Correlation of morphometric properties to meat yield and fatness index in the red strain of the saltwater hard clam Meretrix meretrix.

To determine the relevance of morphometric properties attributed to the meat yield and fatness index of the saltwater hard clam Meretrix meretrix. A new strain of M. meretrix with red shell color was produced after five generations of selection within a family of full-sibs. 7 morphometric traits, including shell length (SL), shell height (SH), shell width (SW), ligament length (LL), projection length (PL), projection width (PW), and live body weight (LW), and 2 meat characteristics, including meat yield (MY) and fatness index (FI) were measured from 50 individuals of three-year-old M. meretrix. The correlation coefficients, path coefficients, determination coefficients among attributes were analyzed. The results indicated that correlation achieved very significant levels (P<0.01). In addition, the multiple regression equations were formulated by considering the meat yield and fatness index as the dependent variables, respectively, and 7 other morphometric traits as independent variables. The correlation indices (R2) of morphometric traits against the meat yield and fatness index of clams were 0.901 and 0,929, respectively, indicating that the live body weight and shell length were the common main factors influencing the meat characteristics. By testing the significance of partial regression coefficient and gradually removing the non-significant morphometric traits, a multiple regression equation was established to estimate the relationship between shell length (SL, mm), live body weight (LW, g), ligament length (LL, mm) and meat yield (MY, %), fat index (FI, %): MY (%) = 0.432SL+0.251LW and FI (%) = 0.156SL+0.067LL+0.42LW-3.533. The study draws a conclusion that live body weight and shell length have a predominant direct effect on the meat yield and fatness index, which provides theoretical information for the breeding of M. meretrix.

Distribution of phosphorus species and their release risks in the surface sediments from different reaches along Yellow River.

In order to further explore the relationship between water body eutrophication of some reaches of Yellow River and phosphorus species in sediments, and evaluate phosphorus release potential from sediments to overlying water, we investigated the distribution of P species and their release risk in the surface sediments from different reaches along Yellow River, as well as the influence of artificial dam on phosphorus cycle in Yellow River. The results show that the content of calcium phosphorus (PCa) is higher than the content of bioavailable phosphorus (BP) (BP = Pex + PFe; in the formula, Pex means exchangeable phosphorus and PFe means iron phosphorus) in the surface sediments from Yellow River. Among all the surface sediment samples from 21 stations, only Dayudu section (H15) has a ratio of W (BP)/W (PCa) higher than 0.5; the results show that the intensity of phosphorus release from H15 is high, and there is a potential risk of eutrophication in water, while the phosphorus release level of water sediment in other reaches of Yellow River is low. The content of BP and total phosphorus (∑P) in surface sediments along the Yellow River is in descending order: middle reaches of Yellow River > upper reaches of Yellow River > Yellow River downstream, while the content order of total phosphorus (TP) in the overlying water is as follows: Yellow river downstream > middle reaches of Yellow River > upper reaches of Yellow River (except the H7 station), indicating that extensive artificial corresponding damming in Yellow River basin makes the concentration of TP increasing significantly in overlying from upstream to downstream. The establishment of Haibowan water conservancy project in Yellow River makes the total particulate matter (TPM) concentration in the water to reduce to very low lever in Wuhai H7 section, and the phosphorus concentration in the overlying water reaches 0.136 mg L-1.