How to Farm Blue Crabs in Fresh or Brackish Water
By Aurora Porter
Blue crabs (Callinectes sapidus) have long been considered a delicacy on the Eastern coast of the United States. Sadly, as a result of decline and pollution in the Chesapeake Bay, fishing for wild blue crabs off the coast has become difficult. Some U.S. restaurants and crab suppliers have turned to Asian hatcheries, but scientists from the University of Maryland and reporters from the Baltimore Sun and Science Daily have discovered that it's possible to farm and raise blue crabs in fresh water.
Photo Courtesy of www.tocookashellfish.com
Things You'll Need
- Mature female blue crabs (inseminated)
- Grow-out Tank
- Old World AquaFarm Bog filtration system
- Hatching tank system (1.020 Salinity Specific gravity)
- Male Blue Crab Tank
- Female Blue Crab Tank
- Feed for Zoeae or Rotifiers
- Feed for Growing Mature Blue Crabs
- 125 um filters around Hatchery pump
- Hatchery Pump
- Large Tank Pump
Prepare Larvae for Hatching
- Place a 2-inch layer of sand on the bottom of all tanks. Fill the tank with clean freshwater and add sea salt to create a salinity level of 3 parts per thousand (3 grams sea salt/ per liter of fresh water). Install one Old World AquaFarm Bog filtration system to filter crab waste for all of the tanks. Except for the hatchery tank. It will have its own Bog Filtration tank as the salinity level is much higher than in the other tanks. Place inseminated female crabs with eggs in the Hatchery tank and monitor for fighting. Separate if possible. Feed the female crabs a small handful of food pellets (about five or six) per crab once a day. Monitor the egg mass that appears on the crabs' abdomens. Crabs can become cannibalistic when living in close quarters
- Place a 2-inch layer of sand on the bottom of the Hatchery tank. Fill the tank with freshwater and add salt to create a salinity level of 3 parts per thousand or a specific gravity of 1.0022. Install one Old World AquaFarm Bog filtration system to filter crab waste in the tank. When the egg mass appears strained and ready to hatch, transfer the female crabs to the hatchery tank. Be sure the tank has cycled in. Secure the 125 μm mesh filters around pump suction in each larvae tank, so the larvae aren't filtered out with waste. After hatching, larvae will float to the top of the tank water.
- Place sand on the bottom of the Grow-out, Adult Male, and Female tanks (necessary if tank bottom is concrete) to create a layer about 2 inches thick. Fill the tanks with freshwater and add salt to create a salinity level of 3 parts per thousand. Calculate at 3 grams sea salt for every liter.(in larger systems use water softener salt and fertilizer 10/24 -34/8 -10) Install one Old World AquaFarm Bog filtration system to filter crab waste for the tanks.
- Feed the crab larvae 150 mg of rotifers (free-swimming plankton) per gallon once a day. Crabs will begin to noticeably mature in 44 to 55 days.
- Monitor small crabs for aggression and cannibalism and separate them inside the tanks as needed.
- Remove mature crabs from the tanks and eat or sell them.
How to Farm Grow Blue Crabs in Brackish Water
(From Egg to Market)
Breeding (Estuaries < 10 ppt salinity)
Female Blue Crabs mate only once in their lifetime during their pubertal molt. Once the mating process is complete, a migration begins in late Spring prior to 1st clutch which 4-7 weeks after mating. Up to 8 clutches within a 25 week season is common. The ideal bottom salinity of 20-25 ppt for the beginning of spawning to a typical maximum salinity of 35 ppt is also common.
Peak migration spawning begins in April/May and again in August/September, with 1st clutch possible in May thru June.
Larval duration development goes thru 7 zoae stages in the first 4-5 weeks. The larvae feed on rotifers.
Migratory behavior of adult female blue crabs, Callinectes
sapidus, in Pamlico Sound: implications for assessment and
protection of the spawning stock
Feeding Zoae (Microalgae)
“Zoeae are phytoplanktivorous and readily consume algae, phytoplankton and zooplankton. Megalope are considered general scavengers, bottom carnivores, detritivores, and omnivores. Megalope are more omnivorous than zoeae and prey upon fish larvae, small shellfish, and aquatic plants
Feeding Crab (Juvenile Thru Adults)
Blue crabs are classified as general scavengers, bottom carnivores (eats other animals), detritivores (eats decaying organic matter), and omnivores (eats either other animals or plants). At various stages in the life cycle, blue crabs serve as both prey and as consumers of plankton, benthic macroinvertebrates, fish, plants, mollusks, crustaceans (including other blue crabs), and organic debris. Food is located by a combination of chemoreception (chemical sense) and taction (touch). Blue crabs may play a significant role in the control of benthic populations.
Macroinvertebrates are organisms without backbones (e.g., insect larvae, annelids (leeches), oligochaetes (worms), crustaceans (crabs, crayfish and shrimp), mollusks (clams, oysters and mussels), and gastropods (snails)) and inhabit bottom substrates (e.g., sediments, debris, logs, macrophytes, and filamentous algae.)
Juvenile blue crabs feed mostly on benthic macroinvertebrates, small fish, dead organisms, aquatic vegetation and associated fauna
Adult blue crabs prefer mollusks such as oysters and hard clams as their primary food sources. The crab uses the tips of its front-most walking legs to probe the bottom for buried bivalves and to manipulate them after they are located. Some other common food items include dead and live fish, crabs (including other blue crabs), shrimp, benthic macroinvertebrates, organic debris, and aquatic plants and associated fauna such as roots, shoots and leaves of sea lettuce, eelgrass, ditch grass, and salt marsh grass. It will also prey on oyster spat, newly set oysters and clams, or young oysters and quahogs if other food is unavailable.
By-Catch feed caught by commercial net trawls, ground, packaged, and stored
Commercial feed purchased from grain mills, discount feed stores, etc
Storing feed in pest free containers (Metal cans)
Water temperature requirements vary and are considered important, but no optimal range is reported.
When air temperatures drop below 50°F (10°C), adult crabs leave shallow, inshore waters and seek deeper areas where they bury themselves and remain in a state of torpor throughout the winter. That is why the sand is needed. Blue crab growth is regulated by water temperature. Growth occurs when water temperatures are above 59°F (15°C). Water temperature above 91°F (33°C) is lethal. Blue crabs are susceptible to sudden drops in temperature.
Salinity is important, but requirements vary by life stage. Generally optimum is 3 ppt for (Adults) thru 35 parts per thousand (ppt) for zoea. However, 3% or 3 grams salt/liter is an option for growth with a temperature greater than 59 degrees fahrenheit.
Tolerance range is pH 6-8. Less than 6 is lethal”. (Quotation excerpts from https://www.bluecrab.info/lifecycle.html)
Harvesting Blue Crab
Blue Crab can be harvested in the State of Louisiana at any size by permit. We do have a source in Louisiana. The company is currently (as of October 2020) working with us to get a permit to sell and transport Blue Crab. We expect this to happen within the next 2 months. It will be posted here when the specialized permit is obtained. We will also provide pricing, availability, and Shipping (2-3 days) information as it becomes available.
Pricing Blue Crab
Pricing depends on yield, equipment depreciation, labor, other operating conditions, profit, and availability.
Old World AquaFarm™ Bog Filtration System
1 large growout tank (optional: 1 small hatchery tank)
Crab Ladder (to prevent escape)
2500-3000 gal/hour submersible pumps 115 vac
Feeder and or harvester
Oyster Spats, Clams, Eel grass, Sand, gravel, Salt grass, and other aquatic animals or vegetation
Micro Algae Growing Kit (rotifers)
Air Pump or cavitation paddles
Salt water plants (date palm, tomato, banana, coconut, and much more)
Hydrometer, pH tester, Nitrite, Nitrates, Ammonia, Temperature, and oxygen level devices. Water quality should be tested weekly
Hoses, clamps, PVC pipe & fittings, screens, semipermeable membrane between females to prevent cannibalism in the hatchery
Example of the tank being built in Louisiana:
The pond or tank is 40 feet wide by 150 feet long and 5 feet deep with a clay and sand bottom and tapered sides on a 3 /1 foot slope. Lining the pond with 3 layer pvc vinyl prevents leakage. Roughly 135,000 gallons. Install crab ladder around tank. Line the bottom of the tank with 2 inches of beach or playground sand. The sand allows a place for the crabs to bury up in the colder months. Also known as toupor state. The crabs still eat but are too skinny for sales (poor quality) in this toupor state. A floating dock is recommended for the pond but not required. Crabs are cannibalistic. Providing structure is required. Two liter soda bottles with the top cut off and/or milk jugs, basically anything with an overhang. If plastic is used, Pet and Hdpe are the best eco friendly products. The tanks maximum holding capacity is 6,000 full grown animals.
Pump setup will determine the frequency of filter cleaning. A total 5,000 gallons per hour is required for this tank. All of the tank water should pass thru the filter every 24 hours. Two submersible pumps (2500-3000 gal/hr) will be utilized. Each to be installed and ran separately to the filter. A visible Pee line should drain into the top of the filter to determine if each pump is continuously operating. The pumps should be 50 feet from each end of the tank along the midline of the tank. Separate power for each pump is required. The power connections should be waterproof with ground fault protection outlet to plug the pump into.. The depth of the pumps intake should be mid water depth and stabilized. A t-post driven into the bottom of the tank with a circle hook attached to the t-post for the pump to hang. This eases pump change out if necessary. A screen placed on the suction end of the pump prevents smaller crabs from being stuck to or sucked into pump.
The Old World AquaFarm designed Bog filter is critical for aquatic animal survival. For this application the filter is 15 feet wide by 15 long and 3 feet deep. The filter should be in the middle of the tank on dry land to ease in cleaning and drainage. It is built out of dirt (sandy clay) or concrete blocks. Each block is 8x8x16 inches (172 required). Stagger the blocks when building the filter. If cinder blocks are used, place rebar in every other hole and fill with sandy-clay dirt. If solid blocks are used then drive t-posts at least 2 feet into the ground surrounding the filter on 2 foot centers. The t-posts should touch the exterior of the filter to prevent the filter from collapsing . A 5 foot t-post will be sufficient. Strapping along the top of the filter will hold it together. The blocks should be concreted or mortared. The bottom & sides of the filter are lined with waterproof vinyl (pvc).and tapered towards the drain. We prefer recycled billboard material. Fold and tuck in corners. The corners should be taped. Place a 2 inch pvc drain in the bottom middle for cleaning. The drain should exit the filter and drain to an area away from the pond or animal tank. I have had to clean my filter roughly every 5 years.
Cleaning the Bog filter: Good bacteria grows in the filter. After cycling in the water coming from the top of the filter will be crystal clear. To tell if the filter needs cleaning, dig down into the pea gravel 6-8 inches. If the pea gravel has sand, dirt, or or any other debri in it, it is time to rinse the filter out. Cleaning to the point of removing this good bacteria requires the filter to cycle in again. Therefore, only rinse it to remove excessive debris. Simply use a water hose. Spray the surface of the filter with fresh water until the drain line runs clear water from it. That is all there is to it.
Installing the pump lines into filter: The discharge lines should be run above pond surface (for visible leakage) along the floating or permanent dock to the top of the filter. Once the discharge lines have been run to the top of the Bog filter it is time to install them into the filter. The discharge lines enter from the top of the bog filter. Place 2 inch pvc schedule 40 pvc pipe on 12 inch centers. The pipes are 13 feet long (14 required). The connector pipes are 8 1/2 inches long ( 12 required). Four 90;s are required for the corners. To connect the pipes together requires a Tee (24). Two additional tee's are required to connect the pump discharge lines. Another option is to use flexible 2 inch swimming pool hose instead of the pvc pipe and connectors (200 feet required). The flexible pipe should be placed in a S type configuration on 12 inch centers. The flexible hose will require two 2 inch 90's to connect to the pump discharge line. Make sure you install Pee lines to discharge line before filling Bog filter with pea gravel in either case drill 3/8 inch holes every 6 inches along the pipe. The holes should be drilled at the 10 o'clock and 2 o'clock positions in an alternating fashion. Place 1-2 inches of well rinsed pea gravel into the bottom of the filter and spread out evenly between the pipes to hold them securely. The pipes will be partially visible above the pea gravel. Then place used plastic pallets ( some cutting is required to cover the bottom of the filter) on top of the pipe and gravel. Do not use wood or metal pallets. A 6-8 inch air space is required between the absolute bottom of the filter and the top of the pallets. Place plastic mesh on the top of the pallets to prevent filter media (rinsed pea gravel) passing thru to the air space. Make sure you install Pee lines to discharge line and connect discharge pipes coming from the pumps before filling Bog filter with pea gravel. Fill filter with rinsed pea gravel to within 8 inches from the top of the filter. The Bog filter and tank is ready for filling. Fill tank half full. Begin dissolving sea salt in warm water (68 bags required or 3400 pounds). Add at the rate of 1000 pounds of salt solution per week. Once the tank is filled (2 to 3 weeks) to capacity, see section on cycling in the system. Do not place animals into tank until the system is cycled in.
Planter Boxes are designed to water from the bottom and are optional. However they are advisable, i f not planting in the bog filter. One can plant in both. With that in mind, the bottom of the planter box must be higher than the top of the pond. They are designed to feed the plants off the tank water and assist in cleaning the water for the aquatic animals. We found that plant roots grow to the water and food. What does that mean. The plants can be placed much closer together than traditional gardening. Over the years we have learned that plants can be planted as close as 4 inch intervals. Keep in mind seeds cannot be planted in the salt water environment, only seedlings will grow and mature. The planter boxes are at least 18-24 inches in depth and up to 4 feet wide. In this system design we will not be using planter boxes.
Planting in the filter is the easiest method of water cleaning and additional filtration. Simply place the seedlings into the top of the gravel. Place them deep enough to stabilize the plant. Banana trees require at least 12 inches separation. Tomatoes only require 4 inches of spacing.
Cycling in the system (pond and filter): Cycling in the system is an absolute requirement. The system must be running 24/7 to cycle in the tank and bog filter. After filling the tank and the filter take water samples. Document the results. The following items must be checked weekly. Take all samples from the middle of the tank at mid water level. Or in this case, take two samples one from just above each pump. The following tests are required. Oxygen level, tank temperature, nitrites, salinity, ammonia, pH, and nitrates are the testing fields. Document and compare test results. Test the tank when it is full of fresh water initially. Then add the first salt solution (1000 pounds). Test again in two days after adding salt solution. Two days before next testing add another 1000 pounds of salt solution. Test all parameters again. Continue until all parameters are satisfied. The hydrometer reading 3 ppt salinity at 60 degrees fahrenheit is 1.0023. Add 10 24 8 fertilizer (15 pounds mixed into the water salt solution over a 3 week time period (5 pounds per week). Pond should be cycled in by the fourth week. Follow these instructions to the letter.
Placing animals in the pond: Do not add animals until the tank or pond has cycled in. The tanks maximum holding capacity is 6,000 full grown animals. One crab per square foot of bottom surface area. However, all crabs in the tank will not be the exact same size. Smaller crabs require less space. Therefore, 27,000 animals can be in the tank. Seasonal bait, soft shell production crabs, standard crab, jumbo crab, as well as cannibalism/other loss will determine stocking frequency and maximum level. Begin with 6000 -12,000 animals. Add additional animals based on sales and loss.
Sorting Table: The sorting table is designed as an aid to packaging for sales. the crabs will be packaged and sold alive. The table is 4 feet wide and has 5-8 inch sides. The sorting table is 6-8 feet long. There is a slot on one end for the crabs to slide into a hanging bushel basket. The basket is hung from a set of scales. Simply weigh the crabs and place them in a box with ice on the bottom. Put half the crabs in the box, add more ice. Put the rest of the crabs in box and top off with more ice. Continue until the order is filled. Small crabs are sent to the other end of the sorting table where they slide back into the pond. A ramp is built to roll a wheelbarrow up to the table and dump the crabs onto the sorting table.
Feeder and Harvest Cage: The cage is optional. The cage works to catch and feed the crabs. The crabs will learn to go into the cage at feeding time. The cage is built with a square metal frame for the top. Cables on each corner allow ease in lifting out of the water by a tractor with a jib pole attached. A float is attached where the cables meet for ease of lifting. The bottom of the cage has 3/4 inch mesh webbing (similar to a net). Two foot sides with a shrimp net type tied bag at the bottom. The cage can be dumped into a wheelbarrow or taken to the sorting table and dumped.
Click on: Troubleshooting Pondwater Quality at the bottom of this page
What Plants Will Produce Fruit or Vegetables in Brackish Water?
Green tomatoes grown in clusters on brackish water ripen simultaneously.
Sweet cherry tomatoes, luscious wine grapes, and tasty olives flourish in the Negev, the desert region that accounts for nearly two-thirds of Israel’s land. Even fish—barramundi and bass—thrive there.
The small amount of rain (2 to 4 inches a year) and the desert soil, much of it sandy, would hardly seem conducive to farming. Even the discovery of a huge aquifer under the Negev, part of a regional aquifer under the Sinai Desert, would not seem to be much help, because its water is brackish (saltier than fresh water but less salty than seawater).
But Israeli scientists have discovered ways of using both the Negev soil and the brackish water to grow crops that are even better than those grown in seemingly more favorable conditions.
True, seeds and young plants need fresh water, but then brackish water can be introduced gradually.
“The secret is the [precise] mix of fresh and brackish water,” said Raz Arbel, tourism manager of the Ramat-Negev Regional Council, who recently showed journalists the area’s research institute and local farms.
Once scientists at the Ramat-Negev AgroResearch Center developed the appropriate mix of fresh and brackish water, they created a computer program that would provide it automatically.
Cherry tomatoes pollinated by bees account for 90 percent of the crops in the area. Rooted in sand in above-ground Styrofoam boxes, they yield about 100 tons per acre (which seems to be more than five times the average yield of tomatoes in the US). They fetch about $4 a pound in European markets.
In a seeming paradox, the “torture” of being irrigated with brackish water gives the tomatoes a longer shelf life and makes them three times as sweet as tomatoes grown on fresh water. The trick now is to get all the tomatoes in a cluster to ripen at the same time, Arbel said. One solution is to grow green tomatoes.
Chives, too, thrive on brackish water, and when it is used at its natural temperature (104° F), their flavor is more pronounced.
Not all fruits and vegetables have succeeded on brackish water. Sweet potatoes and watermelons, for example, were indeed sweet, but lacked their characteristic color and thus were unattractive to consumers. Several varieties of strawberries have not been successful because they require a large percentage of fresh water, Old World AquaFarm will be testing different plants which will tolerate a 3ppt and a 35 ppt salinity. Once plants are grown, pictures and data will be available.
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