Recirculating aquaculture systems (RAS) are growing in popularity as they can be used to supply high-valued, fresh never-frozen marine shrimp inland to local metropolitan markets year-round. When operated in a controlled environment, RAS allows for high animal stocking densities and limited water exchange while utilizing minimal space. Artificial sea salts are required with inland marine shrimp operations, and the use of a complete sea salt mixture is typically a substantial production cost. If an alternative salt formulation that includes only the most important ions needed for shrimp can be developed, production costs may be reduced. This project examined shrimp production and water quality dynamics using various mixtures of a low cost salt (LCS) mixture and a complete sea salt (CSS) formulation.
This experiment compared six salt mixtures, dictated by different inclusion levels of LCS and CSS. The LCS included: NaCl (75%), MgCl2 (5%), MgSO4 (12%), KCl (1%), NaHCO3 (0.5%), CaCl2 (4%), and the CSS was Crystal Sea® Marinemix (Marine Enterprises International). The mixtures that defined each treatment were as follows: 100% LCS, 97.5%/2.5% LCS/CSS, 95%/5% LCS/CSS, 90%/10% LCS/CSS, 80%/20% LCS/CSS, and 75%/25% LCS/CSS. Each treatment included four, randomly assigned 1 m-3 culture tanks operated at a salinity of 15 ppt; each system included an external settling chamber and biofilter, operated continuously. The tanks were stocked at 263 shrimp/m3 with an average initial weight of 2.9 g. An α-value of 0.05 was used to determine if significant differences existed between treatments regarding water quality and shrimp production data.
Significant differences were detected in DO, pH, TAN, and NTU water quality data between treatments. However, these differences were relatively subtle and inconsistent among salt mixtures and were not believed to have impacted shrimp production. No significant differences were detected in shrimp production metrics such as average weight (g), biomass (Kg/m3), survival (%), FCR, or growth rate (% growth/week). However, with regard to the cost of salt per kg of shrimp produced, the 100% LCS, 97.5%/2/5% LCS/CSS, and 95%/5% LCS/CSS all were significantly lower than the 75%/25% LCS/CSS. The 100% LCS mixture cost $8.83 to make 1 m3 of water at 15 ppt salinity, compared to $12.89 to do the same using the 75%/25% LCS/CSS mixture. The results from this study indicate that using the 100% LCS formulation may lower artificial salt costs by 70% while having no significant impacts on shrimp production.