Reproductive biology and early development of two species of sleepers, Eleotris acanthopoma Bleeker, 1853, and E. fusca (Forster, 1801), were investigated in streams on Okinawa Island in southern Japan. Gonadal examination and morphology of the genital papillae indicated that E. acanthopoma matured at a smaller body size (ca. 28 mm in standard length) than E. fusca (ca. 50 mm). Mature ovaries were composed of oocytes that could be categorized into two size classes. Larger females of both species had several hundred thousand developed oocytes in the larger size class and may spawn them at one or several consecutive spawning events. Egg masses of both species were found in habitats typically occupied by adults and were deposited, often sparsely, on the underside of objects. Form of the egg masses and morphology of eggs and newly hatched larvae of both species were almost identical. Eggs were a nearly spherical pyriform in shape, with the widest diameters measuring approximately 0.4 mm. Newly hatched larvae were very small (1.0–1.4 mm in notochord length) and undeveloped. The mouth opened and the eyes became pigmented 3 days after hatching, and all of their yolk was consumed 4 days after hatching. Reproductive strategies of both species were characterized by high fecundity through production of small eggs and small newly hatched larvae, with high fecundity likely to mitigate the presumed increased risk associated with widespread larval dispersal.
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Vol. 62 • No. 3