Relationships of otolith size to fish size – a study on pumpkinseed (Lepomis gibbosus) from Topola Reservoir (Serbia)

Abstract

Otoliths are calcareous structures commonly used for fish age, size, and taxon determination. Information obtained from the analysis of otoliths can be of great importance for the management of fish populations, including invasive fish species. Pumpkinseed (Lepomis gibbosus) is one of the most successful invaders of Serbian freshwaters. It preys on aquatic invertebrates, fish eggs, and small fish. This species shows high plasticity of life history traits and can tolerate harsh environmental conditions, including hypoxia and high water temperatures. In October of 2020, a total of 28 pumpkinseed individuals from Topola reservoir (44.268229 N, 20.691564 E) were caught with electrofishing device Villager VGI2400 (230 V, 8.7 A, 2.0 kW). In order to determine relationships of otolith to fish size, a total length (TL) and body weight (BW) of each fish were measured as well as otolith area (OA), perimeter (OP), length (OL), and weight (OW). There were no significant differences between left and right otolith regarding OA, OP, OL, and OW (t-test, P>0.94). Significant and strong correlations were recorded for TL and OA (r2=0.936, P<0.0001), TL and OP (r2=0.958, P<0.0001), TL and OL (r2=0.945, P<0.0001), and TL and OW (r2=0.838, P<0.0001). Additionally, significant and strong correlations were recorded for BW and OA (r2=0.844, P<0.0001), BW and OP (r2=0.819, P<0.0001), BW and OL (r2=0.828, P<0.0001), and BW and OW (r2=0.795, P<0.0001). Results indicated that TL-OP relationship is the best predictor of pumpkinseed length, while BW-OW relationship is the weakest predictor of pumpkinseed weight. The common linear regression equations were determined: y = 0.9004x + 3.2643 for OA-TL, y = 0.9079x – 0.4816 for OP-TL, y = 2.4873x – 0.6667 for OL-TL, y = 523.2832x + 5.2364 for OW-TL, y = 3.2985x – 9.6439 for OA-BW, y = 3.2389x – 22.5237 for OP-BW, y = 8.9825x – 23.5786 for OL-BW, and y = 1966.5664x – 2.7114 for OW-BW. The obtained equations allow the calculation of pumpkinseed TL and BW based on the set of data on the morphological characteristics of the otoliths. Of the considered otolith parameters, otolith weight is the least suitable character for estimation of pumpkinseed size.