Optimizing Culture Density for Brocade Baffo Clam in Beibu Gulf: A Study on Growth and Survival Rates

To investigate the suitable culture density and growth characteristics of 'bafoofoam' in the Beibu Gulf in Guangxi, experiments were conducted from January 2022 to August 2023 in the experimental areas of Beihai, Fangchenggang, and Qinzhou Rhinoceros. These experiments included basket culture and net cage culture. The growth parameters of the clams were measured regularly during the experiment, and regression analysis was used to establish growth equations for shell length-body mass during the mid-cultivation period (when the clams were 3 months old), the basket-raising period (when the clams were 9 months old), and the net-cage culture period (when the clams were 18 months old). This allowed for the comparison of growth performance and survival rates of the clams at each stage of the culture process.

Findings demonstrated that:

1. The suitable density of the clams in the experimental sea areas of Beihai, Fangchenggang, and Qinzhou during the mid-cultivation period was 2000 seeds per basket, 2000 seeds per basket, and 1000 seeds per basket, respectively. The growth indexes and survival rate of the clams in the same density group in the Beihai sea area were better than those in the Fangchenggang and Qinzhou sea areas. All growth indexes and survival parameters showed a decreasing trend with the increase in density during the mid-cultivation period.

2. During the cultivation period, the shell lengths and body masses of the clams in the three sea areas were measured using the growth equations at 18 months of age. The three sea areas of the brocade bafoon clams were suitable for raising a density of 60 grains per basket, 50 grains per basket, and 40 grains per basket, respectively. The growth indexes and survival rate of each density group were ranked as Beihai > Fangchenggang > Qinzhou. Except for the survival rate in the experimental sea areas of Beihai and Fangchenggang, which initially increased and then decreased, the remaining growth indexes showed a decreasing trend with the increase in density.

3. The growth indexes and survival rate of the mesh-cage-hang-cultivated Bafia clams in the sea area of Bailong Pearl Bay of Fangchenggang showed a decreasing trend with the increase in density. The three density groups of high, medium, and low increased yields by 34.98%, 25.36%, and -3.13%, respectively.

4. In the sea area of Bai Long Pearl Bay of Fangchenggang, the growth indexes of the mesh-cage-hang-cultivated Bafia clams increased by -3.13%. The growth equation showing anisotropy reveals that the brocade bafia clam exhibits positive anisotropy at the stage of 3 months of age and negative anisotropy at the stage of 9 months of age and 15 months of age during the rearing period in the marine area. The growth parameters 'b' were 3.709, 2.546, and 2.712, respectively.

The results of the survey of environmental factors and phytoplankton in the marine area showed that the annual average water temperature, beach temperature, and salinity in the Beihai Sea area were the highest among the three designated sea areas for experiments, and water quality changes were relatively stable. The grain size of the mudflat substrate in the Beihai Sea was dominated by coarse sand, while medium sand dominated in Fangchenggang and fine sand dominated in Qinzhou. The number and abundance of phytoplankton were highest in Fangchenggang, followed by Beihai, and lowest in Qinzhou.

The results indicated that it was possible to conduct basket culture and cage culture in Beihai, Fangchenggang, and Qinzhou. The most favorable results were obtained from basket culture in Beihai, followed by Fangchenggang, and the worst in Qinzhou. It was also suitable to use lower density for net cage culture in 1.5-year-old shellfish sea areas to enhance the production rate and prevent production decline.