Red claw eggs go through several identifiable stages during development. The length of development varies depending on water temperature. The stages are identified by colour changes and appearance of body structures in the developing embryo.
The sequence of development stages and approximate timing at 82o F is:
- stage 1 - light cream colour (day 1-3),
- stage 2 - dark brown (day 12- 14)
- stage 3 - eye spots (day 20-23)
- stage 4 - hatched, orange-red in colour (day 28-35)
- stage 5 - released (day 35-40).
Hatching can occur within 30 days at 82o F but may take as many as 45 days at 75o F. Females in hatching tanks should be grouped according to similar egg development and should not be disturbed during early stages of egg development.
Young remain attached to the females’ swimmerets for about 7 to 10 days after hatching, becoming independent of the mother over a period of several days. This post-hatch period appears to be important to the survival of the young.
Therefore, females should be removed from the hatching tanks only after the young are no longer observed clinging under her tail. One word of caution: females have been observed cannibalizing their young if crowded into small hatchery tanks or aquaria.
The keys to good juvenile survival in the hatchery are stocking density, size uniformity, cover, nutrition, and water quality. Stocking density of juvenile red claw should not exceed 25 per square foot of nursery tank bottom.
At this density 50 to 75 percent survival should be expected. Again, juvenile numbers can be estimated from the females’ size. Many producers prefer shallow (6 to 12 inches deep) tanks for this phase.
Handling the newly hatched juveniles during the first few weeks should be avoided as they are easily injured. Research has shown that formulated feeds and adequate substrate in juvenile rearing tanks increase overall growth and survival.
Juveniles 2 inches or longer (>1 gram) will have a much higher survival rate when stocked into ponds. Indoor hatcheries can improve the quantity and quality of juveniles available for stocking and could make larger juveniles available for differential stocking.
Older (i.e., larger) juveniles tend to cannibalize smaller ones, hence the need to group females together in the hatching tanks that have a similar egg stage or larval development. Juvenile red claw growth rates will vary. After four weeks a few individuals may be five times larger than others in the tank.
Overall survival can be improved by grading or removing the larger juveniles. Netting or screening should be added to juvenile tanks, providing hiding places to reduce cannibalism. Any habitat that provides a large surface area, adequate water flow, and access to the bottom for feeding should improve survival.
Some substrates which have been used effectively are fiberglass window screen, shade cloth, and mesh bags in which onions and citrus fruits are packaged. Nutrition is also an important aspect in juvenile production.
Newly hatched red claw occupy a very small territory (a few square inches). Therefore, feed must be distributed throughout the tank so that juveniles will have access to it both on the bottom and within the mesh. Several diets have been used to rear juveniles in the hatchery.
At the present time, the best recommendation is to feed a high protein (>33 percent) commercial shrimp diet. Juveniles should be fed at 40 percent of estimated biomass per day, with the feed being fed over three to five feedings a day.
Improved survival and growth have been obtained by feeding brine shrimp (Artemia) during the first week. Newly hatched brine shrimp nauplii are best but frozen adult brine shrimp have been used. Brine shrimp can be substituted for one of the daily feedings of formulated diet.
Care should be taken to ensure young crayfish have all they can eat without overfeeding. Overfeeding can quickly cause deterioration of water quality. Excess food should be removed from tanks by siphoning daily. Feeding behaviour and water quality should be closely monitored.
Maintaining good water quality is always important, especially with young crayfish. Care should be taken to ensure that old feed and wastes do not accumulate and that proper aeration, filtration, and circulation are maintained.
Survival of juveniles in the hatchery should average 50 to 70 percent. Once the juveniles reach about 1 to 2 inches in length and weigh approximately 1 /28 of an ounce (1 gram) they can be stocked into grow-out or production ponds if pond water temperatures are above 68o F.
Authors:
Michael P. Masser and David B. Rouse
