The year-round salinity level of the South-West coastal region provides the opportunity for horizontal and vertically expansion of prawn farming is, therefore, enormous. If prawn and green back mullet could be cultured along with shrimp it would be an appropriate technique to minimize the production loss of farmers due to sudden disease outbreak in main crop of shrimp. By considering these backdrops, the current study was carried out to investigate the production performance of these three species in polyculture with different stocking densities.
On 30 April 2018, after production of sufficient plankton required quantity of specific pathogen free (SPF) shrimp postlarvae (PL) was acclimatized with the pond water and stocked to the in-pond nursery made up of nylon net and bamboo frame. Shrimp and green back mullet were stocked at a rate of 25,000 and 5,000 individuals/ha respectively in each pond whereas prawn were stocked at a rate of 10000, 15000 and 20000 individuals/ha under treatment-1 (T1), treatment-2 (T2) and treatment-3 (T3), respectively. Green back mullet and prawn were stocked in 27 may, 2018 when salinity was decreased. Before stocking the initial mean weights of the fingerlings were measured using sensitive balance (OHAUS Model CS-2000).
Feeding In the nursery, the stocked PL and fries were fed with CP nursery feed. Feed was supplied by spreading at the rate of 100%, 80% and 60% of their estimated biomass on daily basis at 6h intervals in the 1st, 2nd and 3rd week respectively. Shrimp and prawn were fed with commercial CP shrimp feed and green back mullet were fed with commercial CP carp feed at the rate of 10-3% of their estimated body weight.
Growth measurement The growth of experimental fishes was observed weekly basis for each pond by adopting simple random sampling method. At least 30 fishes were sampled with the help of a cast net to measure the growth to assess the health status and to adjust the amount of feed supplied to the fishes.
Physico-chemical properties Water quality parameters such as temperature, water depth, transparency, dissolved oxygen (DO), salinity and pH were determined weekly basis using a Celsius thermometer, a graduated pole, a Secchi-disk, a portable dissolved oxygen meter (HI 9142, Hanna Instruments, Portugal), refractometer and a portable pH meter (HI 8424, Hanna Instruments, Portugal), respectively. Water quality parameters were determined following standard methods (APHA, 1992). Total alkalinity was determined following the titrimetric method according to the standard procedure and methods (Clesceri et al., 1992). arvested by netting and after 178 days of culture each pond was pumped out and all prawn and green back mullet were harvested. After harvesting growth and production of all fishes were estimated and compared.
Data Analysis The mean values for growth, survival and production were tested using one-way analysis of variance (ANOVA), followed by testing of pair-wise differences using Duncan’s Multiple Range Test (Vann, 1972). Level of significance was fixed at 5%. All statistical analysis was done by using the SPSS (Statistical Product and Service Solutions) version21.5. The graphs of water quality parameters were performed using Microsoft Excel.