Yellow watchman goby help

I have a 75 gallon tank and just added two yellow watchman gobys hopeing its a male and female ones lighter in color and one is real neon green.
Well today they began to fight one actually puts the others head in his mouth? This isnt a mating thing is it ? Lol its got me worried
 
They will definitely fight each other unless they're a mated pair. Not sure if they'll mate up naturally or if they will continue to fight.
 
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