Relationship of Relative Weight (Wr) to Proximate

Transactions of the American Fisheries Society 120:509-518, 1991 Copyright by the American Fisheries Society 1991

Relationship of Relative Weight (Wr) to ProximateComposition of Juvenile Striped Bass and Hybrid Striped Bass

MICHAEL L. BROWN AND BRIAN R. MURPHYDepartment of Wildlife and Fisheries Sciences, Texas A&M University System

College Station, Texas 77843, USA

Abstract.The relative weight (W^ index is commonly used to assess fish condition. However,little is known about the relationship of WT to physiological condition. Whole-body proximateanalysis quantifies the general chemical composition of fish but is impractical and too costly forlarge-scale application to natural populations. Relative weight may offer an alternative method toestimate body composition. We raised juvenile striped bass Morone saxatilis and hybrid stripedbass M. saxatilis 9 x M. chrysops 6 under controlled conditions for a 12-week period and thendetermined their proximate compositions. Analysis of relationships between Wr and proximatecomponents indicated that Wr may be used for estimating body composition and gross energy injuvenile striped bass and hybrid striped bass; WT was correlated with percent crude fat, crudeprotein, ash, visceral fat, and ash-free dry-weight gross energy. Additionally, Wr was correlatedwith relative growth and the change in total length for the experimental period. Reserve energy(visceral fat) predicted from Wr may provide a measure of overwintering fitness and suitability ofjuvenile striped bass and hybrid striped bass for stocking.

Physiological condition of fishes has been de-fined as the gross nutritional state (Love 1970) andthe level of reserve nutrients, particularly fat, pres-ent in the body (Gershanovich et al. 1984). Con-sequently, chemical body composition of an in-dividual fish should characterize its physiologicalcondition and, in general, its health. Furthermore,this physiological status determines the indivi-dual's ability to compete successfully (e.g., throughoptimal foraging and reproduction), sustaingrowth, maintain and repair tissues, and cope withstresses induced by environmental changes. En-ergy reserves in fish are primarily expressed asvisceral fat (Love 1970). Changes in chemical bodycomposition generally reflect storage or depletionof energy reserves.

Quantitative analyses of primary body constit-uents of fish have been reported for numerousmarine (Vinogradov 1953) and freshwater species(Jacquot 1961). Generally, live-weight, whole-bodycomposition offish is 70-80% water, 20-30% pro-tein, and 2-12% lipid; however, extreme valuesfor these components may fall well outside theseranges (Weatherley and Gill 1987). Several studieshave shown significant changes in whole-bodycomposition or in the composition of specific or-gans or muscle tissue due to age, diet, feeding fre-quency, migration, ration, season, sex, starvation,and temperature (Chang and Idler 1960; Brett etal. 1969; Groves 1970; Savitz 1971; Niimi 1972;Elliot 1976; Craig 1977; Grayton and Beamish1977; Millikin 1982; Weatherley and Gill 1983).

Condition, as applied to fish population ecolo-gy, has been described as an indication of fatness,general well-being, or gonad development (amongother traits) of an individual or a group of indi-viduals (Le Cren 1951). To put it simply, condi-tion is the relative plumpness or well-being offish(Wege and Anderson 1978). These definitions arecharacterized by indices based on empiricalweight-length relationships. The relative condi-tion factor (Kn; Le Cren 1951) provides a measurefor comparison of individual fish weight to a pre-dicted weight derived for that population or sub-group, whereas relative weight (Wr; Wege and An-derson 1978) measures the variation betweenindividual fish weight and a length-specific stan-dard weight (Ws) for the species in question. Pres-ently, the Wr index is in wide use among fisheriesmanagement agencies (Murphy et al. 1991), pri-marily because of the comparative attributes ofthe index among species and between individualsof different lengths within a species. Anderson(1980) suggested that a Wr of 100 (individualweight = standard weight) may reflect ecologicaland physiological optimality; however, little em-pirical evidence of the relationship of these factorsto Wr has been shown.

The measurement of physiological condition,determined by comparison with a standard weight-length relationship, may provide reliable esti-mates for determining body composition of livefish. Typically, body composition of fish is as-sessed by chemical proximate analysis, which is

509

Carol.JacobsonText Box193-F

510 BROWN AND MURPHY

expensive and time-consuming and requires thedeath of the fish. If body composition can be es-timated reliably from a mathematical conditionindex such as Wr, this would allow fish to bereleased unharmed after weight-length measure-ments. Additionally, this method would have ap-plications to aquaculture: fat and protein levelscould be monitored indirectly at various stages ofgrowth. Thus, the specific objectives of this studywere (1) to determine the empirical relationshipbetween Wr and proximate composition of indi-vidual juvenile striped bass Morone saxatilis andhybrid striped bass M. saxatilis $ x M'. chrysops3 raised under controlled conditions, and (2) toevaluate the relationships between Wr and variousgrowth characteristics.

MethodsExperimental design. We obtained 30 juve-

nile striped bass (mean weight, 184.1 g 33.3SD) and 30 hybrid striped bass (543.2 g 89.0)from the San Marcos National Fish Hatchery andTechnology Center, San Marcos, Texas, andstocked them in 109-L aquaria equipped with si-phon drains. Stable conditions were maintainedby a closed recirculation system (total volume,4,357 L) that delivered water to each aquarium ata rate of about 1 L/min; partial exchange (50%)with well water occurred every 3 d. Total am-monia, nitrites, alkalinity, hardness, dissolved ox-ygen, and pH were measured weekly. Water qual-ity complied with standards suggested for stripedbass culture (Bonn et al. 1976; Lewis and Heidin-ger 1981; Rogers et al. 1982). Water temperaturewas maintained at 24-26C with a chiller unit.This temperature has produced optimum growthof juvenile striped bass under laboratory condi-tions (Cox and Coutant 1981). Fluorescent light-ing, controlled by an automatic electric timer, pro-vided a light: dark cycle of 12:12 h.

Fish were fed a pelleted grower diet (Bioprod-ucts, Warrenton, Oregon) in both experiments (4-mm-diameter pellet for striped bass; 9-mm-di-ameter pellet for hybrid striped bass). This diet, asemimoist extruded feed formulated to producerapid growth of salmonids, meets the known nu-tritional demands of juvenile striped bass (Bonnet al. 1976; Millikin 1982, 1983; Zeigler et al.1984). All fish were conditioned for 2 weeks byfeeding them at a rate of 2% (0.05 g) of dry bodyweight per day (BWPD). After the pretreatmentperiod, five randomly selected replicates were eachfed one of six ration levels (0.25, 0.50, 0.75, 1, 2,

or 3% 0.05 g BWPD) for 12 weeks (striped bass,July-September; hybrid striped bass, December-February) in order to stratify proximate bodycomponents across the six treatments. Analysis ofvariance indicated that initial relative weight (Wr)and ration level were independent (P > 0.2). Ra-tion levels were expressed as dry weight based on78.4% and 75.6% dry matter for 4-mm and 9-mmpellets, respectively. Feeding frequency was lim-ited to once per day (0800 hours). Generally, con-sumption ceased in 10-15 min, and pellets notconsumed were counted immediately to estimateconsumption by difference (Talbot 1985); uneatenfood and fecal waste were siphoned from eachaquarium shortly thereafter. Weight (striped bass,to 0.5 g; hybrid striped bass, to 0.1 g) andlength (mm) measurements were made at 2-weekintervals; feed allotments for the next interval thenwere adjusted for observed weight gains.

Analyses. At the end of each experiment allfish were starved for 48 h, measured, blotted dry,and weighed. Individuals were frozen immediate-ly (-20Q to prevent protein denaturation andoxidation of unsaturated fatty acids pending prox-imate analysis. Before analysis, visceral fat wasexcised and weighed (to 0.001 g) for calculationof relative visceral fat weight (visceral fat weight/wet body weight). The liver was removed fromeach striped bass (Hvers of hybrids were not an-alyzed) and weighed for calculation of the liver-somatic index (LSI, liver weight/body weight;Novinger 1973). Visual examination of reproduc-tive organs confirmed all fish were sexually im-mature. Excised tissues were replaced and wholebodies were individually passed through a meatgrinder (3-mm-diameter sieve). We used two sam-ples per individual in all stages of analysis. Ho-mogenate samples (4.00 g 0.001 g) were takenfor determination of water content and were oven-dried at 100C until constant weight was attained(AOAC 1984). The remaining slurry was freeze-dried (-75Q for 48 h and rehomogenized in astainless steel blender. Because freeze-dried sam-ples were about 97% dry, 4.00-g samples (0.001g) were oven-dried at 100C to constant weight toprovide a correction factor for dry-weight calcu-lations of remaining analyses. We ashed dry-mat-ter samples at 600C in a muffle furnace to a con-stant weight to determine the ash fraction (Lovell1975). The crude-fat fraction (2.00-g samples,0.001 g) was determined by petroleum ether ex-traction (Lovell 1975) in a Goldfisch fat extractor.Nitrogen (0.500-g samples, 0.0001 g) was de-

RELATIVE WEIGHT AND PROXIMATE COMPOSITION 511

termined by the macro-Kjeldahl technique (AOAC1984) and converted to total protein equivalents(percentage crude protein = percentage nitrogenx 6.25). Crude fat, crude protein, and ash wereexpressed as dry-weight percentages. We calculat-ed gross energy content of whole bodies on ash-free dry-weight samples with standard conversionfactors recommended for fat (39.54 kj/g) and pro-tein (20.08 kj/g) (Brett and Groves 1979).

Our threshold of statistical significance was P< 0.0001 unless noted otherwise. The z-test didnot reveal any significant differences for proxi-mate component replicates for individuals (P >0.05), so means for duplicates of individuals wereused in all analyses. Variances associated with ra-tion treatments were homogeneous, so untrans-formed values were reported. Tests for differencesamong ration treatments for final Wn percentagewater, crude fat, crude protein, ash, and visceralfat were based on analysis of variance (ANOVA)and Tukey's W-procedure (Lentner and Bishop1986). We evaluated residual plots for regressionanalyses to select best-fit models; all relationshipsevaluated in this study produced linear models.Parameters were derived for calculation of pre-diction intervals for new data (Neter et al. 1989).

We calculated relative weight (Wr\ Wege andAnderson 1978) at the beginning of each experi-ment and at the end of each growth interval as

Wr = -^x 100;

Wv& the actual weight of an individual and Ws isa length-specific standard weight. Standard-weightequations used to derive index values were

-4.924 + 3.007 log10TL

for striped bass (TL is total length) andlogio^, = -5.201 +3.139 logloTL

for hybrid striped bass (Brown et al. 1989). Wecalculated relative liver weight (Lr\ Legler 1977) as

LW is the liver weight for an individual, and weestimated the liver-somatic index as LSI = 100x liver weight/wet body weight.

To determine relationships of growth to Wf9we estimated relative growth, change in totallength, growth efficiency, and instantaneous growthrates. Relative growth was the percentage weight

gain for each experiment (Brown 1957). Totalgrowth efficiency (Et) was calculated biweekly as

*-G is weight gain (g) and / is dry-weight consump-tion (g) (Warren and Davis 1967). The instan-taneous (specific) growth rate (IG) was deter-mined as

WT is the final weight at time T, and Wt is theinitial weight at time t (T t was about 14 d),derived from the rate expression

YT is the final weight and Yt is the initial weight(Brown 1957).

Growth efficiency and instantaneous growth rateassessments were based on Wr values derived forthe interval associated with the growth period andon Wr values for a lag phase of one interval beforeand after calculation of growth characteristics. Wedetermined the absolute change in Wr (for a bi-weekly period) for evaluation against growth char-acteristics in the aforementioned manner.

Results and DiscussionRelationship of Wr to Proximate Components

Crude fat. Regression analyses of the final Wr-crude-fat relationships produced significant re-gression models for striped bass and hybrid stripedbass (Table 1). Crude-fat values increased withincreasing Wr (Figure 1). Therefore, the significantpositive relationship of crude fat to Wr appears toprovide an acceptable means of estimating the ap-proximate level of total body fat.

Energy storage sites. The percentage of vis-ceral fat relative to wet body weight was used toevaluate the relationship of final Wr to one of theprimary lipid storage sites: the visceral depot(Weatherley and Gill 1987). Extrapolation fromthe regression equations (Table 1) predicted 0%visceral fat at Wr values of 63 and 64 for stripedand hybrid striped bass, respectively (Figure 1).Excess energy is primarily stored as fat (triglyc-erides) (Love 1980; Weatherley and Gill 1987),and this depot constitutes the main energy sourcefor maintenance (Weatherley and Gill 1987). Fatreserves are necessary in mature fish of most spe-


Striped bass

75 90 105 120

75 90 105 120

60 75 90 105 120

75 90 105 120

75 90 105 120

82i7874706662

6(T

28i25;22191613;10-_

6070i

6662585450 _

60615

Hybrid striped bass

36i3024181260'

Relative weight

75 90 105 120

75 90 105 120

75 90 105 120

60 75 90 105 120

60 75 90 105 120

FIGURE 1.Scatter plots depicting the relationships of percent crude fat, visceral fat, crude protein, ash, andwater to final relative weight for individual juvenile striped bass and hybrid striped bass. Crude fat, crude protein,and ash are expressed as percent of dry body weight. Visceral fat is expressed as percent wet body weight.

cies for periods of migration (Chang and Idler1960), overwintering, and gonad maturation (Craig1977; Medford and Mackay 1978; Dawson andGrimm 1980). Such reserves in sexually immaturefish are necessary for growth (Brett et al. 1969)and overwintering (Oliver et al. 1979; Wicker andJohnson 1987). Therefore, fish entering a pro-longed period of natural starvation or other stress

(e.g., overwintering) at minimum Wr values maynot survive.

The assessment of liver tissue as another storagedepot of energy reserves (lipid and glycogen) hasbeen used to evaluate condition for several species(Novinger 1973; Tyler and Dunn 1976; Heidingerand Crawford 1977; Delahunty and de Vlaming1980; Adams and McLean 1985). Regardless of


TABLE 1.Variables for least-squares regression analysis of striped bass and hybrid striped bass relationships forcrude fat, visceral fat, crude protein, absolute protein (g), ash, water, gross energy (kj/g), relative growth (%), andthe change (A) in total length (mm) versus final Wr (P < 0.0001). Crude fat, crude protein, and ash are expressedas dry-weight percentages. Visceral fat and water are expressed as wet-weight percentages. Absolute protein is basedon wet weight of striped bass (310 mm) and hybrid striped bass (369 mm). The sums of squared deviations for Wrare 2,431 and 1,687 for striped bass and hybrid striped bass, respectively. Means for Wr are 93 and 86 for stripedbass and hybrid striped bass, respectively.

Linear equation

Crude fat - -36.766 + 0.661 WrVisceral fet = -15.064 + 0.240 WrCrude protein = 95.735 - 0.407 WrAbsolute protein - -73.973 + 1.428 WrAsh = 44.706 - 0.313 WrWater = 100.070 - 0.308 WrGross energy - 9.416 + 0.076 WrRelative growth - -306.566 + 4.337 WrA total length = -123.211 + 1.858 Wr

Crude fat = -14.963 + 0.461 WrVisceral fet - -9.321 + 0.146 WrCrude protein - 76.499 - 0.244 WrAbsolute protein - -94.187 + 2.359 WrAsh = 39.491 -0.256 WrWater = 93.721 -0.291 WrGross energy - 9.387 + 0.134 WrRelative growth = -96.850 + 1.304 WrA total length = -32.742 + 0.536 Wr

Mean square error

Striped bass3.1801.2222.1168.5481.7341.7510.833

28.03311.738

Hybrid striped bass2.6410.9131.883

12.9021.4101.9400.8098.3865.476

SE of Wr coefficient

0.0640.0120.0430.1730.0350.0360.0180.6750.240

0.0640.0220.0460.3140.0340.0470.0200.2040.133

fi

0.7900.7700.7620.7080.7390.7290.7270.6750.685

0.6560.6150.5120.6760.6730.5850.6320.6020.374

condition, liver weight was highly correlated withbody weight in our study (liver weight = 0.306+ 0.008 wet body weight, r2 = 0.808). Regressionanalysis of LSI against Wr for striped bass did notprovide a meaningful relationship (r2 = 0.128).Calculation of the Lr index (Legler 1977) for stripedbass did not provide higher correlations with en-ergy storage than did Wr. Percentage crude fat (r2= 0.369) and percentage visceral fat (r2 = 0.336)provided only moderate correlations when re-gressed against Lr. Based on these observations,Wr appears to provide better estimates of reserveenergy in striped bass than does LSI or Lr (Table1).

Crude protein.The relative quantity of crudeprotein decreased linearly with increasing Wr val-ues (Figure 1), thereby reflecting the concurrentpositive relationship between percentage crude fatand Wr. Predictive equations derived from ourstudy appear to provide good estimates of per-centage whole-body protein (Table 1). The rela-tionship between absolute protein (g) and Wr wasdetermined by adjusting protein to a mean length(striped bass, 310 mm; hybrid striped bass, 369mm). Regressions of absolute protein (g) againstfinal Wr provided positive relationships (Table 1).

Other authors have reported similar results basedon whole-body analyses (Phillips et al. 1960; Ni-imi 1972; Dawson and Grimm 1980).

Generally, there is little change in the proteinfraction until periods of prolonged starvation re-duce fat reserves to a point at which protein iscatabolized (endogenous metabolism) to meet en-ergy requirements. Sexually mature fish, especial-ly females, displace muscle protein to the repro-ductive soma during gonad maturation (Craig1977; Medford and Mackay 1978; Dawson andGrimm 1980). The striped bass and hybrid stripedbass in this study were sexually immature; there-fore, whole-body protein dynamics were attrib-uted to changes in feed intake.

Ash. Whole-body ash fraction decreased withincreasing Wr values (Figure 1). Linear regressionof percentage ash against final Wr provided sig-nificant predictive equations (Table 1). Other in-vestigators have reported increasing relative ashvalues with declining body fat (Savitz 1971; Niimi1972). Scales and vertebrae probably constitutethe major depots for elemental mineral concen-trations, thereby providing the least-sensitivecomponents to changes in absolute values. Love(1970) reported that relative muscle ash declined


after water content reached a critical point duringstarvation, though absolute values hardly reflectedthe depletion.

Water. Regression analysis provided correla-tions of about 0.7 and 0.6 (Table 1) for the inverserelationship of water content versus final Wr forstriped bass and hybrid striped bass, respectively(Figure 1). Several authors have noted that bodywater content (%) increases with starvation (Idlerand Bitners 1959; Groves 1970; Savitz 1971; Ni-imi 1972). This relationship to Wr was expectedbecause of the inverse water-crude-fat relation-ship.

Gross energy. Whole-body gross energy (kj/g)content was calculated for ash-free dry-weightsamples based on available-energy assumptionsfor fat and protein (Brett and Groves 1979). Re-gression analysis of the combined energy contentof these components against final Wr producedsignificant positive linear relationships (Table 1).Because fat and (to a lesser extent) protein con-stitute the primary energy sources in fish, the Wrindex may be used to estimate the level of whole-body gross energy for striped bass and hybridstriped bass.

Wr Relationship to Growth CharacteristicsEvaluation of relative growth (i.e., percent

change in weight for the experimental period) ver-sus final Wr resulted in significant positive linearrelationships for striped bass and hybrid stripedbass. Models for this relationship provided thehighest correlations for any growth analysis (Table1).

The change in total length (mm) as a functionof final Wr provided significant linear models forstriped bass and hybrid striped bass. This evalu-ation indicates that a moderate amount of thevariance associated with the change in the totallength increment is accounted for by final Wr.This should be expected since the ability to attainskeletal growth is conditionally regulated by thenutritional history of the fish.

There was no apparent relationship of Wr togrowth efficiency in either experiment. Further-more, lagging Wr did not produce any meaningfulrelationships with instantaneous growth or growthefficiency. Evaluation of instantaneous growth- Wrrelationships produced low correlations (stripedbass, r2 = 0.303; hybrid striped bass, r2 = 0.240).Regression analysis of the relationship betweeninstantaneous growth and the absolute change inWr accounted for a moderate amount of the vari-ability in Wr (striped bass, r2 = 0.458; hybridstriped bass, r2 = 0.604).

Interdependencies of Proximate ConstituentsOur regression analyses for the relationships of

crude fat, crude protein, and ash versus water con-tent produced highly significant linear models forstriped bass and hybrid striped bass (Table 2).Linear relations between proximate componentshave been observed for various species in previ-ous studies (Brett et al. 1969; Groves 1970; Elliot1976). Love (1970) categorized bony fish speciesbased on the relationships of fat and protein towater content; fatty fish (e.g., Salmonidae) exhibitan inverse relationship between fat and water, andnonfatty fish (e.g., Gadidae) show an inverse re-lationship between protein and water. Based onthese criteria, striped bass and hybrid striped bassmay be classified as fatty fish because both dis-played inverse linear crude-fat-water relation-ships and positive linear crude-protein-water re-lationships (Figure 2) in this study. This increasein water content was due to extensive cellularshrinkage with a concurrent increase in extracel-lular fluid (Love 1980). The highest water value(81%) and lowest crude-fat value (5%) were ob-served for a striped bass; ash (27%) and crudeprotein (68%) values were also highest for thisindividual. Values of an individual striped bassfor the other condition extreme were 67% water,33% crude fat, 53% crude protein, and 13% ash.A less extreme range for proximate componentvalues was observed for hybrid striped bass. Theindividual in the poorest condition contained 73%water, 17% crude fat, 61% crude protein, and 23%ash, whereas the individual in the best conditioncontained 63% water, 31% crude fat, 51% crudeprotein, and 13% ash.

Significant differences across feeding treatmentswere most frequently detected between the 0.25%BWPD ration and all other rations in our stripedbass study (Table 3). Low variability betweentreatments was due to highly variable consump-tion rates among individuals within a ration treat-ment. Means for water, crude protein, and ashwere lowest at the 2% BWPD level; highest meanvalues for crude fat, visceral fat, and Wr were alsoobserved at this level. This pattern was reversedat the 0.25% BWPD level. Mean consumption levelwas highest for the 2% BWPD treatment.

Significant differences across effects were mostfrequently seen between the 0.25 and 0.50%BWPD rations and all other rations in our hybridstriped bass study (Table 3), although differencesbetween treatments were not as discernible as thoseseen for striped bass. The hybrids, larger than thestriped bass used in this study, apparently did notfeed as well in the isolated experimental environ-


3630

a? 245 1B13 12

6j0

Striped bass Hybrid striped bass

58 62 66 70 74 78 82

9 70? 66I 62

Q- 58

!o so-58 62 66 70 74 78 82

36*T 30

126058 62 66 70 74 78 82

36;

3024181260^

.1^*^

58 62 66 70 74 78 82

7066]62585450

363024181260

Water (*)

58 62 66 70 74 78 82

58 62 66 70 74 78 82

FIGURE 2.Scatter plots reflecting the relationships of crude fat, crude protein, and ash to water for individualjuvenile striped bass and hybrid striped bass. All components (except water) are expressed as percent dry weight.

ment. This may have been because they were heldin a pond before the study. We observed generalincreases in crude fat, visceral fat, and Wr withincreasing ration for both striped bass and hybridstriped bass; concurrent decreases were noted inwater content, crude protein, and ash.

We conclude that the Wr index appears to pro-vide a viable alternative to proximate analysis for

estimating body composition and gross energy injuvenile striped bass and hybrid striped bass. Re-serve energy (visceral fat) predicted from Wr pro-vides a measure of overwintering fitness and per-haps of suitability for stocking. If Wr can acceptablypredict stored energy in mature fish, it can be ex-tended to traditional fall population assessmentsto predict overwintering fitness of the general POP-

TABLE 2.Variables for least-squares regression analysis of striped bass and hybrid striped bass relationships forwater versus crude fat, crude protein, and ash (f < 0.0001). All independent variables are expressed on a dry-weight percentage basis. The sums of squared deviations for water are 317.19 and 244.79 for striped bass andhybrid striped bass, respectively. Means for water are 71.53 and 6S.79 for striped bass and hybrid striped bass,respectively.

Linear equation

Crude fat * 165.206 - 1.968 waterCrude protein = -23.564 -1- 1.141 waterAsh = -48.775 + 0.902 water

Crude fat = 108.106 - 1.215 waterCrude protein = 1 1.440 -f 0.642 waterAsh - -30.186 + 0.694 water

Mean square errorStriped bass

2.0542.0261.524

Hybrid striped bass2.6281.8781.308

SE of water coefficient

0.1150.1140.086

0.1680.1200.084

r*

0.9120.7820.798

0.6590.5140.719


TABLE 3.Means for proximate components, visceral fat, and final Wr derived from striped bass and hybridstriped bass feeding treatments. Mean comparisons are based on Tukey's HP-procedure; means followed by thesame letter within effect rows are not significantly different (P > 0.05).

Ration level (% of body weight per day)Effect

WaterCrude fatCrude proteinAshVisceral fatFinal Wr

0.25

77 y12 x65 x22 x0.2 w

76 x

0.50

72 z23 y60 y16y

1.5 x92 y

0.75

Striped bass71 z26 y58 yz14yz2.5 y

92 y

1

71 z26 y56 yz15yz2.0 yx

95 yz

2

68 z32 z54 z13z3.8 z

103 z

3

70 z28 yz56 yz14yz2.7 y

98 yzHybrid striped bass

WaterCrude fatCrude proteinAshVisceral fatFinal Wr

72 y17y59 x21 y

1.4 y76 y

70 yz23 z57 yx18yz2.4 yz

83 yz

69 yz25 z55 yz17z3.6 y

86 yz

68 yz28 z55 yz16z3.7 y

89 z

67 yz28 z54 yz16z3.8 y

92 z

66 z27 z53 z15z4.5 y

89 z

ulation and possibly the reproductive potential ofstriped bass in the following spring. However,equations developed in our study were based onjuvenile striped bass (240-340 mm) and hybrids(300-400 mm). The results of this study shouldnot be extended to mature fish. Numerous authorshave reported marked variability of proximatecomponents within a species due to age, sex, sea-son, diet, and combinations of these factors. Fatappears to be the component most affected by thesefactors because of energy demands associated withoverwintering starvation in juvenile and maturefish and eventual gonad maturation in sexuallymature fish; protein and ash, to a lesser extent,are not as dynamic as fat. Additional research isrequired to clarify the relationship of Wr to thesefactors for wild and adult stocks.

AcknowledgmentsThis project was completed with partial funding

from the Kansas Department of Wildlife and Parks(contract 122) as part of Texas Agricultural Ex-periment Station (TAES) project 6843-H; this pa-per represents TAES contribution TA-24939.Special thanks are extended to Cathy Dryden forassistance with laboratory analyses. Manuscriptreviews were provided by Richard O. Anderson,Delbert M. Gatlin, and H. Del Var Petersen.

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Received May 8, 1990Accepted December 3, 1990

Documents

Relationship of Relative Weight (Wr) to Proximate