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Single gene inheritance of red body coloration in Taiwanese red tilapia
Aquaculture, 74 (1988) 227-232 Elsevier Science Publishers B.V., Amsterdam
227 -
Printed
in The Netherlands
Single Gene Inheritance of Red Body Coloration in Taiwanese Red Tilapia C.M. HUANG’z4, S.L. CHANG*, H.J. CHENG” and I.C. LIA03 ‘Institute of FisheriesScience, National Taiwan University, Taipei (Taiwan) ‘Tungkang Marine Laboratory, Tungkang, Pingtung, 92804 (Taiwan) 3Taiwan Fisheries Research Institute, 199 Hou-Ih Rd., Keelung, 20220 (Taiwan) 4To whom correspondence should be addressed *Contribution No. 76 from Tungkang Marine Laboratory. (Accepted
21 April 1988)
ABSTRACT Huang, CM., Chang, S.L., Cheng, HJ. and Liao, I.C., 1988. Single gene inheritance coloration in Taiwanese red tilapia. Aquaculture, 74: 227-232.
of red body
Randomly selected red tilapia (Oreochromis mossambicus X 0. niloticus) broodfish were mated in aquaria and small concrete ponds at a ratio of one male to three females. Eggs were collected from individual females and artificially incubated. Body color was examined when the fry were 2 weeks old. A phenotypic ratio of three red to one black colored tilapia was obtained. Results of F2 progeny obtained from crosses of various body color combinations of the Fl progeny showed that red body coloration was inherited as a single gene with incomplete dominance. The study demonstrated that of the six possible matings, pinkxpink, pinkxred, pinkx black, redxred, red x black, and black x black, the first three produce only pink or red tilapia. Thus, it is suggested that RR is the genotype for pink color, Rr for red color, and rr for black color.
INTRODUCTION
The red tilapia has become an increasingly important cultured fish species because of its attractive coloration, fast growth and consumer preference. It is now cultured in many parts of the world including Israel, the U.S.A., Taiwan, Thailand, the Phillippines, India and the Bahamas. The many papers on various aspects of red tilapia culture, husbandry and genetics presented at the Second International Symposium on Tilapia in Aquaculture held in March of 1987 in Bangkok, Thailand, witness the recent worldwide interest in the study and culture of red tilapia. Taiwanese red tilapia were first found by a tilapia farmer in southern Taiwan and development of a broodstock began at the Taiwan Fisheries Research Institute in 1969 (Kuo, 1969). The founder fish were reported to be a hybrid
0044-8486/88/$03.50
0 1988 Elsevier Science Publishers
B.V.
228
produced by crossing the red mutant of Oreochromis mossambicus with 0. niloticus (Liao and Chen, 1983 ) . Tave (1987) suggested three hypotheses for the inheritance of body coloration in red tilapia: (1) a single co-dominant gene, (2) two recessive genes with epistasis, (3) two independent genes, each of which has complete dominance and produces a separate phenotype. The color of red tilapia has also been attributed to two or three gene pairs exhibiting dominance (Behrends et al., 1982). On the other hand, Mires (1987) reported that red or pinkish colored mutants of 0. ndoticus are recessive to black colored fish. The purpose of this study was to investigate the mode of body coloration inheritance of red tilapia in Taiwan. MATERIALS AND METHODS
Taiwanese red tilapia brood fish with red color were randomly selected for mating. These red tilapia have been maintained at Tungkang Marine Laboratory (TML) for many years. The selected broodstock were placed in 500-l aquaria and in outdoor concrete ponds (3.4 m2). In the parental generation, the matings were set up with a ratio of one male to three females. Females kept in aquaria were individually tagged. Continuous aeration was maintained in both the aquaria and the concrete ponds. Matings among the Fl progeny of pink, red and black phenotypes were set up in glass aquaria with one male to one or two females. Female tilapia were observed daily for spawning. In the aquaria when mouthbrooding was observed, the spawners were gently caught with a finemesh dip net and all the eggs were washed out and collected in a bowl. In the outdoor concrete ponds, eggs were collected from females every 10 to 14 days by draining the pond water to a shallow level. Only eggs or young larvae in the mouth of brooding females were collected. Eggs collected from each individual spawn were counted and recorded. Some batches of eggs were collected from repeat matings of the same pair of brood&h. The developing eggs were transferred to plastic jars for artificial incubation. After larvae had absorbed their yolk sac, the fry were transferred to a plastic container. Each container was continuously aerated. Separation of red and black colored fry can be made after the yolk sac has been fully absorbed. Fry from each spawn were therefore scored for red and black color 2 weeks after hatching. A single gene model of inheritance was postulated with a 3:l phenotypic ratio among offspring of a mating between two heterozygotes. Observed segregation ratios were tested by Chi-square for acceptance or rejection of the hypothesis of a single gene model of inheritance of body color. Additional data from the crosses between F2 progeny of various color types were also used to test the postulated mode of inheritance.
229
RESULTSANDDISCUSSION The ratio of red to black color from the crosses between Taiwanese red tilapia was consistent with an expected 3:l ratio. A total of 28 spawns was obtained in the parental generation. The total number of fry produced by each brood fish ranged from 216 to 1668. In all but one case, crosses of redx red gave a segregation ratio not significantly different from an expectation of 3 red to 1 black, indicating a single gene model of inheritance with red color dominant over black color. This is in agreement with the reports of Behrends et al. (1982) and Behrends and Smitherman (1984). For the one anomalous result, all 483 fry were red in color. A close inspection of the parents used in this mating indicated one to be pink in color. It appears that all red tilapia brood fish used for mating were heterozygous. Progeny ratios from crosses among Fl individuals with various color combinations are presented in Table 1. Pink x pink matings produced only pink F2 progeny. Pink x red matings resulted in both pink and red progeny in a 1:l ratio. When pink x black or black x pink matings were made, all progeny were red. A 3:l ratio of red to black coloration was obtained from redx red crosses when some pink appearing progeny were included in the red category. However, the pink and red colors were very difficult to distinguish at the young larval stage. Red x black and black x red matings produced a ratio of 1:l red to black progeny. Black x black mating produced only black individuals among the F2 progeny. There were no significant departures from expectations in any of the matings (P < 0.05 ) . The genotypes for each body pigment can be proposed on the basis of results obtained in this study (Table 2 ) . Pink individuals are homozygous dominant and have a genotype RR. Red individuals are heterozygotes (Rr) and black individuals are homozygous recessive (rr ) . The results indicate that red color of Taiwanese red tilapia is inherited as a single gene showing incomplete dominance. It is possible that pink and red color could be distinguished at the young larval stage, but the ratio of 1:2:1 for pink, red and black color has only been observed at the young fingerling stage. An attempt was made to classify the pink and the red color for every brood at the larval stage but it was not easy to separate the fry accurately into these two color groups. Pink and red color can be clearly distinguished when the fish are 2 months of age or older. The results of this study are in contrast to those of Behrends et al. (1982) who suggested that two to three gene pairs influence the color and pigmentation of red tilapia. However, Behrends and co-workers did not provide any specific data on segregation ratios to support their hypothesis. In another study, Behrends and Smitherman ( 1984) crossed Tilupia (Oreochronis) aureus to red tilapia and obtained 50% red and 50% black color phenotypes. This would indicate a single gene coding for red color which is in agreement with the results
230 TABLE 1 Body color segregation of F2 progeny from interbreeding of Fl individuals of various body color combinations Mating type QXd”
Brood fish number
Number of offspring
Body color Pink
Red
Black
Pink X Pink
1 2
141 94
141 94
-
-
-
Pink X Redb
1 2
67 180
30 67
28 57
-
0.06 0.80
Pink X Black
1 2 3 4 5
150 217 110 441 205
-
150 217 110 441 205
-
-
Black X Pink
1 2
476 158
-
476 158
-
-
Red X Red
1 2 3 4 5 6 7
570 626 321 181 453 358 222
-
428 469 244 135 344 267 169
142 157 77 46 109 91 53
0.00 0.00 0.17 0.01 0.21 0.03 0.15
Red X Black
1 2 3 4 5
375 721 219 283 596
-
181 384 123 131 287
194 337 96 152 309
0.46 3.06 3.33 1.56 0.82
Black x Red
1
482
248
234
0.40
Black x Black
1 2 3
340 34 318
-
340 34 318
-
-
Chisquare”
“Expected phenotypic ratio of 3:l for red to black color was tested for red X red mating and a ratio of 1:l for pink X red and redX black mating. bBody color was examined when fry were 2 months of age. Some fry died before examination.
of this study. The red color mutant in 0. niloticus reported by Mires (1987) was due to a simple recessive gene. Thus, the 0. niloticus gene must represent a different mutation for red body color in tilapia. There were some minor variations within the red color group. For example, a number of red tilapia showed some melanic spots or patches on the body and fin area. However, these fishes were considered to belong to the red color group
231
TABLE 2 Phenotype and genotype of the offspring based on matings of the various phenotypes and genotypes of the parents Offspring
Parent Phenotype
Genotype
Phenotype
Genotype
Pink x Pink Pink X Red Pink x Black Red x Red Red x Black Black x Black
RRxRR RRxRr RRXrr RrXRr Rrxrr rr x rr
All Pink Pink, Red All Red Pink, Red, Black Red, Black All Black
RR RR, Rr Rr RR, Rr, rr RR, rr rr
even though the color was not uniform among the same brood of fish. It was also observed that some of the pink color tilapia were subvital, less vigorous and showed some deformities which suggested that the R gene may have pleiotropic effect on viability, vitality and even some minor color variation. The pleiotropic effect of a dominant gene, associated with the light-yellow pattern, has been reported in Japanese carp (Katasonov, 1973). In Taiwan, tilapia farmers who culture red tilapia generally make red x red crosses which produce red and black colored fry. The black fry are removed in order to culture only red tilapia. This requires added labor costs to sort out the red tilapia fry. The results of this study show that pink and red tilapia fry can be produced by mating pink x pink, pink x red and pink x black. ACKNOWLEDGEMENT
This research was partially supported by a grant from the National Science Council, Taiwan (NSC 76-0409-B055a-01).
REFERENCES Behrends, L.L. and Smitherman, R.O., 1984. Development of a cold-tolerant population of red tilapia through introgressive hybridization. J. World Maricult. Sot., 15: 172-178. Behrends, L.L., Nelson, R.G., Smitherman, R.O. and Stone, N.M., 1982. Breeding and culture of the red-gold color phase in tilapia. J. World Maricult. Sot., 13: 210-220. Katasonov, V. Ya., 1973. A study of pigmentation in hybrids between the common and the decorative Japanese carp. I. A study of the dominant pigmentation types. Genetika, 9: 59-69. Kuo, H., 1969. Notes on the hybridization of tilapia. JCRR Fish. Ser. No. 8, pp. 116-117. Liao, I.C. and Chen, T.P., 1983. Status and prospects of tilapia culture in Taiwan. In: L. Fishelson and Z. Yaron (Compilers), Proceedings of the International Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel, pp. 588-598. Mires, D., 1987. The inheritance of black pigmentation in Oreochromis niloticus from two African
232 origins. Presented at the Second International Symposium on Tilapia in Aquaculture, Bangkok, Thailand, 16-20 March, 1987. Tave, D., 1987. Genetics and breeding of tilapia. Presented at the Second International Symposium on Tilapia in Aquaculture, Bangkok, Thailand, 16-20 March 1987.
227 -
Printed
in The Netherlands
Single Gene Inheritance of Red Body Coloration in Taiwanese Red Tilapia C.M. HUANG’z4, S.L. CHANG*, H.J. CHENG” and I.C. LIA03 ‘Institute of FisheriesScience, National Taiwan University, Taipei (Taiwan) ‘Tungkang Marine Laboratory, Tungkang, Pingtung, 92804 (Taiwan) 3Taiwan Fisheries Research Institute, 199 Hou-Ih Rd., Keelung, 20220 (Taiwan) 4To whom correspondence should be addressed *Contribution No. 76 from Tungkang Marine Laboratory. (Accepted
21 April 1988)
ABSTRACT Huang, CM., Chang, S.L., Cheng, HJ. and Liao, I.C., 1988. Single gene inheritance coloration in Taiwanese red tilapia. Aquaculture, 74: 227-232.
of red body
Randomly selected red tilapia (Oreochromis mossambicus X 0. niloticus) broodfish were mated in aquaria and small concrete ponds at a ratio of one male to three females. Eggs were collected from individual females and artificially incubated. Body color was examined when the fry were 2 weeks old. A phenotypic ratio of three red to one black colored tilapia was obtained. Results of F2 progeny obtained from crosses of various body color combinations of the Fl progeny showed that red body coloration was inherited as a single gene with incomplete dominance. The study demonstrated that of the six possible matings, pinkxpink, pinkxred, pinkx black, redxred, red x black, and black x black, the first three produce only pink or red tilapia. Thus, it is suggested that RR is the genotype for pink color, Rr for red color, and rr for black color.
INTRODUCTION
The red tilapia has become an increasingly important cultured fish species because of its attractive coloration, fast growth and consumer preference. It is now cultured in many parts of the world including Israel, the U.S.A., Taiwan, Thailand, the Phillippines, India and the Bahamas. The many papers on various aspects of red tilapia culture, husbandry and genetics presented at the Second International Symposium on Tilapia in Aquaculture held in March of 1987 in Bangkok, Thailand, witness the recent worldwide interest in the study and culture of red tilapia. Taiwanese red tilapia were first found by a tilapia farmer in southern Taiwan and development of a broodstock began at the Taiwan Fisheries Research Institute in 1969 (Kuo, 1969). The founder fish were reported to be a hybrid
0044-8486/88/$03.50
0 1988 Elsevier Science Publishers
B.V.
228
produced by crossing the red mutant of Oreochromis mossambicus with 0. niloticus (Liao and Chen, 1983 ) . Tave (1987) suggested three hypotheses for the inheritance of body coloration in red tilapia: (1) a single co-dominant gene, (2) two recessive genes with epistasis, (3) two independent genes, each of which has complete dominance and produces a separate phenotype. The color of red tilapia has also been attributed to two or three gene pairs exhibiting dominance (Behrends et al., 1982). On the other hand, Mires (1987) reported that red or pinkish colored mutants of 0. ndoticus are recessive to black colored fish. The purpose of this study was to investigate the mode of body coloration inheritance of red tilapia in Taiwan. MATERIALS AND METHODS
Taiwanese red tilapia brood fish with red color were randomly selected for mating. These red tilapia have been maintained at Tungkang Marine Laboratory (TML) for many years. The selected broodstock were placed in 500-l aquaria and in outdoor concrete ponds (3.4 m2). In the parental generation, the matings were set up with a ratio of one male to three females. Females kept in aquaria were individually tagged. Continuous aeration was maintained in both the aquaria and the concrete ponds. Matings among the Fl progeny of pink, red and black phenotypes were set up in glass aquaria with one male to one or two females. Female tilapia were observed daily for spawning. In the aquaria when mouthbrooding was observed, the spawners were gently caught with a finemesh dip net and all the eggs were washed out and collected in a bowl. In the outdoor concrete ponds, eggs were collected from females every 10 to 14 days by draining the pond water to a shallow level. Only eggs or young larvae in the mouth of brooding females were collected. Eggs collected from each individual spawn were counted and recorded. Some batches of eggs were collected from repeat matings of the same pair of brood&h. The developing eggs were transferred to plastic jars for artificial incubation. After larvae had absorbed their yolk sac, the fry were transferred to a plastic container. Each container was continuously aerated. Separation of red and black colored fry can be made after the yolk sac has been fully absorbed. Fry from each spawn were therefore scored for red and black color 2 weeks after hatching. A single gene model of inheritance was postulated with a 3:l phenotypic ratio among offspring of a mating between two heterozygotes. Observed segregation ratios were tested by Chi-square for acceptance or rejection of the hypothesis of a single gene model of inheritance of body color. Additional data from the crosses between F2 progeny of various color types were also used to test the postulated mode of inheritance.
229
RESULTSANDDISCUSSION The ratio of red to black color from the crosses between Taiwanese red tilapia was consistent with an expected 3:l ratio. A total of 28 spawns was obtained in the parental generation. The total number of fry produced by each brood fish ranged from 216 to 1668. In all but one case, crosses of redx red gave a segregation ratio not significantly different from an expectation of 3 red to 1 black, indicating a single gene model of inheritance with red color dominant over black color. This is in agreement with the reports of Behrends et al. (1982) and Behrends and Smitherman (1984). For the one anomalous result, all 483 fry were red in color. A close inspection of the parents used in this mating indicated one to be pink in color. It appears that all red tilapia brood fish used for mating were heterozygous. Progeny ratios from crosses among Fl individuals with various color combinations are presented in Table 1. Pink x pink matings produced only pink F2 progeny. Pink x red matings resulted in both pink and red progeny in a 1:l ratio. When pink x black or black x pink matings were made, all progeny were red. A 3:l ratio of red to black coloration was obtained from redx red crosses when some pink appearing progeny were included in the red category. However, the pink and red colors were very difficult to distinguish at the young larval stage. Red x black and black x red matings produced a ratio of 1:l red to black progeny. Black x black mating produced only black individuals among the F2 progeny. There were no significant departures from expectations in any of the matings (P < 0.05 ) . The genotypes for each body pigment can be proposed on the basis of results obtained in this study (Table 2 ) . Pink individuals are homozygous dominant and have a genotype RR. Red individuals are heterozygotes (Rr) and black individuals are homozygous recessive (rr ) . The results indicate that red color of Taiwanese red tilapia is inherited as a single gene showing incomplete dominance. It is possible that pink and red color could be distinguished at the young larval stage, but the ratio of 1:2:1 for pink, red and black color has only been observed at the young fingerling stage. An attempt was made to classify the pink and the red color for every brood at the larval stage but it was not easy to separate the fry accurately into these two color groups. Pink and red color can be clearly distinguished when the fish are 2 months of age or older. The results of this study are in contrast to those of Behrends et al. (1982) who suggested that two to three gene pairs influence the color and pigmentation of red tilapia. However, Behrends and co-workers did not provide any specific data on segregation ratios to support their hypothesis. In another study, Behrends and Smitherman ( 1984) crossed Tilupia (Oreochronis) aureus to red tilapia and obtained 50% red and 50% black color phenotypes. This would indicate a single gene coding for red color which is in agreement with the results
230 TABLE 1 Body color segregation of F2 progeny from interbreeding of Fl individuals of various body color combinations Mating type QXd”
Brood fish number
Number of offspring
Body color Pink
Red
Black
Pink X Pink
1 2
141 94
141 94
-
-
-
Pink X Redb
1 2
67 180
30 67
28 57
-
0.06 0.80
Pink X Black
1 2 3 4 5
150 217 110 441 205
-
150 217 110 441 205
-
-
Black X Pink
1 2
476 158
-
476 158
-
-
Red X Red
1 2 3 4 5 6 7
570 626 321 181 453 358 222
-
428 469 244 135 344 267 169
142 157 77 46 109 91 53
0.00 0.00 0.17 0.01 0.21 0.03 0.15
Red X Black
1 2 3 4 5
375 721 219 283 596
-
181 384 123 131 287
194 337 96 152 309
0.46 3.06 3.33 1.56 0.82
Black x Red
1
482
248
234
0.40
Black x Black
1 2 3
340 34 318
-
340 34 318
-
-
Chisquare”
“Expected phenotypic ratio of 3:l for red to black color was tested for red X red mating and a ratio of 1:l for pink X red and redX black mating. bBody color was examined when fry were 2 months of age. Some fry died before examination.
of this study. The red color mutant in 0. niloticus reported by Mires (1987) was due to a simple recessive gene. Thus, the 0. niloticus gene must represent a different mutation for red body color in tilapia. There were some minor variations within the red color group. For example, a number of red tilapia showed some melanic spots or patches on the body and fin area. However, these fishes were considered to belong to the red color group
231
TABLE 2 Phenotype and genotype of the offspring based on matings of the various phenotypes and genotypes of the parents Offspring
Parent Phenotype
Genotype
Phenotype
Genotype
Pink x Pink Pink X Red Pink x Black Red x Red Red x Black Black x Black
RRxRR RRxRr RRXrr RrXRr Rrxrr rr x rr
All Pink Pink, Red All Red Pink, Red, Black Red, Black All Black
RR RR, Rr Rr RR, Rr, rr RR, rr rr
even though the color was not uniform among the same brood of fish. It was also observed that some of the pink color tilapia were subvital, less vigorous and showed some deformities which suggested that the R gene may have pleiotropic effect on viability, vitality and even some minor color variation. The pleiotropic effect of a dominant gene, associated with the light-yellow pattern, has been reported in Japanese carp (Katasonov, 1973). In Taiwan, tilapia farmers who culture red tilapia generally make red x red crosses which produce red and black colored fry. The black fry are removed in order to culture only red tilapia. This requires added labor costs to sort out the red tilapia fry. The results of this study show that pink and red tilapia fry can be produced by mating pink x pink, pink x red and pink x black. ACKNOWLEDGEMENT
This research was partially supported by a grant from the National Science Council, Taiwan (NSC 76-0409-B055a-01).
REFERENCES Behrends, L.L. and Smitherman, R.O., 1984. Development of a cold-tolerant population of red tilapia through introgressive hybridization. J. World Maricult. Sot., 15: 172-178. Behrends, L.L., Nelson, R.G., Smitherman, R.O. and Stone, N.M., 1982. Breeding and culture of the red-gold color phase in tilapia. J. World Maricult. Sot., 13: 210-220. Katasonov, V. Ya., 1973. A study of pigmentation in hybrids between the common and the decorative Japanese carp. I. A study of the dominant pigmentation types. Genetika, 9: 59-69. Kuo, H., 1969. Notes on the hybridization of tilapia. JCRR Fish. Ser. No. 8, pp. 116-117. Liao, I.C. and Chen, T.P., 1983. Status and prospects of tilapia culture in Taiwan. In: L. Fishelson and Z. Yaron (Compilers), Proceedings of the International Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel, pp. 588-598. Mires, D., 1987. The inheritance of black pigmentation in Oreochromis niloticus from two African
232 origins. Presented at the Second International Symposium on Tilapia in Aquaculture, Bangkok, Thailand, 16-20 March, 1987. Tave, D., 1987. Genetics and breeding of tilapia. Presented at the Second International Symposium on Tilapia in Aquaculture, Bangkok, Thailand, 16-20 March 1987.