Effect of feeds, feeding and natural foods on freshwater prawn production
Published: March 15, 2007
By: SHAWN COYLE and JAMES H. TIDWELL - Kentucky State University (Courtesy of Alltech Inc.)
Evaluation of complete feeds, supplemental feeds, and organic fertilization
Feed costs constitute 40-60% of operational costs in production of the freshwater prawn Macrobrachium rosenbergii (D’Abramo and Sheen, 1991). Corbin et al. (1983) suggested that the major portion of macronutrients (protein, etc) for freshwater prawns needs to be supplied by prepared feeds, but that required levels of micronutrients (vitamins and minerals) could be derived from natural productivity, or stimulated productivity of natural foods in the culture ponds.
A better understanding of the role of natural productivity in prawn nutrition and development of methods for selective management of desirable components is needed (MacLean et al., 1989). This could result in decreased production costs based upon providing a combination of pelleted rations and pond organisms to satisfy nutrient requirements (Corbin et al., 1983). This study was designed to evaluate production and population characteristics of pond-raised prawns fed a complete diet, a supplemental diet (a similar formulation but with fish meal and vitamin and mineral supplements removed), or the supplemental diet with an adjunct organic pond fertilization regime to enhance secondary productivity within the ponds. The relationships of treatment to type and quantity of potential prawn forage organisms (benthic macroinvertebrates) were also examined.
Experimental diets were formulated to contain 32% protein. Ingredient composition of the complete diet was similar to that of the diet utilized by D’Abramo et al. (1989) and Tidwell et al. (1993), and contained 15% fish meal. In the formulation of the supplemental diet, fish meal was eliminated, distillers dried grains with solubles (DDGS) was added at 40% of the formulation, and soybean meal was increased slightly to maintain the crude protein level. The DDGS used in the study was a homogeneous composite from seven distilleries.
Treatments were evaluated in triplicate 0.04 ha ponds stocked at 40,000/ha with 0.5 g prawns. Based on sample data there were significant differences between the regression lines for average weights over time (growth) in prawns fed the complete diet and supplemental diet without organic pond fertilization and between those fed the supplemental diet with and without fertilization.
There was no significant difference between regression lines for prawns fed the complete diet and those fed the supplemental diet with an organic pond fertilization regime. At harvest, average values over the three treatments were: yield 943 kg/ha, survival 76%, individual weight 31 g and feed conversion 3.9. Deletion of vitamin and mineral supplements and replacement of fish meal in prawn diets was associated with a reduction (P<0.05) in total benthic macroinvertebrate populations, possibly due to increased predatory pressure by prawns (Figures 1 and 2). In ponds where prawns were fed the supplemental diet, organic fertilization increased (P<0.05) total benthic macroinvertebrates and increased by 15% average prawn weight at harvest. Results indicate that prawns may increase predation when essential nutrients are deleted from prepared diets and that the supply of potential forage organisms may be increased by organic fertilization.
Prawn production and natural food availability in unfed, fertilized, and fed systems
Tidwell et al. (1995) suggested that prawns fed diets with varying nutritional quality in ponds could compensate by increasing predation on macroinvertebrates. Although the nutritional role of natural productivity is obviously important, it remains ill-defined. This lack of understanding limits the potential for developing management procedures to maximize the availability of desirable organisms (Corbin et al., 1983). A second study was designed to generate information on: 1) effects of prawns on macroinvertebrate populations in ponds; 2) invertebrate taxa preferred by prawns as food; 3) level of prawn productivity supported by natural productivity; and 4) relative effects of organic fertilization and formulated feed on macroinvertebrate populations and prawn production.
Relative prawn production rates in unfed, organically fertilized, and fed pond systems were evaluated. Populations of benthic macroinvertebrates that potentially serve as forage organisms in these systems were also evaluated and compared with ponds without prawns to evaluate forage preferences. Juvenile prawns (0.36 ± 0.02 g) were stocked into nine 0.04 ha ponds at a density of 39,520/ha. Prawns in three ponds were not fed, prawns in three ponds were fed a complete diet, and three ponds received organic fertilization. Three additional ponds (0.02 ha) served as controls (not stocked with prawns and receiving no nutrient input).
At harvest, survival averaged 86% overall, and was not significantly different among treatments. Average weights of prawns fed complete feed or raised in fertilized ponds (36 and 33 g, respectively) were not significantly different. Prawns in unfed ponds were smaller (P<0.05) (13 g). Average prawn yields in fed, fertilized, and unfed ponds (1261, 1056, 426 kg/ha, respectively) were all significantly different from each other (Figure 3).
In ponds receiving no nutrient input, macroinvertebrate densities were higher (P<0.05) in ponds without shrimp (controls) than in those stocked with shrimp (Figure 4a). In ponds stocked with shrimp, macroinvertebrate densities in fed and fertilized treatments were greater (P<0.05) than in the unfed treatment, but not significantly different from each other. Insect taxa showed a greater negative response to prawn predation than noninsects (Figure 4b). Non-insect taxa demonstrated a more positive response to fertilizer and feed than insects (Figures 4c and d).
Although prawn production in organically fertilized ponds was surprisingly high (>1000 kg/ha), economic analysis demonstrated higher net returns when prawns were fed a prepared diet, principally due to the production of greater numbers of large, high value prawns (Figure 5).
Figure 1. Effects of a complete diet containing fish meal and a supplemental diet based on DDGS with or without organic pond fertilization on macroinvertebrate numbers.
Figure 2. Effects of a complete diet containing fish meal and a supplemental diet based on DDGS with or without organic pond fertilization on macroinvertebrate types.
Comparison of phase feeding and standard prawn diets in intensive prawn production
Recent developments in prawn production technologies such as added substrate, increased stocking densities, size grading, and increased feed rates have increased production rates from 900- 1000 kg/ha to over 2500 kg/ha (Figure 6). While prawn can receive substantial nutritional benefit from natural foods at the lower biomass densities, at higher production rates prawns are likely more dependent on prepared diets. To ensure that maximum production is being achieved by these new production technologies, growth rates must not be nutritionally constrained. This study was conducted to compare the current recommended technology of phase feeding of different quality feedstuffs to prawn of different sizes with the feeding of a high quality penaeid diet throughout the production season.
Figure 3. Effect of formulated feed and organic fertilization on freshwater prawn production.
Figure 4. Effect of formulated feed and organic fertilization on macroinvertebrates, insect and non-insect taxa of freshwater prawn ponds.
Figure 5. Effect of formulated feed and organic fertilization on prawn size distribution.
A previous study indicated that even when prawn production is intensified beyond 2000 kg/ha the use of higher protein, high fish meal diets early in the production season is not justified. A follow-up study was designed to determine if the phase feeding regime was economically justified compared to the use of a 32% protein diet throughout the production period.
Two treatments were evaluated. Treatment 1 was phase feeding (current technology, Control) where prawn were fed unpelleted diets based on distillers grains with solubles (DDGS) for the first four weeks, for weeks 5-12 a 28% protein prawn diet, and for weeks 13-18 a 40% protein penaeid diet. In Treatment 2, prawn were fed the 40% protein penaeid diet throughout the entire production period. Feeding rates in both treatments were based on a feeding table.
There were three replicate 0.04 ha ponds for each treatment. All ponds were stocked at 59,280/ha and provided with artificial substrate in the form of polyethylene ‘safety fence’ oriented vertically to increase available surface by 50%. At harvest, there was no significant difference in average weight, survival, total production, or feed conversion in prawns fed according to the two diet regimes. However, the number of prawns achieving market weights (>20 g) was significantly higher in the phase-fed treatment and total production of premium size prawns was also higher in phase-fed ponds (Figure 7).
Feed costs were 9% higher in phase-fed ponds.
If differential pricing for different size categories is not available, then phase feeding may not be justified. If the market pays higher prices for larger prawn sizes, then phase feeding may be advantageous.
Figure 6. Effect of graded amounts of added substrate on prawn production.
Figure 7. Effects of phase-feeding versus a panaeid diet on percentage of marketable prawn produced.
Summary
- Prawns can increase utilization of natural foods if fish meal or macronutrients are eliminated from feed.
- The carrying capacity of an unfed pond is approximately 425 kg/ha. Organic fertilization can support approximately 1000 kg/ha.
- Pelleted feeds primarily benefit large individuals, which cannot forage as efficiently.
- Phase feeding is based on efficient utilization of natural foods at low prawn biomasses. Initially organic fertilizers are used. Prawn pellets are phased in as prawn biomass increases and natural foods become depleted. High quality penaeid diets are provided to provide large individuals with access to nutrient dense food items.
- Use of penaeid diets through the production season does not appear to be economically justified, even at prawn production rates >2,000 kg/ha.
- Use of prawn pellets through the production season appears to be the most economical feeding method unless the market is based on large individual sizes (>45 g).
References
Authors: SHAWN COYLE and JAMES H. TIDWELLCorbin, J.S., M.M. Fujimoto and T.Y. Iwai, Jr. 1983. Feeding practices and nutritional considerations for Macrobrachium rosenbergii culture in Hawaii. In: CRC Handbook of Mariculture (J.P. McVey, ed). CRC Press, Boca Raton, Fl, pp. 391- 423.
D’Abramo, L.R., J.M. Heinen, H.R. Robinette and J.S. Collins. 1989. Production of freshwater prawn Macrobrachium rosenbergii stocked as juveniles at different densities in temperature zone ponds. J. World Aqua. Soc. 20:81-89.
D’Abramo, L.R. and S.S. Sheen. 1991. Nutritional requirements, feed formulation and feeding practices for intensive culture of the freshwater prawn Macrobrachium rosenbergii. Rev. Fisheries Sci. 2:1-21.
Karplus, I., G. Hulata, G.W. Wohlfarth and A. Halevy. 1986. The effect of density of Macrobrachium rosenbergii raised in earthen ponds and their population structure and weight distribution. Aquaculture 52:307-320.
MacLean, M.H., K.J. Ang, J.H. Brown and K. Jauncey. 1989. The effect of organic fertilizer and formulated feed in pond culture of the freshwater prawn, Macrobrachium rosenbergii (De Man): Prawn production. Aqua. Fisheries Man. 20:399- 406.
Tidwell, J.H., C.D. Webster, D.H. Yanceyand L.R. D’Abramo. 1993. Partial and total replacement of fish meal with soybean meal and distiller’s byproducts in diets for pond culture of the freshwater prawn (Macrobrachium rosenbergii). Aquaculture 118:119-130.
Tidwell, J.H., C.D. Webster, J.D. Sedlaceck, P.A. Weston, W.L. Knight, S.J. Hill, Jr., L.R. D’Abramo, W.H. Daniels, M.J. Fuller and J.L. Montanez. 1995. Effects of complete and supplemental diets and organic pond fertilization on production of Macrobrachium rosenbergii and associated benthic macroinvertebrate populations. Aquaculture 138:169-180.
Aquaculture Research Center, Kentucky State University, Frankfort, Kentucky, USA
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