There are currently seven species of New Zealand bullies but Dr Shelley says it is likely there may be several more by the time he completes his research by the middle of next year.
The ability to more easily identify cryptic species has become possible with the development of new generation genetic testing.
"It can be hard to tell species apart because you can only pick up so much with the human eye and people can overlook minute differences" Dr Shelley says.
"But when you look into the genetics of a species you create something similar to a family tree.
"This enables you to see how closely or how distantly related the two groups are."
And while two species may look the same, they each have their own place in the ecosystem with quite distinct ecological functions.
Bullies are an ecologically diverse group, some inhabit the tops of catchments; others the lower parts. Some are migratory and travel to sea; others spend their entire lives in freshwater.
Ecologist and fish enthusiasts have recognized that some are morphologically diverse as well.
For instance, the common bully (Gobiomorphus cotidianus) from lakes tend to be shorter and stockier than their river dwelling relatives. This makes them good candidates for investigation.
Dr Shelley said it was important to know about and describe cryptic species for conservation and management purposes.
"If we don't know they're there, we can't protect them. But if you can determine what a species is and exactly where it is found, you're able to work to effectively conserve it."
Advanced genetic testing has revolutionised the identification of species in recent years.
"Previously you had to sequence one gene at a time. Now, using next generation technology, you can sequence thousands of genes very quickly at an affordable price.
"The number of recognised New Zealand species has increased by about 50 per cent since 1990 thanks in large part to genetic based studies."
Examples include the Dune Lake galaxid and several species of Central Otago galaxids.
Dr Shelley also says it is possible that every New Zealand species could now be examined and the true number of species in New Zealand revealed.
"We are in a great position as a fairly small country.
"There is no reason you can't look at every population of every different species and analyse their genetics.
"This is a unique situation where you can get an absolute picture of the diversity here, how it has evolved and where there are hot spots of diversity are that require better protection."
