Water quality control in a closed re-circulating system of Pacific white shrimp (Penaeus vannamei) postlarvae co-cultured with immobilized Spirulina mat

Immobilized Spirulina mat was co-cultured with Pacific white shrimp (Penaeus vannamei) postlarvae for water quality control in a closed re-circulating system. During the culture period, the experimental Spirulina mat system showed total ammonia nitrogen and nitrate accumulation rates lower by 32.92 and 32.26 %, respectively, compared with the system without the mat. The water exchange rate in the system with the mat was comparatively reduced by 40 %. Moreover, survival rate, growth rate, and size (length) of the co-cultured shrimp larvae were greater than those of the control (P < 0.05): 72.3 +/- A 5.2 versus 61.3 +/- A 4.4 %; 0.55 versus 0.44 mm day(-1); and 9.8 +/- A 0.5 versus 8.7 +/- A 0.3 mm, respectively. The most frequently observed microbes by PCR-DGGE, either with or without Spirulina mats, were species related to classes gamma-, alpha-, and beta- of Proteobacteria (95-98 % similarity), i.e., Nitrosomonas marina, Pseudomonas sp. ITRI66, Fusobacterium ulcerans, and Exiguobacterium arabatum, and species related to Bacteriodetes, i.e., uncultured Flavobacteriales (with a similarity of 96 %). However, species related to Nitrobacter winogradskyi and Stenotrophomonas maltophilia were present only when the mats were applied, suggesting a mutualistic role in the aquaculture system. These bacterial communities, in cooperation with Spirulina sp., could enhance the shrimp response against disease, as well as growth and survival rates, and also improve the shrimp culturing water quality.