Abstract Information on the spawning migration, spawning ecology and life history of tropical eels in the Indo-Pacific region is very limited. The physiological and morphological characteristics of tropical freshwater eels, Anguilla bicolor bicolor and A. bengalensis bengalensis collected in Malaysia were examined in relation to their downstream migration patterns. A total of 455 eels were collected over monthly intervals between February 2014 and January 2016 and we examined both gonadosomatic index and gonad histology features. In both species, close positive relationships between advanced maturation stages and eye, fin, gonadosomatic indexes were found in males and females. A. bengalensis bengalensis was found to be larger and heavier than A. bicolor bicolor at the time of seaward migration. The final stage of maturation for seaward spawning migration occurred throughout the year in A. bicolor bicolor, although that of A. bengalensis bengalensis was estimated to six months due to the limited number of samples. These results suggest that year-round spawning in the open ocean occurs in the tropical eel. This non-seasonal spawning ecology is notably different from that of temperate eels, which are known to follow a well-defined spawning season, with spawning migrations generally taking place during autumn months.

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Abstract

Information on the spawning migration, spawning ecology and life history of tropical eels in the Indo-Pacific region is very limited. The physiological and morphological characteristics of tropical freshwater eels, Anguilla bicolor bicolor and A. bengalensis bengalensis collected in Malaysia were examined in relation to their downstream migration patterns. A total of 455 eels were collected over monthly intervals between February 2014 and January 2016 and we examined both gonadosomatic index and gonad histology features. In both species, close positive relationships between advanced maturation stages and eye, fin, gonadosomatic indexes were found in males and females. A. bengalensis bengalensis was found to be larger and heavier than A. bicolor bicolor at the time of seaward migration. The final stage of maturation for seaward spawning migration occurred throughout the year in A. bicolor bicolor, although that of A. bengalensis bengalensis 

Sci Rep. 2017; 7: 41649.

Opportunistic spawning of tropical anguillid eels Anguilla bicolor bicolor and A. bengalensis bengalensis

Takaomi Arai^a,1 and Siti Raudah Abdul Kadir²

Abstract

Information on the spawning migration, spawning ecology and life history of tropical eels in the Indo-Pacific region is very limited. The physiological and morphological characteristics of tropical freshwater eels, Anguilla bicolor bicolor and A. bengalensis bengalensis collected in Malaysia were examined in relation to their downstream migration patterns. A total of 455 eels were collected over monthly intervals between February 2014 and January 2016 and we examined both gonadosomatic index and gonad histology features. In both species, close positive relationships between advanced maturation stages and eye, fin, gonadosomatic indexes were found in males and females. A. bengalensis bengalensis was found to be larger and heavier than A. bicolor bicolor at the time of seaward migration. The final stage of maturation for seaward spawning migration occurred throughout the year in A. bicolor bicolor, although that of A. bengalensis bengalensis was estimated to six months due to the limited number of samples. These results suggest that year-round spawning in the open ocean occurs in the tropical eel. This non-seasonal spawning ecology is notably different from that of temperate eels, which are known to follow a well-defined spawning season, with spawning migrations generally taking place during autumn months.

海洋產卵遷移的成熟的最後階段全年發生在雙色雙色，雖然孟加拉孟山藥的估計為六個月，由於樣本數量有限。這些結果表明，在熱帶鰻魚中，在海洋中全年產卵。這種非季節性的產卵生態學特徵與溫帶鰻魚的生態學特徵有所不同，溫帶鰻魚已知遵循明確的產卵季節，通常在秋季出現產卵遷徙。