Shrimp Feed Management in Outdoor Ponds for Litopenaeus vannamei

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Feed is the highest variable cost for shrimp production and feed management have a greater influence on harvest feed conversion ratio than feed quality

Uniform size and clean shrimp at harvest, Indonesia.

By Dean M Akiyama and Dany Yukasano

There is a general understanding that for successful shrimp production, emphasis must be placed on dedicated farm management (at 50-60%), post larvae quality and handling (at 20-25%) and consistent feed quality (at 20-25%). Additionally, key to shrimp farming is the motivation and dedication of farm staff where it is critical that all staff are implementing and completing assignments correctly and without delay when required.

Feed management accounts for 65-75% of the variation in feed conversion ratios (FCRs) at harvests. This is because the amount fed at each feeding, number of feedings per day, distribution of the feed in the pond and feed quantity adjustments have greater influence on the harvest FCR than on feed quality alone.

A standard growth curve for each shrimp production site needs to be developed, adjusted as needed and maintained for proper pond and feed management. Individual pond daily growth rates should be monitored and compared to the standard growth curve. If the growth rates are within ±10% of the standard, the pond conditions and feed management are acceptable. If the growth rate is below the standard curve, the farmer needs to check whether the water quality, pond bottom and/or animal health are at acceptable levels. If these are good, then increase the feeding rate. If the growth curve is above the standard curve, pond conditions are good but maybe survival rate is lower than expected. Consider lowering the feeding rate to maintain acceptable FCR.

Figure 1. A standard growth curve for each shrimp production site needs to be developed, adjusted as needed and maintained for proper pond and feed management. DOC=days of culture

Variable Costs in Production

Feed cost is the highest variable cost for shrimp production. The feed cost will range from 50-60% of the total production cost. The percentage of total cost will vary by country or region because of the pricing variations for manpower, electricity, post larvae and supplies. However, proper shrimp feed management will ensure that total feed cost is acceptable with more consistent production costs which increases the feasibility of shrimp production.

Proper feed management will also improve the water quality stability and lower pond bottom deterioration. There will be less feed wastes which directly affect water quality and pond bottom cleanliness.

Recommended shrimp feed sizes

Current small diameter shrimp feeds are a function of market or market demand rather than technical shrimp requirement. Shrimp do not swallow feed pellets when feeding. Shrimp will cut and crush feed with their mandibles located before their mouth and these particles are then eaten. Thus, pellet size is of minor importance. However, smaller pellets will have a greater number of pellets/kg feed which is an advantage. Attractants and water-soluble vitamins and minerals will leach faster from the smaller-sized feed. Smaller feed particles are also more easily lost in the pond sediments (Table 1).

Table 1. Some general recommended pellet type and sizes in shrimp farming in relation to average body weight (ABW).

Feeding time and amount

There should be a minimum quantity of feed allocated for any feeding time by area of pond and not necessarily by feeding rate based on biomass of shrimp less than 4.0g (Table 2). A blind feeding rate table is recommended until shrimp average about 3.5g and when shrimp start to appear on the feeding trays (Refer to appendix I. Blind Feeding Program, 500,000 shrimp in 0.5ha pond (100/m2).

Monitoring daily feed consumption

There have been many systems developed for monitoring daily feed consumption. However, the most common and widely practised system is the use of feeding trays. The proper use of feeding trays is dependent on dedicated and experienced farm technicians. These technicians must interpret the data for feeding tray consumption, shrimp size, estimated biomass/survival rate, weather conditions and water quality at the feeding times.

Feeding trays are normally square or circular. The sides of the feeding tray should be 10cm high. This is important because when trays are raised slowly, the shrimp will remain in the feeding tray. You can observe the health condition of the shrimp as well as size uniformity. The feeding trays are weighted so they will sink evenly without the feed being flushed out from the trays.

Raising feeding tray slowly allows the observation of shrimp health status and size uniformity, Indonesia. Feeding trays are normally square or circular.
Sturdy concrete walkway for feeding tray checking, Indonesia

Sturdy concrete walkway for feeding tray checking, Indonesia.

Table 2. Example of feed distribution depending on number of feed applications/day.

Feeding trays are attached to the walkways on the side of the pond. The walkway should extend into the pond at a minimum of 2m from the pond dyke. The feeding trays should be placed 30-50cm from the pond bottom. Stable walkways should be built so the technician can easily work the feeding trays and observe the shrimp.

There should be a minimum of 4 trays/0.5ha pond with trays on each side of the pond. Larger ponds will require more feeding trays; 1ha: 6-8 trays and 2-3ha: 8-10 trays. To accurately calculate the feeding quantity per day, it is necessary to have accurate shrimp size (g, cast net sample) and accurate pond biomass (survival rate x stocking density x size but this is difficult to estimate accurately).

The actual stocking density may vary from 80% of bought numbers with poor transport and acclimation procedures to 120% with free post larvae given as top up to actual number bought. The estimated % survival rate calculated from a table is not reliable. The biomass estimate should be an average of the past 3 days running average of feed consumption to account for normal daily fluctuations. Good farm technicians can estimate biomass within 10% of actual total. This is critical to keep FCR low especially with low survival rates. Good farm technicians do not blindly follow feeding tables.

Feeding tray consumption levels

 This is a tool for biomass and survival rate estimations with shrimp weight sampling using a cast net. The biomass estimate is also important at harvest, to determine the number of transport containers and ice required.

The technician will need the last 3 days average feed consumption, initial stocking density, ABW of shrimp and feeding table for the following calculations. 3-day average feed consumption (kg)/% feeding rate for shrimp size = kg biomass kg biomass/shrimp ABW(g) = number of shrimp population Number of shrimp/stocking density = Survival rate (%) Example: ABW = 14g, 3-day average feed consumption = 65kg, stocking density = 200,000 shrimp, feeding rate for 14g shrimp = 2.7%; 65kg/0.027 = 2,407kg biomass; 2,407kg/14g = 146,214 shrimp; 146,214 shrimp/200,000 shrimp = 73.1%.

Table 3. Feeding trays observation programs

Good feed management requires checking actual feed consumption rates after every feeding or at least daily (Table 3). The amount of feed consumed can be compared to the previous day or days and adjustments can be made. Usually, feeding rate may be adjusted to an amount between +5% increase to -10% decrease. Attention should be given to lowering the feeding rate to maintain good water quality and low harvest FCRs.

However, if the shrimp growth rate is consistently below the established standard growth curve and acceptable water quality, consider increasing the feeding amount. Accurate daily feed consumption levels will also help to determine the standing biomass of shrimp.

Table 4. Allocation of score and feeding adjustment programs based on feed left in feeding trays.

A minimum of 75% of trays (3 of 4 trays) should be scored for feed rate adjustment. For example, a score of 0000 or 0001, feeding rate will be increased by 5%. A score of 0011 or 1111 or 1122, the feeding rate will remain the same. A score of 1222 or 2222, the feeding rate will be reduced by 10% (Table 4).

Table 4. Allocation of score and feeding adjustment programs based on feed left in feeding trays.
Table 5. Quantity of feed consumed per month over a 90-day cycle, 120-day cycle

Most of the feed is consumed during the last 2 months of the shrimp production cycle (Table 5). Proper feed management is more critical during these times. During the first 30 days, the percentage of feed being fed is small, thus the blind feed system is recommended.

Feed management concepts

Feeding tables are only “guidelines”. Under normal conditions, actual daily feed consumption will fluctuate between 5-20%. This is primarily due to fluctuating pond conditions, temperature, dissolved oxygen, pond bottom, animal health and other factors. Therefore, the farm can develop a detailed feeding table which may look good, but it is of little value if daily feed consumption is not measured accurately (Table 6).

Table 6. Shrimp (Litopenaeus vannamei) feeding rate

More feeding times per day of smaller quantities is better for shrimp than less feeding times of larger quantities of feed. Shrimp will eat more feed if fed many times resulting in faster growth and lower FCRs. An additional benefit will be more stable water quality because the leaching and feed waste will be more even during the day. However, there should be a minimum of 5kg feed given at any one time regardless of the stocking density, thus, with 2 feedings per day, there should be a minimum of 10kg feed per day.

The feeding rate for lowest FCR and fastest growth varies by 10-15%. If a higher growth rate is desired, the farm can increase the daily feeding amount by 15%. But an increase in growth rate of 10% (20g to 22g) increases FCR of 0.2-0.3 points (FCR 1.5 to 1.7-1.8). The water quality also needs to be monitored more carefully as there will be 15% more feed added to the pond daily. To achieve the lowest FCR, it is recommended to feed slightly less than satiation. Shrimp may forage the pond bottom for food but if too much sediment is observed in the water column, then the farmer should increase the feeding rate (Table 7).

Central sludge and waste area accumulation because of water circulation, Indonesia

Water and pond bottom quality critically affect shrimp growth rate, survival and FCR. Over feeding is the major cause of deteriorating pond conditions. If pond conditions are bad, the farm should exchange water and/or reduce feed quantity per day till pond conditions improve.

Low dissolved oxygen and low water temperatures directly reduce shrimp appetite and feed consumption levels. If these two water quality parameters are not optimal, shrimp appetite declines and the feeding rate should be reduced. If the levels are low in the morning, the feeding rate should be reduced too. As dissolved oxygen and temperature increase during the day, shrimp appetite will increase.

Shrimp are poikilotherms; they are cold blooded animals which are different from terrestrial warm-blooded animals. Their appetite and growth are regulated by external water temperatures. Lower water temperatures directly lower shrimp metabolism and growth. For every 1°C difference in temperature there is an 8-10% difference in growth; 30°C will have 15% faster growth than 28°C.

In the morning, shrimp will normally eat less feed than in the afternoon. Daily water temperatures will fluctuate during the day due to regional differences and weather: wind, rain, clouds. The water temperature fluctuation makes it difficult to estimate actual feed consumption at any feeding time.

Clean vannamei shrimp with a full gut an hour after feeding, Indonesia.

Currently, genetically improved shrimp are bred for maximum growth performance. The growth rate of shrimp is the primary physiological stress on the animal. The faster the shrimp growth rate, the greater the stress on the animal. Therefore, water quality parameters should be stable; good water quality results in less energy for animal maintenance. Important water quality parameters include dissolved oxygen, pH, salinity and transparency and among them, dissolved oxygen is most critical. Low dissolved oxygen levels reduce activity and metabolism. Shrimp stocks need a minimum and consistent dissolved oxygen level of 6.0ppm. At lower levels, shrimp may not die but are not growing at optimal levels.

Proper aeration levels should be used not only for maintaining dissolved oxygen levels but also for mixing the colder pond bottom water layer with the warmer top layer. In a deep pond of 1m depth without proper mixing of the water, the temperature difference between the top water and the bottom water layer can be 2°C. Higher dissolved oxygen and warmer water temperature at the pond bottom will improve animal performance.

With unpredictable weather conditions and fluctuating water quality conditions in outdoor production systems, there is no fixed daily nutrient requirement and intake for shrimp. Shrimp will eat more or less feed according to their physiological requirements at any one time. If no feed is available, shrimp will forage in the production environment for food. At times of shrimp stress due to water quality issues, it is recommended to reduce feeding by 50% or completely stop feeding for 2 to 4 days. Shrimp will forage for food and “clean” the pond bottom and reduce excessive algae.

When changing feed sizes, there should be 2 to 3 days interval where both feeds are mixed at a 50:50 ratio. This will make the transition from one size to another smoother and without loss of feed consumption. When feed size is abruptly changed, there may be a 2-3 days of lower feed consumption as the shrimp learn to adjust to the new feed. This is primarily because the attractant level and type may change slightly due to the formula and/or feed processing conditions.

Shrimp are nocturnal animals and are more active at night. Shrimp are actively feeding at night and will normally consume 50-60% of feed at night. However, this feeding behaviour is made complicated by the lower water temperatures and lower dissolved oxygen levels which decline at night. dissolved oxygen levels will still be decreasing at sunrise and will start to increase only about 2 hours after sunrise.

Avoid feeding at the centre of the pond where sludge and wastes accumulate because of paddlewheel water circulation. This area will have toxic gasses such as hydrogen sulphide from decaying organic material. A layer of oxidised material will cover the sludge area and if this layer is disturbed, these toxic gasses will be released into the pond water.

Table 7. Days of culture (DOC) with estimated survival rate (%) based on +/- 70% harvest survival

Appendices to this article are available from these links

Appendix I. Blind Feeding Program, 500,000 shrimp in 0.5ha pond (100/m2).

Appendix II. Feeding Program for L vannamei, 500,000 shrimp in 0.5ha pond (100/m2). Harvest production of 20.0 tonnes/ha, 70% survival rate, final body weight 28.0 g, FCR of 1.45.

Authors:

Dean M. Akiyama, PhD. is an Aquaculture Advisor, based in Jakarta, Indonesia.
Dany Yukasano is a senior farm manager and trainer. He has 28 years of experience in shrimp farm management based in
Jakarta, Indonesia.

This article was published in the print edition of Aqua Culture Asia Pacific in July/August 2022

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