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Aquaculture 185 2000 281–289 www.elsevier.nlrlocateraqua-online
A comparison of mixed-sex vs. monosex growout and different diets on the growth rate of freshwater
ž crayfish Cherax albidus
C.S. Lawrence , Y.W. Cheng, N.M. Morrissy, I.H. Williams
Fisheries WA, Research DiÕision, P.O. Box 20, North Beach, WA 6020, Australia Accepted 7 November 1999
Abstract
Growth and density in freshwater crayfish are inversely related and this is compounded by Ž
. uncontrolled reproduction in growout ponds. Growth rates of yabbies Cherax albidus were
compared in monosex and mixed-sex populations using three feeding regimes to assess whether preventing reproduction in ponds and improving feed quantity or quality could reduce stunting.
Male monosex populations grew on average 68 faster than female monosex populations and 53 faster than mixed-sex populations. Female yabbies in monosex culture grew 9 slower than
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males and females combined in mixed-sex 50:50 populations. Both males 17 and females Ž
. 31 in monosex culture grew faster than males and females in mixed-sex culture. Stocking
ponds with only male yabbies resulted in a 70 greater gross value of animals produced than normal mixed-sex production. While growth in monosex and mixed-sex populations was improved
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y2 y1
. by either increasing feed rates of lupins 2.5 to 5 g m
week or using a formulated diet, male
monosex populations still grew faster. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Cherax albidus; Monosex; Diet; Growth; Crayfish; Yabby
1. Introduction
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Yabbies Cherax albidus are indigenous to central and eastern Australia, and have Ž
received considerable aquaculture interest Smallridge, 1990; Brown et al., 1997;
. Lawrence, 1998 . Although some yabbies are produced from ponds on purpose-built
Corresponding author. Tel.: q61-08-9246-8415; fax: q61-08-9447-3062. Ž
. E-mail address: clawrencefish.wa.gov.au C.S. Lawrence .
0044-8486r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 0 4 4 - 8 4 8 6 9 9 0 0 3 5 8 - 0
farms, the vast majority of commercial yabby production in Australia comes from trapping self sustaining, multigenerational populations of essentially wild yabbies out of
water storage dams on farms. Poor growth of yabbies reduces the value of farm dam crayfish production, since the price received per kilogram for crayfish is directly related
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to individual weight of the animals Lawrence, 1998 . Several mechanisms, other than direct food supply, may limit the growth of crayfish
at increased densities. These include increased energy requirements to compete for food, Ž
or diversion of energy from somatic growth to reproductive effort i.e., competition for .
mates and production of gametes . Female crayfish develop large yolky eggs, and the energetic cost of this reproductive effort can be observed in female yabbies, which grow
at the same rate as males until sexual maturity at about 20 g, after which their growth Ž
. slows markedly relative to males Woodland, 1967 .
The yabby is an r-selected species and, consequently, has the potential to reach sexual maturity at an early age and size, and produce large numbers of offspring by
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repeated spawning each season Stearns, 1976; Faragher, 1983; Lake and Sokol, 1986 . If population growth is uncontrolled by mortality due to periodic drought, yabbies can
rapidly reach population densities where individual growth rates are greatly reduced. One way to control population density is to prevent reproduction. Juvenile yabbies
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are produced during the warmer months of the year September–May by broodstock contained within farm dams where there is currently little or no control by harvestors
over yabby reproduction or density. However, if farm dams were to be stocked with single sex individuals then reproduction could not occur and densities could not
increase.
Controlling reproductive effort and density by stocking ponds with individuals of only one sex has been shown to be an effective way of increasing production in other
freshwater crustaceans. For example, monosex culture of the freshwater prawn, Macro- brachium rosenbergii, has demonstrated increased average weights for male populations
Ž relative to mixed-sex or female-only populations Sagi et al., 1986; Cohen et al., 1988;
. Ž
. Hulata et al., 1988 . Monosex culture of redclaw Cherax quadricarinatus , a tropical
freshwater crayfish, has demonstrated improved growth rates for male-only populations Ž
. Ž
. 1.12 grweek over mixed-sex populations 0.52 grweek and female-only populations
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. 0.27 grweek
Curtis and Jones, 1995 . Some reproduction occurred in ponds in their experiment and the superior growth rate of all-male populations compared to all-female
and mixed-sex cultivation was attributed to changes in density as well as retardation of female somatic growth due to the onset of sexual maturity. A more recent experiment
evaluating the monosex growout of redclaw crayfish also demonstrated improved
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Ž growth for male-only populations 2.93 grweek over mixed-sex populations 1.31
. Ž
. Ž .
grweek and female-only populations 1.06 grweek Sagi et al., 1997 . The improved
growth rate for redclaw in this experiment, compared with that reported by Curtis and Ž
. Jones 1995 , may be attributed to the use of weight frequency histograms by Sagi et al.,
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1997 to distinguish between stocked and newly recruited individuals. This research was aimed at evaluating the potential of single sex production as a
method for producing faster growth and larger yabbies. It also considered how feed quantity and quality influenced growth rate and size in conjunction with single sex
production.
2. Materials and methods
