Search

Search Results

• Effects of Temperature on Population Growth and Resting Egg Production of Freshwater Rotifer (Brachionus calyciflorus)

  Doan Thi Nhinh, Pham Thi Lam Hong, Truong Dinh Hoai, Kim Van Van

  Received: Jun 10, 2020 / Published: Dec 31, 2020

   Abstract PDF

  Resting egg production of rotifers provides critical advantages in larviculture of most fish species due to the reduction in the costs of labour and algae production. The study was conducted to investigate the effects of temperature on population growth and resting egg production of a freshwater rotifer, Brachionus calyciflorus, collected in Northern Vietnam. The rotifer was pre-cultured at 27ºC before being transferred to the cultures at 15 and 35ºC while the control was maintained at 27ºC. One-liter beakers filled with 500mL culture medium were used with three replicates for each temperature group. Stock rotifers were inoculated at an initial density of 200 ind ml-1 and fed with concentrated fresh algae. The results indicated that population growth rate (r) of rotifers cultured at 27 and 35ºC were significantly higher than that of rotifers at 15ºC while the highest density was attained from the treatment of 27ºC, at 608.3 ind mL-1, compared to 468.3 and 360.5 ind mL-1 at 35 and 15ºC, respectively. Transferring the cultures from 27 to 35ºC significantly increased the rate of resting egg carrying females with the maximum rate of 31.5% compared to 21.2 and 13.5% of the rotifers at 27 and 15ºC, respectively. The resting egg densities of the cultures at 35ºC were also significantly higher than those at 15 and 27ºC. The resting egg carrying females appeared and increased their rates in concurrence with increases in the population density. The present results are important information for resting egg induction and production of rotifer in larviculture.

• Water Quality Assessment and Eutrophic Classification of Hanoi Lakes Using Different Indices

  Nguyen Thi Thu Ha, Dinh Tien Dzung, Ho Thi Thuy Hang, Trinh Quang Huy, Nguyen Ngoc Tu

  Received: Nov 05, 2020 / Published: Dec 31, 2021

   Abstract PDF

  The trophic levels in urban lakes are typically based on the forms of nutrition and phytoplankton communities in the lakes. In this study, comparisons between eutrophication indices and the water quality index (VN-WQI) were used to classify the water quality of 20 lakes in Hanoi, Vietnam. The results showed that the water quality ranged from very bad to poor. High levels of the eutrophication phenomenon in terms of total N and P were observed in all sampling sites. Cyanobacteria was the dominate algae phylum making up 65.78% of the total population, whereas Chlorophyta (including 19 genera) was the most diverse phylum. The density of the algae was 5,000-14,000 cells mL-1 and the chlorophyll-a level was 10-40 µg L-1. Based on this information, the water quality levels in the lakes were classified from eutrophic to polytrophic. The Trophic Status Index (TSI) and Trophic Level Index (TLI) values ​​were 66.9-86.0 and 54.4-76.0 points, respectively, corresponding from eutrophic to extreme-trophic. Classifications based on algae community structure indices were from oligotrophic to eutrophic, similar and consistent with the TLI classifications. According to the results in this study, the TLI was found to be more accurate and precise than the other indices. It is recommended that the TLI is an applicable tool to classify eutrophication in urban lakes.