An Account of Naturally Occurring and Artificially Produced Cyprinid Hybrids in India
| NACA/WP/86/33 | November 1986 |
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An Account of Naturally Occurring and Artificially Produced Cyprinid Hybrids in India |
Freshwater Aquaculture Research and Training Centre
P.O. Kausalyagang, Bhubaneswar 751002
(Orissa) India
NETWORK OF AQUACULTURE CENTRES IN ASIA BANGKOK, THAILAND
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H.A. Khan & G.V. Kowtal
Freshwater Aquaculture Research and
Training Centre
P.O. Kausalyagang, Bhubaneswar-751002
(Orissa) India
1 INTRODUCTION
Several interspecific and interganeric hybrids of Indian major carps : Catla catla, Labeo rohita, Cirrhinus mrigala and Labeo calbasu (Chaudhuri 1959, 1971 & 1973; Naseem Hamza 1971; Naseem Hamza & Alikunhi, 1971; Varghese & Sukumaran, 1971; Chondar 1977) and those of Indian major carps with exotic carps viz. common carp (Alikunhi & Chaudhuri 1959; Kowtal & Gupta 1984, Khan et al; 1986 and Gupta et al; 1986) and silver carp (Ibrahim et al; 1980) have been artificially produced through hypophysation.
From natural ecosystems such as reservoir and dry bundhs, several hybrids have been recorded (Desai & Rao, 1970; Tripathi et al; 1974, Tripathi and Sharaf 1974; Natarajan et al; 1976 & Prasad 1976). Many of these hybrids were found to be intermediate in characters of the parent species. Only a few hybrids, both artificially produced and naturally occurring, have been studied in detail for their cultural qualities and adaptability to various environments. In the present communication an account of economically important hybrids of Indian major carps have been given and their role in the development of reservoir fisheries as well as in increasing fish production in aquaculture has been discussed and use of hybrid index, multivariate techniques and genetic markers in identifying hybrids has been emphasised.
2 NATURAL HYBRIDS
Cyprinids are more prone to interbreeding than other groups of fishes (Slastenenko, 1954). A number of interspecific and intergeneric hybrids, which play a special role in enhancing fish production in impoundments have been reported in India. Some of these are described as follows;
2.1 Catla x rohu hybrid:
These putative hybrids have been reported from a perennial irrigation tank in Madhya Pradesh (Desai & Rao, 1970) and from Rihand Dam in Uttar Pradesh (Natarajan et al; 1976). They resemble catla in body appearance and rohy in mouth profile. The morphometric features of the hybrids are shown in Table I. The hybrid from Rihand Dam is reported to be detritophytoplanktonphagic displaying a much wider food spectrum with Ceratium forming an important food item, grows as fast as catla and matures earlier than parents (Natarajan et al; 1976).
SYMOSIUM ON CONSERVATION AND MANAGEMENT OF FISH GENETIC RESOURCES OF INDIA
2.2 Rohu x catla hybrid :
This hybrid has been reported from Achartal Lake in Madhya Pradesh. Various morphometric ratios of the putative hybrid are given in Table I, Based on its morphometric characteristics and the position of the pectoral and anal fins, this hybrid has been recognised as a cross between male rohu and female catla. The growth rate of the hybrid is an fast as that of catla (Tripathi et al; 1974).
2.3 Rohu x mrigal :
This putative hybrid has a smaller head and bigger inferior mouth than rohu, body width, prepelvic and length of caudal peduncle smaller than both parents. The above hybrid competes with rohu in its food but grows slower than the former, thus being of not much utility in aquaculture. It has been reported from Adhartal Lake (Tripathi and Sharaf. 1974).
2.4 Labeo fimbriatus x L. goniua and Labeo calbasu x Catla catla
These hybrids have been recorded from Rangwan Reservoir (Uttar Pradesh) and have been suggested to be utilised as a substitute for L. gonius and L. calbasu respectively in reservoirs (Prasad, 1976).
3 ARTIFICIAL HYBRIDS
Some of the artificially produced hybrids of Indian major carps showing the heterosis in respect of growth, viability and maturity and suitability for aquaculture are mentioned.
3.1 Catla* x rohu and rohu* x catla hybrids :
Table I summarises the morphometric measurements of both the hybrids. The hybrid index of both hybrids has been calculated by the present authors from the data given by Reddy and Varghese (1980) and incorporated in Table I. Both are intermediate in most of the taxonomic characters. They have smaller head than catla and body broader than rohu. The ratio of total length/predorsal in catla x rohu shows greater value than both the parents, whereas it is similar to catla in case of rohu x catla hybrid. Caudal peduncle broader than both parents. Gill rakers moderately long and closely set. The most distinguishing feature of both hybrids is that, in catla x rohu, pectorals almost reach ventral base, whereas in rohu x catla pectorals do not reach the ventral base, leaving a wide gap (Reddy and Varghese, 1980). Colour of scales and fins in both the hybrids is derived from that of the male parent. Based on these characteristics, the hybrid described by Desai & Rao (1970), (as seen from its photograph) can be tentatively described as rohu* x catla hybrid.
3.2 Mrigal* x catla :
Hump less than catla, eye diameter more than both parents, fin rays nearer to catla and lateral line to mrigal. The hybrid has been reported to grow slower than both of parents and the reciprocal hybrid (Ibrahim 1977) but faster than mrigal x rohu hybrid (Varghese & Shan thayam, 1979).
3.3 Catla* x mrigal :
Hump nearer to patternal parent, head towards maternal and gill rakers more than both parents. It grows faster than parent species and reciprocal hybrid (Ibrahim, 1977).
3.4 Rohu* x mrigal and mrigal* x rohu hybrids Y
Both hybrids matured in 2 years (Chaudhuri, 1971) and showed slower growth than either parents (Basvaraju and Varghese, 1980), thus serving no useful purpose in aquaculture.
3.5 Rohu* x calbasu hybrid :
It has small head and is reported to grow faster than calbasu. Attained full maturity in 2 years (Chaudhuri, 1971).
3.6 Catla* x calbasu and calbasu* x catla:
These hybrids showed more flesh yield than either parents and can be profitably used in aquaculture in place of calbasu (Chaudhuri, 1971).
4 CULTURAL TRAITS OF HYBRIDS
4.1 Growth
Catla x rohu grew faster than rohu although not as quick as catla (Chaudhuri, 1971 & Natarajan et al; 1976). Reddy and Varghese (1980) observed that catla x rohu hybrid when reared along with parent species - catla and rohu in prepared cement cisterns showed faster growth (average weight 63.3 g) than rohu (average weight 58.5 g), but poorer than catla (average weight 129.5 g) per 126 days. This was because of the competition for food by the rohu with the hybrid showing similar feeding habits. Further experiments revealed that in polyculture catla x rohu hybrid grew faster than rohu x catla, but, in monoculture, both hybrids showed faster growth rate than rohu bu less than catla (Reddy & Varghese 1980 a, and Keshavanath et al, 1980). Alikunhi et al (1971), however, reported that male rohu x female catla grew better than catla in monoculture and combined culture systems. In monoculture catla and rohu x catla when each stocked @ 2,500/ha, having an initial weight of 31 g, attained 130 g and 159 g respectively in 6 months. In combined culture at the same stocking density and in equal proportion and having an initial weight of 64 g each, they recorded 228 g in catla and 285 g in rohu x catla hybrid in 6 months.
4.2 Food :
Catla x rohu is basically detritophagic in pond environment, subsisting on detritus, decaying vegetation, mud and sand (Chaudhuri, 1973) but showed much wider food spectrum including Ceratium in its diet in the reservoir (Natarajan et al, 1976). These authors suggested the use of catla x rohu hybrid for stocking in higher altitude reservoirs like Bhakra Dam which contains Ceratium in abundance. Bhowmick et al (1981) xhowed that the hybrid, in addition to the above natural food, also subsisted on supplementary feed in the pond environment.
4.3 Yield :
In separate experiments two hybrids viz calbasu x catla and catla rohu were stocked with catla, rohu, mrigal, silver carp and grass carp at a total stocking density of 5175 – 5334 and 5175 – 7840 respectively. The ratio of calbasu x catla was 0.97 – 1.33% in 1971-72 experiments and of catla x rohu 0.36 – 1.33% in 1973–74 experiments. It was observed that calbasu x catla attained 430–620 g/year and contributed to 0.43 – 0.49% of the total fish production in 1971–72 and catla x rohu, 718 – 925 g per year sharing about 0.21 – 0.77% of the total production in 1973–74 experiments (Chaudhuri et al., 1975)
4.4 Reproduction and viability :
Of specially great significance is the unimpaired fertility of Indian major carp hybrids. Catla x rohu attained maturity in 3 years and one four year old female F1 hybrid weighing 4.1 kg released 0.5 million eggs and yielded 0.135 million F2 spawn (Chaudhuri, 1973). Bhowmick et al, (1981) obtained 0.325 million fertilised eggs and 0.075 million F2 hatchlings from one F1 hybrid female weighing 1.35 kg.
Rohu x calbasu matured in 2 years, though a few males attained sexual maturity in one year. From one female F1 hybrid of 1.2 kg, 0.12 million fertilised eggs with 65% fertilization, yielding 4,500 F2 spawn were obtained (Chaudhuri, 1973).
4.5 Flesh quantity :
Catla x rohu, when compared to equal-sized parents, contains more quantity of flesh (54%) than catla (44%) and rohu (48%) (Chaudhuri, 1973 and Bhowmick et al., 1981). Catla x calbasu and calbasu x catla also showed more flesh yield than both the parents (Chaudhuri et al., 1975).
4.6 Hybrid F2 :
The F2 generation of catla x rohu and rohu x calbasu hybrid were obtained showing very high rate of fertilisation. Both hybrids in F2 generation were observed to be intermediate in morphomeristic character with parent species. In rohu x calbasu F2, variation in the colouration of the body fins, barbels and in caudal spot were observed. It attained a growth of 133 mm in 3.5 months (Chaudhuri, 1973).
F2 spawn of catla x rohu when stocked @ 50,000 spawn in one 0.04 ha and @ 80,000 in another 0.06 ha pond showed a survival of 31.1% and 16.5% respectively after 3 weeks of rearing, and attained a size of 90–185 mm (average length 126.5 mm) in 100 days. Catla x rohu fry grew faster (av. wt. 311 g) than rohu (av. wt. 169 g) but slower than catla (av. weight 365 gm) in 6 months, when reared together in 0.1 ha pond. The diet of F2 juveniles of catla x rohu (65–142 mm in length and weight 2–30 gm) consisted of mud, sand particles, detritus and decaying vegetation, forming about 90% of the diet and the rest 10% consisted of Oscillatoria.naviculids, Comphonema, Scenedesmus and a few green algae thus resembling rohu in feeding habit (Chaudhuri, 1973).
5 DISCUSSION AND CONCLUSION
In natural spawning habitats as in reservoirs and dry bundhs the interspecific and the intergeneric hybridization of Indian major caprs is facilitated when there is dominance of one species and the scarcity of the other and both spawning in close proximity. The morphology of natural hybrids of Indian major carps will probably be more variable because of increased environmental and genetical variations. The identification of these hybrids and their parent species as well as the artificially produced ones is based on morphological analysis, assuming that hybrids are morphologically intermediate between the parent species and the additive inheritance is greatly responsible for phenotypic expression in hybrids. In case of the above natural hybrids of Indian major carps, their identification has been based on the analysis of a few selected morphological traits in small number of specimens, which are not enough to exhibit variation in characters. Even in case of artificial hybrids such as catla x rohu and rohu x catla, which have been studied slightly in more detail (Reddy & Varghese, 1980), all morphological characters have not been taken into consideration. The character expression may vary among individuals of the same cross (Hubbs, 1955) and within and between sexes. Artificial counts (left and right) of each bilateral character have not been used in meristic counts. However, by comparing the identified morphological characters of artificially produced hybrids catla x rohu and rohu x catla of known parentage with those reported from natural ecosystems, it has been possible to pinpoint the hybrid reported by Tripathi et al (1974) as a cross between male rohu and female catla.
No uniform system of the analysis of the morphological characters of various hybrids reported above has been followed. In some cases the least square method has been applied to find the significant differences. The generally followed method is the hybrid index of Hubbs and Kuronuma (1942) to measure the degree of the hybrid intermediacy, and is reasonably an effective method for evaluation of hybrids (Goodman, 1967). As this index is based on the assumption that hybrids are morphologically intermediate between the parent species it influences the index value of those characters that are not intermediate and also this method does not indicate any measure of correlation of characters, because it is assumed that uncorrelated characters are used (Neff & Smith, 1979). These defects, however, can be removed by using selected characters, based upon marked phenotypic differences of parents. The other more recently developed hybrid indic (Misra, 1971, Keenlyside et al., 1973) and multivariate techniques (Rohwer, 1972 and Smith 1973) have been used to measure the intermediate status of hybrids between two putative parents. However, it is generally assumed that the phenotypic expression of fish hybrids may be controlled by the additive inheritance, their genotypes can be identified by knowing the gene frequencies of various groups as most of them will be polymorphic to several electrophoretic loci. Besides morphometrics, studies on important aspects of biology and biochemical genetics of hybrids and parent species are of utmost importance in evaluating the cultural qualities of the hybrid.
In aquaculture, many carp hybrids have been produced, but only a few e.g. catla x rohu have been studied in terms of growth, food and feeding habits, flesh contents and fertility. But even these studies are incomplete. The greatest obstacle in testing many hybrids of economic importance is the non-availability of large number of ponds to conduct genetic experiments, lack of knowledge of the parental (Lineage) identify illdegal migrants, though apparently looking alike but having recessive genes, In the larval and early juvenile/fingerling stages, individuals cannot be marked and identified, hence the need for genetic marking, which provides basic tool for implementing advanced breeding programmes of Indian major carps.
With the aid of genetic markers, it is possible to identify breeds, to draw effective experimental designs on the basis of known genetic markers for drastically reducing the number of experimental ponds required for genetical research; to construct the design of full-sib within half-sib families for genetic analysis of cultural characteristics and to conduct family selection (Moav et al., 1976). While planning a genetic marking programme, two considerations should be borne in mind, (i) such a genetic marker should be selected that is not obviously associated with any negative characteristic (Allendrof and Utter, 1979). Controlled tests should be carried out on selected and parent stocks to be sure that both stocks are comparable for measurable variables other than the selected marker, (ii) the other consideration is the inbreeding encountered in finite fish population. The inbreeding depression reflects factors including the expression of harmful genes and the reduction of beneficial interaction both within and between loci. This problem can be overcome if a large number of brood stock is randomly mated. Thus it is suggested that a combination of morphometric, biological and biochemical characterisation of the hybrid and parent species are to be studied simultaneously in future to identify hybrids and their parents, to know their cultural qualities, dominance of both maternal and patternal characters, and to measure the heterosis and genetic variability of both hybrids and brood stock for drawing effective breeding programmes.
ACKNOWLEDGEMENTS
The authors express their gratitude to Dr. A.V. Natarajan, Director, Central Inland Fisheries Research Institute, Barrackpore for encouragement ana to Dr. V.R.P. Sinha, National Project Director and Head, Freshwater Aquaculture Research and Training Centre for critically going through the manuscript. Thanks are also due to Sri S.D. Tripathi Senior Scientist for offering helpful suggestions.
6 REFERENCES
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