Scale development and age determination in New Zealand freshwater eels (Anguilla spp.)

The appearance and development of scales in Anguilla australis Richardson and A. dieffenbachii Gray were studied to assess the value of scales in age determination. Scales first appear in an area two‐thirds along the anus‐tail tip distance, when eels are 16–20 cm long. The rate of lateral and longitudinal scale spreading, scale size, and the number of scale rings were all positively related to fish length. The formation of new scale rings showed no seasonal pattern, so these rings cannot be used for age determination. Age could not be determined from length‐frequency histograms owing to overlapping of data from adjacent year‐classes. However, examination of otoliths prepared by burning showed that the otolith rings were annual in formation, and could be satisfactorily used to calculate age.

Notes

Present address: Fisheries Research Division, Ministry of Agriculture and Fisheries, Private Bag, Christchurch, New Zealand