A comparison of growth performance and genetic traits between four selected groups of African catfish (Clarias gariepinus burchell 1822)

Camp.Biochem.Physiol.Vol. 102A.No. 2, pp.373-377,1992

0300-%29/92SS.00+ 0.00

0 1992 Pergamon Press Ltd

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A COMPARISON OF GROWTH PERFORMANCE AND GENETIC TRAITS BETWEEN FOUR SELECTED GROUPS OF AFRICAN CATFISH (CLARIAS GARIEPINUS BURCHELL 1822) J. P. GROBLER, H. H. Du PREEz and F. H. VAN DER BANK Research Unit for Aquatic and Terrestrial Ecosystems, Rand Afrikaans University, P.O. Box 524, Johannesburg, 2000, Republic of South Africa (Received

15 October 1991)

Ah&act-l. Fast growing individuals (three groups) in a progeny batch of African catfish were identified and isolated from the main population, 2. At the age of 36 weeks, the mean mass of two fast growing groups (169.6 and 232.Og) was significantly (P < 0.05) higher than that of the rest of the population (88.81087 g). 3. A comparison of specific growth rates revealed that these differences were the result of superior growth at an early age. 4. An electrophoretic evaluation of the different mass classes showed little or no difference between the LDH allele frequencies of the fast growing groups, but did indicate significant differences between the frequencies of fast and slow growing groups. 5. The present study represents the first attempt to establish the role of genetic characteristics in the control of growth in African catfish, and suggests the feasibility of genetic selection for rapid growth in Clarias gariepinus.

The occurrence of fast growing individuals in African catfish (Clurias gariepinus) populations has been reported by several authors (Britz and Hecht, 1987; Uys and Hecht, 1988). Selection for fast growth

could be of considerable economic importance for catfish farmers (Van der Bank, 1989). Genetic selection for rapid growth is, however, only possible if variation exists in the genes controlling growth performance (Allendorf and Utter, 1979). A genetic evaluation of control and select groups of C. gariepinw from a lowveld catfish hatchery has been ~dertaken by Grobler (1990), who found notable differences between the allelic frequencies of catfish selected for rapid growth and those of control specimens. Grobler (1990) concluded that the results achieved were possibly indicative of diversity in genes controlling growth of C. gariepinus. It would, however, be desirable to verify the apparent association between certain biochemical markers and growth under controlled environmental conditions before embarking on any selection ventures. The major goals of the present survey were thus (1) to identify and isolate fast growing individuals from a progeny batch of C. guriepinus under controlled environmental conditions, (2) to establish the extent of performance differences between fast and slower growing caffish and (3) to compare the fast growing catfish with the rest of the population in order to determine whether genetic differentiation exists or not. MATERIALS AND METHODS

One thousand 24hour-old C. gariepinus larvae were obtained from a catfish hatchery in the Eastern Transvaal

(24’22’s and 30”52’E, South Africa). These larvae were kept in a 300 1 glass aquarium at 27 f 1°C until the age of 6 weeks. During this period, the larvae were fed with a dry feed mixture formulated by Uys (1988). The catfish were transferred to a recirculating system at the age of 6 weeks. This system consisted of four circular pools linked to a water purification system, with a total volume of 27001. The catfish were kept at a temperature of 27 f 1°C and a photoperiod of I2L:l2D. Commercial feed pellets (47% protein) were fed to the catfish daily at 9.00 a.m. and 3.00 p.m., in accordance with a feeding schedule proposed by Uys (1988). The catfish population was divided into four groups based on mass differences observed in the period from week 6 to week 18. The groups G6-10, GlO-14 and GM-18 contained fast growing individuals identified and isolated during the periods 6-10, IO-14 and M-18 weeks, respectively. Group G-N consisted of the remaining population. The average mass, specific growth rate and food conversion ratio of each group were determined at 14 day intervals until the age of 36 weeks. The following formulae, as suggested by Degani et al. (1988) were used: Specific growth rate (%) = (1nWr - In We/number of days) x 100, where R’o and Wt denote the mass at the beginning and end of each period, respectively, and food conversion ratio = food intake (dry mass g)/body mass gain (g). The individuals in each mass group were evaluated by means of protein electrophoresis at the end of the comparative growth experiment. Vertical ~lya~la~de gel eiectrophoresis, as described by Avtalion and Wojdani (197 t ). was used for the evaluation of blood serum. Six per cent gels were used, and sera were combined with a 40% sucrose solution in a ratio of 7 p 1serum to 43 ~1 sucrose. A current of 250 mV (17 mV/cm) was used for the creation of an electrical field to facilitate migration of proteins. Staining and interpretation of gels were as described by Harris and Hopkinson (1976), Ferreira er al. (1984) and Grant (1989). Gels were stained for lactate dehydrogenase to confirm a 373

314

J. P. GROEWR er al.

Table 1. The mean mass ( f standard error), specific growth rate and food conversionratio of four groups of C. garfepimwfrom the ages 6-36 weeks PCriod (weeks) 6-8 &IO IO-12 12-14 14-16 1618 18-20 20-22 22-24 24-26 26-28 28-30 30-32 32-34 34-36 Mean

G-N 0.3kO.2 0.7 f 0.4 1.0 f 0.6 1.5 f 0.5 2.9 f 1.5 4.6 * 2.3 7.6 * 3.5 12.3 * 6.4 18.8 * 9.1 28.5 * 13.0 43.0 * 18.1 50.4 * 20.5 58.5 f 27.6 80.1 f 38.1 88.8 f 51.3

Mean mass (g) G6-10 G1&14 10.0 f 16.0 f 21.8 * 31.7 f 37.9 * 48.5 f 66.3 k 71.6 * 93.9 k 121.5 * 139.8 5 159.5 + 201.3 f 232.0 +

5.6 7.6 8.9 12.1 14.1 19.3 23.7 28.8 43.5 65.8 70.1 111.5 152.1 180.0

4.9 * 1.1 1.8 * 2.5 15.6 f 4.6 20.9 * 5.2 31.6 + 8.1 51.3 f 14.9 65.7 * 20.8 87.0 & 28.1 105.8 f 34.9 121.2 & 31.4 133.1 * 31.1 159.5 f 54.5 169.6 k 51.3

GlC18

5.0 f 1.3 9.3 * 2.4 12.5 + 2.3 18.4 f 4.7 27.8 + 8.5 36.6 f 8.1 47.4 * 16.3 59.1 If: 19.9 13.6 f 21.8 85.2 f 25.2 97.3 + 30.6 108.7 f 33.6

Sprcific growth rate (%) G6-10 GlO-14 GlCl8

GN 4.69

-

6.49 2.79 2.82 4.97 3.20 3.56 3.44 3.00 2.95 2.95 1.13 1.66 2.24 0.74 2.65

possible association of this enzyme with fast growth in C. gariepinus, as reported by Grobler (1990). Analysis of variance (Sokal and Rohlf, 1973) and Scheffe’spaired sample testing were used for the statistical analysis of results obtained. RESULTS

The mean mass, specific growth rate and food conversion ratio of each group of C. gariepinus for each period from 6 to 36 weeks is presented in Table 1, with a statistical analysis of these results in Table 2. The mass of individual catfish at the end of week 36 ranged from 21 to 597 g. Analysis of variance indicated significant (P < 0.05) differences between the masses of certain groups at week 36. Scheffe’s paired sample test showed no significant difference between groups G6-10 and GlO-14, but did indicate significant differences between these two groups and groups Gl4-18 and G-N. No significant differences were found between groups G14-18 and G-N.

4.14 3.37 2.21 2.66 1.12 1.93 2.23 1.12 I .36 1.84 1.00 0.94 1.66 1.01 1.54

-

-

2io 3.30 4.95 2.09 2.95 3.46 1.76 2.00 1.40 0.97 0.67 1.29 0.43 2.00

q 4.40 2.11 2.16 2.95 1.96 1.84 1.58 1.57 1.05 0.95 0.79 2.00

Feed conversion ratio (%) G-N G6-10 GlO-14 GlU8 1.62 1.19 2.41 2.57 0.90 1.83 1.54 1.35 1.58 1.46 1.19 3.66 3.58 1.14 3.97 2.00

1.82 2.72 1.73 3.86 1.92 1.57 2.46 2.00 1.43 2.75 2.98 1.37 2.29 2.22

Sum of squares

2.23 1.41 0.97 2.40 1.55 0.96 1.49

1.39 1.93 2.88 4.38 2.19 6.63 2.34

0.86 2.14 1.53 1.46 1.89 2.22 2.43 1.96 2.66 2.90 3.58 2.15

Specific growth rates of the four groups ranged from 0.74 to 6.49% (Table 1). Group G-N displayed the highest average specific growth rate (2.65%), whereas group G6-10 had the lowest mean growth rate (1.54%). No significant (P > 0.05) differences were observed between the average specific growth rates of the various groups (Table 2). Food conversion ratio ranged from 0.9 to 6.63 (Table I), with the most favourable average food conversion ratio being observed in group G-N (2.0); group GlO-14 had the least favourable conversion ratio (2.34). Analysis of variance showed no significant (P > 0.05) differences between the food conversion ratios of the four groups. Activity of one polymorphic LDH locus with two co-dominant alleles was observed in C. gariepinus blood serum. The relative mobilities and frequencies of the alleles for each catfish group are presented in Table 3. The frequency of the most common allele (100) showed little variation between the three high mass groups (0.70, 0.73 and 0.72) but was lower in

Table 2. Analyses of statistical signiticance of differences between the average mass, specific growth rate and feed conversion ratio of four groups of C. gariepinus Analyses of variance Source of variation

-

Degrees of freedom

Average mass Groups Error Total

Mean square

40 528 3 121 585 2 955 203 899 69 325 484 72 F 0.05(2).3,69 = 3.34 (significant differences are present) Specific growth rate Groups 8.47 4 2.118 Error 49.13 50 0.983 Total 57.60 54 F 0.05(2),4,50 = 3.07(no significant differences) Feed conversion ratio Groups 1.oo 3 0.333 Error 53.18 40 1.330 Total 54.18 43 F 0.05(2),3,40 = 3.46 (no significant differences) Schcffe’s paired sample testing for average masses of groups G6-IO and GlO-14 -34.89/l 17.89 26.30/180.70* G6-IO and G14-18 52541189.38’ G6-10 and G-N 1.80/122.20* GlO-I4 and G14-18 GlO-14 and GN 30.90/127.90’ 014-18 and G-N -32X)/67.30 *Significant diftcrence for Schdfe’s paired sample test.

F 13.72

2.15

0.25

Growth in catfish

375

Table 3. The relative mobilities and allelefrequencies of LDH alleles observedin C. gdepinususing blood serum

2.6 times heavier than the 88.8 g of group G-N. This loss of mass advantage can be explained by the Group association between mass and specific growth rate GIO-14 G14-18 Relative mobility G-N G&IO already mentioned. It is, however, also an indication 0.28 0.40 0.30 0.27 60 that mass differences in catfish populations are 0.72 0.60 0.70 0.73 100 mainly the result of growth rate differences at a very early age. The mass differences between groups observed at later stages could thus be a result of events at an early age, and are not necessarily an indication group G-N (0.60). The phenotype 6OjlOO was found of continuous superior growth buoyance in the in the majority of catfish in group G-N (60%), but high mass groups. The advantage attained by certain had a lower frequency in the three high mass groups individuals at an early age is nevertheless sufficient to (48%) (Table 4). Conversely, the phenotype IOOjlOO ensure that most of these individuals will retain their had a high frequency among fast growing individuals advantage until a marketable size is reached. (48%) but occurred in only 30% of individuals in The average feed conversion ratio recorded during group G-N. the present survey is slightly lower than values reported by other authors. Feed conversion ratios of C. guriepinus on commercial hatcheries range from 0.95 DISCUSSION to 1.3, with an average of 1.2 (IIecht and Britz, 1988; Uys, 1988). Prinsloo et al. (1989) reported a food The results of the present survey confirm that conversion ratio of 1.9 with the use of a low protein considerable size variation exists within progeny diet, whereas Degani et al. (1988) observed a food batches of C. g~r~epinu~. A comparison between different mass groups provided si~ifi~nt insight into conve~ion ratio of 0.94 to 1.6 with a 45% protein diet. The above-mentioned values are, on average, the relative growth performance of these groups. more favourable than the 1.89 to 2.30 observed Analysis of specific growth rate showed that group during the present study. The more favourable G-N, the group with the lowest mass, had the highest feed conversion ratios attained at commercial hatchspecific growth rate over most of the 14 day periods as well as during the total experimental period. This eries are probably due to the availability of natural observation creates the impression that the smaller food in production ponds. These live food organisms catfish were gradually gaining on the larger mass supplement the normal feed ration and can result in groups, However, this phenomenon is the result of an artificially high value for the food conversion differential growth rates between all small and large ratio. The exclusive use of blood serum restricted the catfish. Hoogendoorn et al. (1983) created a model to predict the growth rate of C. gariepinus at various extent of the genetic evaluation, but was unavoidable temperatures, according to which the growth rate of as the experimental catfish were needed for continued breeding. A comparison of LDH allele frequencies catfish will always decrease as mass increases. For example, at 27°C catfish of 1 g will grow at 9.2% of revealed little variation between the three groups of body mass per day, whereas catfish of 200g will fast growing catfish (Table 3). However, the allele frequencies of LDH in group G-N differed notably grow at a rate of only 1.4% per day. The seemingly superior growth rate of group G-N over most from those in any of the faster growing groups. The periods is, therefore, a straightforward consequence observation that three groups of catfish selected for of this group’s low mass. A decrease in the specific rapid growth, having almost exactly the same allele growth rate of this group would almost certainly frequencies for LDH seemed highly significant. follow as the mass of individuals in the group inDifferences between the allele frequencies of LDH creases. of slow and fast growing channel catfish, Ictalurus An important goal of the present survey was to punctatus, have previously been reported by establish whether catfish which have superior mass at Hallerman et al. (1986). These authors found differan early age can maintain their size advantage until ences of 2-l]% between the allele frequencies of the a marketable size is reached. The results of the two groups. The results of the present study are thus present survey indicated that the lead of high mass a confi~ation of the findings by Hallerman et al. individuals was gradually decreased. A comparison (1986) in that selection for rapid growth can result in between the masses of groups G-N and G6-10 changes of enzyme allele frequencies, including those illustrates this point clearly. At the age of 24 weeks, of lactate dehydrogenase. group G6-10 had an average mass of 16 g, 16 times Comparison of banding pattern phenotypes as heavier than the average of 1 g of group G-N. By described by Reinitz (1977), revealed significant freweek 36, the mass of group G6-10 (232 g) was only quency differences between rapid and slow growing

Table 4. The relative frequencies of four LDH banding pattern phenotypes in blood serum for four C. gariepinwsub-populations

Phenotype 6w@ 60/100 ]~/I~

G-N VW 10 60 30

G6-IO fW 0 60 40

Group GlO-14 w 9 36 s5

Gl4-18 W) 0 56 44

Total for three high mass W) 4 48 48

376

J. P. GROBLERet al.

individuals. In the present study, the heterozygotic phenotype 60/100 was the predominant phenotype in group G-N (60%) but was present in only 48% of the individuals in the rapid growth groups. The monomorphic phenotype lOO/lOOwas found in 48% of fast growers, but occurred in only 30% of group G-N. It thus seems that a low occurrence of heterozygotes and a high percentage of the phenotype lOO/lOO for LDH could possibly be linked to rapid growth in C. gariepinus. An association between LDH phenotypes and rapid growth of C. guriepinus in a lowveld population has previously been reported by Grobler (1990). This author observed a low occurrence of heterozygotes (42%) among rapid growing individuals and a much higher occurrence (75%) in the rest of the population. The results of the present study, as well as the trend observed by Grobler (1990), thus indicate an association between a low frequency of LDH heterozygotes and high mass in African catfish populations. The question arises whether or not the biochemical differences observed are the only cause of performance differences observed between rapid and slow growing catfish. Environmental factors were standarized as far as possible during the present survey. One factor which could, however, not be eliminated is competition. Intrapopulation competition can provide severe problems for aquaculture geneticists (Doyle and Talbot, 1986). If the largest individuals in a population merely represent those individuals obtaining the most food through behaviour domination, superior growth rate could conceivably have no link with genetic factors (Weatherley, 1976; Hedgecock et al., 1982). Allee et al. (1948) reported that socially dominant Lepomis cyanellus eat more and grow faster than the rest of the population, even though all individuals have equal access to available food. For Salmo salar it was reported that growth rate differences can be attributed to starvation of socially subordinate individuals (Li and Brockson, 1977). Further examples where social factors caused growth rate differences were reported by Molander and Molander-Swedmark (1957) and Purdom (1974). The potential effect of competition on growth performance of C. gariepinus, therefore, requires further investigation. One possible way of eliminating social interaction would be to raise a population of catfish with each individual in a separate container, as proposed by Weatherley (1976). Individuals displaying rapid growth under such circumstances would have a high probability of carrying genes responsible for favourable growth performance. Even this extensive process is not without shortcoming, as Weatherley (1976) reported that the disruption of social structure can in itself lead to alteration of growth performance. Growth of C. guriepinus seems to be a multi-dimensional process, affected by genetic as well as environmental factors. Social interaction (domination) can probably lead to considerable size variation within catfish populations. On the other hand, the results of the present survey, as well as the more comprehensive genetic survey by Grobler (1990), indicate that rapid growth in C. gariepinus might be attributed to genetic factors. These results suggest that successful mass selection of African catfish using biochemical mark-

ers may be feasible. Such genetic selection should nevertheless not be attempted without due consideration for the inffuence of non-genetic factors on the growth performance of C. gariepinus. Acknowledgemenrs-The authors wish to express their gratitude to Dr Wynand Uys for providing thecatfish larvae used during this study and the Foundation for Research Development for tinancial support.

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