Potential sperm limitation of the swimming crab Portunus trituberculatus was examined during the reproductive season from September 2006 to April 2007 in the East China Sea. We documented developmental variations between the spermatheca and ovary and distinguished these into 5 stages. We counted the number of stored sperm in paired spermathecae and found that more than 50% of sperm initially received during mating disappeared as the sperm plug degenerated; around 1.70 × 10 8 were used for final fertilization, and there was significant correlation between the final number of stored sperm and female carapace width. Lastly, using knowledge of the reproductive characteristics of P. trituberculatus, we calculated potential sperm:egg ratios of 221:1 or 153:1 for the first brood, and 55:1 or 38:1 for lifetime broods -either from the perspective of a fishery resource assessment or from the perspective of seed production. From comparison to sperm:egg ratios of Callinectes sapidus (for lifetime broods this ranges from 10:1 to 42:1), we can infer that female P. trituberculatus in the East China Sea may be at low risk of sperm limitation under current fishing practices. This may be the result of greater fishing mortality of females, causing an increase in the operational sex ratio. The present study improves our knowledge of sperm limitation in brachyurans as fishing management in China is non-selective, which differs from other exploited decapod crustacean species around the world. KEY WORDS: Portunus trituberculatus · Sperm limitation · Non-selective fishing · East China SeaResale or republication not permitted without written consent of the publisher Aquat Biol 20: 145-153, 2014 (OSR) of males to females (Hines et al. 2003, Carver et al. 2005. Therefore, sperm limitation can contribute to the structure of mating systems (Wedell et al. 2002), and knowledge of the process of sperm limitation may be beneficial to conservation and management efforts (Conover & Munch 2002, Sainte-Marie et al. 2002.A critical step in estimating the risk of sperm limitation in brachyurans is to determine whether the final quantities of sperm stored in female spermathecae are 'sufficient' to meet the possible minimum ratio of spermatozoon to oocyte for fertilization, to ensure reproductive success. However, there are relatively few reports concerning these important reproductive parameters. In Chionoecetes species, ratios for high fertilization success are reported to range from 'several' sperm per egg (Adams & Paul 1983) to actual expenditure of an estimated 70 stored sperm per egg for the first clutch extruded (SainteMarie & Lovrich 1994); females failed to extrude any eggs when the sperm:egg ratio was below 7:1 (SainteMarie & Lovrich 1994). In comparison, sperm:egg ratios in C. sapidus were estimated at 100:1 to 400:1 for the first brood, and only 20:1 to 30:1 for maximum lifetime broods over the 2 possible reproductive seasons, suggesting that approximately 67 × 10 6 sperm are used per brood of 3 × 10 6 eggs (Hines et al. 2003)....

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