GENETIC IMPROVEMENT OF CULTIVATED FRESH-WATER FISH SPECIES

Janos BAKOS

An economical aquaculture production either extensive or intensive requires an early and efficient return on investments.
Fish producers and scientists have focused primarily on short-term programs in nutrition, water quality management, stocking density and disease control to provide immediate increase in production.
As the industrialised fish production achieved a presumed top level and profit possibilities have decreased, the necessity and benefits of genetic improvement have become more obvious.
In the last few decades, genetic improvement has been achieved in common carp Chinese carps, Indian carp, tilapias, American catfish, European catfish, trouts and salmonides.
There are large differences in genetic features of cultured species. These differences can be broadened bt manipulation to about further increase in productivity of a particular species.
The general question should be draw up once more, how can we develop the most ideal fish, which would be satisfactory for the consumers, commerce, fish producers and finally for the geneticists? The answer seems to be very simple, to know everything about the fish, and utilise the most appropriate methods of selection combining the basic research with the practical breeding work.

CHARACTERISATION OF CULTIVATE SPECIES FROM THE VIEW-PRINT OF HIS GENETIC IMPROVEMENT

Common carp is on of the oldest cultured and most domesticated fish in the world. His farming and breeding has a long history which can be estimated for about 4000 years in China and for several hundred years in Europe. During that time it was developed special breeding centres in some several regions of Europe like Germany, Check republic, Poland and Hungary. The Eastern-European culturing activities were located to Russia and Ukraine. China and Japan are the ancient culturing centres in Asia, but during the last decades India and many of Mediterranean countries started to culture common carp as a result of the conscious fish imports. Local population or land-races of common carp were developed within the cultivated species as a result of various environmental conditions within the cultivated species as a result of various environmental conditions and particular breeding efforts of fish farmers.

These land-races are different in his genotypes and comparing his qualitative and quantitative characteristics each other significant differences had been detected which was inherited is his progenies.

The common carp as a result of his special biological characters has numerous advantages for several genetic manipulations, like

-  The high fecundity which results more hundreds of thousands eggs and larvae per season

-  an external fertilisation and

-  a well developed, practical method of artificial reproduction.

-  good possibilities for hybridisation

-  high variability of quantitative traits.

Beside these advantages some undesirable facts makes more difficult the breeding work, like

-  the long generation interval, which is 3–5 years in Europe

-  the low degree of heritability mainly by the quantitative traits.

The characteristics of common carp determining directly or indirectly the productivity can be divided to two main groups.

The qualitative characters are external or morphological peculiarities which are not influenced by the environmental conditions, inherited generally by the Mendelian laws and they are easy to modified appropriate methods of selection. Coloration, scales, the structure of fins, lateral line, pharyngeal teeth, number of gillrackers, number of vertebrae, number of inter muscular bones and transferring genotypes are well measurable.

The quantitative traits which are closely connected with the productivity are polygenic, some of them are determined by many thousands of genes. They are sometimes strongly influenced by the environmental effects. In consequence of this, both of inherited genetic variance and environmental variance are playing significant role in his appearance in the next generation.

The growth rate, survival, feed conversion, slaughter value, quality of meet and resistance against diseases are the main quantitative traits. The genetic improvement of these characters using the traditional methods of selection resulted slow progress by the common carp. Intra-specific hybridisation of different land-races have been more effective. Measurable positive heterosis effects had been obtained in some important characteristics, and as a result of this crossing numerous F1 hybrid populations are used economically in the commercial fish farming in several countries.

Producing inbreed lines for hybridisation artificial gynogenesis and hormonal sex reversal are easily and widely used methods.

CATFISHES

Three main groups of catfish-type species are distinguished from the viewpoint of fish culture.

AMERICAN CATFISH

The North American catfish species like Channel-Blue, White-, Bullhead-and Flathead catfish are the main representatives of this group. As a subject of commercial fish production the channel and blue catfish are the most important species.

The American catfish species has many of advantageous traits to be a useful fish for an industrialised production. Catfish does not reproduce in culture ponds, so the farmers has control over the stocking density. There is an easy and practical semi-artificial or controlled reproduction system, and a large number of fingerlings are easily obtained. The fish accepts prepared artificial feeds, it has a relatively wide tolerance to temperature and oxygen level because of its good adaptability.

Improving productivity with traditional genetic methods mass selection and family selection are effective, but hybridisation both inter-specific and inter-specific programmes are used successfully.

EUROPEAN CATFISH

The European catfish (Silurus glanis) are endemic fish of natural waters in Europe and some Mediterranean countries but during the last decades it became the useful predator of pond fish culture and a promising broiler fish of industrialised production. His favourable characters are the fast growing ability, good acclimatisation to the super-intensive rearing condition and en excellent quality of meal. Completely developed artificial reproduction method and his high fecundity guarantees to produce many ten thousands of fingerlings as a progeny of a single pair of broodfish.

In Hungary four several land-races, were detected and his different genotypes offers good possibilities to plan special crossbreeding programmes.

CLARIAS

Clarias (Clarias gariepinus) is a favourable species of the African and Asian countries which is some new in Europe on the market and in aquaculture as well. Significant research was carried out in Holland and developed a practical artificial reproduction system.

This species has numerous production and breeding advantageous namely the good adaptability to the industrialised rearing conditions, has a tasty and boneless meet, tolerate were the oxygen deficiency easy to transport, growing fast 500–600 g/6 months and convert the feed with ration 1,2–1,4 to one kg meet production.

Two directions are recommended by the scientists to improve the economic characters of production

-  a rational feeding system

-  the genetic improvement with selection and producing monosex male populations.

The advantageous of males in his growing is 32% and his feed conversion can be estimate 28% better than that of female populations.

The fish are able to reproduce during all the year. The chromosome number was detected 2N = 56 and the sex chromosomes of males shows (♂ZZ and the females (♀ WZ, heterogametic formations.

Succesful triploidizaion experiments was carried out using cold shock 2–4 minutes after fertilization.

TILAPIA

Tilapia species has a great importance in aquaculture, mainly in the tropics and subtropics. About 100 species are known. Tilapia species are indigenous in Africa and eastern Mediterranean areas. They have introduced in Latin America and South East Asia (Wohlfarth at al). Tilapias are under domestication generaly but they are domesticated in his ancient living places where they are reproduced and cultured.

The name group of fish is devided to two different genus depending on his breeding behavior. The Tilapias as the substrate breeders are saratherodons and as the mouth breeder species. In this lecture let me term all the genera “tilapia”.

The yeald improvement of Tilapia culture has different ways

-  increase the total area of culture

-  improvement of management systems

-  genetic improvement of broodstocks.

The main characteristics for evaluation the suitability of species are

-  growth capacity

-  feeding habits

-  temperature and salinity tolerance.

Growth: only a few performance tests have been carried out for growth rate of Tilapia species. Mostly the hybrids and monosex male populations revealed some differences in his growth capacity during the comparative examinations. Niloticus x Aureus and niloticus x hornorum were similar but both of them had faster growth than that of mossambicus x hornorum (Wohlforth and Hulata 1983).

FEEDING HABITS

The Tilapia species are very heterogeneous in his feeding habits.

Under culturing condition most of them are consuming artificial pellet food. It is an important task for geneticists to improve the feed conversion ratio under the industrialised production conditions. The polycultural stocking system of different Tilapia species is economical, to utilise wide range of natural food. Niloticus + Zillii.

TEMPERATURE TOLERANCE

The normal water temperature range for tilapias is 20°–30°C but some species are able to survive lower temperature like 10–13°C (Wohlfarth 1983). Feeding and food conversion are depending on the water temperature so we can say about and optimum water temperature for maximum growth between 19–28°. The optimal temperature range for spawning is 26 to 29°C. the upper temperature limit is 37–41°c.

SALINITY TOLERANCE

Tilapia species are freshwater fish but many of the tilapias are survive, growth and reproduced in salt water as well, when the salinity range is changing between 5 to 45% thousands depending on the species.

To utilise brachish waters with tilapias it is important to develop hybrids with better tolerance for water salinity.

QUALITATIVE TRAITS AS COLORATION

-  Dark coloured skin (S. hornorum and vulcani) and the hybrid S. niloticus and S. hornorum all male population in some places has reduced market values, but the same coloured fish are very popular in the Latin American countries.

-  Red tilapia with a white flesh and colourless skin are cultured in Philippines, Florida and Taiwan and have a great market potential in Japan and USA as a cultured substitute for red sea bream (Wohlfarth, 1983).

FECUNDITY

The fecundity of substrate breeders is generally higher than that of mouth breeding species (Wohlfarth, 1983). The early maturity, the short generation interval and the uncontrolled spawning causes serious problems for large scale fish production. The only economic way to reduce non desirable overpopulation of market fish production ponds are to develop monosex populations.

Geneticists should draw more attention to this problem, namely avoid reducing the basic fecundity of cultured species and by the other hand to develop practical breeding systems for producing monosex populations.

CHINESE CARPS

The group of Chinese carps includes silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella) as herbivorous species, bighead (Aristichthys nobilis) as a zooplankton feeder, the black carp (Mylopharyngodon piceus) as snail eating and the mud carp (Cirrhina molitorella) as a detritus consuming fish. This species are the main representants of traditional polycultural Chinese aquaculture. Widely used artificial and semi-artificial reproduction system, high fecundity, particularly feeding habits and many other useful characters are increasing his culturing value. Some of the Chinese carps, particularly silver carp and grass carp have been introduced to other countries and were used in several kinds of polyculture in the USA, Eastern Europe, Indian Sub continent, South-East-Asia and even in the Mediterranean countries.

These species on the beginning of his domestication should be effectively reacted to different types of selections improving some quantitative characters, but intraspecific and interspecific hybridisation offer more effective results in the existing and future breeding programs.

INDIAN MAJOR CARPS

Indian major like Rohu (Lebeo rohita), Catla (Catla catla) and Mrigal (Cirrhinus mrigala) are the most important species of Indian Subcontinent but during the last few decades, in consequence of a worldwide acclimatisation activity have been introduced to numerous Asian and Mediterranean countries. The fast growing catla and the Rohu with his excellent quality of meat are the most important members of polycultural fish production.

As relatively wild species short-term selection programs are characterised of this genetic improvement, and inter-specific hybridisation efforts are described with moderate effect directly to the production.

PRACTICAL METHODS OF GENETIC IMPROVEMENT OF FISH

Choosen the most appropriate method for genetic improvement it is necessary to be acquainted with

-  the biological potential of cultivated fish

-  the main characters, has to be improved and

-  the given genetic and breeding methods

SELECTION

Selection is one of the oldest and simple method of genetic improvement in which fish families or individuals are selected as broodstock to change the performance of the next generation by his heritable genetic potentials.

Selection is effective when

-  there is a wide variability of preferred characters

-  heritability of characters is high, and

-  the interval between generations is short.

The main aim of mass selection to chose individuals having better characters like the average population. If the higher performance of plus variant individuals is resulted by an additive genetic variance, higher productivity can be wait, but the environmental variance caused positive differences no genetic response in the next generation.

Successful research work was carried out by Israel scientists with so called bidirectional selection. Plus variant, minus variant and average size of a given carp population were selected as a brood stock and reproduced during four generations. Performance tests of these experimental groups verified, that

-  the progenies of the early plus variants were not better in his performance than that of average populations, but

-  the offspring of minus variants introducing lower result comparing to the average group consistently.

It comes to the conclusion that the positive phenodeviants during the fingerling stage are not genetically determined in his higher performance, but the background of such a characters are direct for indirect environmental effects.

Family selection uses four or five several lines with different origin but the within family members should be closely related each other. As a result of comparative testing the two outstanding family will be the basis of selected females and males. The family selection should be effective when heritablity or quantitative characters are lower or the foreselected individuals should be killed to collect the necessary data of experiment, like slaughter value and quality of meat.

The selection as a widely used method of genetic improvement should be effective by the wild fish species either of quantitative characters but the common carp with his old breeding history has a very slow progress in growth rate as a respons to the selection.

Inbreeding is a direct pairing of closely related individuals having genetic similarities, with the following purposes:

-  to fix the useful traits of a population in his progenies and to concentrate some genes in homozygote stage which are determining desirable characteristics.

-  to produce inbreed lines for intra-specific hybridisation to gel higher heterozic effect

-  to develop uniform populations for intensive fish production which has the same responds to environmental conditions like high stocking densities, feeding, chemical treatments and several stress effects.

Inbreeding increases the frequencies of homozygous genotypes but not the gene frequencies within the population. Unintentional inbreeding is very often in fish breeding in particular in smaller farms or hatcheries using a few number of broodfish. Artificial reproduction is an other source of inbreeding when one to one ratio of females and males are used. Harmful inbreeding depression may occur when the degree of inbreeding coefficient is over 10/20%. This standard of value by the fish species are not so serious like by the domestic animals because of its high fecundity. Inbreeding depression by gynogenetic carp population could be realised only after his third or fourth generation. To avoid inbreeding depression it is necessary.

-  to know the origin and genetic background of broodfish

-  using an individual marking system

-  the parental stock should consist of different line of females and males

-  the anatomically defected individuals should be eliminate when young brood stock candidates are selected.

HYBRIDISATION

Inraspecific hybridisation is a genetic manipulation when crossing individuals, originating from the same species. By interspecific or intergenetic hybridisation the crossed female and male fish are originated from two different species.
Hybridisation does not produce new genes but the existed genes of two parents are combined. Intraspecific hybridisation in carp breeding are very common because of the good results of crossing experiments in Hungary, Israel, Russia, Poland and Czech republic.

The explanation of superiority of hybrids resulted by intraspecific crossing is the heterozis effect, when Fl hybrids in some characteristics are able to surpass of both parental lines in his productivity. Heterozis effect by the growing capacity of common carp should reach 20–25%, but the most important heterozis effect can be detected by the higher survival rate of hybrids.

Results of interspecifc hybridisation are described by numerous of several species, but those result generally were published as scientific peculiarities and not so many result for practical fish production. Numerous examples of interspecific hybridisation can be find among cyprinid species.

common carp ♀ x silver carp ♂
silver carp ♀ x bighead ♂ and reciprocal cross
grass carp ♀ w bighead ♂
Grossing experiments with Indian major carps introduces several viable hybrids like catla ♀ x rohn ♂. Interspecific hybrids of cyprinid species are generally steryl.

Among the tilapia species 30 interspecific crosses are described. S. niloticus and S. hornorum gaves numerous hybrids with several combinations of other species. The niloticus represents good growing ability and the S. †hornorum as a male parent are promising to produce all-male hybrid populations. Crossing the American catfish species Channel ♀ x Blue ♂ and his reciprocal hybrids has higher growth rate and tolerate better the oxygen deficiency.

Artificial gynogenesis as a genetic method of producing highly inbreed lines became a widely used system during the last two decades. The inbreeding level of first gynogenetic generation is equal with the inbreeding ratio of twelve generation of sister-brother pairing. Gynogenetically inbreed phenotypic male populations can be easily developed with methyltestosterone hormon treatment of genotypically female populations. This process needs laboratory conditions. The gynogenetic inbreed female and male populations requires more attention to carry out crossing experiments developing gynogenetic “super hybrids” for commercial aquaculture.

BREEDING PROGRAMS

The aim of a breeding program is to develop the most suitable fish population for the requirements of production, environment and the market… The breeding program includes all the genetic and selection methods which are most suitable for improving productivity of a given fish population.

SHORT TERM BREEDING PROGRAM

By the short term breeding program the fish chooses the young broodstock which will be the parents of next generation.

THE CRITERIA OF BROOD FISH SELECTION

-  to have detailed information about the morphological and production characteristies of the population

-  market size fish with the same age within the population are the population are the most suitable

-  the average size and the plus variants should be preferred

-  to take into account desirable sex ratio

-  to avoid inbreeding

-  the selected young broodfish candidates should be marked individually or using group marking

LONG TERM BREEDING PROGRAMS

Elaboration the long term breeding program of cultivated fish species those methods of genetic improvement should be applied which can be properly fitted to the biological, genetical and production capacity of different species.

To fulfil a well designed long term breeding program special personal, technical and biological conditions are needed including several lines or varieties of cultivated species.

The consciously designed breeding programs should be to certain production or breeding purposes like

-  increasing productivity of one or more quantitative characters

-  improving quality of the final product

-  to develop more resistant strain against diseases

-  to get better adaptability to the environment of intensive production

-  to develop monosex female or male populations, and finally

-  to preserve the basic genetic diversity of a population maintaining them in a live gene bank.

COMMON CARP

Introducing long term breeding programs of cultivated warm water fish species Some strains of common carp during his domestication and ancient breeding history became geneticaly improved, highly productive subjects of intensive fish production even as a result of various breeding programs. In Hungary the general working processes and time schedule of the developed carp breeding program are as follows:

Realisation of our breeding program three different hybrid carp populations has been developed for the commercial pond fish farming in Hungary with outstanding productivity. (figure)

The Szarvas 215 hybrid mirror carp originated from the Sz.22 maternal, and Sz. 15 paternal lines. As a three-line hybrid has 16.5% better growth and 7.6% higher survival rate comparing to his parental lines. (figure) The Szarvas P.31 heterozygote scaly three-line cross originated from the Sz. P.3 homozygot scaly carp as a maternal line and from the Sz. 15 mirror paternal line. The growth rate of this hybrid resulted + 10.2% and in his survival + 1.9 higher productivity that of the selected parental strains. (figure)

The Sz.P.34 homozygot scaly hybrid carp developed by crossing of Sz.P.3 maternal line with the scaly Amur wild carp. Achievement of this hybrid considering the parental lines in his growth rate +26.0% and +3.2% in his survival.

This breeding program demands a continuous and strict co-operation among the research institute, the fish producers and the state officials controlling the breeding value of new hybrids. As a result of this program 80% of Hungarian carp production is based on the hybrids of Szarvas research institute.

The Russian Ropsha carp has a long breeding history. (figure) Prof. Kirpichnikov developed two crossbreed lines using the local mirror carp of Leningard region and the wild carp from Amur river.

The hybrids were back-crossed with the paternal line and after four generation were selected fluently in three independent crossbreeds up to the 7th generation. The main aim of this program was to improve the cold resistance of North-Russian local strain.
Similar carp breeding programs are described in Czech Republic, Poland Israel, Vietnam and Indonesia.

CHINESE CARPS

One of the most important breeding purpose by the Chinese carps to maintain pure lines of silver carp and bighead. This two species are crossed very often in fish hatcheries without any special conception and as a result of hybridisation feedings habits of hybrids were changed losing the phytoplankton consumption by the silver carp. The growth rate of hybrids in both crossing combinations became lower in the second and third generations. Special breeding program are exists in Vietnam with the Chinese and Vietnamese varieties of silver carp (Hypophthalmichthys molitrix and Hypophthalmichthys harmandi) with special regards to maintain the two varieties in poor lines and crossed them getting higher productivity in the F1 hybrid generation.

TILAPIA

The tilapia species has several types of breeding programs

-  With the aim of effective hybridisation of different species and getting 100% of monosex male populations pure lines or pure breeds should be developed and maintained using shortterm breeding programs.

-  There is an important subject of long - term breeding programs to develop monosex male populations of avoid uncontrolled reproduction in growing ponds and to obtain useful heterozis effect in the growing ability by the F1 hybrid generations (figure)

AMERICAN CATFISH

In the short term or minimal breeding program of channel catfish farming the following guidelines can be used:

-  The wild forms of fishes has generally lower production capacity, therefore young brood stock always should be chosen from domesticated and selected lines

-  These basic population can be find in good managed commercial fish production pond.

-  Avoid inbreeding at least 5 pairs of randomly selected brood fish should be collected as far as from several places, and finally

-  Continuous notes of production and breeding occurrences are important to realise the probably changes the production capacity of the brood stock.

In this long term breeding program two land-races of channel catfish are crossed and the intraspecific Fl hybrid is used for commercial fish production (Figure). An other long term program applying interspecific hybridisation of channel and blue catfish species. The hybrid as a result of this crossing is more tolerant of lower dissolved oxygen concentrations and more uniform in size. Nowadays the undesirable off-flavour of the meat is a subject of geneticists in catfish farming.

CLARIAS

Clarias, as representatives of African catfish species in this breeding programs the growing capacity has the most important role. To approach this problem producing monosex male populations are the most promissing way because of his 30% higher growing ability comparing to the bisexual mixed populations.
This program based on selection, several methods of chromosome manipulations and hybridisation are in an early developing condition in Hungary.

EUROPEAN CATFISH (SILURUS GLANIS)

The main aim of his long term breeding program in Hungary to develop a suitable strain or hybrid for intensive industrialised fish production. The general expectation from such a hybrid is first of all an outstanding adaptability to the artificial environment of closed production systems. By this evidently important fast growing, economical feed conversion and disease resistance some new characters should be focused like stress resistance wide tolerance to changing oxygen and ammonia level.

To develop such a hybrid a live gene bank with four different genotype of Silurus are the basis of selection in the Hungarian Fish Culture Research Institute (Figure)
The first part of this breeding program is a comparative family selection to estimate productivity of the strains. In the second part strict inbreeding is applied using artificial gynogenesis to get higher positive heterosis effect.

INDIAN MAJOR CARPS

Several articles are introduced results of interspecific hybridization of these species. Considerable work on interspecific hybridisation has been carried out in India and the performance of the best Rohu x Catla hybrid was compared with that of parent species. As a result of this program the productivity of this hybrid was intermediate, being better than rohu but lower than catla.

PROGENY TESTING

One of the most important part of genetic improvement to control and verify the effectiveness of breeding work. Several types of performance tests offering possibilities for the practical aquaculture to compare the new populations each other in his productivity. In the fish culture there is difficult to standardise environmental conditions of production so lack of traditional selection indexes comparative testing systems seems to the most usable methods for the practical fish culture.
The basic criteria of the comparative testing are as follows:

-  permanent fish marking system

-  equal group of fish in his age, in his short life histrory and health condition

-  the comparative testing should be arranged under production conditions either in a common pond or in rearing tanks separately with more replications.

Using a standard control population makes easier to evaluate the experimental groups remove the undesirable environmental differences.

MAINTENANCE AND CONSERVATION OF GENETIC RESOURCES

Environment pollution and undesirable over fishing of natural waters result in a permanent reduction of the existing fish species. The genetic structure of cultured species changes rapidly, partly following the continous changes in the environment and due to the “hazardous” selection activity of humans. The practice of artificial propagation and the relatively limited amount of available broodstock are narrowing the genetic diversity continuously. Fish farms producing huge amounts of fry help in this significant gene erosion by transportation of broodstock to great distances. The conscious selection and hybridisation work of producers-with the aim of reaching particular levels of production - knowingly favour special gene combination fully excluding other genes from the population. However, it is presumable that by the end of the century only a narrow, production-oriented genetic structure of the cultured species will be left behind for coming generations.

Therefore, special attention should be paid to conservation and maintenance of the fish gene pool. Among the applicable methods, the establishment of a live gene bank seems to be the most important. A live collection of species and, among them, that of geographic land races should be maintained, considering the origins and habitats of particular species.

The live gene bank of the cultured common carp species in Hungary could be a good example for that. It was established in 1962 in the Fish Culture Research Institute, Szarvas. At present, 30 different species are maintained here, some 30–100 individuals of each. All the species are replaced after 8–10 years by artificial reproduction.

Deep freezing and storage of sexual products - eggs and sperm - is another way of maintaining the genetic material. Practical and industrial deep freezing of eggs should be elaborated. Deep freezing of sperm has been partly elaborated for some species, but further studies are required so as to solve the problem of deep freezing and longer storage of sperm doses.
Apart from live collection of species, a gene bank of deep frozen eggs and sperm should also be established, in which the genetic material could survive serious water pollutions or environmental catastrophes.

REFERENCES

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Bakos, I., Crossbreeding Hungarian races of common carp to develop more productive hybrids, in Advances in Aquaculture, Pillay, T.V.R. and Dill, Wm. A., Eds., Fishing News Books, Farnham, 1979, 633.

Balon, E.K., Domestication of the carp, Cyprinus carrpio L.,R. Ont. Mus. Life Sci. Misc. Publ., 1974, 37.

Bondary, K., Reproductive performance, growth and survival of selected and will x selected channel catfish. Theor. Appl. Genet. 68, 391–395, 1984.

Dunham, R.A. and Smitherman, R.O., Response to selection and realized heritability for body weight in three strains of channel catfish, Ictalurus grown in earthen ponds, Aquaculture, 33, 89, 1983.

Gall, G.A.E., Genetic of fish: a summary of discussion. Aquaculture, 33, 383–394, 1983.

Gjedrem, T., Genetic variation in quantitative traits and selective breeding in fish and shellfish, Aquaculture, 33, 51, 1983.

Huisman, E.A. and Richer, C.J.J., Reproduction, growth, health control and aquacultural Potential of the African Catfish, Clarias gariepinus (Burchell 1822). Aquaculture, 63, 1–14, 1987.

Hulata, G., Wohlfarth, G.W. and Halevy, A., Mass selection for growth rate in the Nile tilapia (Oreochromis niloticus), Aquaculture, 57, 177, 1986.

Hulata, G., Wohlfarth, G. and Rothbard, S., Progeny testing selection of tilapia broodstocks producing all-male hybrid progenies-preliminary results, Aquaculture, 33, 263, 1983.

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Krasznai, Z. and Marian, T., Induced gynogenesis on European catfish (Silurus glanis L.), in Selection, Hybridization and Genetic Engineering in Aquaculture, Tiews, K., Ed., Heenemann Verlagsgesell., Berlin, 1987, 261.

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Fig. 1: The breeding sheme of the Szarvas 215 three-line hybrid mirror carp

Fig. 2: the breeding sheme of the Szarvas P. 31 three-line hybrid scaly carp

Fig. 3: The breeding sheme of the Szarvas P. 34 two-line hybrid scaly carp A: wild carp from river Amur (Russia)

Figure 1: Project plan for industrial catfish culture research

Figure 2: Project plan for genetic and selection research