Evaluating the interactive effect of inoculum and C/N adjustment strategy on water quality and growth performance of Litopenaeus vannamei in biofloc system

The present study compared the supplementation of Litopenaeus vannamei tanks with inoculums generated by different nitrogen sources (NH4Cl or feed). The interactions of inoculums and C/N adjustment strategies on water quality and growth performance were also investigated. After preparation of inoculums, shrimp juveniles were reared for 39 days at 142 shrimps/m(3) in four treatments: T1, NH4Cl-based inoculum + heterotrophic C/N adjustment; T2, NH4Cl-based inoculum + mixotrophic C/N adjustment; T3, feed-based inoculum + heterotrophic C/N adjustment; and T4, feed-based inoculum + mixotrophic C/N adjustment. At the end, two-way ANOVA analysis showed significant interactions of time x inoculum or time x C/N adjustment strategy on dissolved oxygen, pH, and settleable solids. Alkalinity was significantly affected by the time x C/N adjustment strategy interaction, while inorganic nitrogen species (TAN, NO2-N, and NO3-N) were altered depending on the time x inoculum effect. Inoculum and C/N adjustment strategy significantly altered alkalinity and TAN levels. TAN levels in T1 and T2 treatments accumulated for 2 weeks, and organic carbon addition was not effective in mitigating high TAN levels. The mixotrophic strategy significantly reduced solids levels, while enhancing DO levels. No significant interactive effects of inoculum x C/N adjustment strategy were detected on the water quality indicators. The final body weight (FBW), feed conversion ratio (FCR), and weekly growth rate (WGR) of shrimp were significantly improved in tanks supplied with feed-based inoculum. Also, the inoculum x C/N adjustment strategy led to significantly higher FBW, weight gain, specific growth rate, and WGR in tanks supplied with feed-based inoculum and heterotrophic C/N adjustment. In conclusion, feed-based inoculum prevented the accumulation/peak of nitrogen species, reduced the nitrification establishment time, and enhanced growth performance. In addition, inoculum effectiveness was affected by the C/N adjustment strategy, highlighting the advantageous performance of mixotrophic approach. This information can develop efficient management practices for biofloc systems.