Estimation of shrimp and crab aquaculture capacity in seawater ponds based on nitrogen and phosphorus loads

Objective From the perspective of ecological and environmental protection, combined with the current status investigation, based on the total phosphorus (TP) load, total nitrogen (TN) load and tail water discharge standards, two models were used to estimate the annual aquaculture capacity and density capacity of Litopenaeus vannamei and Portunus trituberculatus in seawater ponds.

Methods In this study, the seawater ponds in the restricted area of Daguanban industrial and urban sea area (Guanban Town area) were used as the research area. Based on TP load and TN load models, the aquaculture capacity of L. vannamei and P. trituberculatus in two breeding stages within one year was estimated, and the maximum aquaculture capacity in the area was determined based on the minimum value estimated by the two models.

Results The estimation results based on TP load showed that the maximum aquaculture capacity and density capacity of L. vannamei in the first culture stage (from March to June) were 588 t and 1.31 t/hm², respectively; the maximum aquaculture capacity and density capacity of P. trituberculatus in the second culture stage (from June to February of the next year) were 714 t and 1.59 t/hm², respectively. Based on the estimation results of TN load, the maximum aquaculture capacity and density capacity of L. vannamei in the first stage were 415 t and 0.93 t/hm², respectively; the maximum aquaculture capacity and density capacity of P. trituberculatus in the second culture stage were 356 t and 0.79 t/hm², respectively. By comparing the aquaculture capacity based on TP and TN load estimations, the minimum value was used to determine the maximum aquaculture capacity of L. vannamei and P. trituberculatus in the study area. The recommended values of L. vannamei and P. trituberculatus were 415 t and 356 t, respectively, and density capacities of which were 0.93 t/hm² and 0.79 t/hm², respectively.

Conclusion In this study, the aquaculture capacity based on TP load estimation is significantly higher than that based on TN load estimation, and the aquaculture capacity is generally low, which is closely related to the requirements of influent and effluent quality and emission standards in aquaculture ponds. From the perspective of environmental protection, the key is to increase the self-purification capacity of water bodies, thereby increasing environmental aquaculture capacity. Therefore, it is suggested to improve the aquaculture capacity and density capacity of the region by enhancing training and awareness campaigns, improving the replacement rate of compound feed, exploring multi-trophic level breeding methods, improving self-purification capacity, implementing ecological and environmental protection measures, and reducing pollutant emissions, so as to help the green and high-quality development of aquaculture.