2.1 Description of the study area and duration The study was conducted in the pond complex of Bangladesh Fisheries Research Institute, Brackish water Station, Paikgacha Upazilla (22º35.3'N 89º20.2'E), Khulna district, Bangladesh. Pond management of green back mullet was conducted for a period of 5 months (March-July) with three trials (each with 150 days of culture) in 2015 in nine experimental ponds.
2.2 Pond preparation The ponds were prepared by drying, liming the bottom soil (@ 250kg/ha of CaO) and enclosed by fine nylon mosquito net. Then after five days, ponds were filled up with tidal water. Water of the ponds will be treated with rotenone and dipterex, both @ 1.5 ppm to kill all unwanted animals. After removing all dead animals, ponds will be treated with dolomite @ 20 ppm. After five days of liming, water of the ponds will be fertilized with 25 ppm urea and 30 ppm TSP to enhance growth of plankton and waited for a week to allow the water becoming suitable for stocking.
2.3 Stocking of fish After two weeks of fertilization, fingerlings of Green Back Mullet (C. subviridis) were stocked at the rate of 60000, 90000 and 120000/ha under treatment-1 (T1), treatment-2 (T2) and treatment-3 (T3) on 01 march 2015. Before stocking the initial mean weights of the fingerlings were measured using sensitive balance (OHAUS Model CS-2000).
2.4 Feed supply Fry of mullet will be fed with commercial quality feed (35% protein) @ 15% of estimated fish biomass for the 1st 15 days. The rate of feeding will be gradually reduced with the growth of fish and feed will be supplied @ 3% of fish biomass in the last month of culture. Growth of fishes will be checked fortnightly and feed will be adjusted. During the culture trial, in every month all the ponds were limed at the rate of 125 kg/ha to maintain pH and water qualities.
2.5 Growth measurement The growths of fishes of all ponds were monitored fortnightly by using random sampling method. At least 50 fishes were sampled with the help of a cast net to measure the growth to assess the health status and for feed adjustment.
2.6 Water quality parameters The pond environment parameters such as surface water temperature, water depth, transparency, dissolved oxygen and pH was measured weekly using a Celsius thermometer, a graduated pole, a secchi-disk a portable dissolved oxygen meter (HI 9142, Hanna Instruments, Portugal), Salinity by refractometer and a portable pH meter (HI 8424, Hanna Instruments, Portugal). Total alkalinity and ammonia-nitrogen was determined following the titrimetric method according to the standard procedure and methods.
2.8 Harvesting of fish After five months of rearing, the fish were harvested by dewatering the ponds. During harvest, they were counted and individually weighted to assess survival, growth and production. Specific growth rate was estimated as: SGR (% bw/d) = [In (final weight)-In (initial weight]/culture period (days) x 100.
2.9 Data analysis Comparison of treatment mean was carried out using one-way analysis of variance (ANOVA), followed by testing of pairwise differences using Duncan’s Multiple Range Test. Significance was assigned at the 5% level (P>0.05). All statistical analysis was done by using the SPSS (Statistical Package for Social Science) version-17.5.