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| The gobies are the largest family of reef
fishes worldwide, with 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 numerous
genera and, unfortunately, many groupings of closely-related species that make
species-level identifications for larval gobies particularly challenging. The
larvae of almost all of the shallow-water goby genera of the region are described
here, but there are several obscure deep-water genera for which I have not identified
the larvae. | | |
| Since there are too many Caribbean
species to deal with on one webpage, I 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, nonetheless I first separate 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 same page (even though they have fused pelvic fins). Then I distinguish
the "long" gobies, i.e. those with 12 or more dorsal and anal fin elements, as
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. | |
| The great taxonomic diversity
of gobies is certainly reflected in their early life history stages. Larval gobies
exhibit the full range of larval sizes at transition, from about 4 mm 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
most readily by their two separated dorsal fins with the first having 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). Some larval
gobies also 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. | |
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| 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. |
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| | | Quick Key
to Genera: in order of increasing anal fin elements | |
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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 | |
| | 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).
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| 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 |
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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) |
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| | Fin
ray counts | |
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| 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) |
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| | | 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. | |
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| There
is variation in the timing of changes in the early life history of gobies: 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. |
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| 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 during the early life history: 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. | |
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| 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. |  |
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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. | |
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| 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 below 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. |
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| 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. | |
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| 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. | |
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Pelvic fin morphology |
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| 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. | | | |
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| | | 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. |  |
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