Low salinity rearing of Litopenaeus vannamei requires the transfer of postlarvae (PL) from high salinity hatchery systems to low salinity conditions. In order to determine effective transfer methods, fifteenday-old postlarvae (PL15) were acclimated from a salinity of 30 ppt to endpoint salinities of 1 and 5 ppt using single-step and gradual salinity reduction procedures. Higher survival rates were obtained with gradual acclimation than with single-step acclimation. Survival of PL15 acclimated to 5 ppt was better than that of PL15 acclimated to 1 ppt. Survival of PL15 and juvenile stages in various low salinity treatments ranging from 0-5 ppt was also compared. In the PL stage, survival rates were good (>85%) in salinities over 1.5 ppt. Tolerance to low salinities increased with age and survival rate of juveniles (65%) was higher than that of PL (2%) in freshwater. In our long-term growth trials of juvenile shrimp maintained in different salinities, optimal growth comparable to that in normal seawater was observed in animals reared in a salinity of 5 ppt, demonstrating that L. vannamei can be successfully cultured in low-salinity inland systems.

Crustacean aquaculture is a multibillion-dollar industry worldwide that continues to show significant growth. Shrimp farming has been intensified for decades, and super-intensive closed culture systems have now been developed to improve productivity and reduce environmental burdens. Here, we used bio-economic approaches to investigate the mechanisms and economic productivity of shrimp farming. We used three steps: (1) path analysis by using structural equation models to determine the candidate factors associated with productivity; (2) modeling of population dynamics and profits; and (3) simulations based on the models to clarify the productive characteristics of a super-intensive closed culture system. Our findings suggest that the population dynamics of the system were limited by unidentified factors that differed from those found in many experimental studies, such as water temperature, salinity, dissolved oxygen, and nitrogenous waste. The unidentified factors were related to the number of days of rearing and cumulative biomass mortality. The production plan suggested by our simulation required frequent culture rotation to increase profits. Our case study provides important practical information about the characteristics of super-intensive shrimp farming, implications for efficient economic management, and new research subjects for the future.

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The article "Bio-economic analysis of super-intensive closed shrimp farming and improvement of management plans: a case study in Japan", written by Junpei Shinji, Setsuo Nohara, Nobuyuki Yagi and Marcy Wilder was originally published electronically on the publisher's internet portal on 17 September 2019 without open access.