- Immunostimulants, probiotics and phage therapy: alternatives to antibiotics
- Designing a biosecurity plan at the facility level:
criteria, steps and obstacles
- Importance of host-viral interactions in the control of shrimp disease outbreaks
- Nutrition and shrimp health
- Practical feed mnagement in semi-intensive systems for shrimp culture
- Selective breeding of shrimp
- Better management and certification in shrimp farming
Practical feed management in semi-intensive systems for shrimp culture
Crustacean farming has developed during the past forty years with an average annual growth rate of 18% which is the highest for aquaculture production (FAO 2009). In 2006, aquaculture accounted for 70% of shrimp and prawns produced worldwide, accounting for 23% of the total value from aquaculture production (FAO 2009). The industry has also seen a growing concern for improving the profitability and sustainability of their practices, especially in relation to nutrition and feed management. Modern shrimp feeds are generally nutritionally adequate and provide essential nutrients in the proportions necessary for good performance. However, good performance is only obtained if the feed is properly applied and environmental conditions are favorable for good growth and survival. Shrimp feed usually represents 40 to 70% of the variable costs of most farming operations, and constitutes the major pollutant source for aquatic ecosystems. Improvements are needed with the use of high-quality, water-stable feeds that contain no more nitrogen and phosphorus than necessary. In addition, appropriate feeding techniques should be implemented to prevent both overfeeding and wasted feed. Suitable feed inputs may improve water and soil quality, as well as reduce production costs.
Feed management comprises selection, evaluation and acceptance of the feed at the farm, inventory management and storage, and finally delivery to the shrimp in ponds through appropriate feeding practices. The first several steps are related to feed quality, while the last one is critical for assuring sustainable production and profitability. Despite the importance of feed management in aquaculture, few scientific studies have focused on evaluating different feed management techniques (Davis et al. 2006). Even fewer studies have specifically addressed feed management as it relates to the culture of shrimp in semi-intensive systems.
At the farm level, the first step in proper feed management is to select and purchase a feed that will maximize production under the conditions in which shrimp are cultured. Performance of shrimp to feeds can vary among farms as well as among ponds from the same farm. It is a well known fact that all feeds are not created (or manufactured) equal; hence selection of an appropriate feed that meets all of the dietary requirements of the shrimp is paramount for proper feed management. The dietary requirements of commonly cultured shrimp species such as the Pacific white shrimp, Litopenaeus vannamei, are well known (D’Abramo et al. 1997), and most modern feed mills utilize proven and tested formulations. Farmers should exercise extreme caution when requesting alterations to existing formulations to cut costs, as saving money on this end might translate to money lost at the end of the production season.
One factor that should be considered when selecting a feed and applying it to a production system is that feed conversion varies with the nutrient density of the diet and feed inputs must be adjusted accordingly. If higher concentrations of a nutrient are in the feed, we would offer less feed. For example, a well-balanced diet containing 40% protein and fed at 75% of the ration delivers the same protein as a diet containing 30% protein offered at 100% ration (with this being near or at satiation). Although the higher protein feed is more expensive the lower ration size used with this diet can compensate for the differences in feed cost (Patnaik and Samocha 2009). Understanding the potential feed conversion of a good feed is critical to feed management. Using a few assumptions from nutrient retention we can make a few quick calculations with regards to feed conversion ratio (FCR). To produce 1 kg of shrimp using a 40% crude protein feed we would need 1.25 kg of feed, which means an FCR equal to 1.25:1.0. On the other hand, to produce the same 1 kg of shrimp using a 30% crude protein feed we would need 1.67 kg of feed, which means an FCR equal to 1.67:1.0. If the lower-protein diet meets the nutritional requirements of the animal under a given set of conditions, increasing protein intake by increasing the daily ration does not lead to better growth, but raises feed conversion ratio as well as pollution loading of the system. Similarly, if one chooses to increase the level of protein in the diet and feed the same quantity, growth does not improve, but feed conversion stays the same. In this case, the efficiency of protein use decreases and nitrogen waste, a by-product of protein metabolism, increases. Matching nutrient density of the diet with proper feed inputs to provide just enough nutrients to maintain the desired level of growth is very important.
Feed evaluation and acceptance
Feed evaluation should typically be performed for each batch of feed that comes into the farm and should commence immediately following the arrival of the feed at the farm. Parameters that should be evaluated include physical characteristics such as color, water durability, ingredient particle size, pellet size, moisture, excessive fines, and presence of mold. The color of a pellet is not important to shrimp in terms of attractability, consumption or nutritional quality of the feed. It is indicative of ingredient composition and manufacturing variables. Many commercial shrimp producers prefer feeds dark in color, which historically was associated with the presence of dark fish meal. However, one has to realize that the color of fish meal will vary from batch to batch, source of the fish as well as processing conditions; furthermore, there are numerous light and dark ingredients (fish meal being one) that are often utilized resulting in variations in pellet color. For example, switching fish meal types or increasing the levels of plant protein sources may produce lighter color, which does not mean an inferior quality of feed, simply a shift in color. Quite often, the smell of the feed is also evaluated, as with color the smell has little to do with attractability or quality of the feed, although, it does correlate to ingredient content and rancidity of the oils. Shifts in color and smell are related to ingredient content but also vary with ingredient batches so they are not clear indicators of feed quality.
Feed pellets have to be consumed by the shrimp quite often after an extended period of time in the water (e.g. 30 minutes); hence they should not fall apart before they are ingested by the shrimp, a trait that is known as the water stability of the feed. The fact that shrimp consume feed slowly requires feed with higher water stability than organisms that eat floating feed. The pellet durability and water stability of the feed is dependent on proper manufacturing procedure and inclusion of natural ingredients or artificial bindings. A pellet stability of 3-4 hours is appropriate. Evaluation of this characteristic is very subjective, and involves random sampling from each feed shipment. There are numerous techniques to estimate feed stability over a short period of time or methods using longer time periods. As there is no standard method, it is more important to be consistent in how this is done than following any particular procedure. For instance, a sample of approximately 100 pellets is dropped in a beaker containing pond water to measure percentage of floating pellets (minimum) and visually observe pellet stability. Similarly, a quantified amount of feed can be directly submerged in water (e.g. 100g placed in a beaker of water) or submerged using a porous container (e.g. tea strainer) and allowed to degrade. Percentage of the feed that is lost or disintegrated is recorded at a specific time interval or intervals and compared to standards (Figure 1). These results could be either visually quantified, or actual weight losses determined. The higher the weight loss over a given time frame, the lower the water stability of the pellet.
Figure 1. Determining feed stability
Ingredient particle size is another factor that needs to be considered. Ingredient particle size is dependent on the grinding process, and affects both the binding and physical formation of the pellet. In addition it can also influence consumption due to the ability of shrimp to reject/select small particles, which may cause loss of availability of nutrients. Feed particle size depends on the size of the shrimp, ranging from very small in larval feeds (less than 50 microns) to 3/32 in diameter (2.38 mm) in production diets to over 1/8 inch diameter (3.18 mm) in some maturation feeds. It is imperative that farmers offer the appropriate size feed depending on where the shrimp happens to be at that point in its lifecycle. Differences in size of feed particles are related to shrimp feeding behavior and adequate feed distribution. Typically, the manufacturing of crumbles (fine, medium and coarse) requires fracturing 3/32 inch diameter pellets with a roller type crumbler. Hence, feed ingredients must be adequately mixed to maintain similar nutrient composition in all particles within the pellet.
Contamination of feed by mold is also a problem faced by farmers, particularly those in high humidity environments. Feed may be contaminated by a greenish-brown mold (Aspergillus flavius) due to improper handling of ingredients and processing, or improper transportation and/or storage. Feed contaminated with mold must be rejected at the moment the feed is received at the farm. Training of personnel to identify potential problems with feed should be a priority in capacitating programs.
In addition to the previous evaluations it is recommended that proximate analysis of the feed be determined on a regular basis, every three to six months. This may be performed by independent analytical laboratories, and results should be compared to corresponding values provided by the feed mill. When implementing such quality control measures it is critical that one properly samples the feed, identifies the batch(s) that was sampled, and provides feedback to the mill. Proximate analyses will not be identical to the guaranteed analyses but should be reasonably close. Furthermore, this will also provide information on the variability of the nutrient content of the feed which is a good indicator of quality control standards at the feed mill.
Following a comprehensive evaluation of the feed, a decision to accept or reject the use of the feed at the farm has to be made. This decision is usually based on one or more of the parameters evaluated for a specific batch of feed. Evaluation of parameters for each specific batch of feed needs to be conducted in a timely fashion and as soon as possible following the arrival of the feed at the farm. Should a problem be detected with a specific batch of feed the manufacturer should be immediately notified. Once the feed has been accepted by the farmer, the feed manufacturers are less likely to accept or acknowledge problems if much time has elapsed following delivery to the farm. Acceptance of the feed at the farm is critical and leads us to the next step in proper feed management.
Inventory management and feed storage
Shrimp farms typically receive feed in polypropylene bags each weighing from 25 to 40 kg, with minimum batches of about 10 tons. In some locations feed is transported in bulk via a feed truck to the farm and stored in feed bins. This is the most cost effective and best method to move feed, albeit it is not available in many countries. Proper storage of feed requires a storage building to avoid moisture and excessive heat which may create ideal conditions for development of fungus, and also reduce nutritional quality of the feed. Feed storage buildings should be constructed of either corrugated metal sheeting (walls, roof) or have concrete walls with a concrete floor. Feed should be stacked in pallets up to 5 to 7 layers above the concrete floor, and then include another pallet to continue stacking feed. Stacks must be separated by about 30 cm each to provide aeration among those pallets, and also they must be separated from walls about 30-50 cm (Figure 2). Contact with walls will lead to temperature differential and subsequent moisture migration which leads to the development of fungi. It also can cause structural problems with the building. Labeling of bags should include manufacturer, date manufactured, mill location, proximate analysis, and list of ingredients.
Use of appropriate inventory techniques must be implemented to allow use of older feed first. Feed inventory should be minimized to reduce the holding time for feeds. The use of feeds older than three months post-manufacture is discouraged albeit there are numerous situations where this cannot be avoided. Large farms might choose to have feed storage sub-stations to optimize feed delivery. These sub-stations must meet minimal requirements including a concrete floor and protection against rain to avoid feed losses. It is also a good idea to train personnel to randomly sample feed on a routine basis, particularly if the feed remains on the farm for more than a couple of weeks prior to being offered to shrimp. This can be accomplished by randomly selecting feed bags at the farm and checking them for mold or deterioration. Most farms implement their own system of checks and balances to ensure feed is offered to shrimp in a timely manner following arrival at the farm. This will ensure that shrimp are receiving a high quality feed at all stages of the production cycle. Since feed is usually the highest cost associated with semi-intensive shrimp farming, extreme care and caution must be taken to allow none of it to go to waste.
Figure 2. Feed storage
Feed management relates to pond preparation, as well as other activities directly related to feed such as point of application, time of application, number of offerings, water quality considerations, rate of feeding, and nutrient delivery.
Shrimp rely on benthic habitat for natural foods and cover. Maintaining a healthy low organic pond bottom is an important component of the culture system and feed management strategies. A properly prepared pond will have enhanced natural productivity and provide a substantial portion of nutrition from non-feed sources. Pond fertilization in the weeks immediately before the stocking of post-larvae is usually implemented to achieve this goal. This source may have a great impact in extensive to semi-intensive production, while its importance is reduced in intensive production systems with higher stocking densities. Pond fertilization is especially important during the first several weeks of production, when distribution of feed to post-larval and juvenile shrimp can be problematic.
Feed Distribution and Frequency
Feed distribution techniques vary based on the size of shrimp and stage in the production cycle. During the first several weeks of culture, shrimp farmers usually provide a small amount of feed around the edge of the pond to supplement nutrition from primary productivity. As the shrimp begin to grow feed is subsequently distributed homogeneously in the pond. Feed distribution can be accomplished using a number of different methods ranging from small boats that apply feed following a zig-zag pattern (Figure 3 a), automatic feeders (Figure 3 b), or even offering the ration in small amounts of feed over many feed trays that have been distributed evenly in the pond (Figure 3c). Some farms also employ land-based blower equipment that are capable of distributing feed out to distances of 15 m from the pond bank (Fox et al. 2001). In some farms feed trays are also used as indicators of feed consumption. Limitations in each of these methods are related to labor, equipment, and time to perform those operations.
It is worth noting that supervision of personnel responsible for feeding is absolutely imperative for sustainable operation of any commercial shrimp farm. Due to the difficulty of supervising personnel during nighttime hours, most commercial shrimp farms restrict the majority of their feeding to daytime hours. In the past some commercial operations have included night rations; however there is no clear benefit of such practices and its use has been discontinued due to practical issues and not being cost-effective (Fox et al. 2001). Feed distribution is an essential component of proper feed management and involves adequate personnel management and training as it relates to feeding practices. Time of application and number of offerings varies greatly among farms, but there is a general trend toward feeding a minimum of two and up to four times a day, starting between 6:00 am to 8:00 am, and ending around 4:00 pm to 6:00 pm.
Practical feeding guidelines
The rate of feeding offered to commercial shrimp production ponds, has been typically calculated based on feed guideline tables (Table 1). These guidelines are based on a percentage of the pond shrimp biomass fed as dry weight. That biomass in turn depends on the estimated number of shrimp (survival) and the mean weight of the shrimp (growth) which must be monitored on a regular basis. Also, as mentioned above, it is common to adjust daily feed allocations based on morning dissolved-oxygen levels, temperature, and quantification of feed remaining on feed trays, as well as past performance of the culture system. These estimations have been found to represent fairly appropriate feed inputs during the first half of the production cycle, but then later in the production cycle those feed inputs tend to continually rise without regards to growth of the shrimp with consequent high feed conversion ratios. For example, given a 35%-protein diet, a current feeding chart might indicate that 10-g shrimp should be fed 2.8% of their body weight, which means they would be offer 0.28 g per day or 1.96 g per week. If 1 g of growth per week is assumed, the feed conversion ratio is equivalent to 1.96:1.0. Then, when the shrimp reaches 14 g, traditional feeding table suggests 2.2% of their body weight or 2.16 g of feed per week, if the shrimp is still growing 1 g per week the FCR would rise to 2.16:1.0. These examples display poor understanding of feed management as well as the desire to push the system. This is exemplified by “if shrimp are growing very good we increase feed inputs, if shrimp are growing just average we increase feed inputs and if the shrimp are not growing we increase the feed inputs” or in other words all management leads to increased feed inputs. The end result is overfeeding, which causes contamination of pond bottoms with accumulation of hydrogen sulfide in anaerobic pond sediments, increased biochemical oxygen demand (BOD), reduction in dissolved oxygen (DO), reduction in feed consumption, and finally increase mortality. In addition, inputs of feed-associated pollutants also increase in the system. On the other hand, underfeeding may result in reduced growth rates and increase mortality due to elevated stress and/or secondary infections.
In order to optimize current feed management practices, Davis et al (2008) recommended a modified approach which considers the expected feed conversion ratio and historical data for the farm. Historical data specific for each farm is essential because growth rates vary with species, genetic line, and environmental conditions. To illustrate if a pond is being over fed it is necessary to understand what the “theoretical” feed conversion would be in the absence of natural productivity. This could be determined under laboratory conditions or we can make a few assumptions and come up with a reasonable number. For example we know shrimp are about 15% protein and that net protein retention is around 30%. Hence to grow 1 kg of shrimp (1000g) we would have to grow 150 g of protein (1000 x 0.15) and to produce this we would have to feed 500g of protein (150/0.3). If we use a 35% protein diet that means we have to feed 1.4 kg of feed (500/0.35). That is to say it takes 1.4 kg of a 35% protein diet to grow 1 kg of shrimp with a theoretical feed conversion of 1.4 to 1. This theoretical feed conversion ratio may be used to assist in feed management. Using this framework, we can put upper and lower limits on our feed management. The upper and lower limits will depend on the estimated survival for the specific pond or farm. Thus, for example a shrimp farm has been stocked at 35 shrimp/m2 with typical growth rates for shrimp (say 1g per week once the shrimp are > 3 g) and an estimated population of 350,000 shrimp per ha. Assuming an 80% survival by the end of the cycle we can compute an upper limit to feed inputs for the later part of production as:
1g/week * 1.4 feed/1g (FCR)* 280,000 shrimp/ha* 1kg/1000g = 392 kg feed per ha per week
392 kg/7 days = 56 kg/ha/day assuming 80% survival
As with all feed calculations one of the limitations is estimating the actual shrimp population of the pond. In this calculation we assumed 80% survival, but on the farm, this limit should be based on what would be a typical optimistic survival for a given farm. If feed inputs are beyond this value we clearly are over feeding. Typically, this value would be reduced based on both historical survivals as well as current estimates of survival. For example, 60% survival is reasonable survival through the end of the cycle so we would actually reduce this value based on our estimated survival at a given point in time or by 60% for the lower end of our production period. This would mean 42 kg/ha/day of feed would be offered, thus creating our lower limit. By calculating these two values we can put limits to where we feel daily inputs should be thus minimizing the desire to over feed. When it comes to determining feed inputs, there are no absolute answers so it is critical to look at feed inputs using a number of tools and base decisions on the best information available.
Water Quality Considerations
Feed management can have a direct effect on pond water and soil quality (Boyd and Tucker 1998, Boyd 2001, Boyd et al. 2007). Water quality parameters such as dissolved oxygen (DO) and temperature need to be taken into account when considering feeding practices. Water quality variables need to be considered in order to implement proactive measurements rather than reactive actions. Thus, reductions in pond DO levels results in modifications of feed inputs, since such reductions may cause stress on the organisms affecting their consumption, and consequently influencing the biological oxygen demand due to accumulation of organic matter. A protocol to manage feed inputs has been suggested in relation to low dissolved oxygen. The guideline is to reduce or eliminate an early feed offering if morning DO levels are lower than 3.0 ppm. Thus if DO is 2.5 - 2.9 ppm, ration would be reduced by half and if DO is lower than 2.5 it would be totally eliminated. A subsequent DO reading at noon will help determine whether or not the next ration will be offered or not. If the DO reading is over 7.0 ppm it could be feed, if DO reading is between 5.0-7.0 it would be offer half of the ration, or if the DO is lower than 5.0 ppm it would be suspended until the next day. Feed consumption is also reduced when temperature drops below 25 oC, and thus appropriate measurements need to be in place.
Feed management is a complex issue which is influenced by a number of factors, some of which can be controlled while others can not. Because numerous variables change from year to year, it is often difficult to predict the performance, feed inputs and shrimp production under commercial conditions. Hence, it is recommended that managers evaluate current and past performance to better improve the system. Increasing feed inputs only increases production if feed is limiting. In well managed systems, feed should be slightly limited as this will optimize the use of natural foods, reduce pollution loading and generally maintain near maximum growth rates. If the shrimp are hungry they are less likely to waste what food is offered and water quality is less likely to be harmed by excess nutrients in the system.
Boyd CE (2001) Management practices for reducing the environmental impacts of shrimp farming. pp. 265-292. In: M.C. Haws and C.E. Boyd (eds.) Methods for Improving Shrimp Farming in Central America. University of Central America Press, Managua, Nicaragua.
Boyd CE and Tucker CS (1998) Pond aquaculture water quality management. Kluwer Academic Publishers. Norwell, MA. 700 pp.
Boyd CE, Tucker C, McNevin A, Bostick K and Clay J (2007) Indicators of resource use efficiency and environmental performance in fish and crustacean aquaculture. Reviews in Fisheries Science. 13:327-360.
Cho CY, Hynes JD, Wood KR and Yoshida HK (1994) Development of high-nutrient-dense, low-pollution diets and prediction of aquaculture wastes using biological approaches. Aquaculture. 124:293-305.
D’Abramo LR, Conklin DE and Akiyama DM (1997) Crustacean Nutrition. Advances in World Aquaculture. Volume 6. World Aquaculture Society, Baton Rouge, LA. 587 pp.
Davis DA, Amaya E, Venero J, Zelaya O and Rouse DB (2006) A case study on feed management to improving production and economic returns for the semi-intensive pond production of Litopenaeus vannamei. 282-303 pp. En: Editores: L. Elizabeth Cruz Suarez, Denis Ricque Maria, Mireya Tapia Salazar, Martha G. Nieto Lopez, David A. Villareal Cavazos, Ana C. Puello Cruz, and Armando Garica Ortega. Avances en Nutricion Acuicola VIII. VIII Simposium Internacional de Nutricion Acuicola. 15-17 Noviembre. Universidad Autonoma de Nuevo Leon, Monterrey, Nuevo Leon, Mexico. ISGN 970-694-333-5.
Davis DA, Roy LA and Sookying D (2008) Improving the cost effectiveness of shrimp feeds. 271-280 pp. En: Editores: L. Elizabeth Cruz Suarez, Denis Ricque Maria, Mireya Tapia Salazar, Martha G. Nieto Lopez, David A. Villareal Cavazos, Juan Pablo Lazo, Maria Teresa Viena. Avances en Nutricion Acuicola IX. IX Simposio Internacional de Nutricion Acuicola. 24-27 Noviembre. Universidad Autonoma de Nuevo Leon, Monterrey, Nuevo Leon, Mexico.
Food and Agriculture Organization of the United Nations – FAO (2009) The state of world fisheries and aquaculture 2008. Rome. 176 p.
Fox J, Treece GD and Sanchez D (2001) Shrimp Nutrition and Feed Management. pp. 65-90 In: M.C. Haws and C.E. Boyd (eds.) Methods for Improving Shrimp Farming in Central America. University of Central America Press, Managua, Nicaragua.
Jory DE and Akiyama DM (2006) Feed management. pp. 86-96 in: Boyd C.E., Jory, D. E. and G.W. Chamberlain (eds.) Operating Procedures for Shrimp Farming: survey results and recommendations. Global Aquaculture Alliance, St. Louis, Missouri, USA.
Kureshy N and Davis DA (2002) Protein requirement for maintenance and maximum weight gain for the pacific white shrimp, Litopenaeus vannamei. Aquaculture 204:125-143.
Lim C and Persyn A (1989) Practical Feeding – Penaeid Shrimps. pp. 205-222 in: Lovell T. (Ed.) Nutrition and Feeding of Fish. Van Nostrand Reinhold, New York, NY. 260 pp.
Mohanty RK (2001) Feeding management and waste production in semi-intensive farming of Penaeus monodon (Fab.) at different stocking densities. Aquaculture International 9:345-355.
Patnaik S and Samocha TM (2009) Improved feed management strategy for Litopenaeus vannamei in limited exchange culture systems. World Aquaculture 40 (1):57-59.
Tacon AGJ and De Silva SS (1997) Feed preparation and feed management strategies within semi-intensive fish farming systems in the tropics. Aquaculture 151:379-404.
Figure 3b. Equipment for feed distribution – Automatic feeder
Figure 3a. Equipment for feed distribution – Manual using small boats
Figure 3c. Equipment for feed distribution – Feed trays
|Table 1. Examples of commercial feed table suggested in different countries|
|Shrimp weight (g)||Biomass (%) Ecuador||Biomass (%) Colombia||Biomass (%) Mexico|