Neogobius melanostomus
   
lateral round goby -title bar


             An identification guide
          to the round goby in the
              Great Lakes region

Trunk Anatomy

Round goby vertebrae have little diagnostic value - other than their small size, the trunk and caudal vertebrae are constructed similarly to other fish.

The trunk vertebrae articulate with the braincase and extend to just past the dorsal fin of the fish; at this point the vertebrae morph into caudal vertebrae which continue to the tail of the fish.

trunk vertebrae, lateral and end-on aspects
caudal vertebrae, lateral and end-on aspects
 
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Pectoral & Pelvic Girdle Anatomy

   
The round goby pectoral and pelvic girdles are unique in that the pelvic girdle is fused to comprise just one bone, and this locks in with the pectoral girdle. This creates a girdle that wraps around the circumference of the fish. The primary girdle bones include the two cleithra and the bone that serves as the attachment for a fused ventral fin.
        Left and right cleithra are identifiable. Primary characteristics of this bone include a dorsal fork, two lobes - one smaller and one larger - which point at an angle to each other, and a smaller process located ventrally that points medioposteriorly. 
right cleithra, anterior aspectright cliethra, posterior aspect

bone attachment for fused pelvic finpectoral girdle perspective set against full body, ventral aspect
The cranial aspect of this bone articulates with the posterior processes of the cleithra, forming a complete pectoral and pelvic girdle.  The fused pelvic fin attaches at the caudal aspect of the bone, allowing the fin to fan out and grip rocky bottoms of the fish's habitat.


      
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Natural History

   
The round goby (Neogobius melanostomus) is a member of the family Gobiidae that is native to the Black and Caspian Seas.  In 1990, it was discovered in Lake St. Clair and by 1995 had spread to all of the Great Lakes.  A 2007 study by Hensler & Jude found evidence that goby larvae float near the surface of water bodies, making it easy for them to get swept by currents or picked up by ships.  Presumably, the fish came over this way, in the ballast waters from freighters travelling from Europe, and likely spread via lake currents and further shipping within the Great Lakes (Jude et. al 1995).  This rapid and successful colonization can be attributed to their broad diet, wide environmental tolerance, long spawning period, and aggressive behavior.
    Round gobies are bottom-dwellers that perch on the substrate via their unique fused pelvic fin.  Gobies prefer rocky substrates, but have been found on sand as well. Their wide diet varies with substrate type, but includes dreissenids, crayfish, aquatic insects, fish eggs, and larvae.  Gobies can live in salt- and freshwater bodies and are more robust to pollution effects than many native fish.  With a breeding period from April to September, gobies reproduce rapidly and aggressively defend their nests, effectively driving off native reproducing fish (Corkum et. al 2004).  Their presence has had an especially negative impact on the mottled sculpin, logperch, and Johnny darter due to competition for spawning sites.  Their egg predation behavior also  has had a deleterious effect on degraded populations of lake sturgeon and lake trout, as well as smallmouth bass when the nest is left unattended (Jude et. al 1995).


                                                                                
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External Anatomy

    Round gobies are small fish, typically between 7.5 - 12.5 cm (3-5 in), but can reach up to 25 cm (10 in) in length. They vary in color, ranging from grey to yellow-green with black and brown splotches throughout.  However, spawning males are typically black in color.  They possess a fused pelvic fin that is diagnostic to the species, as is the dark spot present on the anterior dorsal fin.    

















                                                  
   
                                                                        
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Cranial Anatomy

    Goby jaws consist of several bones, including the premaxilla and dentary bones.  The premaxilla contains a bony dorsal growth at its rostral point, and two other bony upgrowths along its caudolateral ends.  The maxilla runs along each side of the premaxilla from rostral to posterior processes. 

round goby premaxilla, lateral aspectpremaxilla support bone, lateral aspect

    These bones often separate when the fish is consumed, as seen above. However, when the skeleton is intact the premaxilla-maxilla complex appears as below:

premaxilla complex
    The dentary is a slender bone that articulates tightly with the angular; it widens at its caudal end where it articulates with the anguloarticular. These three bones are shown fused together in the dentary complex; they tend to remain fused together even through digestion.        
dentary, lateral aspect


The anguloarticular of the dentary complex and the maxilla articulate at their posterior edges to form the major components of the complete anterior jaw structure.                                         
anterior jaw complex
One of the most distinct bone structures to look for in a goby is the set of four jaw plates - two dorsal pharyngobranchial plates and two ventral dentigerous plates.  These are located just caudal to the hyoid apparatus, and ventral to the braincase. 
plates set against lateral aspect of round goby
round goby jaw plate layout

    The pharyngobranchial plates are oval-shaped and average approximately 3-4 mm in length.  They have a slight asymmetry, where the medial edge is shorter than the lateral edge and the anterior edge is slightly narrower than the posterior edge.  This asymmetry is difficult to see, but can be used to identify right from left.  Dentigerous plates pair together as seen above to form a large triangle - connective tissue lies at their junction, making it difficult to see that there are actually two plates.  There is a ventromedial process at the posterior junction which helps to identify right from left.  Additionally, the posterior corner of each plate turns up slightly.  These plates average approximately 6-7 mm in length.  The dorsal surface of all plates is covered with disorganized caniniform teeth, which often fall out to leave gaping sockets in their place.
pharyngobranchial platedentigerous plate
    The hyoid apparatus is a complex of bones that lies in the ventral cranial region, lying just caudal to the dentary.  The ceratohyal forms the long axis of the complex, connecting between the interhyal and the epihyal. The branchiostegal rays project posteriorly from the ventral edge of the eiphyal. The dorsally-projecting processes at the anterior end of the complex are the basibranchial bones.
hyoid complex hyoid complex with focus on epihyal
   
     The braincase in the round goby is dorsoventrally flattened, with broad wing-like processes that project laterally on either side.  A rostral section projects anteriorly, which often breaks off when the fish is eaten or during the course of natural decomposition.
braincase with rostrum, dorsal aspectbraincase with rostrum, ventral aspect
Within the braincase lie two sets of three otoliths; within a set there is one large otolith and two smaller ones that are difficult to find.  The large otoliths are diagnostic to the species; they are dorsoventrally flattened with multiple radial processes.  Small white concentric rings are also present, but may be difficult to see in degraded specimens.

    Since oftentimes the rostral section breaks off due to wear and tear, the below illustrations show the braincase appearance when the rostum has been broken away.
partial braincase diagram
  
The rostral section, when separated from the braincase, remains distinct in appearance even after becoming disconnected.  These sections are shown below:
rostral sections, dorsal and ventral aspects

The operculum can be difficult to identify if it is degraded, since it is a thin, delicate structure which can snap easily and thus lose its overall shape and identifying structures.  A complete operculum has a narrow ventral process, which can become folded with degradation, or even be shorn away. The overall shape is similar to a butterfly wing.  Midway down the anterior edge is a knob structure that articulates with the body. 
left operculum, medial aspectleft operculum, lateral aspect
                           



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Background Note:
This website was constructed with the purpose to aid NMU research staff in their identification of round goby bones from the gut contents of birds that have died due to botulism.  The drawings and photos of this site attempt to show what the bones appear as when in this state, taking note of the inevitable degradation that occurs when passing through a
GI tract. This is why there are diagrams of partially intact structures alongside fully intact structures
round goby on rocks photograph
                                                                                        credit: David Jude