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Introduction to Larval Gobies
Group1
Group2
Group3
Group4
The gobies are the largest family of reef fishes and there are well over a hundred Caribbean species and doubtless a few more to be described. Although almost always small and not particularly conspicuous, they occur in large numbers in all reef-associated habitats. There are many genera and, unfortunately, many groups of closely-related species that make species-level identifications for larval gobies particularly challenging. The larvae of most of the shallow-water goby genera are described here, but there are several obscure deep-water genera for which the larvae are not identified.

Since there are too many Caribbean species to deal with on one webpage, I have decided to subdivide the family into four groups. Phylogenetic groupings may make sense to a few taxonomists, but most people need more practical features to divide up the family. This is a somewhat difficult and arbitrary task, but I have settled on first separating out the gobies with divided pelvic fins into Group 1. They comprise a mixed grouping of mostly obscure genera and, since it is a small group, I include Bathygobius spp. on the page (they have fused pelvic fins). Then I distinguish the "long" gobies, i.e. those with 12 or more dorsal and anal fin elements (Group 4). The remainder, the "short" gobies with fused pelvic fins, are divided up into the six dorsal-spined gobies in Group 2 and the seven dorsal-spined gobies in Group 3. The number of dorsal spines is often used as a taxonomic character among gobies, although it may not accurately reflect relatedness.

Larval gobies are quite variable in appearance, reflecting their great taxonomic diversity. They exhibit the full range of larval sizes at transition, from about 4 to almost 30 mm SL. In general, however, they are small and nondescript with a long, narrow and thin body. They tend to have small to medium-sized terminal mouths, small heads without spines, and flexible spines in the fins. They can be recognized by their two separated dorsal fins, the first with only a few spindly spines. In addition, they often have fused pelvic fins and typically light markings (often comprising variations on a ventral midline series of melanophores: at the isthmus, pelvic fin base, anal fin base, and caudal peduncle). Many larval gobies have markedly narrowed and tilted eyes. Since Caribbean goby genera are often quite speciose and the larvae only become distinct during transition or even later, it is likely that some groups will require DNA sequence analyses for the identification of individual larvae to the species level.
GOBIES OF THE CARIBBEAN
there are a total of about 120 Caribbean species
Sources for taxonomy and fin ray counts include Fishbase, Gobiidae.com, the FAO key, Randall's Caribbean Reef Fishes, Peterson Field Guides Atlantic Coast Fishes, Bohlke and Chaplin's Fishes of the Bahamas, McEachran and Fechhelm's Fishes of the Gulf of Mexico, Richards' Early Stages of Atlantic Fishes goby chapter, Bohlke and Robins' Western Atlantic Gobies (PANS Phila.) and their Revision of ... Coryphopterus and specific literature.
 
  
Quick Key to Genera: in order of increasing anal fin elements 
 
 
Pelvic fins Anal fin elements1st dorsal spinesanal fewer than dorsalequalanal more than dorsal
divided7-117x
Gobuluspartial10-117x
Pycnommadivided97x
Varicusdivided8-97x
Chriolepisdivided8-107x
Robinsichthysdivided117x
FAMILY ELEOTRIDAEdivided9-106x
Bathygobiusfused96x
Lythrypnusfused96x
Lophogobiusfused96x
Priolepisfused96x
Coryphopterus 1fused106 x
Coryphopterus 2 divided9-116 x
Barbuliferfused107x
Gobiosomafused*9-107x
Elacatinusfused9-117x
Ginsburgellusfused107x
Risorfused107x
Evermannichthysfused9-123-7x
Awaousfused106 x
Sicydiumfused116 x
Gnatholepisfused126x
Nesfused11-137x
Ctenogobiusfused 6 x
Oxyurichthysfused 6 x
Evorthodusfused 6 x
Vomerogobiusfused 6 x
Bollmanniafused 7x
Parrellafused 7x
Gobionellusfused 6xx
Akkofused 7x
Gobioidesfused 7 x
Microgobiusfused 7x*x
Palatogobiusfused 7x*
Pariah 8
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Introduction to Larval Gobies
Goby larvae are typically the most abundant larvae collected in most reef fish larval collections, both in diversity and often in total numbers. Indeed, Ctenogobius saepepallens, the dash goby, is the most frequently-occurring larval type in my Panama collections, followed closely by the bridled goby, Coryphopterus glaucofraenum.
Since the process of elimination is critical to the identification of larval gobies, the diversity within this group makes for some difficulty in species ID. A variety of other factors add to the complexity of identifying goby larvae:
  • Melanophore Patterns
  • Fin Ray Counts
  • Transformation
  • Size Variation
  • Larval Eye Morphology
  • Pelvic Fin Morphology
    Melanophore patterns
    The larval melanophore patterns within the family tend to be conservative, with many larval types sharing a sparse basic pattern of a ventral midline series of melanophores: at the isthmus, pelvic fin base, anal fin base, and caudal peduncle.
    Melanophore patterns of larval gobies can be quite variable within types- many individuals, especially earlier-stage larvae, are missing one or a few of the standard complement. Which melanophores are missing often varies between species, and it can be consistent, providing a sometimes useful character (e.g. Lythrypnus spp. larvae seem to always have a melanophore at the angle of the jaw and Coryphopterus glaucofraenum larvae are often missing their dorsal midline melanophore).
     
    Melanophores can also be contracted, appearing as discrete dots, or expanded into either complex dendritic star-shapes or linear forms. Linear melanophores often merge with adjacent melanophores into long streaks. In addition, the intensity of melanophores can vary a great deal, with many preserved larvae showing faint or indistinct melanophore patterns (in some species this variation is
    pronounced, for example in larval Ctenogobius spp. ). Furthermore, melanophores on the delicate membranes between the fin rays can easily be lost in handling as the fins get frayed and thus the frequency of these markings in the few larval types that have these are undoubtedly higher than observed. Fin membrane melanophores occur on several common larval gobies, including Bathygobius soporator, Coryphopterus glaucofraenum and Microgobius signatus, as well as on some eleotrids. (photographs of melanophore streaks in larval Eleotris amblyopsis right and contracted vs. expanded in Bathygobius mystacium below)
     
    Fin ray counts
    The fin soft ray counts often vary by at least one or two in Caribbean gobies, unlike many other reef fish families that have very conservative fin ray formulas. In addition, the reported modal fin ray counts from different sources in the literature can sometimes vary by one ray. Nevertheless, modal fin ray counts are critical to species diagnosis.
     
    The oft-used character of six vs. seven spines in the first dorsal fin is not only difficult to see (since the seventh spine is tiny), but reportedly can vary. Although it is not that useful for practical screening of larvae, the number of spines can be very useful for genus diagnosis, separating genera with otherwise similar appearances and fin ray counts. There is some variation in dorsal spine counts; but it is helpful to recognize that six-spined gobies usually have five close spines and then a distant sixth, while seven-spined gobies have five close spines and then two more spaced out farther. Thus some of the variants can be recognized as anomalous (i.e. four close and two spaced out is likely a variant seven-spined goby).
    A corollary to the problem is that some literature sources count total dorsal spines and total dorsal fin soft-rays, confusing whether the spine count is including the first, often spinous, element of the second soft dorsal fin. It is best to count total elements in the second dorsal and anal fins to avoid this problem (and the issue of whether the first element of the second dorsal fin and anal fin in some gobies is spinous or soft, which... surprise, can also vary).
    Transformation
     
    Larval gobies tend to initiate transformation from larval to juvenile phase (also transition, or metamorphosis) while still pelagic and many transitional individuals can be collected in waters over the reef. Indeed, in some collections, the majority of specimens are in transition. As a result, larval goby samples can often include a surprisingly wide range of morphological appearances.
     
    Head Shape: The head shape of transitional gobies varies greatly. Pre-transformation goby larvae usually have thin pointed heads with terminal mouths. As they initiate transformation, the head usually thickens and the snout often becomes more rounded. In those species with blunt head profiles, this change can be marked and the mouth can move subterminally. (photographs below of larval Gobionellus oceanicus transitional series)
     
    Eye Shape: The eye shape can change radically during transition and the process is somewhat consistent within larval types. Both the shape itself and the size at which the changes are observed can be an important character for species identification. As larvae initiate transformation, narrowed eyes become round, tilted eyes become vertical, and in some species the eye becomes markedly larger (in a few it gets smaller, e.g. larval Nes longus). Eye shapes can thus be valuable for inferring the stage of goby larvae, i.e. in a species with narrowed eyes in pre-transitional larvae, the presence of round eyes in a small individual indicates that it is in transition. This becomes particularly useful in practical larval sorting where the size at which larvae develop round eyes can be an important character, as in Lythrypnus spp. vs. Coryphopterus spp. (photograph at right of transitional changes in the eyes of larval Lythrypnus nesiotes)
     
    Body Shape: The body of pre-transition larvae is typically thin and becomes thicker and bulkier at transition. This change needs to be distinguished from effects of condition of larvae. Clearly some emaciated larvae appear very thin and narrow. This appearance can be found in some larvae with round eyes and even metamorphic melanophores, indicating that they are not just immature early-stage larvae.
     
    The fins of those species who develop long pectoral and pelvic fins as juveniles show a marked increase in the length of these fins at transition. In a few cases, where juveniles have a characteristically short fin, that fin length may decrease at transformation.
     
    There is variation in the timing of changes: some larval gobies develop transitional morphological changes, especially rounded eyes and blunted snouts, before acquiring any transitional markings, as in the larval Lythrypnus spp. at right. In contrast, it is common with larval gobies to see individuals of the same species and in the same collection that have started to develop metamorphic melanophores while still morphologically in mid-transition, at least in body and head shape. However, the eyes of larval gobies almost always start rounding before transitional markings develop; it is exceptionally rare to see a larva with dense metamorphic melanophore patches and narrow eyes. Two larvae at the ends of the spectrum easily look like they could be different species.
    Metamorphic Melanophores: These arrays of additional melanophores, leukophores, and iridophores are usually smaller and limited to the skin surface, compared to the large, discrete, and often deeply-penetrating larval melanophores. In many other reef fish families, the metamorphic melanophores are typically in dense patches that often begin on the head and develop posteriorly following the pattern of the juvenile markings of the species. In gobies, however, the size difference of the melanophores is less obvious, and metamorphic melanophores can often be just as large as larval melanophores and are distinguished mostly by their graded appearance, i.e. the accumulation of more markings in a pattern starting around the mouth and head, then at the caudal peduncle and dorsal midline, and then filling in from forward to rear (photographs below of a transitional series of Bathygobius soporator). This phenomenon helps a great deal in providing missing links for species IDs, but also contributes to the confusing variety in the appearance of larval types. This is especially the case when the metamorphic melanophores can show up in very different sequences, as is common in larval Coryphopterus glaucofraenum.
    Size Variation
     
    Of course there is some variation in the size of larvae within a species. There can be two sources of this variation and distinguishing between them is important.
     
    One is the simple size increase with growth and development: younger and less-developed larvae are smaller than older ready-to-settle larvae. This variation can be detected by the well-known ontogenetic landmarks to be expected with growth, i.e. first the flexion of the notochord, then the full development of the fin ray elements and finally the eye and head shape changes as settlement approaches. Among the late-stage larvae collected over reefs, almost all have passed the flexion stage and have developed their full complement of fin rays. The subsequent body and eye-shape changes and the degree of development of metamorphic melanophores are the features that vary most in these settlement-stage larvae.
    The second source of variation is individual variation in size at the same stage of development. This variation can be large in gobies, and, of course, the observed range increases with sample size. This variation can be confusing, and the occasional extreme size variant can look like a different species entirely. For example, the photograph at right shows the extreme one percent variation in size at transformation for the common Coryphopterus glaucofraenum larval type. Note that these are all transitional larvae that have already developed round eyes. The larval sizes in the photograph range from 5.1 to 8.6 mm SL, but 90% of the larvae of this species that I have collected are concentrated between 6.5 and 7.3 mm SL.
    Larval eye morphology
     
    Larval gobies of different species and different stages of development exhibit an amazing variety of shapes of the eyeball, most often a narrow vertical oval but, in some species, irregular or even squared. These eye shapes, along with other eye-related morphological features, likely reflect adaptations to the pelagic world of reef fish larvae, either to degrees of darkness or differing wavelengths of light. Fortunately, these shapes tend to be consistent within species and can be used as characters to help identify larvae.
     
    The primary variations are in eyeball shape, most often a narrowed vertical oval, but sometimes squared or another irregular shape. The oval sometimes can show a pronounced tilt, usually forward, but sometimes backward. The direction of the tilt is not always consistent within larval types, for example larval Evorthodus lyricus commonly show tilts both forward and backward (this is true to a lesser degree for larval parrotfishes, family Scaridae, as well as the wrasses of family Labridae). As a rule, the eyes of larval gobies become fully round at the end of the settlement transition.
     
    In addition, there can be indentations in the iris, usually, but not always, dorsal and/or ventral. Many very early-stage larvae of all kinds of fishes show these indentations as part of the development of the eyeball, but in larval gobies these indentations can persist, sometimes throughout transition. Persistent indentations in various quadrants of the iris can be a consistent character for certain larval types. The photograph at left shows a persistent dorsal iris indentation in a 9.6 mm SL transitional larvae of Ctenogobius saepepallens. The photograph below right shows a 5.5 mm SL Bathygobius curacao larva with persistent off-center-axis dorsal and ventral indentations of the iris despite being in transition.
     
    Another occasional feature of the eyeball of larval gobies is the presence of an additional speckled membrane overlying the black surface of the upper iris. This feature is mostly consistent within larval types and can thus aid in identifications. In several larval goby types, this membrane is visibly lifted off from the eyeball. In some species the speckled membrane is only along the top quarter of the eyeball, while in others it extends further down, usually overlying the posterior half of the iris. The photograph above shows the pigmented membrane over the eyeball of a 9.4 mm larval Microgobius signatus. It appears to be a balloon-like membrane lifted off of the underlying black layer. At right, the oblong shaped eyeball of a 7.2 mm SL larval Coryphopterus glaucofraenum, shows the distinctly speckled membrane overlying the upper and rear of the iris.
     
    A very common feature in the eyes of larval gobies is an extension of the shiny iris in the posterior-inferior quadrant. The extension appears to have a more flattened appearance than the rest of the iris. In some larval types this extension is quite prominent. Some rare individuals show clearly abnormal outgrowths of the eyeball in this same quadrant, perhaps a developmental anomaly related to whatever might be the function of this extension. The photograph at left shows a 6.9 mm SL larval Coryphopterus glaucofraenum with the abnormal outgrowth.
     
    A rare feature in some larval gobies is a bizarre outgrowth of tissue from the eyeball into the adjacent compartments of the head. Interestingly, in Microgobius signatus this can occur in several individuals in the same collection, suggesting that whatever is causing the anomaly may be an environmental effect. The photograph below shows the head of an 8.0 mm larval Microgobius signatus.
    Pelvic fin morphology
     
    Gobies are perhaps best known for their fused pelvic fins that often act as a sucking disk to anchor them to the substrate. The degree of fusion of the right and left pelvic fins and the overall shape of the disk are important characters in gobioid taxonomy, although the feature is certainly far more labile than taxonomists would desire. Unfortunately the degree of concordance between larvae and adults in pelvic fin morphology is still an open question. In my collections, it is clear that the presence or absence of divided pelvic fins can differ between larval and adult stages, as in Coryphopterus personatus.
      
     
    There are several basic states of pelvic fin morphology in larval gobies. The pelvic fins on the right and left can be completely separate, with the base of the innermost fin ray clearly separated by a space from the base of the ray on the other side. This state is uncommon in gobies, but characteristic of the related sleepers of the family Eleotridae. The pelvic fins can be divided down to the base, or only partially-divided, leaving the proximal innermost fin rays still fused (as in larval Gobulus myersi, pictured at left). Alternatively, the pelvic fins can be completely fused along the length of the rays, the most common condition among the larval
    gobies. Lastly, within the completely-fused pelvic fin group, there can be a frenum, or anterior connecting band, joining the outermost pelvic fin spines on the two sides to form a cup-shaped fin. This cup can be flat and inconspicuous, as in the 9.9 mm SL larval Ctenogobius saepepallens at right, or an obvious large sucking disk as in the 7.7 mm SL larval Elacatinus saucrus pictured above right.
    All contents © copyright 2006 Benjamin Victor. All rights reserved.