Combined effects of the farming methods and density on the survival rate, growth, yield, and economic efficiency of otter clam (Lutraria rhynchaena) in Van Don, Quang Ninh Province

This study was conducted to evaluate the effects of farming methods and density on the survival rate, growth, yeild and economic efficency of commercial otter clam in the sea waters of Van Don, Quang Ninh. The otter clams with an initial length of 18,36 mm and an average body weight of 4,12 g were used in this study. Two farming methods were arranged: cage culture (basket) hanging on the raft (including experiments TN1, TN2, TN3 and TN4) and cage culture placed on tidal flats (including experiments TN5, TN6, TN7 and TN8). For each culture, there were 4 formulas for stocking density of 25 individuals\cage (100 individuals\m2) (TN1, TN5), 35 individuals\cage (140 individuals\m2) (TN2, TN6); 45 individuals\cage (180 individuals\m2) (TN3, TN7); and 55 individuals\cage (220 individuals\m2) (TN4, TN8). Each treatment was triplicate and lasted for 12 months, the results showed that the density and farming methods had different effects on growth, survival rate and yield of commercial otter clam. The weight of the commercial otter clam ranged from 28,76 to 41,74 g\individual, the length varied from 51,17 to 72,69 mm\individual, and the survival rate fluctuated from 57,4 to 78,3%. The highest growth was recorded in the TN1 with density of 25 individuals\cage, the difference between treatments was statistically significant (p≤ 0.05). The average yield of commercial otter clam increased with the increase of stocking density, ranging from 21,7 to 38,3 tons\ha, the difference was statistically significant (p≤ 0,05). However, economic accounting showed that the economic efficiency was highest in TN2, the ottet clams were arranged in the cage hanging on rafts and stocking at a density of 35 individuals\cage (140 individuals\m2). In this experiment, the average growth in weight was 38,91 g\individual and in length was 68,47 mm\individual, the survival rate was 76,4%, and the yield was 32,9 tons\ha the economic profit reached 0,883 billion of Vietnam Dong and the profit rate reached 28,1, respectively. Based on these research results, it could be recommended to farmers to stock the otter clam with a density of 35 individuals\cage.