Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

James W. Avault, Jr

Abstract

In most of the United States, overwintering redclaw crayfish (Cherax quadricarinatus) is necessary because they cannot withstand winter temperatures. Consequently, hatcheries are required to produce juveniles for pond stocking. The objectives of this study were: (1) identify biological factors affecting production of juvenile redclaw, (2) determine production capabilities of a redclaw crayfish hatchery, and (3) determine the economic potential of redclaw hatcheries. Experiments were designed to assess fecundity and factors influencing spawning such as stocking density, male/female weight, diet, mortality, and cannibalism. Research was also conducted to determine egg development time, hatching success, and juvenile growth and survival. Pooled survival and spawning data were used to estimate total production. Production data and information available from redclaw producers were compiled to determine the economics of juvenile redclaw production. Results of these studies showed no suppression of spawning at densities up to 32 crayfish/m$\sp2$ (P = 0.59). Male size did not affect spawning success when males were within 25 g of each other (P = 0.39), but mixed males (small, medium and large, together) resulted in a 49% reduction in spawning (P $<$ 0.05). Female size did not affect spawning activity (P = 0.57). Varying dietary protein levels from 30% to 45% and adding beef liver or soybean supplements had no effect on the number of eggs per gram of female (P = 0.42). Total broodstock mortality increased linearly with increasing stocking density (P $<$ 0.05), and was lower (P $<$ 0.05) in tanks containing small males (40-65 g). Cannibalism was lower when crayfish were fed a 30% protein crustacean diet with beef liver supplements (P $<$ 0.05). Average number of eggs per gram of female body weight was 6.3 $\pm$ 3.8 (mean $\pm$ SD). Egg incubation took 40.9 $\pm$ 3.2 days (mean $\pm$ SD) at 28$\sp\circ$C, from the first developmental egg stage (khaki/olive color). Egg loss through incubation was high (60.5%), partly due to handling stress. Juvenile production was 3.9 $\pm$ 0.9 juveniles per gram of female when grown to 0.5 g (mean weight). During the experiments, gravid females were encountered at a rate of 4.8% per week while total mortality (cannibalism and death) averaged 2.8% per week. Economic results indicate that raising redclaw is limited for markets in which juveniles will be sold for pond stocking. Based on production and economic data, juvenile costs are approximately $0.49 each.

Pages

82

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