Wednesday, August 10, 2011

Red Claw : Reproduction and Hatchery Techniques

Red Claw / Females
Red claw generally reach sexual maturity by the age of 6 to 12 months at which time they range from 2 to 3 ounces in weight. Mature male red claw develop a distinctive red or orange patch on the outside margin of the claws. Individuals of this same size without the reddish claw patch are usually females. The sexes are best identified, however, by examination of the genital openings on the underside of the cephalothorax at the base of the walking legs. Females have a pair of genital pores at the base of the third pair (counting from the head) of walking legs. Males have a pair of small genital papillae (small projections) at the base of the fifth pair of walking legs.

Red Claw / Males
In a hatchery red claw can spawn almost continuously throughout the year if conditions are suitable.
Individual females do not spawn when going through a growth phase (i.e.,molting). Each female will produce 100 to 1,000 eggs per spawn depending on her size and general health. The first spawn of young females usually has fewer eggs than latter spawns. Newly spawned eggs average 10 eggs per gram of female. About 30 percent of the eggs are lost during incubation, resulting in an average of 7 eggs (that hatch) per gram of female. For example, a female weighing 3 ounces (85 grams) would produce about 600 eggs. can be used to estimate the number of eggs a female of a given size will produce.

Natural reproduction will occur in ponds if the animals are mature and the water temperature is above 70oF.  Most Australian producers simply collect juveniles from ponds stocked with mature red claw. Juveniles seek shelter in suspended substrate like burlap, shade cloth, onion bag mesh, or window screen mesh hung vertically from the surface to the bottom of the pond from floats. These collectors are periodically checked and juveniles carefully removed from the mesh. This method results in low returns/survival, only 5 to 10 percent.  Juvenile growth and survival are limited because of lack of access to adequate food and to cannibalism which occurs among the juveniles. Production of red claw outdoors
in the southeastern U.S. is limited to five to seven of the warmest months. Therefore, outdoor spawning is not practical. The use of indoor hatcheries to spawn adults and rear juveniles during the winter months is the most practical and economical method in the U.S. Mature adults moved into hatcheries during late fall can be spawned during the winter. Young from these spawns can be reared indoors using natural and formulated feeds, then stocked into grow-out ponds the following spring. Stocking a one acre growout pond, at 10,000 to 12,000 juveniles per acre, will require approx-imately 70 adult females and 25 adult males (considering spawning and survival rates).
The key points to sucessful maintenance and reproduction o broodstock in indoor holding systems
1. select healthy  mature adults,
2. maintain warm  temperatures  (preferably 75 to 85oF),
3. maintain good  water quality,
4. provide proper nutrition, and
5. isolate berried females to hatching tanks.

Broodstock should be selected based on size, vigor, and general health. It is important to select large, healthy animals. Before introducing broodstock into the hatchery it may be a good practice to treat them with a salt or formalin dip to eliminate potential external pathogens. Specific studies on prophylactic treatments for red claw have not been conducted but recommended fish treatments (e.g., a prolonged bath of 1,000 to 2,000 ppm salt or 15 to 25 ppm formalin) have been used experimentally. These treatments did not seem to harm the red claw and have appeared to be effective at preventing introduction of para-sites. At present, there are no approved therapeutics for red claw.

Good water quality must be maintained in the holding tanks by using either a flow-through system utilizing warm water (e.g., geothermal) or a heated, recirculating system with particulate and biological filtration.  Water temperature in the system should be maintained between 75 and 85oF. Warmer water temperatures (80oF) and a longer photoperiod (12 to 14 hours of light) in the hatchery will increase spawning rates. Research has shown that peak spawning occurred at water temperatures of 82oF and 14 hours of light.    Light intensity should be low (just enough light for hatchery person- nel to work). Dark colored tanks with partial covers can reduce stress associated with intense light and movement around the tanks. Also tanks with smooth surfaces, like fiberglass or stainless steel, minimize damage to the exoskeleton of the crayfish. Damage or abrasions of the exoskeleton can lead to disease problems.
Red Claw Broodstock

Broodstock should be stocked into holding tanks at 1 to 3 animals per square foot of bottom area. Males should be of similar size (within an ounce of each other in weight), or spawning can be suppressed by nearly 50 percent. The ratio of females to males in each tank should be between 1 to 3 females for each male. Good spawning success has occurred using tanks with water depths of 1 to 3 feet. Small rectangular tanks of 15 to 20 square feet, as well as large circular tanks of 15 feet in diameter have been used successfully. Shallow rectangular tanks (8 to 10 feet long by 2 to 3 feet wide) with water 12 to 18 inches deep are commonly used. Red claw are excellent climbers and escape from tanks if the water level is near the tank top or if equipment such as air line tubing or heater cords extends over the sides of the tank. To reduce escapes, equipment should be suspended from overhead so that it does not touch the sides of the tank.

Source : Southern Regional Aquaculture Center / SRAC Publication No. 244 April 1997

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