Crayfish Culture in British Columbia
Crayfish have never been the object of a traditional target fishery in British Columbia. However, the value of crayfish in the marketplace, particularly in Europe, has increased interest in developing the culture technology for producing this animal. Sweden and France are large consumer countries of crayfish. August in Sweden is the time when numerous crayfish parties (Kraftkalas) are held and the demand, and price, for crayfish skyrockets. The claws and tail are the main parts consumed, each of course, followed by a toast of vodka! A disease which decimated the indigenous swedish stocks of crayfish has forced the country to rely on imports from China, Turkey and the United States. The species of crayfish that occur in British Columbia are highly valued by the marketplace, providing a significant incentive for the development of crayfish culture operations here.
Species and Habitat
Pacifasticus leniusculus is the name of the crayfish species occurring in British Columbia of which there are three sub-species. Crayfish can be found in freshwater environments such as ponds, streams and lakes. Their distribution, especially along coastal British Columbia, is limited by the avaialbility of natural bodies of hard water. Crayfish absorb calcium compounds from the water which as necessary for the proper development and hardness of the crayfish shell. These animals find an ideal habitat in old quarries that have become flooded with water from watershed runoff. Limestone quarries in particular are sought out by crayfish. Because a crayfish can travel over land, as long as it stays moist, thse animals have been able to access and inhabit otherwise inaccessible quarries. They prefer a body of water where the pH is between 7 and 7.7. They have a wide temperature tolerance range, from 0.5oC to 20+oC. At 23-24oC, however, they begin to display sign of stress.
Planning Production
Crayfish are not commonly reared under conditions where the life cycle is completely controlled. In many areas, crayfish are grown in flooded areas or ponds where no control of reproduction occurs and where no prepared feeds are used. In areas of the southeastern USA, for example, crayfish are introduced into a flooded rice field after the harvest. They will feed on the stalks and will be later harvested. In British Columbia, however, the lack of extensive natural habitat for crayfish means that more effort will be undertaken to control the entire production cycle, including breeding and feeding. The first requirement for setting up a crayfish farm is to acquire an abandoned flooded quarry with appropriate water hardness.
The production cycle to produce market size animals, 100-120 grams each, is approximately two years, but with better production control, growers are hoping to be able to reduce it to 14 months.
Steps of Production: Hatchery and Breeding
Crayfish do not require sophisticated hatchery equipment and conditions for breeding. A sufficient number of male and female crayfish are separated and put into separate cages in August. The animals are well fed and by September are ready to breed. They mate in groups of three. The male deposits a sperm packet into the female and the eggs are fertilized. The females are held in cages and fed normally. After three or four months the female extrudes the eggs onto the outside of the body where they are held until the eggs hatch, usually in March or April. The young will be held on the female’s pleiopods until they are 3-4mm in size at which point they will drop off and begin independent life.
When the hatchlings are ready to drop from the mother, she is placed in a tray with a screen bottom large enough for the juveniles to drop through. This tray is floated in a juvenile rearing container constructed with mesh small enough to prevent escape of the small crayfish.
Nursery Rearing
Juvenile crayfish are reared in nursery pens for several months. These pens are similar to growout pens except that they are constructed with finer mesh. The restriction to water flow through the fine mesh necessitates the the introduction of a continuous flow of fresh water into the cage. This will be accomplished inexpensively by air-lifting water into the pens. Although crayfish are omnivorous, the juveniles do not have the same ability to consume algae and aquatic plants that adults do. They will consume green rhizoclonium weed which grows naturally in the quarry, but at this stage, the special requirements of a juvenile crayfish diet are not well known at all. An initial experiment conducted by the company showed that ground olive pits may provide a good nutrition base for a juvenile diet formulation. Mountains of this material is available from California, where it is a by-product of olive processing and regarded as waste. Further research on juvenile diets is under investigation as part of a crayfish nutrition and diet project funded by the National Research Council. Diets will need to be composed entirely of plant-derived materials.
Grow-out
After 8 months of juvenile rearing, some of the crayfish may be released into the quarry to maintain the natural population. These animals will consume the excess algal and aquatic plant growth, mainting water quality and good pond condition. Mature crayfish can be harvested from the quarry. The majority of the stock, however, will be contained in grow-out cages where they will be held and fed until the animals reach the target market size of approximately 120 grams.
The perimeter of the pen system consists of a floatation frame, constructed either from foam or pvc pipe (e.g. 4 inch diameter). Each pen in the system has an outer mesh strung from the frame. Into each pen there is an insert consisting of a draped mesh material supported by an aluminum or pvc frame. The folds of the mesh provide a significantly increased surface area within the pen, allowing for the production of large numbers of crayfish in each pen.
The size of the pen illustrated here is one cubic meter and will contain up to 1000 crayfish of marketable (120g) size. Feeding of the crayfish is accomplished by opening the top screen and dropping in a bucket of aquatic plant material. This operation is currently harvesting duckweed from a nearby fish hatchery waste treatment pond. The duckweed is simply spread on the surface of the pen and the crayfish will swim or climb up to the surface, latch on to a chunk of duckweed and sink back down to consume it at leisure. During peak growth periods in the summer, a pen of 1000 crayfish will consume 20 litres of duckweed overnight.
The goal is to gradually make the transition from collected natural feed, which will always be labour intensive and supply-limited, to prepared feeds. Diet requirements are under investigation. Not only nutritional components, but form and consistency of feed will be important considerations. Crayfish natural feeding behaviour will have to be integrated into the feed design.
The pen insert design takes into consideration another important factor of growing crayfish in containment systems. Like other species of crustaceans, they will fight and sometimes kill and cannibalize eachother. The vertical folds of the mesh in the pen insert minimize the occurrence of serious consequences of crayfish competition. If two fighting animals are on a horizontal surface, they will fight to the death. But on the vertical surfaces of the mesh, one of the competing animals inevitably loses its grip and fall to the bottom and the fight quickly forgotten.
Periodically the crayfish will have to be graded to remove the larger animals from the pen. However, it is important that not all the large animals be removed. Crayfish need the presence of a few large individuals to stimulate continued growth in the rest of the population. If all the large animals are removed, the remaining small animals will slow or cease growth.
The grow-out phase is currently two years, but with advances in prepared feeds, it is hoped to reduce the nursery and grow-out phase to 12-14 months. Scale of production increases or the formation of grower cooperatives is envisioned to meet the requirements for accessing European markets, where orders will typically consist of 1000 or more pounds of live crayfish.
Bio-Remediation
The existence of many abandoned quarries in BC indicates that not only is there a large potential to develop crayfish aquaculture, but that the introduction of crayfish farming into many of these quarries will restore the water quality and maintain the balance of algal and aquatic plant growth and decay. Nutrient-laden runoff water from surrounding land areas leads to massive algal and aquatic plant blooms in many of these quarries. The consumption of the nutrients and subsequent die-off of the plants or algae results in eutrophication of the pond or quarry. The result is not only a foul smell but a lack of capacity of the pond or quarry to sustain diverse forms of aquatic life. Healthy crayfish farms, like marine shellfish culture operations, are signs of a healthy environment.
Printed sources to consult about crayfish:
- “Abandoned quarry the home for new crayfish business on Vancouver Island”, Northern Aquaculture, Volume 8, No. 8, August 2002.
Thanks to Bill Bennett (Pacific Royalty Crayfish Ltd.) for information and photographs.