The integration of hydroponic systems and biofloc-based aquaculture as a resents an opportunity for resource-efficient and sustainable systems with a focus on nutrient recycling and water conservation. This study examined the effects of immunostimulants as dietary supplements on Nile tilapia and romaine lettuce growth within this integrated system. In the fish biofloc system, juvenile Nile tilapia (9.99 ± 0.55 g) were provided with a protease complex (PC) and a humic substance (HS) as immunostimulants in addition to a standard commercial feed (control-Basal) for 60 days. Growth measurements and feed adjustments were performed bi-weekly. The hydroponics system with romaine lettuce consisted of 9 feeding troughs with 15 plants per trough. Weekly water replacement from biofloc settling chambers into feeding troughs was carried out. Plant growth parameters and destructive measurements of lettuce growth were conducted at the end of the 28-day trial. The water quality parameters of both systems were kept at acceptable ranges.
The study revealed that there were no significant differences in fish growth parameters, including percent weight gain (P=0.231), survival (P=0.272), and feed conversion ratio (FCR; P=0.317) among the dietary treatment groups. Likewise, lettuce growth metrics, such as size indices (P=0.276) and leaf number (P=0.084), did not exhibit significant variations across treatment groups. However, the perpendicular width of the PC-treated plants was significantly higher than the control treatment (P=0.010). Notably, the PC-treated water led to higher leaf greenness, as measured by SPAD (P=0.002). Regarding foliar tissue analysis, essential macronutrients met the required plant nutrient levels, and Mg (P=0.011) and Ca2+ (P=0.0006) in control plants displayed significantly higher levels than in PC and HS-treated plants. The micronutrients were also in the required levels (0.05-100ppm), but B in HS-treated plants was higher (P=0.004) than in the other treatments. However, there was a deficiency of copper (Cu) and iron (Fe) in the leaves of plants in all treatments so they should be supplemented into the water.
In conclusion, this study suggests that the inclusion of dietary protease complex (PC) or humic substance (HS) did not substantially impact Nile tilapia growth under the conditions of this experiment. However, PC-treated water demonstrated the potential to enhance romaine lettuce quality and growth. To optimize the biofloc effluents, it is advisable to supplement copper (Cu) and iron (Fe). The results of this trial indicate that utilizing aquaculture effluent as a water and nutrient supplement can lead to favorable outcomes in both the quantity and quality of lettuce production, making it a promising practice for producers.