Cage polyculture of the Pacific white shrimp Litopenaeus vannamei and the Philippines seaweed Kappaphycus alvarezii

Shrimp ponds are traditionally set up in marine coastal areas and can lead to adverse impacts on the environment, especially the destruction of large areas of mangrove forests. Cage culture can be a more sustainable alternative for rearing shrimp, and polyculture with seaweeds may also improve sustainability. The aim of this study was to test the feasibility of co-culturing the Pacific white shrimp Litopenaeus vannamei and the Philippines seaweed Kappaphycus alvarezii in floating cages. The experiments were carried out in an offshore area near the Aquaculture Research Center of São Paulo State's Fishery Institute in Ubatuba — SP — Brazil (24°26′S; 45°04′W). Experimental grow-out cages (1.00 m long × 1.00 m wide × 1.00 m deep) were constructed with a polyester/PVC 5 mm-mesh and fixed in PVC floating frames. Postlarvae of L. vannamei were acclimatized and nursed in cages for 20 and 53 days, respectively. Afterwards, juveniles (2.39 ± 1.62 g) were transferred to 6 experimental grow-out cages at a density of 100 shrimp/m2. Commercial pellets consisting of 35% crude protein was supplied once a day, and shrimp were harvested after 103 days of growth. In order to test the use of available space in the water column, thalli of the seaweed K. alvarezii were fixed on ropes and attached to floating tubes and set up inside 3 shrimp grow-out cages. Shrimp yield reached production rates as high as 3.23 kg/m2/yr with a mean of 2.36 ± 0.76 kg/m2/yr. Seaweed production reached rates of 23.70 kg/m2/yr with a mean of 17.47 ± 5.71 kg/m2/yr. There were no negative interferences in co-culturing shrimp and seaweed inside the same cage. Student's t-test showed no statistical differences between the two treatments (monoculture and polyculture) for shrimp weight gain, survival rate, and food conversion ratio.