Relationship among foam volume, environment parameters and biofloc situation in biofloc system in Litopenaeus vannamei culture

Biofloc technology (BFT) regulates the carbon-to-nitrogen ratio to promote the growth of heterotrophic bacteria, which assimilates ammonia nitrogen in the water into microbial nitrogen, reducing the accumulation of ammonia nitrogen during aquaculture and forming a biofloc consisting of bacteria, organic particles, extracellular polymers, and plankton. It is widely used in Litopenaeus vannamei culture. In practical production, relying solely on monitoring indicators such as pH, dissolved oxygen, total ammoniacal nitrogen (TAN), and nitrite nitrogen (NO₂⁻-N) cannot comprehensively reflect the real-time formation progress and health status of biofloc. This limitation poses challenges to effective biofloc control, demanding the identification of more appropriate monitoring indicators to ensure biofloc stability. Within the biofloc culture system, foam is a surface feature. Therefore, studying the relationship between biofloc and foam, and identifying effective monitoring indicators is crucial for achieving adequate control over the operational status of the biofloc system. This approach is important in maintaining biofloc stability and ensuring safe production during aquaculture. This study employed three commercial biofloc culture systems for L. vannamei and conducted a 100-day experiment focusing on plankton and foam. Parameters such as foam volume, water surface tension, and water environment parameters were measured. By tracking and monitoring the changes in foam volume, the relationship between plankton, foam, and the operational status of the biofloc culture system was analyzed. This allowed for determining of the biofloc's operational condition through the patterns of foam volume. Pearson correlation coefficient was employed to analyze the correlation between foam volume, water surface tension, biofloc mass, water quality factors, and other parameters, investigating the relationship between foam volume and operation status of biofloc. The results revealed that water surface tension did not significantly affect foam. It also showed a positive correlation between foam volume and total ammoniacal nitrogen (TAN) with a correlation coefficient of 0.571. According to the existing evaluation system, when TAN peaked and began to decline, it signified the biofloc entering stage 2. Additionally, the date for the foam volume changed from increasing to decreasing was highly correlated with the date for biofloc began to form, with a time difference of less than five days. With the formation of formation, the foam volume gradually decreased. Therefore, when foam volume started to decline from its peak could serve as an auxiliary indicator to determine the initiation of biofloc development. When the biofloc was stable, and water quality conditions were favorable, the foam volume remained at a relatively low level. A consistently low and stable foam volume could be used as an indicator to assess the stability of the biofloc. This experiment maintained the foam volume during stable biofloc operation below 0.011 0 m³/t (0.011 0 m³ of foam per ton of water). The research results can be valuable for better control of biofloc and provide essential guidance for promoting the L. vannamei culture in biofloc technology.