Assessing the use of sectioned otoliths and other methods to determine the age of the centropomid fish, barramundi (Lates calcarifer) (Bloch), using known-age fish

Abstract

The use of stocked fish of a known age provide an opportunity to determine the practicality of use of otolith morphometrics and fish length to estimate the age of barramundi (Lates calcarifer) and determine accuracy of sectioned otolith age estimates. Otoliths were collected from 119 stocked barramundi and were compared against the known age of the fish (range: 0.75-8.64 years). The otoliths of barramundi appear to grow in three distinct phases when compared to the total length of the fish (TL), with a final change in otolith growth coinciding at the approximate size of sex change for this species (900mm TL). Otolith growth is correlated linearly in all directions throughout to total growth of the otolith. Linear relationship of the sectioned otolith age estimates and known ages was highly significant (r2=0.89), with nearly 88% of the fish assigned to the correct age class with an index of average percent error (IAPE) of 3.2%. The otolith weight-age relationship for the known-age fish described by the equation, age=17.43 (otolith weight)+0.981, accounted for more than 71% of the variability. The use of any of the three otolith dimensions (length, breadth, width), otolith weight or fish total length (TL) provided a similar population age structure to that of sectioned otoliths ages (P>0.05). Because of significant time savings and costs associated with the techniques, use of otolith weight or even fish TL relationships with fish age offer a real alternative to reading sectioned otoliths, as long as enough samples are used to account for any bias from sampling error. Use of otolith weight alone could reduce laboratory costs by 96% when compared to sectioned otoliths, and has real utility for use in long-term monitoring.