Morphological changes in silvering stages of Anguilla bicolor bicolor collected from Segara Anakan, Central Java, Indonesia

To understand the morphological changes during the silvering stages of Anguilla bicolor bicolor, 68 males and 39 females were collected from Segara Anakan in Cilacap, Central Java, Indonesia during December 2015 - September 2016, May 2017 and June 2018. Specimens were categorized into 5 stages based on body and pectoral fin coloration: Y1, Y2, S1, S2 and S3. Total length of silver males ranged from 342 mm to 501 mm, with mean ± SD 414.83 ± 40.38 mm and were notably smaller than silver females which ranged from 674 mm to 937 mmï786.11 ± 68.98 mmï¼. Silver females were present in catches throughout the year, with peak collection during the dry monthsï¼May and Juneï¼. This corresponded to the only period when silver males were caught. Locomotion indices such as, tail, dorsal fin, anal fin, pectoral fin and eye increased with progression in silvering stages, while feeding behavior indices such as, both upper and lower jaw in males showed increasing, lower lip depth in females showed decreasing and upper lip depth in females showed decreasing and snout remained constant. The increase in locomotion indices suggested that A. bicolor bicolor from Segara Anakan underwent morphological changes in preparation for spawning migration similar to those of temperate species, but increasing upper and lower jaw in males together with all samples caught using baited traps, suggested that these tropical eels remained as feeding individuals even at late stage silver eels. © 2023 CSIC Consejo Superior de Investigaciones Cientificas. All rights reserved.