Establishment of the gene bank of common carp
Facilities and maintenance of gene bank
The live gene bank of common carp as a basic element of a national carp breeding programme
Morphological characterisation of common carp strains
Comparing performances of populations, progeny testing
Comparison of quantitative characteristics of strains
Common carp (Cyprinus carpio L) is one of the oldest cultured and most domesticated fish in the world. References can be found to its appearance in Europe in the late glacial epoch and during the Hellenic and Roman Empires mention is made to the keeping and storing of common carp as a particularly favourite dish (Balon, 1974). Culturing and breeding common carp has a long history dating back about 4000 years in China and several hundred years in Europe. During that time special breeding centres have developed in several regions of Europe, like the Czech Republic, Germany and Hungary, as well as Russia and Ukraine. China and Japan are the ancient culturing centres in Asia, but during the last decades India, Indonesia and Vietnam have started to culture common carp as a result of conscious fish importation and acclimatisation activities. During the sixteenth century common carp was introduced to England and after the discovery of the New World it reached North America and Canada as well (Sarig, 1966).
When culturing began, wild forms from ancient populations dominated. Some of them exist up to the present day as elongated scaly forms of wild carps enriching the local fish fauna, but most cultured carp now look different to their ancestors. The major limiting factor to expansion of the species is temperature: in the southern hemisphere it is found in all continents except the icy Antarctic, but in northern latitudes the range is only up to 60°N.
Common carp is a very adaptable species in both the wild and in culture conditions. As a consequence, variability of qualitative and quantitative characteristics are enriched and its genetic diversity increased.
Local populations of cultivated common carp were developed within the species as a result of various environmental conditions, particular breeding efforts of fish farmers and eventually the relatively small population size of broodstock as a result of strictly closed breeding systems. Different genotypes were specifically developed after the middle of the last century and are called "landraces" (Bakos, 1979).
Historical survey
The genetic improvement of common carp in Hungary started in 1962 at the Fish Culture Research Institute, (FCRI) Szarvas, (Bakos, 1964). Common carp strains from the most significant Hungarian fish farms were collected as ready-to-spawn broodfish. Several marking methods were used to facilitate breeding, such as branded signs and figures and fin clipping. Since 1993 the PIT-TAG system, which uses a magnetic microcapsulated digital signalling unit injected to the body cavity of fish, has been in operation (Gorda, 1994).
Significant differences were established in the strains in both qualitative and quantitative characters. Using traditional methods of selection intraspecific crossing experiments were initiated in 1964. As a result of hybridisation, heterosis was detected in some quantitative traits of the first hybrid generation (Bakos, 1979).
The projected long-term breeding program necessitated maintaining, completing and preserving the strains of common carp collected at Szarvas as a live form of gene bank. Production of foreign strains was accomplished by an international gene exchange agreement established in 1981 among the countries of the former Soviet Union.
The maintenance and conservation of common carp strains as a live gene bank were motivated by several factors:
- The mixing of genetically differentiated races, as a result of the development of intensive forms of fish farming; spreading of artificial propagation methods; specialisation of fish production; and uncontrolled fish transportation, put the original races at risk.- The desire to conserve existing strains of common carp, many of which had already disappeared from their native habitat, for the future scientists and aquaculturist.
- Traditional strains would be totally eliminated as a result of intensive genetic improvement activity giving preferences to the highly productive hybrids.
- As an insurance against possible incidents of catastrophe, water pollution, radiant contamination, drought or flood dangers, etc..
- Finally the collection of common carp strains can serve as an example of live gene banks for some other endangered species of fishes.
The young and adult individuals of selected strains are kept in earthen fishponds. Eight ponds are available for maintaining broodstock, each with an area of one hectare and a depth of 1.2m. A further 25 ha are used in performance tests and grow-out trials. Continuous water exchange ensures optimal environmental conditions throughout the year. The stocking density of 1000 to 1500 kg fish/ha, depending on the size of fish, proved to be the optimal biomass in the pond. This translates to around 200 spawners, each having a body weight of 5 to 8 kg.
During the growing season the breeders are fed ad libitum using wheat and special broodstock feed containing appropriate levels of animal protein and other necessary ingredients suitable for common carp in the two months before reproduction commences.
The minimum population size of broodstock within the strains was determined to be 50 individuals, inbreeding coefficient is quite low (F=0.01), thus the negative effects of inbreeding can be eliminated (Pirchner, 1964, and FAO, 1981).
The broodstock in the gene bank is renewed every 8-10 years. During the artificial propagation a mixture of eggs and sperm from a minimum of ten females and ten males is used from each strain, simulating panmictic population conditions.
The Fish Culture Research Institute in Hungary has a permanent research topic on the genetic improvement of cultivated fish species. The main species at the centre of this subject is common carp and researchers focus on a comprehensive breeding programme for the Hungarian fish culture department. The staff dealing with fish genetics includes three scientists, two laboratory assistants, one technician (fish culturist) and six fishermen maintaining 33 hectares of research ponds (including the 8 hectares of gene bank ponds).
The research work on carp genetics and the live gene bank of common carp work well together and constitute the basis of a production orientated scientific activity.
During the last three decades several research methods into genetic improvement have been adopted and adapted. Different types of selection, such as inbreeding (including gynogenesis and hormonal sex-reversion) and several forms of intraspecific hybridisation, have resulted in production and testing of more than 150 crossing combinations from the maintained common carp strains of the live gene bank. As a result of these research efforts three outstanding hybrids of common carp were developed. Called the Sz215 mirror, the SzP31 and SzP34 scaly hybrids, these represented 80 percent of the total carp production in Hungary.
In the final phase of the national breeding programme in Hungary the FCRI provides the fish farms and fish seed production units with parental lines of hybrid common carp.
Morphological description of strains includes the qualitative characters determining the external features and also taxonomic classification.
The scaliness of common carp as a determining factor consist of four different basic forms: scaly, mirror (scattered), linear and leather (naked) varieties. These types of scaliness are determined genetically by four alleles at two loci, designated Ss and Nn, that display Mendelian inheritance.
The scaly carp results from the SS,nn and Ss,nn combinations. The ancient, primitive populations and the oldest cultured forms are covered with a regular pattern of scales.
The mirror carp results from the homozygote recessive ss,nn genotype exclusively. The typical mirror pattern is a single unbroken row of scales on the top of the back, some scales near the tail and at the base of fins. Preferably there are no scales along the lateral line or scattered across the surface of the body in the mirror carp.
The linear carp is basically similar to the mirror, but the lateral line is completely covered by a wide line of scales. This is determined by the SS,Nn and Ss,Nn genotypes.
The leather carps result from the ss,Nn genotype and are absolutely scaleless. Irregularly, a few scales can be found at the base of fins.
Transitional forms of scaliness similar to linear or leather varieties can sometimes be observed in mirror carp (ss,nn genotype), but these are called strongly- or slightly-scaled irregular mirror or scattered carps.
Kirpichnikov (1981) described genetic experiments that revealed the homozygote NN as a lethal genotype in the progeny.
In Europe, along with the wild scaly carps, the cultivated scaly and mirror forms spread and became popular because of their good survival and growth rate. Linear carp can be found on fish farms in Poland.
The colour of common carp is genetically determined, but some environmental effects, such as colloid content of water and the age of fish influence the shading of inherited colouring. To determine and compare the colour of common carp strains, fish of the same age under the same environmental conditions must be used. In our description of colouring, two or three year old market size fish populations were characterised and compared.
The lateral line is an important connection for transmission between the sensory nerve system and environmental conditions. The lateral line of scaly carps, under the shelter of scales, has a regular continuous appearance, but in the case of mirror carps, divergent and discontinuous forms of lateral line can be observed.
The regularity of fins includes the number of hard and soft rays and the stage of development. Incorrect and degenerated fin structure hinders the fish during development.
The constitutional structure, including external body formation and internal physiological characters of common carp, can be valued as a basic element of a sustainable, genetically determined capacity of production. The most frequent abnormalities detected are the shortening or curvature of the spine, several deformations of the head, mouth and operculum and the extraordinary growth of fins. Some abnormalities might be the result of illness of stress during the juvenile stage, but they may also be inherited defects harmful for the next generations. The abnormalities are appraised at the fingerling stage and reported in the results as a percentage of the population.
The body shape of common carp has a particular significance in the cultured strains. The deep-bodied, round-shaped form, the relatively small head and short tail give the impression of better slaughter value, a higher level of breeding activity and is aesthetically favoured.
Body shape is primarily determined by the massive structure of the skeleton, but in the final appearance, the abundance of food and the intensity of growing conditions play a significant role as well.
For characterisation and identification of strains by body-formation, stereometric indexes were introduced as relative dimensions of several parts of the body: - profile index, the quotient of standard body length and body height; head index, the quotient of standard length and length of the head; body width index, the quotient of the highest and widest distance of the fish; and the corpulence index, calculated from body length and body weight. The above dimensions were measured on two to three year old market-size fish, because later on during the adult phase the body shape of common carp becomes longer and does not represent the typical form of populations.
The transferrin genotype, as a genetic marker, is a readily detected qualitative trait offering acceptable possibilities for distinguishing several strains of common carps. However, during the large-scale analysis of blood samples fairly large variability of transferrin genotypes was observed. The same transferrin genotypes were observed in samples collected from farm-cultured strains, leading to the conclusion that the gene-bank maintained populations, selected for similar production purposes (such as good viability and fast growth rate) had the same genetic response. In other words, a strong joint inheritance can be observed between transferrins and the most important quantitative characters. The transferrins were examined and presented using the formulae of Valenta (Valenta, 1978).
Pharyngeal teeth are a distinguishing characteristic in the Cyprinid family, both by structure and number, but within the strains of common carp there are no remarkable differences.
The common carp strains maintained in this collection were developed under production conditions. Considering the breeding background those characters of selection were determined that would result in reliable survival, faster growth rate, economic food conversion, advantageous slaughter value, stronger resistance against diseases and better adaptability to culture conditions.
As the strains are different in their qualitative and quantitative characteristics, a progeny performance test was designed for the evaluation of some major characteristics to enable comparison of strains.
The progeny groups in the performance tests were kept in identical environmental conditions from spawning until the end of the investigation. The conditions were similar to those of large scale fish farming in Hungary (Bakos, 1979). The progeny groups were always produced by artificial propagation during the natural spawning season. The fish hatchery of FCRI has the capacity to produce 200 million larvae/year. It is possible to maintain and handle spawners inside the hatchery during the time of hormone treatment, stripping, fertilisation and incubation of the eggs. The different progeny groups were produced at the same time. After hatching, the larvae were kept in larval rearing tanks for 2-3 days until exogenous feeding began. In the first stage the larvae were reared in 1 ha size ponds with a low stocking density, until they reached 100-150 g body weight. Because of marking difficulties with the large number of larvae (400-500 thousand individuals), only one group of mirror carp and one group of scaly carp were kept in each pond. At the end of the first growing season, the individuals of the experimental groups were marked, as described in the next section, one by one, and each group had their own sign. After marking, the groups were stocked into the same pond and the weight loss and mortality that occurred during the winter were evaluated. The following spring, at the start of the growing season, the same groups of fish were stocked into the growout ponds for market fish production.
Evaluation of experimental groups was carried out not only in the experimental ponds of the Fish Culture Research Institute, but also in three commercial production farms, located in different parts of Hungary. The associated fish farms, generally State farms, were selected and financed by the National Institute for Agricultural Quality Control, responsible for the official performance testing of cultivated animals, including common carp. Both small ponds (0.4 ha) and large ponds (2 ha) were used for the experiments and the farms themselves were also different from the point of view of productivity. In the Institute, one pond of 1 ha size was stocked with a sample of 200-300 fish from each group and several 1 ha ponds were stocked with large size samples of one particular group. The test pond stocked with samples taken from each group was called the "mixed" structure pond, whilst the ponds stocked with samples from one particular group were called the "pure" structure ponds (Hulata et al, 1982).
During the performance tests, five main features were evaluated that determined the economical value of populations. The parameters used were the survival, weight gain, feed conversion ratio, slaughter value and fat content of the meat.
Survival rate indicates the viability. Number of harvested individuals was counted at the end of the market fish production season.
Weight gain of individuals during the market fish production season was calculated by discounting the initial weight from the final weight of the average fish at the time of harvesting. By considering this over a year, average annual growth rate could be estimated.
Weight gain (g)= final weight (g) - initial weight (g) = g/year
Feed conversion ratio is an estimate of the amount of food required to produce one kg of fish under fishpond conditions.
Common carp, besides foddering, also collect and consume natural food in the pond. This practically unmeasurable source of food, mainly zooplankton and zoobenthos, with its high animal protein content, plays a very significant role in economical fish production and needs to be allowed for in the food conversion ratio. Wire net cages, with an area of 240m2 were built in the testing pond for every experimental group of fish. Fifty individuals of common carp were tested from each strain. They were provided with the same amount of food every day. Presumably, the quality of natural food available for all the tested populations was similar and therefore disregarded during the evaluation of food conversion at the end of the growing season.
The feed used in the test was grain, especially wheat, which is widely used in Hungarian commercial fish farming.
Slaughter value is measured as the cleaned portion of the fish, without the head and viscera, which represents the percentage of bony meat compared to the total live weight of the carp.
The fat content of the meat was determined by acidobutirometric analysis of the edible fillet of common carp and expressed as a percentage.
For determination of slaughter value and fat content, 20 individuals of each group were removed from experimental ponds and analysed in laboratory conditions.
To evaluate accurately the quantitative traits of strains, it is necessary to know about the level and intensity of production. The important data concerning production are the pond area, stocking density, amount of feed, the methods of fertilisation, the net yield and finally the duration of the growing season in terms of days.
Below is a demonstrative example for intensive common carp monoculture in Hungary.
|
- Stocking number of one year old fish |
2300 fish/ha |
|
- Initial weight of each fish |
140 g |
|
- Total weight of stocking |
322 kg |
|
- Number of harvested fish |
2014 fish/ha |
|
- Survival |
87.6 % |
|
- Final weight of each fish |
1160 g |
|
- Total weight of production |
2336 kg |
|
- Net yield |
2014 kg |
|
- Total amount of food (grain wheat) |
7290 kg |
|
- Food conversion |
3.62 kg/kg |
|
- Organic fertiliser (cow manure) |
1000 kg/ha |
|
- Growing season |
178 days |
|
(from 15th of April to 20th of October) |
|
The growing season is 180 - 200 days per year, because of the cold winter season in central Europe. To produce market size fish of one to two kilograms, a three-year growth period is generally needed. During genetic research a two-year growth period was preferred, using an intensive production system for accelerating the progress of the selection programme. The differences between the commercially more common three-year cycle and the experimental two-year cycle were assessed and deemed insignificant. To examine possible genotype × environmental interactions (Wohlfarth et al, 1983) several fish farms were appointed to receive the test populations. The production characteristics of the strains or hybrids were tabulated. Deviations from the controls and from the average values of all populations tested with the experimental group were assessed.
Standard control populations for comparison of performances year to year were:
- The strain of Szeged fish farm (index number 7), with outstanding productivity compared to the other strains. (See: Szeged mirror carp, page 71).The Hungarian strains of common carp maintained in the live gene bank of the Fish Culture Research Institute, Szarvas, have been introduced to several countries throughout the world as part of an international gene exchange agreement. Outstanding results, both of the pure lines and of crosses with the local strains, have been achieved in the Czech Republic, Poland, Romania and in Vietnam.- The hybrid of Szarvas 215 mirror carp (index number Sz215) outperformed the Szeged strain in 1974, 1977, 1978 and 1988. After 1979 this hybrid was used as a standard control for the evaluation of mirror strains and hybrids.
- The hybrid of Szarvas P31 (index number SzP31), a heterozygote scaly carp, has been used as a standard control since 1980, replacing the earlier P2 strain from Tata fish farm and the selected P3 scaly control strain.
Strains of common carp maintained in the Fish Culture Research Institute, Szarvas are as follows:
|
Strain |
Index number |
|
Bikal mirror carp |
6 and "B" |
|
Dinnyés mirror carp |
01 |
|
Felsõsomogy mirror carp |
9 |
|
Göd mirror carp |
"G" |
|
Hortobágy mirror carp |
1 and "H" |
|
Nagyatád mirror carp |
4 |
|
Palkonya mirror carp |
02 |
|
Sumony mirror carp |
8 |
|
Szarvas mirror carp |
5 |
|
Szarvas 22 mirror carp |
2 and 22 (inbred) and Sz22 |
|
Szarvas P33 scaly carp |
P3 and P33 (inbred) |
|
Szarvas P31 scaly carp |
P31 and SzP31 |
|
Szarvas P34 scaly carp |
P34 and SzP34 |
|
Szarvas 215 mirror carp |
215 and Sz215 |
|
Szarvas red mirror carp |
SzRM |
|
Szeged mirror carp |
7 |
|
Tata scaly carp |
P2 |
|
Tisza wild |
Tisza |
|
Amur wild carp |
Am |
|
Czech scaly carp |
CsP |
|
Czech mirror carp |
CsM |
|
Fresinet scaly carp |
Fres |
|
German mirror carp |
"N" |
|
Nasic mirror carp |
"N3" |
|
Polish linear carp |
"Lo" |
|
Polish mirror carp |
"Lt" |
|
Poljana scaly carp |
"Pp" |
|
Poljana mirror carp |
"Pt" |
|
Ropsha scaly carp |
Rops |
|
Ukrainian scaly carp |
Ukr |
|
Vietnam scaly carp |
Viet |
- 5×1 = Szarvas (female) × Hortobágy (male)- N3G1×01G2 = Nasic first gynogenetic generation (female) crossed with the Dinnyés second gynogenetic generation (this male is sex reversed with methyl testosterone hormone)
- 22 double index number means inbred line of strain no. 2
- Semi-gynogenetic population = gynogenetic female crossed with a normal male (2G1×15)
- Inbreeding = pairing relatives such as sib mating, e.g. 01 (female) ×01 (male)
- Two-line hybrid = crossing two different strains, e.g. 5 (female) ×1 (male)
- Three-line hybrid = crossing three different strains in two steps, e.g. (1 (female) ×5 (male)) ×01 (male) = ((Hortobágy female × Szarvas male) × Dinnyés male)
