Effect of organic fertilization on the occurrence of Nodularia spumigena blooms in Penaeus vannamei shrimp ponds under a biofloc system

Abstract Blooms of potentially toxic cyanobacteria cause high losses in aquaculture worldwide. The species Nodularia spumigena produces toxin capable of significantly affecting feeding, growth rates, and mortality of shrimp in marine farms. As a result, methods for controlling cyanobacterial blooms can increase the production success. The present study was conducted on a commercial scale using six 600 m 3 ponds stocked with 70 shrimp m −2 ( Penaeus vannamei ), in a biofloc system, lasting 15 weeks. The experimental groups were divided into unaffected ponds (WN—without Nodularia ) and affected ponds (N—with Nodularia ), with three replicates ponds per experimental group. Cyanobacterial blooms developed spontaneously in the ponds, and treatments were subsequently designated according to bloom occurrence. During the third week, when the blooms intensified, organic fertilizers consisting of sugarcane molasses and ground commercial feed were added as carbon and nitrogen sources, with the aim of stimulating the establishment of beneficial microbial communities while limiting cyanobacterial proliferation. The water quality parameters were similar between unaffected and affected ponds ( p > 0.05). The microbial community composition was significantly different over time in both grops ( p < 0.05), with the final predominance of chlorophytes. After fertilization, N. spumigena was absent in the affected group (N). The presence of NOD toxin in N. spumigena (66.37 ± 20.87 µg L −1 ) in the second week affected the feed intake of the shrimp and caused mortalities in affected group. However, N. spumigena and the toxin (NOD) was not detected again in the NS group after organic fertilization and the shrimps recovered. The performance results showed significant differences ( p < 0.05) with higher survival and yield in the unaffected group (WN). Therefore, organic fertilization influenced the occurrence and development of Nodularia spumigena blooms, emphasizing its potential role in the dynamics of cyanobacteria in biofloc shrimp farming and supporting further research.