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 (Figure 2).
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.
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.
Figure 3 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 70o F. 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 approximately 70 adult females and 25 adult males (considering spawning and survival rates).
The key points to successful maintenance and reproduction of broodstock in indoor holding systems include:
- select healthy mature adults,
- maintain warm temperatures (preferably 75 to 85o F),
- maintain good water quality,
- provide proper nutrition, and
- 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 parasites. 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 85o F. Warmer water temperatures (80o F) 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 82o F and 14 hours of light.
Light intensity should be low (just enough light for hatchery personnel 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. 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.
Research has shown that red claw are most active in the evening between 6 p.m. and midnight (Figure 4). This should be the best time for daily feeding since the animals are actively foraging during this period.
Broodstock nutrition is extremely important. Broodstock should be fed a complete diet (with vitamin and mineral supplements). Sinking crayfish or shrimp feed (at least 28 percent protein) fed at 3 percent of body weight per day is recommended. Some hatchery operators like to supplement formulated diets with fresh foods.
These supplements have included frozen mixed vegetables, bird seeds, and chopped beef heart or liver. Care should be taken not to overfeed, especially with fresh food, because it may adversely affect water quality.
During mating the male red claw will attach a spermatophore (sack containing sperm) to the underside of the female between the third and fifth pair of legs. The spermatophore is white and about 1 /3 inch in diameter. Within 24 hours the female usually releases eggs from the pore on the base of the third pair of walking legs.
These eggs are fertilized by the spermatophore as they are released. Female red claw, like native crayfish, attach the eggs to the swimmerets under their tail or abdomen. The eggs remain attached through the incubation period (Figure 5). The incubation period may last 4 to 6 weeks depending on water temperature. At 82o F the incubation period averages 30 days.
Individual eggs are oval and about 1 /10 of an inch in diameter. Females carrying eggs are called “berried” females. Berried females are easily recognized because they tightly curl their abdomen under the body for the first 10 to 14 days after spawning. They are also less active during this period.
Berried females should be moved to separate spawning tanks so that the young hatchlings do not have to be captured from the broodstock tanks. Broodstock tanks should be checked for berried females at three to four week intervals.
Berried females must be carefully netted and transferred to hatching tanks (to prevent egg loss). Keep the berried females with their abdomen curled around the eggs during transfer to prevent eggs from being dislodged by tail movements.
Authors:
Michael P. Masser and David B. Rouse
