Length-weight relationship and condition factor of Anguilla bicolor bicolor and Anguilla nebulosa nebulosa in selected perennial reservoirs of Anuradhapura District, Sri Llanka

Abstract

Catadromous freshwater eels migrate between freshwater and offshore spawning grounds to complete their life cycle. Globally, 19 species belong to the genus Anguilla. Two Sri Lankan species, Anguilla nebulosa nebulosa and Anguilla bicolor bicolor, were collected from the landing sites of eight perennial reservoirs in the North Central Province, namely Kalawewa, Rajanganaya, Nachcaduwa, Nuwarawewa, Mahakanadarawa, Mahavilachchiya, Padaviya, and Huruluwewa. A total of 138 eels were collected to ascertain the length-weight relationship and condition factor from July 2019 to January 2021. All statistical analyses were assessed at a 5% level using Microsoft Excel (2013). The total length and weight of the eels were measured to the nearest 0.01 g and 0.1 mm, respectively. Morphological identification was based on previously published body colouration and anodorsal parameters studies. Among the eels collected, most (111) of them was A. nebulosa nebulosa while the rest (n = 27) was A. bicolor bicolor. The mean total length and body weight of A. nebulosa nebulosa were 71.1 ± 13.3 cm and 824.5 ± 519.8 g, respectively, whereas those of A. bicolor bicolor were 66.0 ± 11.8 cm and 663.4 ± 362.8 g, respectively. The length-weight relationship of A. nebulosa nebulosa was TW = 0.0052 × TL²‧⁷⁸⁰³ and that of in A. bicolor bicolor was TW = 0.0181 × TL²‧⁴⁸⁹⁴. Estimated r² and p values of A. nebulosa nebulosa and A. bicolor bicolor were 0.7719, >0.05 and 0.8683, <0.05, respectively. Estimated "b" values (regression slope) of A. nebulosa nebulosa and A. bicolor bicolor were 2.7803 and 2.4894, respectively. The present results indicate an isometric growth in A. nebulosa nebulosa and negative allometric growth in A. bicolor bicolor. The relative condition factor (Kn) for A. nebulosa nebulosa and A. bicolor bicolor were 1.0559 ± 0.7002 and 1.0140 ± 0.1895, respectively. Results of the present study show that Kn values of both species lie between 1 and 1.5, indicating fatness and good growth conditions in the two species.