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Survey of yellowfin tuna in the west-central Indian Ocean was conducted on board of Chinese longliners during 2003, 2004 and 2005, which is a part of Chinese Tuna Fishery Scientific Observer Program (CTFSOP).The reproductive biology has been investigated. A total of 1 023 samples are collected including 417 ovaries and 606 testes. Spawning activities of yellowfin tuna have been studied for both male and female from January to June. The data showed that the average monthly sex ratio is 0.59, and the minimum length at sexual maturity is 101 cm for female and 110 cm for male respectively. Length at 50% sexual maturity is estimated at 113.77 cm for female and 120.20 cm for male, whereas maturation rate is 0.066 cm -1 for female and 0.091 cm -1 for male. Sex ratio by length class indicates that the proportion of male is higher than female's along with size increasing; for instance, in the group of the body length longer than 145 cm, some females have their body length from 145 to 160 cm and males have their body length at 160 cm and even longer. Statistically, yellowfin tuna has a significant seasonal reproduction.

Herbivorous grass carp (Ctenopharyngodon idella) has a powerful capability to digest aquatic weed. Cellulase activity or cellulase-producing bacteria were found in the gut of grass carp. However, it remains uncertain whether the cellulase-producing bacteria were a part of indigenous intestinal microbiota that the ¢sh harboured or were introduced with food. In the present study, the bacterial diversities and population abundance in the gut of starved grass carps have been investigated by sequencing 16S rRNA gene libraries. The16S rRNA gene libraries revealed that 28 parasitic bacteria from gut were a⁄liated to seven genera of Vibrio, Acinetobacter, Providencia, Yersinia, Pseudominas, Morganella or Aeromonas, respectively, and Aeromonas was identi¢ed as the most dominant genus in the gut of C. idella. All of cellulase-producing bacteria isolated from the gut of C. idella in this research belonged to Aeromonas. On the whole, the results in this research showed that cellulase activity within C. idella should be at least partially resulting from bacteria of Aeromonas with cellulase-producing capabilities, which were indigenous and dominant intestinal species.

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