Variable feed allowance with constant protein input for the pacific white shrimp Litopenaeus vannamei reared under semi-intensive conditions in tanks and ponds

Feed input may be reduced in shrimp aquaculture by increasing the protein density of the diet modifying the feeding rate so as to deliver the desired amount of nutrients. To evaluate this strategy, two parallel growth trials were conducted with juvenile Litopenaeus vannamei. In an outdoor tank trial, juvenile (0.57 ± 0.01 g, n = 30) shrimp were reared for 56 days and fed two practical diets formulated to contain 30% or 40% crude protein (CP). Each diet was offered at three different feeding rates (50%, 75%, and 100% ration). At the end of the trial, final weight of shrimp offered the 30% CP diet ranged from 8.1 to 10.3 g, and 8.7-11.3 g for shrimp fed the 40% CP diet. Final weight, weight gain, FCR, and PCE was reduced significantly at every reduced feed ration (50 and 75%). There were no significant differences in final weight (10.3 g, mean weight) of shrimp offered the two treatments with similar protein inputs (30-100% and 40-75%). However, FCR was significantly lower for the 40-75% treatment (1.1 versus 1.4). To demonstrate the effect of variable feed allowance under practical pond conditions 12 ponds were stocked at 35 shrimp/m2 (0.04 ± 0.04 g, n = 56) and assigned three treatments (30-100%, 30-75%, and 40-75%). A fourth treatment (40-100%) was initiated two weeks later utilizing two additional ponds to allow observational data collection. At the end of the trial (114-121 days) the final weight (19.7-21.7 g), FCR (1.0) and survival (75-88%) between the treatments 30-100% and 30-75% were not significantly different. However, production was significantly higher for the treatment 30-100% than for the treatment 30-75% (6482 versus 5054 kg/ha). Based on observational data, yield was numerically higher for the 40-75 treatment than for the 30-75 treatment and it tended to be lower than that of the 30% CP diet offered at standard rate (30-100%). This study demonstrates that increasing the nutrient density (protein content) of the shrimp feed allows for a reduction of feed input without affecting the growth performance of shrimp in tanks. Results of the tank trial could not be verified through the pond trial due to the loss of some experimental units. As interactions of natural productivity and feed distribution may alter the results under pond production conditions further research in ponds is warranted.