Australian longfin eel
This freshwater eel is normally found on the east coast of Australia from Cape York to Tasmania. How and when it arrived in New Zealand is somewhat of a mystery but might be related to changes in the oceanic currents that transport the passive larvae from the spawning grounds in the South Pacific. The presence of Australian longfin eels in New Zealand waters was confirmed in 1997 using vertebral counts and DNA markers from eels caught in the Waikato River. Nineteen eels from age 4 to 11 years were examined during this study. Although this confirmation is recent, anecdotal evidence suggests “reinhardtii” may have been in New Zealand for at least 25 years.
The Australian longfin has conspicuous black blotches all over its body except on its belly. This is the easiest way of distinguishing it from the New Zealand longfin. It has only been officially identified from the Waikato River, but mottled eels have been reported on the west coast from Northland to Taranaki and also on the east coast of the Coromandel, and it may be moderately widespread in the northern North Island.
Although the habitat of the Australian longfin overlaps that of the New Zealand longfin, there is little danger than the Australian longfin will edge out our native species. This is because researchers believe that each eel species has a single spawning ground and it is therefore unlikely that a separate breeding stock would be established for “reinhardtii” that reside in New Zealand. It is thought that their arrival here will continue to be erratic and intermittent, although the confirmed presence of several year classes suggests migration here is certainly more than an isolated event.