No abstract

No abstract

A 3-week nursery phase for giant river prawn, Macrobrachium rosenbergii post larval (PL), was conducted in biofloc systems at increasing carbon-nitrogen (C-N) ratios of 10:1 (C-N10), 15:1 (C-N15), 20:1 (C-N-20) and 25:1 (C-N25) versus a clear water system (40% water exchange every 2 days and no additional carbon). A total 400 PLs (15.90 ± 1.29 mg) were cultured in tanks (100 L) filled with brackish water (12‰), and corn starch was the carbon source. Growth, survival, feed conversion ratio (FCR), whole body proximate composition, water quality parameters, biofloc volume, zooplankton and proximate composition were measured. Total ammonia nitrogen (TAN) and nitrite nitrogen (NO 2 -N) were significantly lower in all biofloc systems as well as containing increased zooplankton groups (ciliates, rotifers and nematodes). Specific growth rate (SGR) was similar between the control (9.29 ± 0.35% day −1 ) and the CN-20 (9.47 ± 0.18% day −1 ) and CN-25 (9.34 ± 0.20% day −1 ) treatments; however, SGR significantly declined in the C-N10 treatment (8.03 ± 0.10% day −1 ). Survival was unaffected by treatments while a higher survival (87.34%) was in CN-20 and it was followed by CN-25 (80.34%), control (80.33%), CN-10 (77.0%) and CN-15 (76.66%) respectively.The best FCR was in the C-N20 treatment at 2.65, but was not statistically different than the control at 3.12. However, crude protein of the PLs was significantly higher in the C-N15, C-N20 and C-N25 treatments compared with the control. The present findings indicate that the water quality was better managed in the biofloc treatments compared with the control; however, lower C-N ratios of 10 and 15 can negatively impact prawn growth compared with the control or higher C-N ratios of 20 or 25.

In the present investigation, zooperiphyton communities comprised protozoa, rotifera copepoda, cladocera, ostracoda, conchostraca, insect’s larvae, oligochaeta, nematoda and mollusca. The group of zooperiphyton on three substrates showed no significant differences (P>0.05). Rotifers and protozoans were the most dominant group of total zooperiphyton abundance among three substrates. The interrelationships between zooperiphyton groups and physicochemical features of water as well as among different groups of zooperiphyton revealed that abundance and growth of zooperiphyton on substrates are influenced by water quality parameters and each with others. The ranges of physicochemical features of water of Dhanmondi lake were suitable for zooperiphyton communities including aquatic biota and also play a significant role to settle zooperiphyton on three substrates. That can help in enhancing productivity of the lake as well as sustaining aesthetic value of aquatic system. Asiat. Soc. Bangladesh, Sci. 40(2): 283-294, December 2014

The effects of periodically adding the cyclopoid copepod, Apocyclops dengizicus, (every four days at a rate of 4 individuals/mL) with biofloc technology (BFT‐C) was compared with conventional BFT (without copepod) or a clear‐water control on the survival, growth, proximate composition, and economics of Macrobrachium rosenbergii postlarvae nursery culture. Water quality and biofloc proximate composition were also measured among treatments. For the BFT, maize starch was applied to achieve C‐N ratio 20:1. Triplicate 125 L polyethylene tanks containing 500 postlarvae each (9.40±1.88 mg) were evaluated. Specific growth rate was significantly (p < 0.05) greater in the BFT‐C (8.40 ± 0.24 % day‐1) than BFT (7.23 ± 0.21 % day‐1) and control (7.12 ± 0.42 % day‐1) groups. Postlarvae survival was significantly (p < 0.05) increased with the BFT‐C (94.46 %) treatment than the BFT (87.33 %) and control (82.60 %). A significantly lower food conversion ratio (1.08) was obtained (p <0.05) in BFT‐C than both the BFT (1.73) and control (1.90), possibly due to significantly higher biofloc crude protein and lipid contents in the BFT‐C than BFT. Postlarvae whole‐body protein and lipid contents were significantly elevated (p <0.05) in BFT‐C compared to the BFT and control treatments. Economics of gross return, net return, and benefit‐cost ratio were significantly better at BFT‐C (p <0.05) than in either BFT or control. This study indicates that copepod additions with BFT enhanced prawn postlarvae survival, growth, whole body protein and lipid, as well as economics, which could augment productivity and sustainability in this industry.