Use of scale patterns to evaluate stocking success of silver perch, Bidyanus bidyanus (Mitchell), released at two different sizes

Abstract

A study was conducted to determine relative success of stocking silver perch (Bidyanus bidyanus) at two different sizes: 35 mm and 50 mm total length. By purposeful manipulation of growth rates of pre-stocked fish it was possible to induce unique markers in scale circulus patterns, thus differentially marking the two size-groups. The scale circulus data were acquired with automated video-digitizing equipment. Both size-classes were stocked into two south-eastern Queensland impoundments. Relative stocking success after two years was quantified by sampling surviving silver perch and using discriminant function analysis to assign individuals to their respective size-at-release groups. Relative survival of fish stocked at 35 mm and at 50 mm was not significantly different in either impoundment. Post-stocking growth rates of 35 mm fish were not compromised due to their smaller size at release. From a management perspective, this suggests that 35 mm is a more cost-effective release size of silver perch than 50 mm. This trial demonstrates the feasibility of using scale circulus patterns to differentially mark multiple groups of fingerlings for such controlled experiments.