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Brown, P.B. 1993. Soft-shell crayfish: A new crop for the Midwest. p. 654-656. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Soft-Shell Crayfish: A New Crop for the Midwest*

Paul B. Brown


  1. AQUACULTURE
    1. Culture
    2. Economics and Marketing
  2. METHODOLOGY
  3. RESULTS AND DISCUSSION
  4. SUMMARY
  5. REFERENCES
  6. Table 1
  7. Fig. 1

Crayfish production consistently ranks as one of the largest aquacultural industries in the United States, typically the second largest industry behind culture of channel catfish (USDA 1991). The primary production areas include Louisiana, Texas, Arkansas, and other southern states, and annual production ranges from 35 to 55 million kg (Huner and Barr 1984; Roberts and Harper 1988). However, supplies of fresh crayfish from those areas are seasonal, typically available from December through June (Huner 1990; Huner and Romaire 1990). Reproductive characteristics of native midwestern crayfish species are offset seasonally from crayfish in the South (Page 1985; Hobbs and Jass 1988); thus, production may be seasonally offset. Preliminary studies to date indicated that the production season in the Midwest will be June through November (Brown et al. 1990). Thus, midwestern farmers have an opportunity to fill a market niche with a native species at a time of year when there is no competition for fresh product.

Crayfish production can be divided into two distinct segments: hard- and soft-shell production (Huner 1990; Huner and Romaire 1990). Hard-shell producers market tail meat, similar to shrimp production, while soft-shell producers market the entire body, similar to soft-shell crab production. Soft-shell production requires a dependable source of relatively large, hard-shell crayfish.

Studies conducted in our laboratory have indicated significant potential for pond production of native species for the tail-meat market (Table 1). In our first attempt at producing the northern or fantail crayfish (Orconectes viriles), production levels were dependent on initial stocking strategy, but ranged from 323 to 807 kg/ha when fed agricultural forages (Brown et al. 1990), which compares favorably with average production levels in the South of 545 to 691 kg/ha (Roberts and Harper 1988). That initial study and two regional symposia on crayfish culture stimulated a great deal of interest in crayfish and construction of ponds was initiated. The next step in providing opportunities to midwestern farmers is evaluation of soft-shell production.

AQUACULTURE

Culture

A typical scenario in producing soft-shell crayfish involves collecting or harvesting hard-shell crayfish from wild populations or aquaculture ponds and transporting them to an indoor, controlled molting facility. Groups of crayfish are then stocked into relatively shallow tanks (<0.3 m), fed any of a variety of feeds including potatoes, whole fish, carrots, or one of the new formulated diets for crustaceans, and premolt individuals are identified and moved to separate molting tanks (Culley et al. 1985). All crustaceans are cannibalistic, particularly when one of their cohorts molts in a communal tank; thus, identifying and moving premolt animals is an important economic consideration.

Economics and Marketing

Soft-shell producers in the South purchase crayfish for $0.07 to 0.50 per kg, transport those animals to controlled, indoor tanks, and wait for the animal to molt, which typically takes 1 to 4 weeks. Soft-shell crayfish retail for $1.80 to $3.60 per kg. Thus, the profit margin and relatively quick turnover of product entices many farmers into soft-shell production.

Markets for crayfish have been expanding in recent years. The market in northern Europe is especially promising, as several festivals in the fall of each year are centered on consumption of crayfish, yet their native species have been decimated by an introduced fungal epidemic (Huner 1990). Southern producers can supply only frozen product during that portion of the year, whereas midwestern producers can supply fresh product.

Our objective in this research was to evaluate the potential of soft-shell production of crayfish using one of the more promising midwestern species, O. viriles. Specifically, we examined the effects of selected rearing temperatures on molting frequency.

METHODOLOGY

Northern crayfish were obtained in September from a producer in Indiana and transported to the Purdue University Aquacultural Research Laboratory. Those individuals weighed 20 to 55 g and pond water temperature was 19° to 24°C at the time of collection. Crayfish were divided into similar groups (equal numbers of male and female) and immediately stocked into crayfish molting trays (2.0 x 0.8 x 0.1 m). Water temperatures were set at either 20°, 25°, or 30°C using submersible chillers or heaters and triplicate tanks were used at each temperature.

All crayfish were fed a commercially-available crustacean diet (Zeigler Brothers, Gardners, PA) to satiation twice daily and individual premolt crayfish (those individuals within 1 to 2 days of molting) were removed to separate tanks. Cumulative molt and survival data were collected from each temperature treatment.

RESULTS AND DISCUSSION

Both male and female crayfish molted at the three temperatures; there were no significant differences among sex. Those reared at 20°C exhibited the largest number of successful molts and the fewest numbers of deaths (Fig. 1), while number of successful molts declined and numbers of deaths increased with increased temperatures. Differences observed at 20deg. vs. 30°C were significantly different (P<0.05). Unpublished data from our laboratory indicated that 25°C was optimal for juvenile O. viriles and weight gain of crayfish at 25°C was significantly higher than those reared at 20°C. Thus, optimal temperature for growth may decrease in older animals.

While the absolute numbers of crayfish that molted over the 30-day experimental period was higher at 20°C compared to higher temperatures, a higher percentage molted in a shorter period of time at 30°C than at lower temperatures. That molting activity was completed prior to significant increases in mortality. Thus, more rapid turnover of crayfish from molting facilities may be possible using controlled temperature manipulations.

Regardless of temperature, there was a biphasic response of molting activity. That response became more dramatic as temperature increased from 20° to 30deg.C. In general, a large number of crayfish molted within the first 5 to 10 days (as many as 64% of the population reared at 30°C), followed by a quiescent period, then another period of molting. This observation has important management implications. For example, if an economically-large segment of any population molts within a shorter period of time than expected (up to 4 weeks), then more rapid turnover of that commodity may be possible, thereby increasing the amount of marketable product through a production season. Several other factors such as length of photoperiod and water levels may influence molting frequency and synchronization within a given population.

SUMMARY

Native midwestern crayfish will molt in controlled situations and that molting is influenced by water temperature. Molting activity is relatively rapid, with a large percentage occurring within the first 10 days. The response, regardless of temperature, was biphasic and probably reflects individuals in different stages of the molt cycle when acquired. Those that were near stage E (ecdysis) in the molt cycle molted within the first 5 to 10 days, while those is earlier stages required approximately 15 days to molt. Management options are now available to aquaculturists that will allow more carefully manipulated molting activity patterns in populations of native midwestern crayfish. The results of this study should be considered promising and, coupled with ongoing studies in our laboratory, will facilitate growth of the crayfish industry in the Midwest.

REFERENCES


*This study was funded by the Indiana Corporation for Science and Technology (now the Business Modernization and Technology Corporation).
Table 1. Mean production of northern crayfish (Orconectes viriles) in deep or shallow pondsz.

Treatment Productiony
±SE (kg/ha)
Deep ponds
Wheat straw 457±107
Corn silage 323±163
Negative control (no inputs) 422±216
Shallow ponds
Wheat straw 807±41
Corn silage 784±101
Negative control (no inputs) 779±73
zData from Brown et al. (1990).
yMeans of three replications.


Fig. 1. Mean cumulative number of male (M) or female (F) crayfish that molted (molt) or died (mort) when reared at 20° (A), 25° (B), or 30°C (C).

Last update September 19, 1997 aw