ABSTRACT. – Otolith Sr/Ca, Ba/Ca and ⁸⁷Sr/⁸⁶Sr ratios and vertebral bone histomorphometry were used to investigate the life-history of Anguilla obscura eels from an enclosed lake, Lalolalo (Wallis Island in the Pacific), with no apparent connection with the sea. ⁸⁷Sr/⁸⁶Sr isotopic ratio from the core region gives evidence of indisputable marine origin of eels caught in the lake suggesting that underground connections between the lake and the sea exist. Sr/Ca and Ba/Ca ratios recorded after the elver mark are undifferentiated from seawater ones, thus limiting their used as marker of entrance in the lake and movement. However, ⁸⁷Sr/⁸⁶Sr isotopic ratio demonstrated that: 1) eels enter in the lake just after their metamorphosis and spend their entire adult life in the lake and 2) the lake chemistry is consistent with 1 % seawater-like contribution and 99 % basalt weathering and/or geothermal spring contribution. The vertebrae do not show a particular demineralization of bone matrix (45-52 %). Reversely, the study of bone compactness shows an important loss of bone that favors the hypothesis of a genital maturation that arises in the ecological state of the lake.