Production of Saltwater Shrimp in Inland Areas of Alabama
David Teichert-Coddington and D. Allen Davis
Department of Fisheries and Allied Aquacultures
Auburn University, AL 36849
Sources of salty water in inland areas of Alabama may be appropriate for the production of saltwater shrimp. The salinity of these waters is low (4 – 6 ppt) relative to seawater (32 – 35 ppt). The initial acclimation of baby shrimp (post larvae) to the low salinity water is one of the most critical components of production. Yound post larvae (PLs) are not well adapted to low salinity. Based on current research shrimp must be at least a PL 15 (15 day old PL) to tolerate low salinity acclimation. As PL are typically shipped from hatcheris as PL 6-8, they very small and should be nursed in protected and controlled environment. The length of the holding period (nursery) can be as short as 3 day (if PL 15's are purchaed) but will typically last for 2 to 4 weeks prior to stocking in production ponds. The nursing period allows PLs to grow to a large enough size to be able to cope with low salinity and escape depredation by aquatic insects, therefore increasing survival of stocked animals. The objective of this article is to outline a good management procedure for an acclimation and nursery system. The stocking rate of PLs in this nursery should not exceed 80 per gallon or 21 per liter.
Definition of Terms
Salinity – Salinity is defined as the total dissolved solids (TDS) in a known volume of water. Salinity is usually expressed as parts per thousand (ppt). For example, 1 lb of salt in 1000 lb of water (120.5 gal) would equal 1 ppt. The TDS may be determined by evaporating a known volume or weight of water and weighting the quantity of salt left over. The salinity may also be determined by electrical conductance. A higher salinity solution is a better conductor of electricity. Salinity is most practically determined with a refractometer that measures the bending (refraction) of light as it passes through a liquid of higher density. Salty water is denser than fresh water. A temperature-compensated refractometer may be purchased for about $300 from aquaculture supply houses.
Nursery Tanks
Nursery tanks can be any shape, but should possess a bottom drain and a standpipe equipped with a 1-mm mesh screen (250, 500 and 1000 um are typically used as the animal grows) to remove water while retaining the PLs. Tanks should be equipped with bubbled aeration, and bottled oxygen should be kept in reserve to oxygenate tanks in case the main aeration system fails. Electrical solenoid switches are available that automatically activate the flow of bottled oxygen when electricity is interrupted. The size and number of nursery tanks depends on the number of post larvae that must be nursed. Based on a stocking rate of 80 PLs/gal, every 100,000 PLs would require 1,250 gal of water.
Preparation of Receiving Water
High health or specific pathogen free post larvae should be obtained from a hatchery that has been certified as disease free. Upon ordering you should request that the PL’s be acclimated to 20 ppt salinity prior to shipping.
At least five days prior to the scheduled arrival of the PL’s the nursery system should prepared. The nursery tanks should be filled 1/4 to 1/3 of the way with low salinity water. The salinity should be adjusted to 20 ppt with sea salt (Marine Enterprises Int., Baltimore, MD; Crystal Sea or Instant Ocean, Aquatic Ecosystems, FL). Do not use rock salt or sodium chloride. Once the salinity has been adjusted, the water should be heavily aerated for at least 24 hrs to allow the salts to completely dissolve.
The following day the water should be sterilized by adding 10 ppm active chlorine (unscented bleach, 5.25% hypochlorite solution, can be used at 72 ml or 2.5 oz per 100-gal). After about two hours the chlorine can be neutralized with sodium thiosulfate (0.04 g/ml or 1.1g/oz of chloral). The quantity of sodium thiosulfate will vary with water chemistry; hence, chlorine must be tested using a pool chlorine test kit. After neutralization, the water should be aerated overnight.
Algae
Best results will be obtained if a good diatom bloom is introduced to the culture system. Hence, the nursery systems should be fertilized with urea (46-0-0), triple superphosphate (0-46-0) and sodium silicate to provide a final nutrient concentration of 10, 1 and 1 mg/l for the N, P and Si, respectively. Every 1,000 gal of water would require 3 oz of urea, and about 1 oz each of triple superphosphate and sodium silicate. If available the tanks should be inoculated with the diatom Chaetoceros muelleri at an initial cell concentration of 50,000 cells/ml (contact the aquaculture extensionist for source of algae). This is equivalent to one carboy (5 gal) of stock solution per 500 gal of tank water. The stock solution should be started about 10 d before inoculation by seeding a plastic carboy with a known culture of the diatom. Carboys should be fertilized with F/2 Algal Formula, which may be purchased from a supply house like Aquatic Ecosystems. Carboys should be aerated and exposed to sunlight or high intensity fluorescent lighting. Prior to starting a carboy, it should be filled with seawater, sterilized with chlorine, neutralized with thiosulfate and allowed to aerate overnight. It will take about 2 quarts of dense algae to inoculate 1 carboy and about 4 days until that carboy is ready for harvest. Each carboy can then be used to inoculate 8 other carboys. If the diatom culture is unavailable, a wild plankton bloom may be introduced into the tanks. Typically wild agae has produce good results, but as the type of algae is not controlled results may vary.
Artemia Production
Artemia are brine shrimp that may be purchased from supply houses as cysts in vacuum-packed cans. Approximately, eighteen hours prior to the arrival of the PL’s, artemia should be hydrated, sterilized and set to hatch. You will need to feed 100 Artemia/PL. Hence for every 1,000 PL’s, 100,000 artemia or about 0.5g of cysts will be required each day. Example: 1) Weigh out cysts and place in a container (25 g cysts/l or 95 g cysts/gal) with strong aeration. Soak for 30-60 minutes or until hydrated. 2) Add chlorine (25 ppm active ingredient) or about 2 ml Clorox to each gallon of water. Aerate for 1 minute. 3) Transfer the cysts to a 100-micron sieve bag and wash with fresh water until the chlorine odor is gone. 4) Transfer the artemia to a hatching cone. (Do not exceed 3 g cysts/liter of water). For best results adjust the salinity to 15 ppt and place a light over the hatching container. Depending on temperature the Artemia will hatch in 18-24 hrs.
Acclimation
The PLs are shipped in plastic bags within Styrofoam boxes. The bags contain some water and are pumped full of pure oxygen. Upon receipt of the PL’s, two to three boxes and bags should be opened and the salinity, temperature and dissolved oxygen (DO) recorded. If the DO is low, or if an ammonia odor is detected, open all bags immediately and aerate. Aeration is generally not required but supplemental oxygen should be available if needed. If all is normal, the remaining boxes should be opened, the bags removed and visually inspected for mortality and shipping problems, and placed (floated) in the larval tanks.
After about an hour the bags should be opened and tank water added in increments. It is easiest to start at one end of a line of bags, adding about 1 quart of culture water into each bag and then repeat the process. After the second addition of water, 2 quarts should be added until a total of 10 quarts have been added. At this point the salinity and temperature of several bags should be checked. If they are similar to the culture system then the PL’s can be released. It should be noted that the salinity and temperature should not be changed more than 2 ppt or 4 C per hour. After the shrimp have been in the nursery tanks for 24 hrs, pond water can be added over the next 2 days to fill the tanks and reduce the salinity. Once the nursery tanks are full, no water will need to be exchanged until the second week.
Once the shrimp have been acclimated and released, newly hatched Artemia should be collected, rinsed with tap water, and fed to the PL’s. Newly hatched Artemia should be offered for the first four days of culture. The shrimp should be fed a 45% protein shrimp post larval feed, such as those produced by Zeigler Brothers, Inc. or Rangen Feeds, Inc. The daily feed rations should be divided into 4 feedings of approximately equal sizes. Based on weight estimates of the shrimp and expected survival (generally 98% if there are no shipping problems) the shrimp should be feed at 25%, 15%, 12% and 10% of their body weight for week 1, 2, 3 and 4, respectively (See attached example). Shrimp should be sampled weekly for health inspections and weight determinations.
Feed example for 100,000 PL’s. Divide the total daily feed amount into at least 4 feedings.
|
Week |
Shrimp wt (g) |
Feeding rate |
Total Daily Feed (g) |
Type of feed |
|
1 |
0.001 |
25% |
25 |
PL ready first few days, then 45% protein 10% squid #0 |
|
2 |
0.010 |
15% |
150 |
Crumble #1 |
|
3 |
0.060 |
12% |
720 |
Crumble # 1 |
|
4 |
0.120 |
10% |
1,200 |
Crumble #1+3 |
Water Exchange and Cleaning Tanks
If shrimp are fed properly, water exchange will not be necessary until the middle or end of the second week. Dissolved oxygen concentrations in tanks should be determined twice a day. If the DO begins to drop below 80% of saturation, then clean the tank bottoms and exchange some water. The volume of water exchanged during tank cleaning should be sufficient. Clean tanks once a day as follows. Fashion a siphon vacuum system by attaching a hose onto a flat plastic vacuum cleaner head. You may have to cut small notches in the head in order for it to drawn water when placed flat against the tank bottom. Create suction by starting the siphon. Vacuum the solids that have accumulated on the bottoms of tanks. Most shrimp will move out of the way of the siphon head, but the water should be discharged through a bucket with a screened outlet to retain shrimp that did not escape the siphon. Replace discharged water with pond water. The salinity of the nursery tank will eventually approach that of the pond water.
Tank Harvest
Nursery tanks may be harvested after 3 to 4 weeks or when shrimp weigh 0.1 to 0.25 g (900 to 1,800 per lb). Harvest by lowering the water level slowly and draining into a container with a screened overflow. Transfer to the pond in the early morning when the water temperature is cool. Make sure that pond and nursery water temperatures are within 2 C of each other. Otherwise, acclimate the shrimp to the pond water by adding pond water to the shrimp transfer container.
The average shrimp weight should be determined before harvest in order to quantify shrimp numbers. An electronic balance with a 600-g capacity and capable of weighing to 0.1 g is necessary for this task. Add a little water (<1/4 full) to a plastic pint-size container with a spout, then tare or zero the scale. Net about 100 shrimp, remove excess moisture with a sponge or paper towel (you are only trying to draw off dripping water) and put shrimp into the plastic container. Record the weight. Add more water to the container and count shrimp back into the tank. Do this at least twice for each tank and calculate the average weight of shrimp in each tank. Estimate the total weight of shrimp to stock into each pond by multiplying the average shrimp weight by the desired stocking number.
List of Supplies and Equipment (most can be purchased from aquaculture supply houses)
1. Refractometer (temperature compensated)
2. Thermometer
3. Electronic Balance: 600 +/- 0.1 g capacity
4. Supply of Forced Air: required for aeration of artemia and nursery tanks
5. 100-ml graduated cylinder
6. Swimming Pool Chlorine Test Kit
7. Artemia Hatching Containers
8.Nursery Tanks: should be equipped with a bottom drain and standpipe; requirements are 1,250 gal/100,000 PLs
9.Shrimp Post Larvae: call extensionist for list of suppliers
10. Sea Salt: 1 lb/120 gal = 1 ppt
11. Chlorox or HTH
12. Artemia: 0.5 g/1,000 PLs per day
13. Chaetacerous diatom algae: call extensionist for suppliers
14. F/2 Algal Formula
15. Sodium Thiosulfate: for removal of chlorine (0.04 g/ml or 1.1 g/oz of chloral)