| The manila clam Ruditapes philippinarum is one of the economically important seashells in our country, with Agamaki clam Sinonovacula constricta, oyster Ostrea and bloody clam Tegillarca granosa together being called "the four greatest farming seashells"traditionally. The manila clam ever distributed widely in the Jiaozhou Bay, and it had more than 70 years of fishing activities. Because of the increase demand of the domestic and international market to the clams, the fisherman enlarged the fishing efforts, which caused the serious decline of natural resources. Currently in the Jiaozhou Bay the clams are mainly farmed, and the main farming areas include the coastal area of Hongdao, Yinghai and Hongshiya.From May 2004 to April 2005, the manila clams Ruditapes philippinarum were sampled with the fixed sites in the Jiao Zhou Bay and measured concerning the biological characteristics, in order to investigate the growth and mortality characteristics of the species. The results mainly included:(1) The relationships between body weight(BW) and shell-length(L), shell-height(H), shell-width(W) were represented by functions BW= 0.0002 L 3.0533(r2 = 0.9857), BW = 0.0004H 3.088R2 = 0.9912), BW = 0.0053W 2.6834(r2 = 0.9784), respectively. The relationships between shell-length and shell-height, shell-width were representd by functions H=0.6674L+0.3059(R2=0.9789) and W=0.4575L-0.9678(R2 = 0.9572), respectively.(2) The clam seedlings mainly from Fujian province had an average body weight of 0.26g, and average shell length of 11.1m, the density was 2500ind/m2. The farmed clam had a similar tendency with the wild clams for the growth, but grew slower than the wild clams. The main growth periods lasted from April to September, and after October the clams grew slowly and slower especially from November to next January. The clams entered the fast-growing periods again after March.(3) The clams grew quickly from age 1 to age 3, and the annual weight increases were 3.88g and 4.02g for the age 1 and age 2, respectively. The growth speed and age were negatively related, and the growth became slower with increasing age.(4) The increase of biomass for age 1 group has the same trend as its individual growth rate in one year. For different age classes, the biomass increased fast for age 1, and the biomass growth got slower for age 2 due to its higher mortality.(5)The ratio of tissues to body weight increased with age between age 1 and age 3. The growth of tissues was faster than that of shell. The variations in ratio of tissues, rate of net flesh and conditional index had similar trends. These indices were higher from April to September with the highest values in June. May and June were the main feeding period for fanned slams, which were different from the clams in Fujian province and the wild clams in the Jiaozhou Bay.(6)At the natural sea, temperature was the main environmental factor that affects the clam growth, and the growth had obvious seasonality. According to the analysis of individual growth, the best harvest age was 3, however, the best harvest age was 2 based on the analysis of the biomass output. The best fishing period was June.This paper also analyzed the present manila clam industry in the Jiaozhou Bay, and discussed the sustainable development of the clam industry. Finally some suggestions were put forward to provide the certain technique supports and decision basis for keeping the clam industry healthly development.
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