Age, growth and reproduction of three conger eel species in the waters off Northeastern Taiwan

• Main Authors: Yi-Hua Yang, 楊憶華
• Other Authors: Hong- Ming Chen
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/25641227071395641095

碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 101 === Conger eel is a demersal fish, living in sandy benthic area at depth from 200 to 400 m, and distributing widely in Taiwan coastal waters. Little is known about the fundamental biology of conger eel, including their early life history, age, growth and reproduction. Conger eel experiences different habitats with a varied depth range during ontogenetic stages, including embryonic, pelagic leptocephalus, juvenile and adult stages. Both physiological and environmental changes will be recorded in otolith trace elemental composition. Present study aimed to investigate the life history of conger eel in the northeastern Taiwan. Monthly samples including Bathycongrus wallacei, Gnathophis heterognathos, and Uroconger lepturus were collected from August 2011 to September 2012 from Daxi and Nanfangao fishing harbor. First, the core, transition zone and accessory growth centre were defined by using scanning electron microscope. Durations of metamorphoses were estimated to be, 123 ~ 173 days for B. wallacei, 103 ~133 days for G. heterognathos, and 84 ~ 128 days for U. lepturus by analyzing otolith daily groth increment. The monthly change of the marginal increment ratio indicated that opaque zones on otolith were formed during January and February and the annulus is formed yearly. Yearly age and growth rate were calculated from otolith and data were fitted to von Bertalanffy growth equation. The growth parameters for B. wallacei is L∞ = 886.60 mm, k = 0.03 yr-1, t0 = - 2.76 yrs; G. heterognathos is L∞ = 886.60 mm, k = 0.03 yr-1, t0 = - 2.76 yrs; and U. lepturus is L∞ = 748.37 mm, k = 0.02 yr-1, t0 = - 5.82 yrs. Electron Prob Microanalyzer (EPMA) were used to analyze otolith Sr:Ca ratios of the three conger eels. The result of the Sr:Ca ratio was significantly variated at different life stage of the three eels, with highest ratio at embryonic stage, gradually decreasing at leptocephalus, and remaining constantly low during juvenile and adult stages. Physiology change during early life stage caused the fluctuating in otolith Sr:Ca ratio, and the constantly low Sr:Ca ratios after juvenile stage indicated that the conger eel did not migrate to estuary or fresh water. The female sex ratio is 55% for B. wallacei, 66% for G. heterognathos and 46% for U. lepturus. Spawning season was estimated to be from August to October based on gonadosomatic index, appearance of gonads and histological examination of gonads. Minimum length of maturation of females are 339.0 mm, 328.4 mm, and 343.5 mm, and males are 356.4 mm, 254.7 mm, 309.5 mm for B. wallacei, G. heterognathos, and U. lepturus respectively. We will hope the results of this study can provide conger eels basic information and conservation of fisheries resources in the future.