THÀNH PHẦN VÀ MỨC ĐỘ ĐA DẠNG SINH HỌC VI TẢO TRONG MỘT SỐ AO ƯƠNG NUÔI CÁ NƯỚC NGỌT TẠI XÃ HỒNG ĐỨC, HUYỆN NINH GIANG, TỈNH HẢI DƯƠNG

This study aimed to assess the composition and biodiversity of microalgae in freshwater fish ponds in Hong Duc Commune, Ninh Giang District, Hai Duong Province. Microalgal composition and density were analyzed in eight freshwater fish ponds, including five grow-out polyculture ponds, one co-cultured tilapia and grass carp fingerlings pond, one tilapia fingerling pond, and one red tilapia pond. Biodiversity indices including species diversity index (H’), dominance index (D) and Wilson-Shmida biodiversity were calculated for all ponds. A total of 173 microalgal species were identified with the following share: Chlorophyta 37%, Euglenophyta and Cyanobacteria each approximately 20-21%, Heterokontophyta 14%, Charophyta 6%, and Dinoflagellata 1%. A total of 10 classes, 23 orders, 35 families, and 57 genera belonging to six phyla were recorded in the studied ponds. The number of microalgal species per pond ranged from 72 to 92. The species diversity index (H’) varied between 2.6 and 4.2, with higher values observed in fingerling ponds compared to grow-out fish ponds. The dominance index (D) values in the ponds ranged from 0.02 to 0.22, suggesting the absence of any dominant phytoplankton species in these systems. Additionally, no significant differences were observed in the Wilson-Shmida biodiversity index among the ponds. The microalgal density in the sampled ponds ranged from 1 × 10⁵ to 4.5 × 10⁵ cells/ml.