THE EFFECTS OF STOCKING DENSITY AND ARTIFICIAL SUBSTRATE ON PACIFIC WHITE SHRIMP Litopenaeus vannamei PRODUCTION AND WATER QUALITY DYNAMICS IN GREENHOUSE-BASED BIOFLOC SYSTEMS
Biofloc systems have a dense microbial community in the water column which helps maintain water quality and may act as a supplemental nutritional source for shrimp. Biofloc facilitates high levels of biosecurity, water conservation, and production of marine species inland. High tunnel greenhouses can help to extend the growing season for warm-weather crops in subtropical and temperate latitudes. High tunnel greenhouses have no artificial heat; they are warmed only through solar radiation, and cooled using passive ventilation and shade clothes. Varying stocking densities and substrates have shown effects on shrimp growth and performance as well as water quality. The purpose of this study was to assess these effects on production, and water quality conditions to help optimize shrimp production in high tunnels.
The experiment included 16 wooden framed tanks lined with a 45 mil rubber liner. Four tanks were located in each of four high tunnels. Each tank contained approximately 11 m3 of water aerated with one 2.5 HP regenerative blower per high tunnel. Solids were controlled using 473 liter conical bottom settling chambers and in-house made foam fractionators with diffused air. Shrimp were fed a 35% protein commercial pelleted diet 3 times daily. Four treatments were used: high density with substrate (HD-S), high density without substrate (HD-NS), low density with substrate (LD-S), and low density without substrate (LD-NS). High density tanks were stocked with 300 shrimp/m3, low density were stocked with 200 shrimp/m3; tanks with substrate contained 4.2 m2 of polypropylene construction safety fence suspended in the water column. One tank from each treatment was randomly assigned to a tank within each high tunnel, thereby blocking for tunnel location. Shrimp were stocked after a 90 day indoor nursery period when they weighed 2.71g, and the experiment was conducted in the high tunnel tanks for 101 days.
Few differences were found in shrimp production metrics during this study, potentially indicating the relative equivalence of growth in shrimp stocked at higher densities in these low-tech systems. The concentrations of ammonia and nitrite were higher in the high density systems compared to low density, suggesting that some degree of caution is warranted when shrimp are grown at higher densities.
Overall, the results of this study are encouraging for the production of marine shrimp in a land-locked, subtropical location such as Kentucky using no supplemental heat. Further investigations will include the financial implications of using low-cost high tunnels to produce fresh, high-quality shrimp near potentially lucrative market places.