With the increase in demand for seafood as well as fresh locally grown products, inland and indoor shrimp production operations have gained popularity in the US and other world markets. Indoor production methods have relatively high startup and operating costs. Two substantial expenses facing indoor production are artificial salt and land or property costs. In recent years, low-cost salt mixes and denitrification methods have been developed to reduce salt cost and reuse water. Low salinities have been used to grow L. vannamei, in some cases as low as 5 ppt or less, however; results have been inconsistent. To maximize the use of space in indoor facilities, several researchers and commercial ventures have explored using shallow tanks, which can be stacked vertically. However, concerns have been raised as the smaller volume may concentrate toxic nutrients such as ammonia. In addition, the shallow water may not facilitate adequate oxygen diffusion as aeration contact time will be reduced. The purpose of this study was to examine the effects of varying salinities and water depths/volumes on L. vannamei performance and water quality over the course of a production cycle.
Six treatments were randomly assigned to 24 tanks providing four replicates per treatment; the experiment included three salinity levels and two water depths: deep (D) and shallow (S). The salinities used for the experiment were 5,10, and 15 ppt. and the volume/depth of water were 1m3/100cm depth (D) and 0.5m3/50cm depth (S). The treatments were as follows: 5ppt-50cm (5-S), 5ppt-100cm (5-D), 10ppt-50cm (10-S), 10ppt-100cm (10-D), 15ppt-50cm (15-S), 15ppt-100cm (15-D). Each flat-bottom tank was 1m2 in bottom area and had an 18.9 L settling chamber and an 18.9 L biofilter, both receiving water from a 1135 LPH pump. Tanks were salted using a low-cost salt mixture to the respective salinities. 250 shrimp were stocked into each tank at an average weight of 1.9g producing stocking densities of 250 shrimp/m3 in the 100 cm treatments and 500 shrimp/m3 in the 50 cm treatments.
Preliminary results suggest some differences in water quality. Lower oxygen concentration and lower pH levels in shallow tanks have been consistently observed. Although the study is currently ongoing, we suspect that these important differences in water quality will result in substantially different shrimp production levels between treatments. Such a finding would have important implications for commercial producers who are considering the use of shallow tanks. These producers will have to weigh the costs of added water quality maintenance against the benefits that come from maximizing the space in indoor facilities.