Application of Polyculture Using Stratified Double Net Cage : A Case Study at Awerange Gulf, Barru, South Sulawesi, Indonesia

Abstract

This research is aimed to develop aquaculture techniques, particularly the use of stratified double floating net cage (SDFNC) for polyculture to increase productivity, and maintain a healthy water ecosystem for sustainable aquaculture. Installation of SDFNC was done at the Gulf Awerange, Barru, South Sulawesi. The polyculture system consisted of macro algae (Euchema cottoni), rabbitfish (Siganus sp.), black tiger shrimp (Penaeus monodon), and Pacific white shrimp (Litopenaeus vannamei). Macroalgae was cultivated by binding to the algae using polyethylene strap transversely from the water surface to a depth of 5 m along the edge cage. A number of 50 ind. m-3 of rabbit fish were farmed in the bottom net cage; 100 ind. m-3 of 12 m3 in total of PL30 Pacific white shrimp and 50 individuals m-3 of 12 m3 in total of PL30 black tiger shrimps were located in the upper net cage. Biomonitoring was carried out by observing the structure of macrobenthic community. The condition of the water at the farmed area was still within the normal range, both at a depth of 1 m and 5 m from the surface, and 1 m of bottom waters. There was a significantly difference between polyculture and reference site, implying that there was a slight environmental disturbance of sedimentary habitat underneath the farm cage. Overall, the area is considerably suitable for the application of SDFNC, with water current range up to 14.1 cm sec-1. The growth of main biotas represented by Siganus sp. and L. vannamei farmed using SDFNC exhibited faster compared to monoculture farm, owing to the relatively high values of the relative growth rate (RGR) (2.3-6.2%) and specific growth rate (SGR) (1.05-1.4%). Key Words: biomonitoring, polyculture, growth rate, Euchema cottoni, Siganus sp.