Salt type, sugar addition, and system type in intensive RAS for Pacific white shrimp (Litopenaeus vannamei) production

Abstract

The use of a low-cost, homemade salt mixture in hybrid RAS may reduce operational costs for inland marine aquaculture producers. The addition of sugar in RAS may benefit shrimp growth by making suspended microbes richer in protein, which shrimp can then consume. Increased digestive enzyme activity has been noted in shrimp raised in systems with a substantial abundance of biofloc particles. However, there is still debate over whether clear-water RAS may be superior to particulate-rich systems. This study examined the effects of system type, low-cost salt, and sugar addition on the production, water quality, and digestive enzyme activity of L. vannamei. In the study, two levels of each experimental factor were used. The factors used were system type (clear water-CW vs hybrid-HY), salt type (Least Cost-L vs Commercial-C), and sugar (presence or absence of sugar addition: S vs. N). There was a total of eight treatments: HY-L-S, HY-L-N, HY-C-S, HY-C-N, CW-L-S, CW-L-N, CW-C-S, and CW-C-N, each of which had three randomly assigned, replicate, 1 m3 tanks. All tanks were stocked with 250 shrimp per m3 (3.1 g average weight), extra filtration was used in CW tanks, and sugar (sucrose) was added at a targeted C:N ratio of 14:1 in the sugar tanks. At the end of the experiment, the hepatopancreas was removed from shrimp for digestive enzyme analyses. Results from the experiment showed no significant differences in the average weight, total harvest, FCR, and growth rate between system types and salt types. However, the use of sugar resulted in significantly reduced mean individual weight of shrimp. Nitrate concentration was significantly lower and solids concentrations were higher in the tanks receiving sugar compared to those with no sugar addition. There were no significant differences in amylase activity between treatments, but trypsin activity was higher in the HY systems than the CW systems. The results of this study indicate that this particular low-cost salt mixture had no adverse effects on the water quality, production, or enzyme metrics tested. Biofloc particles seem to have enhanced trypsin activity in the HY system shrimp. Lastly, the addition of sugar had some substantial impacts on solids and nitrate concentrations, as well as negative effects on shrimp growth. Both independently and in combination, the factors examined in this project may have important implications for the management of intensive shrimp aquaculture operations.