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Stegastes
Microspathodon
Abudefduf
Chromis
The damselfishes are some of the most common and conspicuous coral reef fishes in the region and are often selected as the subjects for ecological and behavioral studies. Their taxonomy is straightforward; there are only four genera in the Caribbean with relatively few species. Two genera include several species each: the ubiquitous Stegastes with six species (and one fresh-water species) and Chromis with two shallow and four deep-water species. There are two Abudefduf species and the single Microspathodon chrysurus. The Caribbean Stegastes have been moved around from genus to genus over the recent past, spending some time as Eupomacentrus and Pomacentrus.
Pomacentrid larvae closely resemble juvenile damselfish in form and are easy to recognize. Larval damselfishes are characterized by a rounded body with a wide caudal peduncle, continuous spinous and soft dorsal fins, large round eyes, a relatively small terminal mouth, and the absence of head spines. Distinguishing species for the larval and newly-settled stages can be a challenge in this family where meristics can broadly overlap, especially within Stegastes. The marking patterns that separate species of Stegastes typically diverge only at the late juvenile stage and new recruits can share many of the features that will later distinguish the species (i.e. ontogenetic homology). The two regional Abudefduf are also very similar as larvae and new recruits. As a result, some descriptions of damselfish early life history and many illustrations of small juvenile damselfishes in guidebooks and on the web are incorrect.
 
Early Stegastes
 
The numerous damselfishes of this genus are known for marked coloration and pattern changes as they grow, mostly converging on a uniform dusky appearance as adults. Pre-transitional larval Stegastes are mostly colorless with few distinguishing markings and overlap extensively in meristics and thus DNA sequencing is necessary to identify many larvae to species. Damselfish larvae rapidly acquire juvenile markings during the night of settlement and transitional larvae are common in collections over the reef, even before they have the chance to transform in a trap.
New recruits of some Stegastes species can share the markings that are used as species-specific diagnostic characters in the later juvenile stages. These shared markings include the pattern of spots and stripes on the head, the size, shape, and position of the dorsal-fin ocellus, the spot at the top of the pectoral-fin base, and the upper caudal-peduncle saddle-spot. These characters may not be consistent for identifying juveniles below 20 mm SL and many species identifications of photographs of small juveniles on the web and in reef fish guides are mistaken. Furthermore, the published descriptions of juveniles of this genus are almost always incongruent and depend on highly variable characters, such as shades of yellow or the degree of striping. The most egregious example of this is the commonplace assignment of any juvenile with blue head stripes to S. diencaeus.
Transient ontogenetic homologies in pomacentrid early life history: This interesting phenomenon of short-lived, presumably vestigial, markings that appear on early juveniles is somewhat analogous to the homologies in ontogeny shown in mammalian embryology. In this case, however, ontogeny may recapitulate phylogeny (in a way) as ancestral markings may persist in the earliest juveniles of an entire clade. The similarity may extend to the mechanism for the persistence: just as obsolete embryological structures persist because of reduced selection pressure within the womb (for example the hindlimbs in dolphin embryos), these early markings may persist because of reduced selection pressure for species recognition among the smallest juvenile stages on the reef. Alternatively, a more intriguing explanation may be that this phenomenon is an adaptation to disguise species identity at the time of extreme vulnerability to competitive interactions from adults.
Species Identification: Among the larval Stegastes, S. partitus diverges first during the transition phase by not developing the dorsal-fin ocellus shared by all of the other reef species. The dorsal-fin ocellus is the first transitional marking appearing on larvae. Immediately afterwards, the outlines of iridescent spots and stripes appear on the head and upper body and the spotted species, S. adustus and S. planifrons, can be distinguished from the striped species, S. diencaeus, S. leucostictus, and S. variabilis.
New recruits of S. partitus share the blue spots and stripes on the head characteristic of other Stegastes, although these are usually not conspicuous and disappear rapidly. Once the dorsal-fin ocellus develops, S. adustus and S. planifrons can be distinguished by having only spots, not stripes, on the top of the head (as well as other distinctive color patterns). The three remaining reef species, all with a dorsal-fin ocellus and stripes on the head, share most basic markings as new recruits (S. diencaeus, S. leucostictus, and S. variabilis). Nevertheless, with the characters described below, juveniles of these species should be categorized correctly. It should be noted, however, that intermediate individuals do occur. This is probably variability within species, although the possibility of occasional hybridization should not be excluded. DNA-sequencing analyses, underway at present on this group, will confirm the identification of larvae and new recruits of these species and explore the hybridization question further.
The most troublesome feature of juvenile markings in these damselfishes is the rapid change in the size, shape, and position of the spots, stripes, and the dorsal-fin ocellus. Overlying these ontogenetic changes is a high degree of variability within species. My DNA sequencing of these damselfishes reveals that many features are inconsistent for separating species at these early stages, especially the size and position of the dorsal-fin ocellus and the intensity of spots on the head and dorsal fin.
 
Stegastes planifrons
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 dorsal-fin soft rays indicate Stegastes and Microspathodon chrysurus. Fin-ray counts broadly overlap among Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays (S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays). Given this overlap, it is likely that pre-transitional larvae will require DNA sequencing to reliably distinguish the species.
Early juvenile markings: New recruits (10-15 mm SL) of S. planifrons have only a few discrete small and round blue spots on the head and upper body with only a single spot on the upper iris (not a stripe). There is a large black ocellus centered on the last three dorsal-fin spines and first three dorsal-fin soft rays (about 40% on the fin, 60% on the body) and a caudal-peduncle saddle made up of a pale area surrounded by dusky shading followed by a distinct black spot. Although it is a diagnostic feature for later juveniles, new recruits do not have a spot at the top of the pectoral-fin base. Ontogenetic homologies include a short-lived blue ring around the dorsal-fin ocellus and blue edging around the caudal-peduncle saddle spot.
Juvenile analogues: New recruits of S. planifrons are separated from S. diencaeus, S. leucostictus, and S. variabilis by having no stripes on the iris or the top of the head. In addition, they are uniformly yellow or dusky yellow (S. diencaeus is the only other species that can be uniformly yellow, although often new recruits are not). New recruits of S. planifrons are separated from S. adustus by color as well as having much smaller blue spots (and only one on the iris) and from S. partitus by having a dorsal-fin ocellus and caudal-peduncle saddle.
Later juveniles (over 15 mm SL) are characterized by a uniform yellow body, a black dorsal-fin ocellus, a large black upper caudal-peduncle spot, and a prominent black spot at the pectoral-fin base.
Description:
Stegastes planifrons new recruit
10.9 mm SL
single spot on iris, ocellus 40% on the fin
Belize, BZ98-704
stegastes planifrons juvenile
  threespot damselfish juvenile
 
Stegastes adustus
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 soft rays indicate Stegastes and Microspathodon chrysurus. Although fin-ray counts broadly overlap among the other Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays, S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays. The two latter species have a slight divergence in anal-fin soft rays, with S. adustus having 13-15, while M. chrysurus have 12-13.
Early juvenile markings: New recruits (10-15 mm SL) of S. adustus have
Juvenile analogues: New recruits of S. adustus are separated from S. diencaeus, S. leucostictus, and S. variabilis by having no stripes
Later juveniles (over 20 mm SL) are characterized by
Description:
Stegastes adustus new recruit
10.9 mm SL
Belize, BZ98-704
 
   
 
Stegastes leucostictus
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 soft rays indicate Stegastes and Microspathodon chrysurus. Fin-ray counts broadly overlap among Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays (S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays). Given this overlap, larvae and even early juveniles can require DNA sequencing to reliably distinguish the species.
Early juvenile markings: New recruits (10-15 mm SL) of S. leucostictus have a pattern of blue stripes and spots on the head and upper body with a broad stripe and two spots on the iris. The upper part of the head and anterior body have a dusky blue background color. The blue stripes and spots are heavier than in other conspecifics and usually there is a third line of blue spots between the top stripe on the head and the stripe directly off the upper eye. Furthermore, the stripes typically break up into a pattern of numerous bright spots on the anterior dorsal fin. There is a large black ocellus ringed in blue centered on the last two dorsal-fin spines and first three dorsal-fin soft rays. The ocellus is typically mostly on the fin (usually 70% or more) and often higher than wide. There is usually one unmarked scale row between the lateral line and the blue ring. In addition, the scales with blue below the ocellus on the body are darkly-outlined rather than merged into a blue line. The spot migrates rapidly onto the fin and, by the time the juveniles reach 20 mm SL, almost all of the black spot is over the dorsal fin. There is a dark spot at the top edge of the pectoral-fin base. There is no caudal-peduncle saddle spot.
Juvenile analogues: New recruits of S. leucostictus are separated from S. planifrons and S. adustus by having stripes along with the spots on the head and iris and from S. partitus by having a dorsal-fin ocellus. The more difficult separation of new recruits (up to 15 mm SL) from S. variabilis and S. diencaeus depends on subtle characters, primarily the dorsal-fin ocellus centered off the body, usually more than 70% over the dorsal fin. In S. leucostictus, there is a space about one scale wide between the blue ring edge and the lateral line, while in the other species the blue ring starts less than a scale above the lateral line. In addition, the blue ring segment below the dorsal-fin ocellus is made up of dark-edged scales in S. leucostictus and merged into a blue line on the other two species. On the head, the blue spots usually form a third row between the top head stripe and the upper-eye stripe, whereas in the other two species this additional row is reduced and appears later, after 15 mm SL. S. leucostictus recruits and juveniles do not have the caudal-peduncle saddle spot, thus its presence excludes S. leucostictus (the absence of the saddle means little in new recruits, when S. variabilis may not yet have developed a saddle and when S. diencaeus variably shows none or a transient mark). Also S. leucostictus recruits and juveniles always show the dark spot at the top of the pectoral fin, thus the absence of the spot excludes S. leucostictus, but its presence does not exclude the other species.

Later juveniles (over 20 mm SL) are yellow with a blue (often bright blue) upper head and anterior body and dorsal fin with numerous iridescent blue stripes and spots, a dorsal-fin ocellus mostly off of the body (often completely over the fin rays and subsequently the edges becoming indistinct and disappearing), a spot at the top of the pectoral-fin base, and no caudal-peduncle saddle. Some juvenile damselfishes are identical in all respects to these S. leucostictus, but do have a caudal-peduncle saddle, and these are automatically assigned to S. variabilis (DNA sequencing should confirm this conclusion).

Description:
Stegastes leucostictus juvenile
21.1 mm SL
- three blue stripes on each side of head
-numerous blue spots on spinous dorsal-fin
-ocellus all on the fin
-pectoral-fin base spot
-no caudal-peduncle saddle spot
St. Thomas, USVI , ST107
stegastes leucostictus juvenile
  beaugregory juvenile
  stegastes leucostictus juvenile
  stegastes larvae
   
 
Stegastes variabilis
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 dorsal-fin soft rays indicate Stegastes and Microspathodon chrysurus. Fin-ray counts broadly overlap among Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays (S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays). Given this overlap, larvae and even early juveniles can require DNA sequencing to reliably distinguish the species.
Early juvenile markings: New recruits (10-15 mm SL) of S. variabilis have a pattern of blue stripes and spots on the head and upper body with two spots and a stripe on the iris. The upper part of the head and anterior body have a dusky blue background color. There is a large black ocellus ringed in blue centered on the last two dorsal-fin spines and first three dorsal-fin soft rays. The ocellus is typically 50% on the fin and 50% on the body. The blue edging below the ocellus on the body is usually an intact blue line and it comes close to the lateral line (usually less than one scale away). There is a characteristic blue-edged black saddle-spot on the caudal peduncle just behind the last dorsal-fin ray.
Juvenile analogues: New recruits of S. variabilis are separated from S. planifrons and S. adustus by having stripes along with the spots on the head and iris and from S. partitus by having a dorsal-fin ocellus. New recruits of S. variabilis develop a prominent caudal-peduncle saddle mark, which serves to distinguish them from the otherwise very similar S. leucostictus and S. diencaeus. Recruits that have not developed the saddle can be separated from S. leucostictus by having the ocellus well onto the body (less useful characters include usually no additional row of spots between the top stripe on the head and the upper-eye stripe, and sparser spotting on the anterior dorsal fin). Early recruits that have not developed the saddle or have an incipient saddle are difficult to separate from S. diencaeus when life colors are not apparent (S. diencaeus recruits should not have the anterior dusky blue wash on the head and upper body and the stripes are more magenta than blue). The problem is that some S. variabilis (up to 20 mm SL) have indistinct caudal-peduncle saddles and many S. diencaeus of the same size have similar-appearing indistinct saddles. In that case, the distinction becomes more subtle: S. variabilis have more dusky blue shading over the head and body, especially including the posterior dorsal fin and the anal fin while this area is not at all blue in S. diencaeus. Unfortunately, degrees of duskiness are poor characters to separate individuals. DNA sequence comparisons underway at present should resolve the line of separation.
Later juveniles (over 20 mm SL) are are yellow with a blue (often bright blue) upper head and anterior body and dorsal fin with numerous iridescent blue stripes and spots, a dorsal-fin ocellus over the body and fin (moving off the body when large juveniles over 30 mm SL), and a prominent black caudal-peduncle saddle.
Description:
Stegastes planifrons new recruit
10.9 mm SL
Belize, BZ98-704
 
   
 
Stegastes diencaeus
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 dorsal-fin soft rays indicate Stegastes and Microspathodon chrysurus. Fin-ray counts broadly overlap among Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays (S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays). Given this overlap, larvae and even early juveniles can require DNA sequencing to reliably distinguish the species.
Early juvenile markings: This species is distinct in the field in having magenta stripes and spots on the head, not strictly blue as in other juvenile damselfishes. This important feature is rarely mentioned in books and guides (in Randall's 2nd edition the
stripes are described as violet, in the 3rd edition as blue). There are several possible reasons for this. One is that the difference is sometimes subtle and affected by lighting. Magenta is made up of equal parts red and blue, and red is a color that attenuates rapidly underwater and thus in deeper water (and in photographs) the magenta would turn towards blue. Also, the red color disappears promptly in preservative, leaving the blue spots and lines indistinguishable from those on other juvenile damselfishes. Add to that the relatively low abundance of the species on many reefs, certainly compared to the ubiquitous S. leucostictus and S. variabilis, and there is ample room for confusion. The possibility that there is some variation in the occurrence of magenta in this species will be explored by DNA sequence identifications. stegastes diencaeus juvenile
Photograph by Gregory Taylor
saltyzoo.com
New recruits (10-15 mm SL) of S. diencaeus have a pattern of magenta stripes and spots on the head and upper body with two spots and a stripe on the iris. There is no additional row of spots between the top stripe on the head and the upper-eye stripe at this stage (this additional row emerges after about 15-20 mm SL, often just three spots in a row). There is a large black ocellus ringed in blue centered on the last three dorsal-fin spines and first three dorsal-fin soft rays (about 50% on the fin, 50% on the body). Although the top of the head and anterior body may be duskier than the rest of the body in new recruits, it is not blue. Ontogenetic homologies include a transient darkening of the scales at the saddle area of the caudal peduncle, a dark spot at the top of the pectoral-fin base, and some darkening of the anterior upper body (but not clearly blue).
Juvenile analogues: New recruits of S. diencaeus are separated from S. planifrons and S. adustus by having stripes along with the spots on the head and iris and from S. partitus by having a dorsal-fin ocellus. New recruits of S. diencaeus are most easily separated from the other striped species when the S. diencaeus have no blue wash over the anterior upper body and head, but some individuals do show a dusky anterior coloration and these individuals can be problematic. Other features separating the new recruits from S. leucostictus are having the ocellus half onto the body, the blue ring below the ocellus a continuous line, no additional row of spots between the top stripe on the head and the upper-eye stripe, and sparser spotting on the anterior dorsal fin. New recruits of S. diencaeus can also be separated from S. variabilis by having only a faint caudal-peduncle saddle (if any) but, when compared to recruits of S. variabilis that have not yet developed their saddle, the distinction is difficult without life colors. Unfortunately, some S. diencaeus recruits up to 20 mm SL have some form of faint caudal-peduncle saddle and some S. variabilis of the same size can have similar unformed saddles. In that case, the distinction can become more subtle: S. variabilis have more dusky blue shading over the head and body, especially including the posterior dorsal fin and the anal fin which are not dusky in S. diencaeus. Unfortunately, degrees of duskiness are poor characters to separate individuals. DNA sequence comparisons underway at present should resolve the line of separation.
Later juveniles (over 20 mm SL) are characterized by magenta stripes on the head and upper body, a relatively uniform yellow body (without obviously blue shading on the anterior upper body and head), a dorsal-fin ocellus distinctly over both the body and fin, no caudal-peduncle saddle spot, and no black spot at the top of the pectoral-fin base.
Occasional problematic individuals do have some blue shading over the top of the head and more than the usual blue spotting and these may be confused with (or hybrids of) S. leucostictus (both species missing the caudal-peduncle saddle). DNA sequence comparisons underway at present should resolve the line of separation.
Description:
Stegastes planifrons new recruit
10.9 mm SL
Belize, BZ98-704
 
   
 
Stegastes partitus
 
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 dorsal-fin soft rays indicate Stegastes and Microspathodon chrysurus. Fin-ray counts broadly overlap among Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays (S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays). Given this overlap, it is likely that pre-transitional larvae will require DNA sequencing to reliably distinguish the species.
Early juvenile markings: New recruits (10-15 mm SL) of S. partitus have
Juvenile analogues: New recruits of S. partitus are separated
Later juveniles (over 20 mm SL) are characterized by
Description:
Stegastes planifrons new recruit
10.9 mm SL
Belize, BZ98-704
 
   
 
Microspathodon chrysurus
Diagnosis: Damselfishes with 12 dorsal-fin spines and a mode of 15-16 dorsal-fin soft rays indicate Stegastes and Microspathodon chrysurus. Although fin-ray counts broadly overlap among the other Stegastes with most species having 13-14 soft anal-fin rays and 18-20 pectoral-fin rays, S. adustus and M. chrysurus have a mode of 21 pectoral-fin rays. The two latter species have a slight divergence in anal-fin soft rays, with S. adustus having 13-15, while M. chrysurus have 12-13. Late larvae and transitional recruits of M. chrysurus have the distinctive blackening of the pectoral-fin rays that confirms the identification. (ML)
Description:
 
Microspathodon chrysurus new recruit, 10.9 mm SL
 
Abudefduf saxatilis
 
Diagnosis: Damselfishes with 13 dorsal-fin spines indicate Abudefduf as well as the deep-water Chromis enchrysura, C. insolata, and C. scotti. Abudefduf saxatilis have a mode of 13 dorsal-fin soft rays and 12 anal-fin soft rays (D-XIII,13 A-II,11-12 Pect-18-19). A. taurus have fewer median-fin soft rays, with a mode of 12 dorsal-fin soft rays and 10 anal-fin soft rays (D-XIII,12 A-II,10 Pect-18-19). The Chromis species have modes of 12/11 or 12/12. (ML)
Description:
Abudefduf saxatilis transitional recruit,
10.6 mm SL
(San Blas, Panama, SB84-523)
 
   
   
   
   
 
Abudefduf taurus

Diagnosis: Damselfishes with 13 dorsal-fin spines indicate Abudefduf as well as the deep-water Chromis enchrysura, C. insolata, and C. scotti. Abudefduf taurus have a mode of 12 dorsal-fin soft rays and 10 anal soft rays (D-XIII,12 A-II,10 Pect-18-19).A. saxatilis have a mode of 13 dorsal-fin soft rays and 12 anal-fin soft rays (D-XIII,13 A-II,11-12 Pect-18-19). The Chromis species have modes of 12/11 or 12/12. (ML)

 
Description:
Abudefduf taurus transitional recruit,
11.1 mm SL
(San Blas, Panama, SB83-137)
 
   
   
   
   
 
Chromis multilineata
Diagnosis: Damselfishes (ML)
Description:
 
Stegastes planifrons new recruit, 10.9 mm SL 10.9 mm SL

All contents copyright 2006-2013
All rights reserved

www.coralreeffish.com by Benjamin Victor

All contents copyright 2006-2013
All rights reserved

www.coralreeffish.com by Benjamin Victor