Abstract: The hydroponic lettuce experiment involved the blending of aquaculture wastewater with water-soluble fertilizer, aiming to determine the optimal ratio of water and fertilizer. This study aims to provide a theoretical foundation for effectively utilizing water resources in industrial aquaculture wastewater. In this study, the research focused on "cream lettuce" as the primary subject. Various quantities of Yamazaki formula water-soluble fertilizer were dissolved in industrial aquaculture wastewater to create a blended nutrient solution. Subsequently, an experiment utilizing the Nutrient Film Technique (NFT) was conducted to investigate its effects. The experiment consisted of five distinct treatments: S1 (123g fertilizer + 150L wastewater), S2 (98.4g fertilizer + 150L wastewater), S3 (73.8g fertilizer + 150L wastewater), S4 (49.2g fertilizer + 150L water), and S5 (24.6g fertilizer + 150L water). Additionally, a control group labeled CK (123g fertilizer + 150L water) was utilized to examine the impact of different treatments on lettuce yield and quality. The TOPSIS comprehensive benefit evaluation model, based on the entropy weight method, was employed to analyze and ascertain the optimal parameters for the water and fertilizer ratio. The results demonstrated that the mixed nutrient solution effectively enhanced the absorption of water and fertilizer. However, it was observed that as the concentration of fertilizer increased, the lettuce's fertilizer consumption exhibited an initial rise followed by a subsequent decline. The water and fertilizer consumption of lettuce under the various treatments was lower than that of the CK treatment. Furthermore, the S1-S5 treatments exhibited fertilizer savings of 25.01%, 19.15%, 34.12%, 51.89%, and 74.10% respectively, in comparison to the CK treatment. The mixed nutrient solution proved to be highly effective in promoting the growth of lettuce. However, it was observed that the growth indicators of lettuce followed a pattern of initial increase and subsequent decrease as the fertilizer concentration increased. Notably, the highest lettuce yield of 1.88 kg·m⁻² was achieved under the S2 treatment, representing a 15.32% increase compared to the CK treatment. Furthermore, the mixed nutrient solution exhibited a positive impact on improving the quality of lettuce. The contents of soluble sugar and soluble protein in lettuce displayed an initial increase and subsequent decrease, with the highest levels observed in lettuce treated with S2. The content of vitamin C(VC) and nitrate exhibited a positive correlation with the fertilizer concentration. Specifically, the S1 treatment resulted in the highest VC content, while the nitrate content under the S1-S5 treatments was lower compared to the CK treatment. The comprehensive benefit evaluation revealed that the S2 treatment was the most favorable for lettuce growth, yielding higher crop output and superior quality. The optimal combination of fish tail water and fertilizer demonstrated significant benefits, enhancing water and fertilizer absorption, improving lettuce yield and quality, and maximizing overall crop production efficiency.

Key words: Aquaculture wastewater, Water-fertilizer coupling, Hydroponic lettuce, Yield and quality, Entropy method, TOPSIS