Aquaculture Research. 2020;00:1–10. wileyonlinelibrary.com/journal/are | 1 © 2020 John Wiley & Sons Ltd 1 | INTRODUCTION Pangasius catfish (Pangasianodon hypophthalmus), also known as Tra catfish, is known as one of the most important aquaculture species in Vietnam, especially within the Mekong Delta (De Silva & Nguyen, 2011; Nguyen & Dang, 2009). According to Vietnam Association of Seafood Exporters and Producers (VASEP, 2019a), pangasius catfish aquaculture utilized 5,400 ha of land area in 2018 with an estimated production of 1.42 million metric tons. Despite high production, the survival rates of fingerlings have been rela- tively low and could be a bottleneck for increasing production. Practically, the survival rate of larvae to fingerlings in earthen ponds varied highly but rarely obtained 10%–15%. One of the most prominent reasons for this might be the lack of an appropriate initial Received: 24 March 2020 | Revised: 23 August 2020 | Accepted: 15 September 2020 DOI: 10.1111/are.14934 ORIGINAL ARTICLE Importance of the freshwater rotifer Brachionus angularis for improved survival rate of early life history stages of pangasius catfish, Pangasianodon hypophthalmus Ngoc U. Vu 1 | Thi H. Pham 2 | Phuoc V. Huynh 1 | Truong G. Huynh 1 1 College of Aquaculture and Fisheries, Tho University, Can Tho, Vietnam 2 Department of Science and Technology, Dong Thap, Vietnam Correspondence Ngoc U. Vu, College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam. Email: vnut@ctu.edu.vn Abstract A study on the use of freshwater rotifers (Brachionus angularis) as initial live feed for pangasius catfish (Pangasianodon hypophthalmus) larvae was undertaken to assess whether this initial feed improved P. hypophthalmus survival during the first 20 days of rearing. This study was comprised of three trials. The first trial contained three treatments and assessed the effectiveness of freshwater rotifers as initial feed com- pared to homemade feed and water flea (Moina macrocopa). In the second trial, P. hypophthalmus larvae were fed with (a) 100% freshwater rotifers, (b) 100% water fleas and (c) a combination of freshwater rotifers and water fleas (freshwater rotifers fed during first 3 days and then water fleas fed for remainder of experiment). In the third trial, the fish larvae were fed 3 densities of freshwater rotifers and then water fleas (3, 5 and 7 individuals per ml) to determine the most suitable feeding density for P. hypophthalmus larvae. Mouth opening was measured at days 0, 3, 6, 9, 12, 15, 18 and 20, whereas growth and survival were assessed at the end of each trial. These experiments demonstrated that P. hypophthalmus larvae: (a) exhibited a significant increase in survival rate when fed B. angularis rotifers or Moina micrura water fleas compared to homemade feed, (b) exhibited a significant increase in growth and sur- vival rates when fed a combination of freshwater rotifers (first 3 days) and then water fleas (remainder) compared to feeding either freshwater rotifers or water fleas only, and (c) preferred a density of 5 to 7 individual freshwater rotifers and then water fleas per ml. KEYWORDS Brachionus angularis, combination feeding, freshwater rotifers, pangasius catfish larvae, survival rate