An assessment of intensive white shrimp (litopenaeus vannamei) and red tilapia (oreochromis spp.) polyculture | |
| Author | Yuan, Derun |
| Subject(s) | Shrimps Red tilapia |
| Note | A dissertation submitted in the partial fulfillment of the requirements for the degree of Doctor of Technology and Science in Aquaculture and Aquatic Resources Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Four experiments were conducted to develop an intensive polyculture system of white shrimp (Litopenaeus vannamei) and red tilapia (Oreochromis spp.) as an alternative to intensive shrimp monoculture to improve its productivity, increase nutrient utilization efficiency, reduce environmental impacts and improve profitability. Intensive zero-waterexchange system was used in all experiments. White shrimp were stocked at a rate of 60 postlarvae m-2 and fed with commercial pellets. Red tilapia of different sizes were stocked at different densities based on the objectives of each experiment. All experiments were conducted in 2.5 x 2.0 x 1.2 m out-door cement tanks with sufficient aeration. Water depth in all tanks was maintained at 1 meter and salinity was maintained at 20 ppt. A 3 X 2 factorial design was used in Experiment I by stocking small (13.8±0.2 g) or large (41.9±0.3 g) mono-sex tilapia fingerlings into shrimp culture tanks separately at low (0.4 fish m-2), medium (0.8 fish m-2) or high (1.2 fish m-2) density with shrimp monoculture as the control treatment. The specific objectives were to investigate the effects of tilapia stocking densities and sizes on shrimp growth, water quality, nutrient utilization efficiency and economic performances under a fixed feeding regime in comparison with shrimp monoculture control treatment. The highest shrimp survival rate of 66.8% was observed in the small-sized lowdensity tilapia treatment, which was significantly higher than those in other treatments and the control. The small-sized low-density tilapia treatment had the highest shrimp yield and lowest feed conversion ratio, which were statistically similar to those in the control and the large-sized low-density and small-sized medium-density tilapia treatments, but significantly better than those in the other treatments. Factorial analyses revealed that the increase of tilapia density from 0.4 to 1.2 fish m-2 and size from 13.8 to 41.9 g negatively affected shrimp production performance but increased the combined yield of shrimp and tilapia. Shrimp and tilapia together in the polyculture systems recovered 36.0 - 49.5% of the total nitrogen inputs and 14.2 - 26.5% of the total phosphorous inputs, which were significantly higher than those recovered by shrimp alone in the monoculture system (27.1% of the total nitrogen and 8.9% of the total phosphorus inputs). The nutrient recovery efficiency increased with increased tilapia stocking density and size. Polyculture with small-sized low-density tilapia treatment had the best economic performance among all treatments and control, and significantly better than small-sized high-density, largesized medium-density and large-sized high-density tilapia treatments. The suitable stocking density and size of red tilapia identified in this experiment were 0.4 fish m-2 and 13.7 g, respectively, under the fixed feeding condition for shrimp. Red tilapia could be stocked at a higher density up to 1.2 fish m-2 and a larger size up to 42 g to maximize system productivity and minimize nutrient waste without affecting shrimp survival, but they could negatively affected shrimp production and economic performance. Competition of tilapia for shrimp feed was suspected to be the reason for the significantly lower shrimp production in small-sized high-density, large-sized medium-density, and large-sized high-density tilapia treatments than in monoculture control. Experiment II was an extension of Experiment I to investigate the effects of addition of red tilapia at different densities and sizes on feeding behaviors of shrimp and tilapia in polyculture systems. At the end of Experiment I, shrimp were sampled at an hourly interval for 6 consecutive hours after shrimp feed was applied and tilapia were sampled one time at the end of the first hour after shrimp feed was applied. Gut contents of both shrimp and tilapia were examined microscopically to identify pellet parts, natural iv food of plant origin mainly consisting of phytoplankton, and natural food of animal origin mainly consisting of zooplankton and benthos. The proportion of each food item was determined by counting identifiable particles of the food item and divided by the total food particles observed. The objective was to assess the effects of tilapia stocking densities and sizes on natural food and artificial feed contribution to shrimp and tilapia diets and feed competition between tilapia and shrimp in order to get better understanding on the interactive mechanism between shrimp and tilapia. Pellet parts accounted for 60.2% to 69.4% of identifiable food particles found in shrimp guts, indicating the importance of artificial feed in intensive shrimp culture. Tilapia had 4.6% to 6.6% of identifiable food particles of pellet origin in their guts. Natural food was the major nutrient source for tilapia. Shrimp in polyculture treatments with tilapia stocking density higher than 0.4 fish m-2 had significantly lower proportion of artificial feed in their guts regardless tilapia stocking sizes. The low proportion was probably caused by physical disturbance of tilapia on shrimp and direct consumption of shrimp feed by tilapia. Regression analysis revealed that both shrimp survival and production were positively related to the proportion of pellet parts in shrimp guts. Timewise comparisons showed that the proportion of pellet parts in shrimp guts increased significantly from the first hour to the end of the second hour after feed was applied, and then declined onwards. Tilapia gut contents were not significantly affected by either tilapia stocking density or size. Experiment III was also based on Experiment I, in which the abundances of total bacteria, presumptive Vibrio and pathogenic luminous Vibro in culture water were measured by plate-counting the organisms in water samples taken at the beginning, middle and end of the experiment. The objectives were to evaluate the effect of presence of tilapia at different densities and sizes in shrimp-tilapia polyculture on bacteria abundances and further to analyze the relationship between bacteria counts and shrimp survival. The counts of total bacteria, presumptive Vibro and luminous Vibro increased significantly from the first to second sampling. The total bacteria count continued to increase from the second to third sampling. The counts of presumptive Vibro and luminous Vibro however decreased from the second to third sampling. Tilapia presence at different stocking densities and sizes did not resulted in significant differences in total bacteria and presumptive Vibrio counts among treatments, and between any polyculture and the control treatment, nor a relationship between the two counts and shrimp survival could be established. Tilapia presence in polyculture however significantly reduced luminous Vibrio at the end of the experiment in comparison to shrimp monoculture. This probably partially explained overall better shrimp survival rates in shrimp-tilapia polyculture than in the monoculture system observed in this study. Experiment IV was conducted in 15 cement tanks (2 x 2.5 x 1 m) to assess the effects of different feeding methods for intensive polyculture of white shrimp and red tilapia on shrimp growth, water quality, nutrient recovery and production performance. Shrimp stocking procedure was the same as of Experiment I. Red tilapia fingerlings with an initial weight of 47.5 g were stocked into the shrimp tanks four weeks later at the density of 0.8 fish m-2. The experiment followed a 2 x 2 factorial design with shrimp feeding (satiation or restricted feeding) as the first factor and tilapia feeding (with or without supplementary feeding at 1% body weight daily) as the second factor. Three tanks with shrimp monoculture were set as the control treatment. Shrimp satiation feeding was determined by close check of feeding trays two hours after feeding and v shrimp restricted feeding followed the same feeding level of the control tanks. All treatment combinations were randomly allocated to the tanks in triplicate. Shrimp were fed three times a day with commercial pellets, and tilapia in supplementary feeding treatments were fed with floating tilapia pellets half an hour before shrimp feeding started. The mean survival rate of shrimp, ranging from 62% to 70%, was the highest in the tanks with satiation feeding of shrimp and supplementary feeding of tilapia, and the lowest survival rate was observed in monoculture control tanks (P<0.05). Shrimp grew to 10.3 to 12.3 g in 70 days. The highest yield of shrimp was obtained from the treatment with shrimp satiation feeding and tilapia supplementary feeding, which was significantly higher than those in treatments with shrimp restricted feeding and shrimp monoculture (P<0.05), but similar to the treatment with shrimp satiation feeding and tilapia without supplementary feeding. Feeding tilapia significantly reduced shrimp FCR (P<0.05) in comparison with no tilapia feeding, while feeding shrimp at different levels did not significantly affect shrimp FCR. Tilapia growth was similar among all treatments except the treatment with shrimp restricted feeding and tilapia without feeding, which had significantly lower tilapia production than other treatments. Shrimp and tilapia together in polyculture treatments recovered 43.6 – 45.5% of the total nitrogen and 18.1 – 19.2% of the total phosphorus inputs which were significantly higher than those recovered by shrimp alone in monoculture (37.4% of the total nitrogen and 12.6% of the total phosphorus inputs). In terms of profitability, the polyculture with shrimp satiation feeding and tilapia supplementary feeding performed the best with an increase of net income by 11% over monoculture control (P<0.05). In contrast, the polyculture with shrimp restricted feeding and tilapia without feeding had the lowest net income which was significantly lower than that of monoculture control (P<0.05). The study concluded that white shrimp could be polycultured intensively with red tilapia with improved productivity, nutrient utilization efficiency, environmental friendliness and profitability. Polyculture of shrimp with tilapia is a better system alternative to intensive shrimp monoculture with proper tilapia stocking density and size and feeding methods. It was recommended that tilapia in such a polyculture system can be stocked at a density up to 0.8 fish m-2 and stocking size up to 48 g where shrimp were stocked at 60 pieces m-2. Shrimp should be fed to satiation and tilapia supplemented with floating pellet feed at 1% body weight daily to achieve the best production performance. |
| Year | 2011 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Aquatic Systems (AS) |
| Chairperson(s) | Yakupitiyage, Amararatne; |
| Examination Committee(s) | Lin, Chang Kwei;Anal, Anil Kumar; |
| Scholarship Donor(s) | Little, David; |