests that melanophores function as shielding, protecting vulnerable organs from sunlight. Indeed, it would be plausible to infer from this pattern that snapper larvae are living near the ocean surface during the day. Melanophores shield the brain and spinal column by running along the top of the brain itself, at the surface over the braincase, along the dorsal fins, and along the dorsal caudal peduncle. Internal melanophores line the dorsal aspect of the vertebral column, often with an additional short row beside or below the column near the tail. Melanophores line the dorsal surface of the swim-bladder and peritoneum (overlying the abdominal organs). In addition, the inner-facing cleithrum (the lower rear wall of the gill cavity) is pigmented and overlies thoracic structures. Additional melanophores present on most species' larvae include a few deep at the lateral midline on the caudal peduncle, a ventral midline caudal peduncle row (often just one or two large melanophores), a few at the insertion of the lower caudal-fin segmented rays, and along the base of the membranes of the anal-fin rays. A distinctive deep melanophore is present from the early stages under the pterygiophores of the last anal-fin rays (an additional "repeat" melanophore is sometimes present on the next segment anteriorly). These internal melanophores can be seen on the transitional larval Yellowtail Snapper photograph below (Ocyurus chrysurus, 17.0 mm SL) and beginning in the early larva of L. griseus, photographed above).