EFFECTS OF SUPPLEMENTAL LED LIGHTING ON WATER QUALITY AND PACIFIC WHITE SHRIMP Litopenaeus vannamei PERFORMANCE IN A CHEMOAUTOTROPHIC-BASED HYBRID SYSTEM

Biofloc-based systems can provide supplemental nutrition to shrimp and have lower startup costs compared to clearwater recirculating aquaculture systems. Indoor biofloc systems have also been shown to respond positively to supplemental lighting. However, nitrification cycles in biofloc based systems can be unstable and lead to a buildup of toxic chemicals in the system including ammonia and nitrite. Hybrid systems combining positive aspects of both biofloc and clear-water systems have been proposed to overcome shortcomings of both system types. This study examined the effects of supplemental LED lighting on such hybrid systems.

Four 1 m³ round tanks were assigned to each of three treatments for a total of 12 tanks. Two treatments had supplemental LED lighting overhead set to 24 hours of lighting (Full Light, FL) and 12 hours of lighting (Partial Light, PL), the third treatment had no supplemental lighting provided (No Extra Light, NL). All treatments were stocked with 250 shrimp at an average weight of 1.2g. All tanks had a settling chamber to remove excess solids from the system and a moving bed bioreactor to provide biofiltration. Settling chambers were run throughout the project but kept at low flow levels early in the experiment to allow biofloc particles to build in the water. All treatments were fed the same amount and each tank was equipped with a 24 hour belt feeder to dispense feed. The DO, pH, temperature, salinity were each measured twice daily and ammonia, nitrite, nitrate, turbidity, chlorophyll, and TSS/VSS were measured weekly.

All systems were harvested after 84 days. We found significant differences in shrimp production between all three treatments. FL systems produced significantly more shrimp than PL or NL systems (4569.5g/tank FL, 3434.6g/tank PL, 3082.8g/tank NL) and FL and PL systems produced significantly larger shrimp than NL systems (25.0g/shrimp FL, 24.2g/shrimp PL, 19.9g/shrimp NL). Feed conversion ratio (FCR) was significantly lower in FL systems compared to PL and NL systems (1.37 FL, 1.83 PL, 2.10 NL) and survival was significanly higher in FL tanks compared to PL tanks (74.1 FL, 57.2 PL, 62 NL). Shrimp growth per week was significantly higher in FL and PL systems compared to NL systems (1.98g/week FL, 1.91g/week PL, 1.56g/week NL). NL systems required a significantly higher amount of NaHCO₃ to raise pH levels over the course of the study than FL and PL systems (222.5g FL, 260g PL, 365g NL). The results of this study show that supplemental lighting in chemoautotrophic hybrid systems can be benefical to shrimp growth. Further research should investigate whether the extra lighting affected the microbial community, the psysiological condition of the shrimp, or both.