Determination of phytoplankton composition in fry pangasius catfish(Pangasianodon hypophthalmus) rearing ponds induced by nutrient powder

Abstract

A 12 days nursery trial was conducted to determine phytoplankton composition in Pangasius catfish fry nursery ponds which were fertilized by a commercial nutrient powder. Three different dosages of nutrient powder were used to induce growth of algae including 0.5Kg, 1Kg and 1.5Kg. The study was carried out in Long Xuyen – An Giang during 12 days of nursery stage. Nutrient powder was applied 2 days before stocking, and continued daily until day 10 of rearing period. The result indicated that there were 67 species of Chlorophyta, 16 species of Cyanobacteria, 36 species of Bacillariophyta, 20 species of Euglenophyta and 6 species of Dinophyta. Densities of phytoplankton varied from 5,211,126 inds/m3 to 59,070,422 inds/m3. In the digestive tract of fish, phytoplankton accounted for 0.23% in treatment 1, 0.11% in treatment 2 and 0.13% in treatment 3. This clearly showed that phytoplankton was not favorite food of Pangasisus catfish, zooplankton was accounted for more than 99% which clearly showed that they are their favorite food during this stage. Treatment 1 grew better with the average body length of 0.94± 0.29cm compared to 0.89±0.28cm in Treatment 2 and 0.91± 0.32cm in Treatment 3. Lower growth in this state mean higher survivability. Therefore, it can be concluded that the best dose should be applied is 1kg before 2 days of stocking.