World Aquaculture 59 protein feed was fed on a isonitrogenous basis to that of the lower protein feed, so shrimp fed the 36 percent CP diet received only 84.2 percent of the ration fed to the shrimp offered the 30 percent protein diet. Rations were adjusted weekly assuming a fixed FCR of 1:1.4, weekly growth of 1.2 g and weekly mortality of one percent. The daily and weekly water quality indicators in the ponds during the experiment were within the acceptable limits for the species. Shrimp fed the higher protein feed on an isonitrogenous basis at the reduced ration level had lower FCR, higher survival and greater yield than those fed the lower protein feed at full ration (Table 4). Although the treatments in the ponds had no replication, the data suggest better performance with the higher protein feed than the lower protein feed when the former was fed on an isonitrogenous basis. Conclusion The studies demonstrated that under limited discharge conditions, better feed utilization can be expected when shrimp are offered a higher protein diet at a reduced ration level compared to a lower protein diet fed at a higher level. Using this strategy as a management tool, a significant reduction in feed utilization can be achieved. The results of the studies clearly depict that under the present experimental conditions shrimp can effectively be raised at high stocking densities with limited water exchange without compromising productivity and with reduced negative environmental impacts from the culture pond effluent. Notes 1Texas Agricultural Experiment Station, Shrimp Mariculture Research Facility, 4301 Waldron Rd., Corpus Christi, Texas 78418. References Cho, S.H. and R.T. Lovell. 2002. Variable feed allowance with constant protein input for channel catfish (Ictalurus punctatus) cultured in ponds. Aquaculture 204:101-112. Cho, C.Y., J.D. Hynes, K.R. Wood and H.K. Yoshida. 1994. Development of high- nutrient-dense, low-pollution diets and prediction of aquaculture wastes using biological approaches. Aquaculture 124:293-305. Cohen J.M., T.M. Samocha, J.M. Fox, R.L. Gandy and A.L. Lawrence. 2005. Characterization of water quality factors during intensive raceway production of juvenile Litopenaeus Table 3. The effect of two commercial diets (30% and 36% CP), when fed at different ration sizes, on mean weights, weekly growth rates, yields, survival and FCR rates in an outdoor tank study with Litopenaeus vannamei when operated under limited water discharge. Treatment Av. Wt* Yield Survival Growth FCR CP–Ration (g) (kg/m3) (%) (g/wk) 30% CP-100% 16.69 ±2.54 a 1.03±0.08 ab 87.7±7.45 a 0.95±0.05 a 1.82±0.13 a 36% CP-84.2% 16.01 ±2.14 a 1.14±0.10 b 89.2±3.43 a 0.91±0.03 a 1.38±0.19 b 30% CP-84.2% 14.46 ±2.09 b 0.98±0.10 a 94.9±4.92 a 0.82±0.07 b 1.66±0.13 a 36% CP-70.9% 13.92 ±2.57 b 1.02±0.05 ab 94.0± 9.76a 0.79±0.05 b 1.33±0.60 b * Mean weight at harvest Column with the same superscript letters suggest no statistically significant differences Table 4. The effect of two commercial diets with 30% and 36% CP, when the higher protein diet was fed at lower ration, on growth, survival and FCR of Litopenaeus vannamei in outdoor ponds under limited water discharge. Diet Av. Wt.*(g) Time (d) Yield (kg/m3) Survival (%) Growth (g/wk) FCR P-30% CP 16.4 137 0.67 55.1 0.84 2.58 P-36% CP 15.8 137 0.80 69.0 0.80 1.88 * Final mean weight vannamei using limited discharge and biosecure management tools. Aquaculture Engineering 32:425-442. Cousin, M., G. Cuzon, E. Blanchet and F. Ruelle. 1991. Protein requirements following an optimal dietary energy to protein ratio for Penaeus vannamei juveniles. Pages 599-606 In S.J. Kaushik, P. Liquet, editors. Fish Nutrition in Practice. Institut National de la Recherche Agronomique, Paris, France. Kureshy, N. and D.A. Davis. 2002. Protein requirement for maintenance and maximum weight gain for the pacific white shrimp, Litopenaeus vannamei. Aquaculture 204:125-143. McIntosh, D., T.M. Samocha, E.R. Jones, A.L. Lawrence, S. Horowitz and A. Horowitz. 2001. Effects of two commercially available low-protein diets (21 percent and 31 percent) on water and sediment quality, and on the production of Litopenaeus vannamei in an outdoor tank system with limited water discharge. Aquacultural Engineering 25(2):69-82. Lawrence, A.L., P. Aranyakananda and F.L. Castille. 1995. Estimation of Dietary Protein and Energy Requirements for Shrimp. Proceedings, American Oil Chemists Association (AOCS) Conference, San Antonio, Texas, Inform 6(4):520521. Tacon A.G.J. and I.P. Forster. 2003. Aquafeeds and the environment: policy implications. Aquaculture 226:181-189. Thakur, D.P and C.K. Lin. 2003. Water quality and nutrient budget in closed shrimp (Penaeus monodon) culture systems. Aquaculture Engineering 27:159-176.
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