The genus Anguilla Schrank, 1798: current state of knowledge and questions [Review]

摘要

The freshwater eels of the genus Anguilla Schrank are widely distributed. They have been considered for a long time to all have a catadromous spawning strategy. However, in a recent work Tsukamoto et al. ( 2002) considered that catadromy should be seen as facultative. They all have a long oceanic larval stage known as the leptophalus stage. A large number of studies on their ecology, biology, and physiology exist but little attention has been focused on their systematics and species-relationships. Ege ( 1939) described 19 species and sub-species based on morphometric data. Castle and Williamson ( 1974) made A. ancestralis a synonym of A. celebesensis. Morphological characters, however, have limitations as taxonomic characters because they overlapped in most species. Biochemical characters, such as mt-DNA, are more informative. Dijkstra and Jellyman ( 1999) found no genetic differences between A. australis australis and A. a. schmidtti, and now 15 species are widely recognized. Phylogenetic studies (Aoyama and Tsukamoto, 1997) suggest descendant-ancestor relationships between Atlantic and Pacific eels, respectively. The most likely dispersal route for the Atlantic eels from the Pacific appears to have been through the Tethys Sea. Two species are found in the Atlantic: A. anguilla and A. rostrata. They both spawn in the Sargasso Sea, but differ in morphometric and genetic traits, and are considered as two separate species with a relatively recent evolutionary divergence. The purpose of this paper is to present knowledge and questions about the life history, taxonomy, and evolution of this mysterious genus.