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A previous survey reported that swimming crabs Portunus trituberculatus (Miers, 1976) in the East China Sea may have a low risk of sperm limitation under the current nonselective fishing practices. In this study, the possible mechanism of avoiding sperm limitation was investigated in a mating season (from July to November 2007) from a male perspective. Males reached 50% gonadal maturity at a carapace length of 99.4 mm and the reproductive measures (vas deferens weights, sperm number, and sperm concentration retained in the vasa deferentia) did not differ significantly throughout the mating season. As shown for other decapods, the quantity of seminal material in the vasa deferentia increased significantly with male size, without a concomitant change in sperm concentration. The proportion of stored sperm transferred at a single mating was calculated, and the results showed that males exhibited low sperm transfer at each mating, regardless of size. These findings indicate that the current fishery pr...

In order to estimate relationships among growth potential and biochemical indicators of Japanese flounder, RNA and DNA as well as protein indices were measured from 5 days after hatching (DAH) to 45 DAH. Results showed that the RNA/DNA ratio and protein/DNA ratio had obvious relations with instantaneous growth rate (GM) and length-based instantaneous growth rate (GL) during the premetamorphic period. Significant negative correlations among protein/DNA ratio and GM and GL were then observed during metamorphosis. During the postmetamorphic phase, the RNA/DNA ratio was positively correlated with GM and GL. Data indicated that body growth of Japanese flounder is mostly hyperplastic before 20 DAH, hypertrophic until 27 DAH, and hyperplastic until the end. In order to investigate the effect of diel periodicity on RNA/DNA ratio in larvae of the fed and starved groups, an experiment was conducted for 2 days. Results showed that the average RNA/DNA ratio in the daytime was higher than that in the dark and the ratio in fed larvae was higher compared with that in starved ones. In order to examine starvation effect on RNA/DNA ratio, experiments were conducted from 20 DAH to 27 DAH. Juveniles were divided into five groups: a fed group and groups starved 1, 2, 3, and 4 days followed by refeeding. Results showed that the RNA/DNA ratio increased in the fed group and declined continuously in the starved group. After refeeding, the recovery of the RNA/DNA ratio was observed for 1-day, 2-day, and 3-day starved treatments but was not found for the 4-day starved treatment.

Potential sperm limitation of the swimming crab Portunus trituberculatus was exam- ined 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 correla- tion between the final number of stored sperm and female carapace width. Lastly, using knowl- edge 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 per- spective of a fishery resource assessment or from the perspective of seed production. From com- parison 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 knowl- edge of sperm limitation in brachyurans as fishing management in China is non-selective, which differs from other exploited decapod crustacean species around the world.