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Analysis of a diallel cross to estimate effects of crossing on performance of red swamp crawfish, Procambarus clarkii
Aquaculture Aquaculture
ELSEVIER
121 (1994) 301-312
Analysis of a diallel cross to estimate effects of crossing on performance of red swamp crawfish, Procambarus clarkii Brian G. Bosworth’, William R. Wolters2,*, Arnold M. SaxtorF3 School of Forestry, Wildlife, and Fisheries, and aDepartment OfExperimental Statistics, Louisiana Agriwltural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA (Accepted 14 October L993)
Abstract A comlplete diallel cross among three populations of red swamp crawfish, Procambarus clarkii, was used to estimate genetic effects for body size traits and dressout percentage. Offspring were grown in 2.4-meter diameter fiberglass pools with rice as forage. Crawfish were harvested after 150 days, sorted by sex and male maturity stage, and measured for dressout percentage and nine body size traits. Estimates of heterosis, line, maternal, reciprocal effects and general combining ability for traits were obtained by forming contrasts among appropriate least squares means. Estimates were made for all animals combined and for rnature males, immature males, and females separately. Significant (PC 0.05 ) heterosis and line effects for dressout percentage indicate identification of strains with higher dressout percentage may be possible. Significant (PC 0.05 ) maternal effects for body size traits of females and mature males suggest a difference in egg size, egg quality or cytoplasmic inheritance among populations.
1. Introduction Procambarid in the United
crawfishes are the only crustacean species cultured on a large scale States. The majority of crawfish are produced in Louisiana, where
*Corresponding author. ‘Present address: 114 Cheatham Hall, Virginia Tech University, Blacksburg, VA 2406 1, USA. ‘Present address: USDA/ARS Catfish Genetics Research Unit, P. 0. Box 38, Stoneville, MS 38776, USA. ‘Present a.ddress: Statistical and Computing Services, P.O. Box 107 1,University of Tennessee, Knoxville, TN 37901-1071, USA. Elsevier Science B.V. SSDIOO4.4~8486(93)
E0252-5
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B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
crawfish culture ponds occupy over 50000 ha and 25-30 million kg of crawfish are harvested annually (Louisiana Cooperative Extension Service, 1986 ). Red swamp crawfish, Procumbarus clurkii, account for over 90% of the commercial harvest in Louisiana. As crawfish culture continues to expand, producers and processors are attempting to increase their profits. Genetic improvement of growth and dressout percentage has been identified as a possible way to increase prolitability (Lutz and Wolters, 1989). Evaluation and crossbreeding of strains have been useful approaches in improving production characteristics of farm animals (Gjedrem, 1983). Tave ( 1986 ) defined a strain as those individuals of a species that come from a particular location or that are produced in a particular breeding program. Because gene frequencies may differ between strains from genetic drift, natural selection, migration and differential mutation (Gardner and Snustad, 198 1 ), strains may also differ in traits influenced by those genes. Crossing of strains to utilize favorable heterotic effects in offspring has been widely used in domestic plant and livestock species. Little information exists on strain evaluation and crossing of crawfish or other decapod crustaceans. Sarver et al. (1979) reported differences in larval development rate between strains of prawns, Macrobrachium rosenbergii. Interspecific crosses between American lobsters, Homarus americanus, and European lobsters, Homarus gummarus, yielded hybrid offspring with growth rates similar to purebred offspring (Carlberg et al., 1978). It may be possible to identify red swamp crawfish strains or crossbreds with faster growth and higher dressout percentage. Objectives of this study were to evaluate three populations of P. clurkii within Louisiana for differences in ten body size traits and estimate genetic effects from all possible crosses and the potential for improving these traits.
2. Materials and methods Broodstock collection, mating, and offspring production During the spring of 1987 approximately 30 male and 30 female adult red swamp crawfish, Procambarus clarkii, were collected from each of three locations in Louisiana. Crawfish from these locations were designated as: Strain B, collected from research ponds at the Ben Hur Research Farm, LSU, Baton Rouge, LA; Strain H, collected from a commercial crawfish pond near Hathaway, LA; and Strain P, collected from a commercial crawfish pond near Plaquemine, LA. Adults were held individually in partitioned 40-liter polyethylene tanks and fed a commercial shrimp ration during the summer of 1987. Matings were initiated on 5 September 1987 using a complete diallel cross model (Gardner and Eberhart, 1966). Prior to mating, each female’s annulus ventralis was cleaned with 95% ethanol and abrasive pads to remove any previously acquired spermatophores (Berrill, 1985 ). Males and females from each strain were divided equally among crosses and allowed to mate at random until all crosses had been completed. Mated females were held individually in covered, parti-
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
tioned 40-liter tanks and and hatch were recorded Offspring from crosses aeration and previously Lutz and Wolters, 1989). each cross and randomly instar juveniles per pool.
303
fed a commercial shrimp ration. Dates of egg deposition for each female. were stocked into Iiberglass pools supplied with diffuse planted with rice for forage (Craig and Wolters, 1988; Offspring were pooled from all available females within stocked into three replicate pools per cross at 30, third-
Data collection and analysis Crawfish were harvested after 150 days and sorted by sex and stage of male maturity (Huner and Barr, 1984). Crawfish were measured for carapace length, carapace width, abdomen length, abdomen width, abdomen depth, chela length, chela width and total length with a standard measuring board or digital calipers, and weighed to the nearest 0.1 gram. Regression of mean total length of crawfish on density at harvest was used to determine if density affected growth (Lutz, 1987 ). Dressout percentage was calculated on five mature males, five immature males, and five females selected at random from each pool. In 10 of 27 pools fewer than five immature males were found, and in 6 of 27 pools fewer than live mature males were present. Percentage of mature males was calculated for each pool based on the number of mature males present. Differences in body size traits, dressout percentage and percent male maturity were analyzed in a nested analysis of variance. Body size traits and dressout percentage were analyzed for all animals combined and for mature males, immature males and females separately. Differences in percent male maturity were analyzed by coding mature males as 1’ and immature males as 0’ (Gjerde, 1984). Differences in trait means were declared significant at ac0.05. Least squares means of crawfish body size traits, dressout percentage and percent male maturity from each cross were compared with a series of estimate statements in the GLM procedure (SAS, 1988) to determine average heterosis, line heterosis, specific heterosis, maternal effects, line effects, reciprocal effects and general combining .ability (Eisen et al., 1983). Estimates were tested for significance with a corresponding series of contrasts, using pool within cross mean squares for error terms (SAS, 1988) and declared significant at a~0.05. The model used in the analysis was (Eisen et al., 198 3 ) :
where Yij~r=trait measured on the Ith individual of sire line i and dam line i in pool k y= = mean of parental lines li = yii- ya - mi = average direct effect of line i mi=y.j.-yj, =average maternal effect of linej, where yj. (y,j) = mean of sire (dam) line,; including the parental line h,= (Y,;+Yji)/2- (JJii+ya)/2=direct heterosis for the (g)th cross ry = r& (mj- mi) /2 = specific reciprocal difference between lines i and j, where: rii= reciprocal effects = (Yij- Yji) /2
CD (mm) All animals Mature males Immature males Females
CW (mm) All animals Mature males Immature males Females
n=168 n= 166 n=346
n=680
n=346
n= 168 n=166
n=680
n=346
n=680 n=168 n= 166
n=680 n=168 n= 166 n=346
TL (mm) All animals Mature males Immature males Females
CL (mm) All animals Mature males Immature males Females
n=680 n=168 n=166 n=346
All animals Mature males Immature males Females
TW (g)
44.2(0.4) 44.3(0.7) 43.9(0.8) 44.5(0.7)
20.8(0.3) 21.8(0.5) 20.7(0.6) 20.3(0.4)
50.1(0.7) 51.9(1.1) 51.1(1.2) 48.5( 1.0)
94.4(1.1) 96.3( 1.8) 95.0(2.0) 93.0( 1.7)
25.2( 1.2) 31.3(2.6) 23.4( 1.9) 22.9( 1.5)
P-P
45.2(0.5) 44.3(0.9) 44.8(1.3) 45.6(0.6)
21.0(0.4) 21.7(0.9) 21.0(0.9) 20.9(0.5)
50.3(0.8) 50.9( 1.7) 51.1(2.0) 49.8(0.9)
95.4( 1.3) 94.2(2.5) 95.8(3.3) 95.5( 1.5)
24.9( 1.3) 29.9(3.3) 26.0(2.2) 23.5( 1.4)
P-B
Cross (female strain-male
42.8(0.5) 43.0(0.6) 43.3( 1.5) 42.6(0.7)
20.5(0.3) 21.7(0.5) 20.6( 1.0) 19.9(0.5)
48.2(0.7) 50.8( 1.0) 48.6(2.1) 46.7(0.9)
91.1(1.1) 93.8( 1.6) 91.9(3.6) 89.3(1.5)
23.4( 1.2) 29.9(2.1) 22.4(3.3) 19.9( 1.5)
P-H
strain)
46.0(0.5) 46.8(0.6) 45.9( 1.0) 45.7(0.8)
27.8(0.4) 23.7(0.6) 21.5(0.7) 20.9(0.5)
54.1(0.7) 54.8( 1.0) 51.8(1.4) 49.9( 1.0)
97.3( 1.2) 101.7(1.6) 97.7(2.4) 95.6( 1.7)
25.9( 1.2) 35.6(2.4) 26.0(2.2) 22.7( 1.4)
B-P
44.8(0.4) 44.9(0.5) 43.5(1.8) 45.1(0.6)
21.8(0.3) 22.7(0.4) 21.0(1.2) 21.5(0.3)
50.4(0.6) 51.7(0.8) 50.2(2.7) 49.8(0.7)
95.2( 1.0) 96.6( 1.3) 93.8(4.5) 94.9( 1.3)
28.2(1.1) 34.6( 1.8) 25.9(3.2) 25.2( 1.2)
B-B
44.2(0.4) 44.2(0.6) 44.3(0.9) 44.2(0.7)
21.7(0.3) 22.9(0.4) 21.7(0.6) 21.1(0.4)
49.0(0.6) 50.9(0.7) 49.2( 1.3) 47.8(0.8)
93.2(1.0) 95.1(1.2) 93.5(2.2) 92.1(1.5)
24.6(0.9) 30.0( 1.5) 23.8( 1.7) 22.1(1.2)
B-H
46.7(0.5) 46.5(0.6) 41.9(1.7) 47.9(0.7)
22.3(0.3) 23.1(0.5) 19.3(0.8) 2.5(0.5)
52.2(0.7) 53.1(0.9) 46.6( 1.8) 52.9(0.9)
98.9( 1.2) 99.6( 1.5) 88.5(3.5) 100.8( 1.6)
31.4( 1.4) 36.9(2.1) 18.4(2.1) 30.1(1.9)
H-P
43.5(0.8) 44.3(0.8) 41.0( 1.4) 45.3(1.1)
20.4(0.4) 20.5(0.7) 19.1(0.7) 20.7(0.7)
48.2(0.9) 51.9(1.4) 46.0( 1.5) 48.7( 1.4)
91.8(1.6) 96.2(2.1) 86.9(2.5) 94.0(2.4)
24.6( 1.5) 33.9(3.5) 19.4(2.2) 25.2(2.1)
H-B
Table 1 Means ( f s.e. ) of body size traits, dressout percentage and percentage male maturity of offspring from a diallel cross among Plaquemine (B) and Hathaway (H) strains of red swamp crawfish, Procumbarus clurkii
44.5(0.5) 47.1(0.6) 42.5 (0.9) 44.3(0.8)
20.6(0.4) 23.3(0.5) 19.2(0.5) 20.1(0.5)
47.3(0.7) 51.9(1.0) 44.7( 1.3) 46.3(1.1)
91.8(1.2) 99.0( 1.6) 87.2(2.2) 90.6( 1.8)
23.8( 1.4) 36.9(2.4) 17.7( 1.7) 20.5( 1.5)
H-H
(P), Ben Hur
B.G. Bosworth et al. /Aquacu&ure 121(1994) 301-312
hhhh
*.I?” 0006 v--v CO-t-ti
ti
i
i
-e-e
22~~~ w--m II II II EEEE
Z%ZZ w--m II
II
II
EEEr
II II
Mature males Line effects P B H (se.)
All animals Line effects P B H (se.) Maternal effects P B H (s.e.) Specific heterosis PxB PxH BxH (se.)
(lips)
-2.1 0.7
0.6 1.5 -0.3 (1.2)
-1.3 2.9 - 1.7 (2.2)
1.6 1.9 - 1.1 (2.2)
-5.5* 1.0
(0.9)
(1.5)
(1.5)
1.8* -0.6 -1.2
1.8 -0.8 (1.3)
-1.0
CL
3.2* -0.4 -2.3
(::04)
-3.8 2.8
TW
3.4* -1.2 -2.3
-2.9 2.5
TL
Trait
0.0 0.7 -0.2 (0.6)
0.8 -0.6 -0.2 (0.4)
-1.1 1.3 -0.2 (0.6)
cw
- 1.2* 0.5 0.8 (0.5)
(0.5)
(1.0)
- 3.4* 0.3 2.0 (1.0)
0.2 0.4 -0.2
0.6 -0.3 -0.3 (0.3)
(&
-0.8 0.8
AD
1.1 0.4 -0.8
(0.7)
1.7* -0.5 -1.1
(ll::)
- 1.9 0.8
AL
-0.9 0.2 0.6 (0.5)
(K )
0.4 0.4
0.4 -0.2 -0.2 (0.3)
(0.4)
-0.5 0.5 0.0
AW
-6.6* 2.1 4.5 (2.5)
-4.2* 3.9* - 1.6 (1.7)
3.4* -1.4 -2.0 (1.2)
-3.7 5.1* -1.4 (1.8)
CHLL
Table 2 Estimates ( T s.e. ) of genetic effects for body size traits and dressout percentage from a diallel cross among Ben Hur (B), Plaquemine (H) strains of red swamp crawfish, Procambarus clarkii
(::: )
-2.9* 0.7
(0.7)
-2.1* 1.2 - 1.3
1.1* -0.4 -0.7 (0.5)
- 1.7* 1.8* -0.1 (0.7)
CHW
0.9 -0.7 -0.2 (0.6)
2.5* -0.5 -0.7 (0.7)
(0.4)
0.0 0.6 -0.6
(2d.Y)
-0.3 -2.2.
DO
(P) and Hathaway
5 :, :
$
P 3 s 2
g
s
2 R
$ x
:
4.9*
(Y )
-3.6 1.2
-4.8 2.4
(Z)
) -1.3 1.5 0.5 (1.5)
0.8 2.5 0.1 (1.4)
-0.7 3.9 (E
2.2* 0.2 -2.4* (1.0)
3.5 1.2 -4.7* (1.8)
0.8 3.7 0.2 (2.5)
-0.2 -4.7* (1.7)
2.5 3.0 -5.5 (2.9)
ci:;,
-(E)
2.4 4.9 -7.3 (4.2)
1.9 -0.8
3.8 -0.4
(E
-1.3 1.1 )
cod.:,
0.1 1.2
1.0* -0.2 -0.8 (0.5)
0.6 1.7 -2.3 (1.3)
1.0 -0.6 -0.3 (0.5)
-1.0 0.6 0.4 (0.6)
-2.9 1.0
-0.6 0.4 0.3 (0.5)
0.3 0.7 0.2 (0.5)
0.6 0.0 -0.5 (0.3)
0.4 0.7 -1.2 (0.8)
0.5 -0.3 -0.2 (0.3)
-3.0 3.2 -0.2 (2.1)
-1.3 1.1 0.2 (0.9)
(2d.56,
-0.6 -1.8*
2.3* -0.7 -2.2* (0.9)
-1.7 1.4 -0.3 (0.8) -3.2 4.1’ (G)
-0.2 0.0 0.2 (0.6)
,?.;
-1.7 -3.4+
0.1 -0.3 0.2 (0.5)
1.1 0.3 - 1.3* (0.5)
0.5 1.8 -2.3” (1.0)
1.2 -0.2 -:.3 (0.7)
2.9* 0.7 - 3.6* (1.3)
2.0 6.1 -go* (3.3)
4.2* -1.1 -3.: (1.7)
length, AD = abdomen depth, AW = abdomen width,
(E)
(Z)
(Z)
0.0 0.6
0.8* 0.0 -0.8 (0.4)
0.2 1.0 -1.2 (1.0)
0.6 -0.4 -0.2 (0.3)
0.0 1.1
2.7* -0.4 -2.2* (0.8)
0.8 1.7 -2.5 (2.1)
2.0* -0.9 -!.! (0.7)
*Significant at P>O.O5. TW = total weight, TL= total length, CL = carapace length, CW = carapace width, AL=abdomen CHW = chela width, CHL = chela length and DO = dressout percent.
Females Maternal effects P B H (s.e.) Specific heterosis PxB PxH BXH (s.e.) Line effects P B H (se.)
3.2 4.7 -7.9 (4.9)
Immature males Line effects P B H (se.)
3.91
- 1.7 -2.3 (1.6)
Maternal effects P B H (se.)
S
$
s “2 g
$ k 6 2 z S
S 2
% ia g
308
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
effect of kth p001 nested in the ( ii) th CROSS eijk/= random error
pijk=
Water temperature and dissolved oxygen were measured twice weekly with a portable meter. Total water hardness in each pool was determined by EDTA titration (Boyd, 1979 ) at the beginning, midpoint and termination of the study. Differences in pool means for water temperature, dissolved oxygen and water hardness were analyzed in a one-way analysis of variance and declared significant at cr
3. Results Water quality Water temperature, dissolved oxygen concentration and total water hardness were not signficantly different between pools. Water temperatures ranged from 4.5 to 23.O”C and total water hardness ranged from 102 to 222 mg/l. Dissolved oxygen concentration was variable and inversely related to water temperature. The lowest dissolved oxygen concentration was 88% of saturation ( 15.0 mg/l at 9.5”C) and the highest was 129% of saturation (9.5 mg/l at 23.O”C). Survival and growth of offspring In each cross one to three females produced offspring used in the analyses. Mean survival of crawfish was 84% (range 60 to 97%). A total of 680 animals was harvested, sexed and measured. Average growth rate for offspring from all crosses was 4.4 mm/week. Average growth rates for mature males, immature males and females were 4.5, 4.3 and 4.4 mm/week, respectively. Total length of crawfish at harvest ranged from 57 to 120 mm. Regression of mean total length on density at harvest was not signficant and no adjustment of total length was necessary (Lutz, 1987). Means of crosses Chela length, chela width and dressout percentage were significantly different between crosses in the analysis of all animals combined (Table 1). Dressout percentages of immature males and females were significantly different among crosses; no traits of mature males were different among crosses (Table 1). Estimation of genetic effects Body size traits - all crawfish combined. Heterosis and line effects were significant for chela width and length (Table 2). Maternal effects were significant and positive for most body size traits of offspring from Plaquemine strain crosses (Table 2). Body size traits -
mature males. Line effects were significant
and negative for
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
most body size traits of mature male offspring from Plaquemine (Table 2). Maternal effects were signficant and positive for total men length and chela length of mature males from Plaquemine (Table 2 ). Other effects were nonsignificant for body size traits of
309
strain crosses length, abdostrain crosses mature males.
Body si.ze traits - immature males. Line effects were significant and negative for chela length and width of immature males from Hathaway crosses (Table 2). No other effects were significant for body size traits of immature males. Body size traits-females. Maternal effects were significant and positive for most body size traits of female offspring from Plaquemine strain crosses (Table 2). Maternal effects were significant and negative for most body size traits of female offspring from Hathaway strain crosses (Table 2). Other effects were nonsignificant for body size traits in female offspring. Dressout percentage and percent male maturity. Positive heterosis for dressout percentage was observed in all animals combined and females from crosses between F’laquemine and Ben Hur strains (Table 2 ) . Negative heterosis for dressout percentage was observed in females from crosses between Ben Hur and Hathaway strains (Table 2 ). Negative line effects for dressout percentage were observed in immature males, females and all animals combined from Ben Hur crosses (Table 2 ). No effects were significant for percent male maturity.
4. Discussion Water temperature, dissolved oxygen concentration and water hardness were within ranges suitable for culture of P. clarkii (De la Bretonne et al., 1969; Huner and Barr, 1984). Average growth rate observed in this study, 4.4 mm/week, was within the range of growth rates ( 1.3-6.0 mm/week) for P. clarkii grown in ponds and experimental pools (Romaire, 1976; Chien and Avault, 1980; Craig and Wolters, 1988; Lutz and Wolters, 1989). Avera.ge survival of crawfish in this study, 84%, was higher than survivals of 4 1% and 64% previously reported in experimental pools (Craig and Wolters, 1988; Lutz and Wolters, 1989) even though water quality variables, forage, and stocking density were similar to those studies. Because of differential survival among replicate pools, previous studies have adjusted body size traits for density at harvest. Nonsignificant differences in survival in this study made density adjustments unnecessary. Crossbreeding the three strains in this study did not result in consistently significant average, line, or specific heterosis for body size traits. Significant heterosis for chela size, observed in the analysis of all animals combined, was probably due more to differences in percent male maturity than to heterosis. Mature males have larger chela than immature males (Huner and Barr, 1984) and thus mean chela size was larger in crosses having more mature males at harvest. Fewer ma-
310
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
ture males were present in crosses that resulted in negative heterosis for chela size. Heterosis was not signficant for chela size when male maturity stages were analyzed separately. Significant specific heterosis, the difference between means of hybrid crosses between two strains and means of the same two purebred crosses, for dressout percentage indicates identification of crosses with higher dressout percentages may be possible in P. clurkii. However, lack of heterosis in males and negative heterosis in one cross suggest that crossing the strains used in this study would not increase dressout percentage substantially. The probability of detecting superior crosses could be increased by crossing more populations and using more geographically dispersed populations. It is not possible to predict which crosses will exhibit heterosis before testing offspring (Tave, 1986). Therefore, the probability of detecting a superior cross increases with the number of lines crossed (Gjerde, 1988 ) . The number of strains crossed in this study was limited by the availability of grow-out facilities. Adaptation to different local conditions and reduction of gene flow would tend to increase differences in gene frequencies between widely dispersed populations of P. clurkii. Because the amount of heterosis in a cross depends on the squared difference of gene frequencies between populations, widely dispersed crosses may be expected to exhibit increased heterosis (Falconer, 198 1). However, many locations in the United States and other countries have recently been stocked with P. clarkii from southern Louisiana (Busack, 1988 ). Records of these stockings are usually not kept and there is a chance of selecting a population which recently came from Louisiana. Differences in reproductive readiness of crawfish from different locations could create problems. Comparison of crosses requires that all broods be approximately the same age to minimize environmental differences during grow-out. Differences in local climates and habitats might result in differences in egg development and time of spawning in broodstock, making it difficult to obtain broods of the same age. Line effects are influenced by both additive and dominance genetic variance (Eisen et al., 1983 ). Significant line effects for dressout percentage indicate that distinct strain differences existed. Lutz and Wolters ( 1989) reported significant heritability for dressout percentage in P. clarkii, indicating additive genetic variance for dressout percentage exists. Significant line effects and heritability for dressout percentage indicate this trait could be improved through selective breeding. The analysis of dressout percentage could be made stronger by using more crawfish than were used in this study (35-45 per cross). Many crawfish died during the time required to take body size measurements and could not be used in the analysis of dressout percentage. A study which focused on dressout percentage alone would allow more crawfish to be used in the analysis. Lack of significant line effects across sexes and male maturity stages make it difficult to conclude strains differed for body size traits. However, negative line effects for body size traits of Plaquemine strain, mature male offspring indicate Plaquemine males may mature at a smaller size. Because crawfish cease growing,
B.G. Bosworth et al. /Aquaculture X21(1994) 301-312
311
at least temporarily, upon maturing (Huner and Barr, 1984)) early maturity could result in smaller size. It may be possible to produce larger crawfish by delaying age at maturity. Investigation of genetic pararmeters affecting age and size at sexual maturity would provide information on the possibility of manipulating these traits through breeding programs. Maternal effects are estimated as the difference between means of crosses involving females of a strain and means of crosses involving males of the same strain. Maternal effects include cytoplasmic inheritance, maternal nutrition via the egg or pre- and post-natal feeding, imitative behavior and interaction between sibs through the mother (Mather and Jinks, 197 1). Because crawfish do not nurture their young after hatch, maternal effects are limited to cytoplasmic inheritance, egg size and egg quality (Gjerde, 1988 ). Significant positive maternal effects for body size traits of female and mature male offspring indicate Plaquemine strain females transmit a desirable effect to their young. Egg size was not measured in this study so it is difficult to determine the source of the maternal effect. Cytoplasmic effects, which are generally due to differences in mitochondrial genes, could also be responsible for significant maternal effects. Palva and Huner ( 1988 ) detected differences between mitochondrial DNA sequences of Procambarus chrkii and Astacus astacus using restriction endonuclease techniques. These techniques could be used to detect differences in mitochondrial DNA between populations of P. clurkii, and may provide information on influences of mitochondrial DNA on important traits. Because of variation in oviposition of female crawfish, only one to three broods from each cross were available for use in this study. Due to the low number of broodstock, some of the differences may have been due to individual genetic effects in ithe broodstock rather than true strain differences (Gjerde, 1988 ). Development of methods for synchronization of spawning and artificial incubation of eggs would allow production of crawfish broods of the same age. Successful artificial incubation of crawfish eggs has been reported (Hessen et al., 1987; Rhodes, 198 1)) but no method for successfully inducing spawning has been reported.
5. References Berrill, M., 1985. Laboratory induced hybridization of two crayfish species, Orconectes rusticus and 0. propinquus. J. Crustacean Biol., 5 (2): 347-349. Boyd, C.E., 1979. Water Quality in Warm Water Fish Ponds. Auburn University Agricultural Experiment !jtation, Auburn, AL, USA, 359 pp. Busack, C.A., 1988. Electrophoretic variation in the red swamp (Procambarus da&ii) and the white river crayfish (P. acutus) (Decapoda: Cambaridae). Aquaculture, 69: 21 l-226. Carlberg, J.M., Van Olst, J.C. and Ford, R.F., 1978. A comparison of larval stages of the lobsters, Homarus americanus and Hommarus gammarus and their hybrids. Proc. World Maricult. Sot., 10: 88&892. Chien, Y. and Avault, J.W., Jr., 1980. Production of crayfish in rice ponds. Prog. Fish-Cult., 42(2): 67-71.
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Craig, R.J. and Wolters, W.R., 1988. Sources of variation in body size traits, dressout percentage and their correlations for the crayfish, Procambarus clarkii. Aquaculture, 12: 49-58. De la Bretonne, L., Avault, J.W. and Smitherman, R.O., 1969. Effects of soil and water hardness on survival and growth of red swamp crawfish, Procambarus clarkii, in plastic pools. Southeast. Assoc. Game Fish Comm., 23: 626-633. Eisen, E.J., Horstgen-Schwark, G., Saxton, A.M. and Bandy, T.R., 1983. Genetic interpretation and analysis of diallel crosses with animals. Theor. Appl. Genet., 65: 17-23. Falconer, D.S., 198 1. Introduction to Quantitative Genetics. Longman, New York, NY, USA, 340 pp. Gardner, E.J. and Eberhart, S.A., 1966. Analysis and interpretation of the variety cross diallel and related populations. Biometrics, 22: 439-452. Gardner, E.J. and Snustad, D.P., 198 1. Principles of Genetics. John Wiley and Sons, Inc., New York, NY, USA, 6 11pp. Gjedrem, T., 1983. Genetic variation in quantitative traits and selective breeding in fish and shellfish. Aquaculture, 38: 5 l-72. Gjerde, B., 1984. Response to individual selection for age at sexual maturity in Atlantic salmon. Aquaculture, 38: 229-240. Gjerde, B., 1988. A complete diallel cross between six inbred groups of rainbow trout, Safmo gairdneri. Aquaculture, 75: 71-87. Hessen, D.O., Taugbol, T., Fjeld, E. and Skurdal, J., 1987. Egg development and lifecycle timing in the noble crayfish (Astacus astacus). Aquaculture, 64: 11-82. Huner, J.V. and Barr, J.E., 1984. Red swamp crawfish. Biology and exploitation. Louisiana Sea Grant College Program, Center for Wetland Resources, Louisiana State Univ., Baton Rouge, LA, USA, 136 pp. Louisiana Cooperative Extension Service, 1986. Agricultural Summary. Louisiana State Univ., Baton Rouge, LA, USA, 200 pp. Lutz, C.G., 1987. Response to selection for growth and correlated response to selection in dressout percentage in red swamp crawfish, Procambarus clarkii (Girard). Dissertation, Louisiana State Univ., Baton Rouge, LA, USA, 72 pp. Lutz, C.G. and Wolters, W.R., 1989. Estimates of heritabilities for growth, body size and processing traits in red swamp crawfish, Procambarus clarkii (Girard). Aquaculture, 78: 2 l-33. Mather, K. and Jinks, J.L., 197 1. Biometrical Genetics. Cornell University Press, Ithaca, NY, USA, 382 pp. Palva, T.K. and Huner, J.V., 1988. Analysis of freshwater crayfish mitochondrial DNA: a short report. World Aquacult., 19(4): 82. Rhodes, C.P., 198 1. Artificial incubation of the eggs of the crayfish Austropotamobiuspallipes (Lereboullet). Aquaculture, 25: 129-140. Romaire, R.P., 1976. Population dynamics of red swamp crawfish, Procambarus clarkii (Girard), in ponds receiving fertilization, and two agricultural forages as supplimental feed. Master’s thesis, Louisiana State University, Baton Rouge, LA, USA, 92 pp. Sarver, D., Malecha, S. and Onizuka, D.. 1979. Development and characterization of genetic stocks of and their hybrids in Macrobrachium rosenbergii: physiological responses and larval development rates. Proc. World Maricult. Sot., 10: 880-892. SAS Institute Inc., 1988. SAS/STAT User’s Guide, Release 6.03 Edition. SAS Institute, Cary, NC, USA, 1028 pp. Tave, D., 1986. Genetics for Fish Hatchery Managers. Avi Publishing Company Inc., Connecticut, 299 pp.
ELSEVIER
121 (1994) 301-312
Analysis of a diallel cross to estimate effects of crossing on performance of red swamp crawfish, Procambarus clarkii Brian G. Bosworth’, William R. Wolters2,*, Arnold M. SaxtorF3 School of Forestry, Wildlife, and Fisheries, and aDepartment OfExperimental Statistics, Louisiana Agriwltural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA (Accepted 14 October L993)
Abstract A comlplete diallel cross among three populations of red swamp crawfish, Procambarus clarkii, was used to estimate genetic effects for body size traits and dressout percentage. Offspring were grown in 2.4-meter diameter fiberglass pools with rice as forage. Crawfish were harvested after 150 days, sorted by sex and male maturity stage, and measured for dressout percentage and nine body size traits. Estimates of heterosis, line, maternal, reciprocal effects and general combining ability for traits were obtained by forming contrasts among appropriate least squares means. Estimates were made for all animals combined and for rnature males, immature males, and females separately. Significant (PC 0.05 ) heterosis and line effects for dressout percentage indicate identification of strains with higher dressout percentage may be possible. Significant (PC 0.05 ) maternal effects for body size traits of females and mature males suggest a difference in egg size, egg quality or cytoplasmic inheritance among populations.
1. Introduction Procambarid in the United
crawfishes are the only crustacean species cultured on a large scale States. The majority of crawfish are produced in Louisiana, where
*Corresponding author. ‘Present address: 114 Cheatham Hall, Virginia Tech University, Blacksburg, VA 2406 1, USA. ‘Present address: USDA/ARS Catfish Genetics Research Unit, P. 0. Box 38, Stoneville, MS 38776, USA. ‘Present a.ddress: Statistical and Computing Services, P.O. Box 107 1,University of Tennessee, Knoxville, TN 37901-1071, USA. Elsevier Science B.V. SSDIOO4.4~8486(93)
E0252-5
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B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
crawfish culture ponds occupy over 50000 ha and 25-30 million kg of crawfish are harvested annually (Louisiana Cooperative Extension Service, 1986 ). Red swamp crawfish, Procumbarus clurkii, account for over 90% of the commercial harvest in Louisiana. As crawfish culture continues to expand, producers and processors are attempting to increase their profits. Genetic improvement of growth and dressout percentage has been identified as a possible way to increase prolitability (Lutz and Wolters, 1989). Evaluation and crossbreeding of strains have been useful approaches in improving production characteristics of farm animals (Gjedrem, 1983). Tave ( 1986 ) defined a strain as those individuals of a species that come from a particular location or that are produced in a particular breeding program. Because gene frequencies may differ between strains from genetic drift, natural selection, migration and differential mutation (Gardner and Snustad, 198 1 ), strains may also differ in traits influenced by those genes. Crossing of strains to utilize favorable heterotic effects in offspring has been widely used in domestic plant and livestock species. Little information exists on strain evaluation and crossing of crawfish or other decapod crustaceans. Sarver et al. (1979) reported differences in larval development rate between strains of prawns, Macrobrachium rosenbergii. Interspecific crosses between American lobsters, Homarus americanus, and European lobsters, Homarus gummarus, yielded hybrid offspring with growth rates similar to purebred offspring (Carlberg et al., 1978). It may be possible to identify red swamp crawfish strains or crossbreds with faster growth and higher dressout percentage. Objectives of this study were to evaluate three populations of P. clurkii within Louisiana for differences in ten body size traits and estimate genetic effects from all possible crosses and the potential for improving these traits.
2. Materials and methods Broodstock collection, mating, and offspring production During the spring of 1987 approximately 30 male and 30 female adult red swamp crawfish, Procambarus clarkii, were collected from each of three locations in Louisiana. Crawfish from these locations were designated as: Strain B, collected from research ponds at the Ben Hur Research Farm, LSU, Baton Rouge, LA; Strain H, collected from a commercial crawfish pond near Hathaway, LA; and Strain P, collected from a commercial crawfish pond near Plaquemine, LA. Adults were held individually in partitioned 40-liter polyethylene tanks and fed a commercial shrimp ration during the summer of 1987. Matings were initiated on 5 September 1987 using a complete diallel cross model (Gardner and Eberhart, 1966). Prior to mating, each female’s annulus ventralis was cleaned with 95% ethanol and abrasive pads to remove any previously acquired spermatophores (Berrill, 1985 ). Males and females from each strain were divided equally among crosses and allowed to mate at random until all crosses had been completed. Mated females were held individually in covered, parti-
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
tioned 40-liter tanks and and hatch were recorded Offspring from crosses aeration and previously Lutz and Wolters, 1989). each cross and randomly instar juveniles per pool.
303
fed a commercial shrimp ration. Dates of egg deposition for each female. were stocked into Iiberglass pools supplied with diffuse planted with rice for forage (Craig and Wolters, 1988; Offspring were pooled from all available females within stocked into three replicate pools per cross at 30, third-
Data collection and analysis Crawfish were harvested after 150 days and sorted by sex and stage of male maturity (Huner and Barr, 1984). Crawfish were measured for carapace length, carapace width, abdomen length, abdomen width, abdomen depth, chela length, chela width and total length with a standard measuring board or digital calipers, and weighed to the nearest 0.1 gram. Regression of mean total length of crawfish on density at harvest was used to determine if density affected growth (Lutz, 1987 ). Dressout percentage was calculated on five mature males, five immature males, and five females selected at random from each pool. In 10 of 27 pools fewer than five immature males were found, and in 6 of 27 pools fewer than live mature males were present. Percentage of mature males was calculated for each pool based on the number of mature males present. Differences in body size traits, dressout percentage and percent male maturity were analyzed in a nested analysis of variance. Body size traits and dressout percentage were analyzed for all animals combined and for mature males, immature males and females separately. Differences in percent male maturity were analyzed by coding mature males as 1’ and immature males as 0’ (Gjerde, 1984). Differences in trait means were declared significant at ac0.05. Least squares means of crawfish body size traits, dressout percentage and percent male maturity from each cross were compared with a series of estimate statements in the GLM procedure (SAS, 1988) to determine average heterosis, line heterosis, specific heterosis, maternal effects, line effects, reciprocal effects and general combining .ability (Eisen et al., 1983). Estimates were tested for significance with a corresponding series of contrasts, using pool within cross mean squares for error terms (SAS, 1988) and declared significant at a~0.05. The model used in the analysis was (Eisen et al., 198 3 ) :
where Yij~r=trait measured on the Ith individual of sire line i and dam line i in pool k y= = mean of parental lines li = yii- ya - mi = average direct effect of line i mi=y.j.-yj, =average maternal effect of linej, where yj. (y,j) = mean of sire (dam) line,; including the parental line h,= (Y,;+Yji)/2- (JJii+ya)/2=direct heterosis for the (g)th cross ry = r& (mj- mi) /2 = specific reciprocal difference between lines i and j, where: rii= reciprocal effects = (Yij- Yji) /2
CD (mm) All animals Mature males Immature males Females
CW (mm) All animals Mature males Immature males Females
n=168 n= 166 n=346
n=680
n=346
n= 168 n=166
n=680
n=346
n=680 n=168 n= 166
n=680 n=168 n= 166 n=346
TL (mm) All animals Mature males Immature males Females
CL (mm) All animals Mature males Immature males Females
n=680 n=168 n=166 n=346
All animals Mature males Immature males Females
TW (g)
44.2(0.4) 44.3(0.7) 43.9(0.8) 44.5(0.7)
20.8(0.3) 21.8(0.5) 20.7(0.6) 20.3(0.4)
50.1(0.7) 51.9(1.1) 51.1(1.2) 48.5( 1.0)
94.4(1.1) 96.3( 1.8) 95.0(2.0) 93.0( 1.7)
25.2( 1.2) 31.3(2.6) 23.4( 1.9) 22.9( 1.5)
P-P
45.2(0.5) 44.3(0.9) 44.8(1.3) 45.6(0.6)
21.0(0.4) 21.7(0.9) 21.0(0.9) 20.9(0.5)
50.3(0.8) 50.9( 1.7) 51.1(2.0) 49.8(0.9)
95.4( 1.3) 94.2(2.5) 95.8(3.3) 95.5( 1.5)
24.9( 1.3) 29.9(3.3) 26.0(2.2) 23.5( 1.4)
P-B
Cross (female strain-male
42.8(0.5) 43.0(0.6) 43.3( 1.5) 42.6(0.7)
20.5(0.3) 21.7(0.5) 20.6( 1.0) 19.9(0.5)
48.2(0.7) 50.8( 1.0) 48.6(2.1) 46.7(0.9)
91.1(1.1) 93.8( 1.6) 91.9(3.6) 89.3(1.5)
23.4( 1.2) 29.9(2.1) 22.4(3.3) 19.9( 1.5)
P-H
strain)
46.0(0.5) 46.8(0.6) 45.9( 1.0) 45.7(0.8)
27.8(0.4) 23.7(0.6) 21.5(0.7) 20.9(0.5)
54.1(0.7) 54.8( 1.0) 51.8(1.4) 49.9( 1.0)
97.3( 1.2) 101.7(1.6) 97.7(2.4) 95.6( 1.7)
25.9( 1.2) 35.6(2.4) 26.0(2.2) 22.7( 1.4)
B-P
44.8(0.4) 44.9(0.5) 43.5(1.8) 45.1(0.6)
21.8(0.3) 22.7(0.4) 21.0(1.2) 21.5(0.3)
50.4(0.6) 51.7(0.8) 50.2(2.7) 49.8(0.7)
95.2( 1.0) 96.6( 1.3) 93.8(4.5) 94.9( 1.3)
28.2(1.1) 34.6( 1.8) 25.9(3.2) 25.2( 1.2)
B-B
44.2(0.4) 44.2(0.6) 44.3(0.9) 44.2(0.7)
21.7(0.3) 22.9(0.4) 21.7(0.6) 21.1(0.4)
49.0(0.6) 50.9(0.7) 49.2( 1.3) 47.8(0.8)
93.2(1.0) 95.1(1.2) 93.5(2.2) 92.1(1.5)
24.6(0.9) 30.0( 1.5) 23.8( 1.7) 22.1(1.2)
B-H
46.7(0.5) 46.5(0.6) 41.9(1.7) 47.9(0.7)
22.3(0.3) 23.1(0.5) 19.3(0.8) 2.5(0.5)
52.2(0.7) 53.1(0.9) 46.6( 1.8) 52.9(0.9)
98.9( 1.2) 99.6( 1.5) 88.5(3.5) 100.8( 1.6)
31.4( 1.4) 36.9(2.1) 18.4(2.1) 30.1(1.9)
H-P
43.5(0.8) 44.3(0.8) 41.0( 1.4) 45.3(1.1)
20.4(0.4) 20.5(0.7) 19.1(0.7) 20.7(0.7)
48.2(0.9) 51.9(1.4) 46.0( 1.5) 48.7( 1.4)
91.8(1.6) 96.2(2.1) 86.9(2.5) 94.0(2.4)
24.6( 1.5) 33.9(3.5) 19.4(2.2) 25.2(2.1)
H-B
Table 1 Means ( f s.e. ) of body size traits, dressout percentage and percentage male maturity of offspring from a diallel cross among Plaquemine (B) and Hathaway (H) strains of red swamp crawfish, Procumbarus clurkii
44.5(0.5) 47.1(0.6) 42.5 (0.9) 44.3(0.8)
20.6(0.4) 23.3(0.5) 19.2(0.5) 20.1(0.5)
47.3(0.7) 51.9(1.0) 44.7( 1.3) 46.3(1.1)
91.8(1.2) 99.0( 1.6) 87.2(2.2) 90.6( 1.8)
23.8( 1.4) 36.9(2.4) 17.7( 1.7) 20.5( 1.5)
H-H
(P), Ben Hur
B.G. Bosworth et al. /Aquacu&ure 121(1994) 301-312
hhhh
*.I?” 0006 v--v CO-t-ti
ti
i
i
-e-e
22~~~ w--m II II II EEEE
Z%ZZ w--m II
II
II
EEEr
II II
Mature males Line effects P B H (se.)
All animals Line effects P B H (se.) Maternal effects P B H (s.e.) Specific heterosis PxB PxH BxH (se.)
(lips)
-2.1 0.7
0.6 1.5 -0.3 (1.2)
-1.3 2.9 - 1.7 (2.2)
1.6 1.9 - 1.1 (2.2)
-5.5* 1.0
(0.9)
(1.5)
(1.5)
1.8* -0.6 -1.2
1.8 -0.8 (1.3)
-1.0
CL
3.2* -0.4 -2.3
(::04)
-3.8 2.8
TW
3.4* -1.2 -2.3
-2.9 2.5
TL
Trait
0.0 0.7 -0.2 (0.6)
0.8 -0.6 -0.2 (0.4)
-1.1 1.3 -0.2 (0.6)
cw
- 1.2* 0.5 0.8 (0.5)
(0.5)
(1.0)
- 3.4* 0.3 2.0 (1.0)
0.2 0.4 -0.2
0.6 -0.3 -0.3 (0.3)
(&
-0.8 0.8
AD
1.1 0.4 -0.8
(0.7)
1.7* -0.5 -1.1
(ll::)
- 1.9 0.8
AL
-0.9 0.2 0.6 (0.5)
(K )
0.4 0.4
0.4 -0.2 -0.2 (0.3)
(0.4)
-0.5 0.5 0.0
AW
-6.6* 2.1 4.5 (2.5)
-4.2* 3.9* - 1.6 (1.7)
3.4* -1.4 -2.0 (1.2)
-3.7 5.1* -1.4 (1.8)
CHLL
Table 2 Estimates ( T s.e. ) of genetic effects for body size traits and dressout percentage from a diallel cross among Ben Hur (B), Plaquemine (H) strains of red swamp crawfish, Procambarus clarkii
(::: )
-2.9* 0.7
(0.7)
-2.1* 1.2 - 1.3
1.1* -0.4 -0.7 (0.5)
- 1.7* 1.8* -0.1 (0.7)
CHW
0.9 -0.7 -0.2 (0.6)
2.5* -0.5 -0.7 (0.7)
(0.4)
0.0 0.6 -0.6
(2d.Y)
-0.3 -2.2.
DO
(P) and Hathaway
5 :, :
$
P 3 s 2
g
s
2 R
$ x
:
4.9*
(Y )
-3.6 1.2
-4.8 2.4
(Z)
) -1.3 1.5 0.5 (1.5)
0.8 2.5 0.1 (1.4)
-0.7 3.9 (E
2.2* 0.2 -2.4* (1.0)
3.5 1.2 -4.7* (1.8)
0.8 3.7 0.2 (2.5)
-0.2 -4.7* (1.7)
2.5 3.0 -5.5 (2.9)
ci:;,
-(E)
2.4 4.9 -7.3 (4.2)
1.9 -0.8
3.8 -0.4
(E
-1.3 1.1 )
cod.:,
0.1 1.2
1.0* -0.2 -0.8 (0.5)
0.6 1.7 -2.3 (1.3)
1.0 -0.6 -0.3 (0.5)
-1.0 0.6 0.4 (0.6)
-2.9 1.0
-0.6 0.4 0.3 (0.5)
0.3 0.7 0.2 (0.5)
0.6 0.0 -0.5 (0.3)
0.4 0.7 -1.2 (0.8)
0.5 -0.3 -0.2 (0.3)
-3.0 3.2 -0.2 (2.1)
-1.3 1.1 0.2 (0.9)
(2d.56,
-0.6 -1.8*
2.3* -0.7 -2.2* (0.9)
-1.7 1.4 -0.3 (0.8) -3.2 4.1’ (G)
-0.2 0.0 0.2 (0.6)
,?.;
-1.7 -3.4+
0.1 -0.3 0.2 (0.5)
1.1 0.3 - 1.3* (0.5)
0.5 1.8 -2.3” (1.0)
1.2 -0.2 -:.3 (0.7)
2.9* 0.7 - 3.6* (1.3)
2.0 6.1 -go* (3.3)
4.2* -1.1 -3.: (1.7)
length, AD = abdomen depth, AW = abdomen width,
(E)
(Z)
(Z)
0.0 0.6
0.8* 0.0 -0.8 (0.4)
0.2 1.0 -1.2 (1.0)
0.6 -0.4 -0.2 (0.3)
0.0 1.1
2.7* -0.4 -2.2* (0.8)
0.8 1.7 -2.5 (2.1)
2.0* -0.9 -!.! (0.7)
*Significant at P>O.O5. TW = total weight, TL= total length, CL = carapace length, CW = carapace width, AL=abdomen CHW = chela width, CHL = chela length and DO = dressout percent.
Females Maternal effects P B H (s.e.) Specific heterosis PxB PxH BXH (s.e.) Line effects P B H (se.)
3.2 4.7 -7.9 (4.9)
Immature males Line effects P B H (se.)
3.91
- 1.7 -2.3 (1.6)
Maternal effects P B H (se.)
S
$
s “2 g
$ k 6 2 z S
S 2
% ia g
308
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
effect of kth p001 nested in the ( ii) th CROSS eijk/= random error
pijk=
Water temperature and dissolved oxygen were measured twice weekly with a portable meter. Total water hardness in each pool was determined by EDTA titration (Boyd, 1979 ) at the beginning, midpoint and termination of the study. Differences in pool means for water temperature, dissolved oxygen and water hardness were analyzed in a one-way analysis of variance and declared significant at cr
3. Results Water quality Water temperature, dissolved oxygen concentration and total water hardness were not signficantly different between pools. Water temperatures ranged from 4.5 to 23.O”C and total water hardness ranged from 102 to 222 mg/l. Dissolved oxygen concentration was variable and inversely related to water temperature. The lowest dissolved oxygen concentration was 88% of saturation ( 15.0 mg/l at 9.5”C) and the highest was 129% of saturation (9.5 mg/l at 23.O”C). Survival and growth of offspring In each cross one to three females produced offspring used in the analyses. Mean survival of crawfish was 84% (range 60 to 97%). A total of 680 animals was harvested, sexed and measured. Average growth rate for offspring from all crosses was 4.4 mm/week. Average growth rates for mature males, immature males and females were 4.5, 4.3 and 4.4 mm/week, respectively. Total length of crawfish at harvest ranged from 57 to 120 mm. Regression of mean total length on density at harvest was not signficant and no adjustment of total length was necessary (Lutz, 1987). Means of crosses Chela length, chela width and dressout percentage were significantly different between crosses in the analysis of all animals combined (Table 1). Dressout percentages of immature males and females were significantly different among crosses; no traits of mature males were different among crosses (Table 1). Estimation of genetic effects Body size traits - all crawfish combined. Heterosis and line effects were significant for chela width and length (Table 2). Maternal effects were significant and positive for most body size traits of offspring from Plaquemine strain crosses (Table 2). Body size traits -
mature males. Line effects were significant
and negative for
B.G. Bosworth et al. /Aquaculture 121(1994) 301-312
most body size traits of mature male offspring from Plaquemine (Table 2). Maternal effects were signficant and positive for total men length and chela length of mature males from Plaquemine (Table 2 ). Other effects were nonsignificant for body size traits of
309
strain crosses length, abdostrain crosses mature males.
Body si.ze traits - immature males. Line effects were significant and negative for chela length and width of immature males from Hathaway crosses (Table 2). No other effects were significant for body size traits of immature males. Body size traits-females. Maternal effects were significant and positive for most body size traits of female offspring from Plaquemine strain crosses (Table 2). Maternal effects were significant and negative for most body size traits of female offspring from Hathaway strain crosses (Table 2). Other effects were nonsignificant for body size traits in female offspring. Dressout percentage and percent male maturity. Positive heterosis for dressout percentage was observed in all animals combined and females from crosses between F’laquemine and Ben Hur strains (Table 2 ) . Negative heterosis for dressout percentage was observed in females from crosses between Ben Hur and Hathaway strains (Table 2 ). Negative line effects for dressout percentage were observed in immature males, females and all animals combined from Ben Hur crosses (Table 2 ). No effects were significant for percent male maturity.
4. Discussion Water temperature, dissolved oxygen concentration and water hardness were within ranges suitable for culture of P. clarkii (De la Bretonne et al., 1969; Huner and Barr, 1984). Average growth rate observed in this study, 4.4 mm/week, was within the range of growth rates ( 1.3-6.0 mm/week) for P. clarkii grown in ponds and experimental pools (Romaire, 1976; Chien and Avault, 1980; Craig and Wolters, 1988; Lutz and Wolters, 1989). Avera.ge survival of crawfish in this study, 84%, was higher than survivals of 4 1% and 64% previously reported in experimental pools (Craig and Wolters, 1988; Lutz and Wolters, 1989) even though water quality variables, forage, and stocking density were similar to those studies. Because of differential survival among replicate pools, previous studies have adjusted body size traits for density at harvest. Nonsignificant differences in survival in this study made density adjustments unnecessary. Crossbreeding the three strains in this study did not result in consistently significant average, line, or specific heterosis for body size traits. Significant heterosis for chela size, observed in the analysis of all animals combined, was probably due more to differences in percent male maturity than to heterosis. Mature males have larger chela than immature males (Huner and Barr, 1984) and thus mean chela size was larger in crosses having more mature males at harvest. Fewer ma-
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ture males were present in crosses that resulted in negative heterosis for chela size. Heterosis was not signficant for chela size when male maturity stages were analyzed separately. Significant specific heterosis, the difference between means of hybrid crosses between two strains and means of the same two purebred crosses, for dressout percentage indicates identification of crosses with higher dressout percentages may be possible in P. clurkii. However, lack of heterosis in males and negative heterosis in one cross suggest that crossing the strains used in this study would not increase dressout percentage substantially. The probability of detecting superior crosses could be increased by crossing more populations and using more geographically dispersed populations. It is not possible to predict which crosses will exhibit heterosis before testing offspring (Tave, 1986). Therefore, the probability of detecting a superior cross increases with the number of lines crossed (Gjerde, 1988 ) . The number of strains crossed in this study was limited by the availability of grow-out facilities. Adaptation to different local conditions and reduction of gene flow would tend to increase differences in gene frequencies between widely dispersed populations of P. clurkii. Because the amount of heterosis in a cross depends on the squared difference of gene frequencies between populations, widely dispersed crosses may be expected to exhibit increased heterosis (Falconer, 198 1). However, many locations in the United States and other countries have recently been stocked with P. clarkii from southern Louisiana (Busack, 1988 ). Records of these stockings are usually not kept and there is a chance of selecting a population which recently came from Louisiana. Differences in reproductive readiness of crawfish from different locations could create problems. Comparison of crosses requires that all broods be approximately the same age to minimize environmental differences during grow-out. Differences in local climates and habitats might result in differences in egg development and time of spawning in broodstock, making it difficult to obtain broods of the same age. Line effects are influenced by both additive and dominance genetic variance (Eisen et al., 1983 ). Significant line effects for dressout percentage indicate that distinct strain differences existed. Lutz and Wolters ( 1989) reported significant heritability for dressout percentage in P. clarkii, indicating additive genetic variance for dressout percentage exists. Significant line effects and heritability for dressout percentage indicate this trait could be improved through selective breeding. The analysis of dressout percentage could be made stronger by using more crawfish than were used in this study (35-45 per cross). Many crawfish died during the time required to take body size measurements and could not be used in the analysis of dressout percentage. A study which focused on dressout percentage alone would allow more crawfish to be used in the analysis. Lack of significant line effects across sexes and male maturity stages make it difficult to conclude strains differed for body size traits. However, negative line effects for body size traits of Plaquemine strain, mature male offspring indicate Plaquemine males may mature at a smaller size. Because crawfish cease growing,
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at least temporarily, upon maturing (Huner and Barr, 1984)) early maturity could result in smaller size. It may be possible to produce larger crawfish by delaying age at maturity. Investigation of genetic pararmeters affecting age and size at sexual maturity would provide information on the possibility of manipulating these traits through breeding programs. Maternal effects are estimated as the difference between means of crosses involving females of a strain and means of crosses involving males of the same strain. Maternal effects include cytoplasmic inheritance, maternal nutrition via the egg or pre- and post-natal feeding, imitative behavior and interaction between sibs through the mother (Mather and Jinks, 197 1). Because crawfish do not nurture their young after hatch, maternal effects are limited to cytoplasmic inheritance, egg size and egg quality (Gjerde, 1988 ). Significant positive maternal effects for body size traits of female and mature male offspring indicate Plaquemine strain females transmit a desirable effect to their young. Egg size was not measured in this study so it is difficult to determine the source of the maternal effect. Cytoplasmic effects, which are generally due to differences in mitochondrial genes, could also be responsible for significant maternal effects. Palva and Huner ( 1988 ) detected differences between mitochondrial DNA sequences of Procambarus chrkii and Astacus astacus using restriction endonuclease techniques. These techniques could be used to detect differences in mitochondrial DNA between populations of P. clurkii, and may provide information on influences of mitochondrial DNA on important traits. Because of variation in oviposition of female crawfish, only one to three broods from each cross were available for use in this study. Due to the low number of broodstock, some of the differences may have been due to individual genetic effects in ithe broodstock rather than true strain differences (Gjerde, 1988 ). Development of methods for synchronization of spawning and artificial incubation of eggs would allow production of crawfish broods of the same age. Successful artificial incubation of crawfish eggs has been reported (Hessen et al., 1987; Rhodes, 198 1)) but no method for successfully inducing spawning has been reported.
5. References Berrill, M., 1985. Laboratory induced hybridization of two crayfish species, Orconectes rusticus and 0. propinquus. J. Crustacean Biol., 5 (2): 347-349. Boyd, C.E., 1979. Water Quality in Warm Water Fish Ponds. Auburn University Agricultural Experiment !jtation, Auburn, AL, USA, 359 pp. Busack, C.A., 1988. Electrophoretic variation in the red swamp (Procambarus da&ii) and the white river crayfish (P. acutus) (Decapoda: Cambaridae). Aquaculture, 69: 21 l-226. Carlberg, J.M., Van Olst, J.C. and Ford, R.F., 1978. A comparison of larval stages of the lobsters, Homarus americanus and Hommarus gammarus and their hybrids. Proc. World Maricult. Sot., 10: 88&892. Chien, Y. and Avault, J.W., Jr., 1980. Production of crayfish in rice ponds. Prog. Fish-Cult., 42(2): 67-71.
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Craig, R.J. and Wolters, W.R., 1988. Sources of variation in body size traits, dressout percentage and their correlations for the crayfish, Procambarus clarkii. Aquaculture, 12: 49-58. De la Bretonne, L., Avault, J.W. and Smitherman, R.O., 1969. Effects of soil and water hardness on survival and growth of red swamp crawfish, Procambarus clarkii, in plastic pools. Southeast. Assoc. Game Fish Comm., 23: 626-633. Eisen, E.J., Horstgen-Schwark, G., Saxton, A.M. and Bandy, T.R., 1983. Genetic interpretation and analysis of diallel crosses with animals. Theor. Appl. Genet., 65: 17-23. Falconer, D.S., 198 1. Introduction to Quantitative Genetics. Longman, New York, NY, USA, 340 pp. Gardner, E.J. and Eberhart, S.A., 1966. Analysis and interpretation of the variety cross diallel and related populations. Biometrics, 22: 439-452. Gardner, E.J. and Snustad, D.P., 198 1. Principles of Genetics. John Wiley and Sons, Inc., New York, NY, USA, 6 11pp. Gjedrem, T., 1983. Genetic variation in quantitative traits and selective breeding in fish and shellfish. Aquaculture, 38: 5 l-72. Gjerde, B., 1984. Response to individual selection for age at sexual maturity in Atlantic salmon. Aquaculture, 38: 229-240. Gjerde, B., 1988. A complete diallel cross between six inbred groups of rainbow trout, Safmo gairdneri. Aquaculture, 75: 71-87. Hessen, D.O., Taugbol, T., Fjeld, E. and Skurdal, J., 1987. Egg development and lifecycle timing in the noble crayfish (Astacus astacus). Aquaculture, 64: 11-82. Huner, J.V. and Barr, J.E., 1984. Red swamp crawfish. Biology and exploitation. Louisiana Sea Grant College Program, Center for Wetland Resources, Louisiana State Univ., Baton Rouge, LA, USA, 136 pp. Louisiana Cooperative Extension Service, 1986. Agricultural Summary. Louisiana State Univ., Baton Rouge, LA, USA, 200 pp. Lutz, C.G., 1987. Response to selection for growth and correlated response to selection in dressout percentage in red swamp crawfish, Procambarus clarkii (Girard). Dissertation, Louisiana State Univ., Baton Rouge, LA, USA, 72 pp. Lutz, C.G. and Wolters, W.R., 1989. Estimates of heritabilities for growth, body size and processing traits in red swamp crawfish, Procambarus clarkii (Girard). Aquaculture, 78: 2 l-33. Mather, K. and Jinks, J.L., 197 1. Biometrical Genetics. Cornell University Press, Ithaca, NY, USA, 382 pp. Palva, T.K. and Huner, J.V., 1988. Analysis of freshwater crayfish mitochondrial DNA: a short report. World Aquacult., 19(4): 82. Rhodes, C.P., 198 1. Artificial incubation of the eggs of the crayfish Austropotamobiuspallipes (Lereboullet). Aquaculture, 25: 129-140. Romaire, R.P., 1976. Population dynamics of red swamp crawfish, Procambarus clarkii (Girard), in ponds receiving fertilization, and two agricultural forages as supplimental feed. Master’s thesis, Louisiana State University, Baton Rouge, LA, USA, 92 pp. Sarver, D., Malecha, S. and Onizuka, D.. 1979. Development and characterization of genetic stocks of and their hybrids in Macrobrachium rosenbergii: physiological responses and larval development rates. Proc. World Maricult. Sot., 10: 880-892. SAS Institute Inc., 1988. SAS/STAT User’s Guide, Release 6.03 Edition. SAS Institute, Cary, NC, USA, 1028 pp. Tave, D., 1986. Genetics for Fish Hatchery Managers. Avi Publishing Company Inc., Connecticut, 299 pp.