BREEDING IN FISH CULTURE

by

K.L. Golovinskaya
All-Union Pond Fishery Institute
Moscow, U.S.S.R.

1 INTRODUCTION

In fish culture breeding of fish is carried out with the primary object of modifying their hereditary properties in the direction required. Vavilov, a well-known selectionist remarked that selection was one of the links in the teaching of evolution, controlled by man (Vavilov, 1935). This statement is applicable to fishes, the process of reproduction of which is to a large extent controlled by man. Such control is possible only to a limited extent in natural water basins, but in pond fish culture it is possible and even necessary to utilize all modern methods of domestic animal improvement, with due regard to the peculiarities in biology and breeding methods of the fishes in question. Breeding practised in pond fish culture also ensures the provision of spawners necessary for obtaining commercial products of good quality in required quantities.

Although very important in their role, selection and breeding are at a rather low level of development in pond fish culture as compared to other branches of animal breeding. Even among carp, which are the oldest cultivated fish, only few species and breed-groups compare with the highly specialized breeds of domestic animals. This is to a large extent due to the fact that carp is not a completely domestic animal. Also, the methods of breeding and management have been far from perfect. The considerable rate of genetic plasticity if carp is of great value, as is the wide range of its paratypic variability.

In fish culture we have certain advantages as compared to other types of animal breeding. Fishes have high fecundity, which allows the use of very strict norms of selection. Fertilization is external in the majority of fishes and this enables exercising of control over their embryogenesis.

2 ORGANIZATION OF CARP BREEDING IN THE U.S.S.R.

The experience of animal breeders in the U.S.S.R. shows that practical results in pedigree farming are best obtained by operating specialized selection - breeding farms, releasing purely commercial production farms from the task of raising pedigree stock. The question of feasibility of such specialization in fish culture was raised by Kirpichnikov (1960) and Golovinskaya (1962); now the commission on pedigree fish culture (which is under the U.S.S.R. Ministry of Fisheries) has adopted three main types of carp breeding farms: selection – breeding farms of the highest type; broodstock production farms; and purely commercial farms.

These categories of farms actually represent the interconnected parts of one system. In the selection - breeding farms the main work is concentrated on the production of new breeds. These farms deliver the spawners of the best breed groups to the brood stock production farms, or the breeding hatcheries. These hatcheries are engaged in mass production of these breed groups and supply spawners to the purely commercial farms. The commercial farms are exempted from rearing the replenishment stock of spawners and are only engaged in commercial production of fingerlings and commercial sized fish.

2.1 Selection-breeding farms

The selection-breeding farms are highly specialized farms. In the U.S.S.R. it is planned to establish only 10–15 of them, with zonal distribution. Besides production of new breeds and breed groups and improvement of the existing breeds, these farms would conduct researches on selection methods, on the systems of pedigree and commercial cultivation (paying special attention to the problems of attainment and fixing of heterosis), on methods of spawner evaluation and estimation by generations and by the utilization of hybridization. These farms would develop scientifically sound biotechnical methods of raising and maintaining pedigree fish. These problems require long-term and close studies and repeated experiments, for obtaining reliable results. The selection – breeding farms should, therefore, be established as highly specialized farms, the staff of which should consist of specialists in genetics and selection, and work under the guidance of competent scientific bodies. Their pond facilities should consist not only of hatchery ponds for rearing spawners, holding and quarantine ponds, but also a system of numerous experimental ponds. When designing such farms it is necessary to provide for a hatchery in order to obtain fish eggs and fry, as well as a well equipped laboratory, aquarium rooms, etc.

In the structure and capacity of selection-breeding farms several gradations are possible depending on their specialization towards selection (for example, resistance to diseases in relation to local conditions and requirements, etc.). It is clear that creation of standard projects for such farms is not feasible, but special methodological directions have been worked out in the U.S.S.R. by the Scientific Research Institute on Lake and River Fisheries (GosNIORKh).

2.2 Broodstock production farms

There are 50–70 of this type of farms in the Soviet Union, some of which are already under operation and others are under construction. One of the main considerations of raising broodstock is the reproduction of two non-related breed-groups or strains for producing spawners with selected characteristics of males and females of different origin. Such a method of commercial breeding has been suggested by Shaskolsky (1954). It excludes the possibility of inbreeding (which is not permitted in commercial fish culture) and allows manifestation of the effect of heterosis. Commercial hybridization of selected carp with Amur wild carp, and crossing of two strains of Ropsha carp yielded interesting instances of high heterosis (Kirpichnikov, 1966).

The tasks of breeding farms are not limited to production of pedigreed fish. It is necessary for these farms to carry out continuous work on further improvement of the breed-groups received, mainly by means of mass selection. Mass selection is one of the most important methods of fish selection. The selection should be strict and directed. Carp selection is carried out in the breeding farms in three stages: among the yearlings; at the age of harvest for commercial use (at two summers in the U.S.S.R.); and at the time of transference from the reserve to the spawning stock at maturity. The ratio of selection intensity (number of individuals left for breeding related to the number reared) should not exceed 50 percent for yearlings, 10 percent for two-year-old fish, 25 percent for young females and 50 percent for young males. Thus, the general ratio of selection intensity for younger groups in carp nurseries should not exceed 5 percent as recommended by Schäperclaus (1961). We introduce additional selection among spawners, bringing the selection intensity up to 1.25 percent for females and up to 2.5 percent for males.

At the first two stages (yearlings and two-summer-olds) the weight of fish is the criterion for selection, though among the two-summer-old fish we take into account exterior features as well. At the third (spawners) the degree of expression of sexual characters is considered in the selection.

This simple scheme permits one to estimate the quantity of replacement broodstock required for obtaining the number of spawners needed, and to calculate the necessary number and area of ponds for separate storage and rearing of replacement broodstock of all ages.

When designing breeding hatcheries, one should not limit the farm plan to the production of spawners only. This is not profitable and, besides, the availability of commercial ponds is useful for checking the quality of pedigreed fish being released. Thus a breeding nursery is a kind of specialized pedigree department of a commercial farm, where release of spawners is planned along with commercial production. In the breeding farms as well as in the selection-breeding farms of the highest type there should be provision for quarantine ponds and a hatchery. The staff of breeding farms should have a specialist on fish selection, and their work should be in close connection with selection – breeding farms of the highest type in the system in which they are included.

The commission on pedigree fish culture established biological standards for designing carp hatcheries for broodstock production, which provide for the system of selection as stated above and estimate the necessary categories and pond areas for reserve broodstock rearing in accordance with the required number of spawners (Table I).

When arranging pedigree activities in carp breeding, we proceed from the generally adopted principle of correlating the work on modification and improvement of genetic structure of stocks with the creation of suitable conditions for raising and keeping. This is absolutely necessary in order to maintain adequate physiological condition of fishes and to obtain the required profitable production. We have therefore introduced certain fish cultural standards for keeping the spawners. These standards provide for optimum densities of stocking for ensuring the necessary profit, conditions of feeding fish and pond fertilization for providing a certain amount of natural food in the ration.

As is known, we follow the two-year cycle in carp farming. High stocking rates are used for raising young-of-the-year and two-summer-fish, which permits, with proper fish cultural techniques, the growth of fish of required commercial standard weight, and at the same time ensures high production in the ponds. For raising young-of-the-year and two-summer fish for replenishment of spawners, such stocking densities are not allowed; moreover, we consider it incorrect to provide these fish with extraordinary conditions of life that differ greatly from commercial conditions. Therefore, for the young-of-the-year and for two-summer fish, rather moderate stocking rates are adopted. They are intended for production of increased gain as compared to the commercial norms, and not for the attainment of maximum possible gain.

Table I

Approximate norms of selection and cultivation of reserve broodstock of carp in breeding nurseries, designed for obtaining 100 redds of spawners per year with cultivation of two breed groups

NOTE: In alternating production of breed groups the number of ponds decreases by half, total area remaining unchanged. In the extreme south the reserve rearing is completed in the fourth year and the number of ponds decreases to six summer and six winter ponds.

For the reserve stock of all ages, separate ponds should be provided. This is necessary not only for better control over the growth and condition of fishes, but also for adequate feeding. When various age groups are mixed, certain confusion is inevitable and older fish of low quality may be confused with the better and younger fish. For two breed-groups raised in a breeding farm, separate ponds are provided, but it is possible to alternate their usage each year.

In Table I is an example of abundance estimation for production of replenishment stock for 100 redds of spawners (a redd= 1 female and 2 males, the usual ratio for natural spawning in carp breeding). The number of young-of-the-year being raised (and accordingly the area of the ponds) is not regulated, but it is necessary to rear not less than 25 000 young-of-the-year, this number being higher as the strictness of selection becomes more severe. Therefore, it is not necessary to design special ponds for the young-of-the-year if in the commercial part of the farm there are proper sized ponds available for rearing and wintering, out of which it is possible to choose the ponds necessary for rearing of breed generations from the selected spawners.

Reproduction of the pedigreed stock in a breeding hatchery should be planned keeping in mind the possibility of an annual change of 25 percent of the spawning stock.

2.3 Commercial farms

These are farms with stocks of spawners for reproduction, but which do not raise their own replenishment stock. They receive the necessary spawners from the breeding farms. The purely commercial fish farms do not require experts in selection, but the fish farmers should be qualified enough to tackle the main problems of breeding, to estimate properly the quality of spawners when judging and matching them for spawning, as well as to make adequate use of biotechnical regulations in fish rearing.

For purely commercial farms, ponds for replenishment stock are not necessary, but there should be holding ponds (summer and winter) in which the spawners have normal conditions for fattening, and ponds for fish to replace loss of spawners.

The quantity of commercial fish (two-year old fish) by weight obtained in one season as the result of spawning of one carp female (or redd) is conventionally taken as an indication of its productivity. This value is summed up from the active fecundity of a female (number of fry transferred for rearing), survival in the process of rearing and adopted standard piece weight of commercial fishes. For example, by the standards adopted when estimating the capacity of a pond farm design, we obtain the following figures of female productivity:

Active fecundity = 125 000 larvae;

young-of-the-year yield (75 percent) = 94 000;

yearlings yield (85 percent) = 80 000;

Two-year-old yield (90 percent) = 72 000

Thus, at a standard weight of 0.5 kg for two-year-old fish the annual commercial production of a female is equal to 36 000 kg.

Active fecundity of carp females can reach the level of 400 000 active fry, not only due to the fecundity of the female herself but due to the efficient incubation methods and fingerling rearing methods used, periods of transferring, etc. However, the importance of the female's fecundity is evident, and practical work carried out has proved that good females can give an annual yield up to 100 000 kg or even higher.

High productivity of females permits one to operate with a few spawners, which in turn facilitates the establishment of better conditions, and permits control over the stock and selection of the best individuals. Surplus spawners do more harm than good for production. The spawning stock (and consequently, the replenishment stock) should be kept only in the quantity desired, with a certain reserve, the amount of which is determined in relation to the health of the individuals. In a healthy farm it is sufficient to have a reserve of 25–50 percent. Such control over the stock of spawners and of the reserve is essential in purely commercial farms and in breeding nurseries for efficient management of work.

3 INVENTORY OF FISH FOR PEDIGREE FISH CULTURE

3.1 Method of inventory

One of the important measures of regular control over the condition of pedigree fishes and broodstock structure consists of adequate arrangment of annual inventory of the whole stock of spawners in purely commercial farms and of spawners and reserve in the selection-breeding farms. Properly arranged inventory takes into account all modifications in the broodstock indexes, which appear as a result of selection work and under the influence of the environment, as well as those essential for carrying out selection.

The accuracy of their determination affects the correct estimation of the pedigree fish's value as well as the formulation of adequate methods of improving them.

Inventory is carried out in spring in the U.S.S.R., directly at unloading of the wintering ponds. Proper facilities should be prepared before hand; i.e., scales, measuring boards, intermediate reservoirs for fish, sorting tables, etc. The fish should be handled with extreme care, female spawners in particular, avoiding any kind of injury. For example, all measurements should be taken with the fish in a secure and stable position - for this purpose, measuring boards with two vertical sides are especially convenient. For weighing, a special container is necessary; we use a kind of cradle for one fish at a time, in keeping with the size of spawners.

The whole group of spawners undergoes individual visual examination, during which all sick fish are rejected, as well as the fish with malformations or serious injuries.

The inventory is started on the spawners, separately by breed-groups and sex. Individuals are sexed and sorted into classes. In the most simple cases, only the females are separated (they are placed in separate ponds) - into three classes:

The same classification is given by Schäperclaus (1961) in his well-known book.

Individual indexes, determined and registered during the inventory (and put down into special logs, kept in the farms) include the following important data: breed-group, sex, age, class, fish tag (group, individual), colouring peculiarities or distinctive marks, in carps the type of scale, the degree of expression of sex characters and readiness for spawning, and individual weight and measurments data by which the indexes of exterior features are determined. All indications which are the cause of immediate rejection are registered separately.

The classification adopted in the U.S.S.R. and the main indications taken into account at inventory, are very close to those described by Schäperclaus. Therefore I shall dwell only upon some of them to which we pay special attention.

3.2 Disease and malformations

First of all it is desirable, and at big farms and breeding farms it is necessary, that an expert on ichthyopathology should participate in the processing of inventory, the opinion of this expert being decisive if there appear any doubts concerning rejection of diseased fish. Fish with malformations (in the fins, head, body proportion, etc.) are excluded from the pedigree fund until they reach maturity. Malformed spawners should be rejected. Schäperclaus (1955) was right to stress that all fishes with inheritable defects should be excluded from the stock. In particular, this relates to the malformations of the bladder, which sometimes result in lopsided fishes, as seen frequently among adult carp.

3.3 Sex and maturity

The first class should embrace only such spawners whose characters are obvious. This is specially important when transferring young fish from the reserve. The majority of carp rejected in our farms during rather severe selection of young fish are young females which are slow in maturing. One must take into account the difference in significance of late and early maturity in different climatic zones, because in hot climates late maturity is a positive feature.

3.4 Age groups

The most productive age of carp in moderate climates is considered to be 6–11 years for females and 5–10 years for males. We do not recommend to refer young females, just transferred from the reserve, to the first class, but they should be kept in the reserve and permitted to spawn even when their participation in the spawning appears unnecessary.

3.5 Weight

As already stated we adopt weight to be the main indicator in mass selection. But the selection of the best spawners for the first class is carried out among fish of various ages; thus the weight is not a decisive factor. For purpose of estimation, the expected productivity of females and their gain in weight in the past season are of importance; for example, a big female which has lost weight in comparison to its weight the previous year has no advantages over a female of smaller weight which has shown marked gain in weight.

Loss in weight as well as poor growth in the absence of other symptoms, usually indicate that the fattening conditions for the females in the post-spawning period were not satisfactory; due to malnutrition, the females fail to make up the spawning losses and are not able to accumulate reserve materials for the next spawning. Therefore, it is recommended that carp spawners be fed with fodder mixtures in the pre-spawning period also, and to refrain from too dense stocking of brooders after spawning for summer fattening. With adequate feeding and separate rearing we can account for normal gain (1 kg or more during a summer period, when stocking 100–150 females and 250–300 males per ha).

3.6 External characters

Much attention has been paid to the external characters in carp breeding, and at one time they were considered as the foundation for the establishment of race (breed) standards; many scientific investigations were carried out to find direct connections between the external characters and rate of growth. We take them into account when selecting the reserve and the spawners, because they are related not only to the species or race peculiarities of fish constitution, but serve as the indications of normal development and growth. We usually determine three minimum indexes for carp:

1. relative body height - l/H, where l is standard length, and H is the maximum body height measured at the dorsal fin;

2. the maximum body width - Br/l, where l is the length; and Br is the maximum body width;

3. coefficient of condition - ; where g is the weight of fish and l the length of fish.

3.7 Coefficients of condition

The index of coefficients of condition, K, is adopted in carp breeding as an indication of expected winter-resistance of the young-of-the-year fishes. This index is useful for the evaluation of other species of pond fish as well. Spawner selection by the values of K ensures improved stock in respect of other characters too. Using auxiliary tables, it is possible to determine K during inventory under field conditions, proceeding from the data on weight and length;the highest appraisal is given to the spawners with the highest K value (within the limits of each species or race group).

When estimating by K, and especially by l/H, it is necessary to ensure that good indexes (high values of K and low of l/H) should not be conditioned by defects in constitution: spine distortion, caudal peduncle shortening, etc. These malformations, very often hereditary, are rather characteristic of cultivated carp; probably their occurrence is related considerably to the selection for body height, to western European fashion for round, fit-into-plate carp.

Determination of individual indexes is necessary for young spawners being transferred from the reserve to broodstock ponds. In younger age groups, individual indexes are determined by proceeding from average (without selection) samples. It is necessary to determine piece weight of all reserve categories (sum weighings are used for this purpose) and, of course, to ensure their accurate registration.

No less important than spring inventory is autumn registration of fattening results. Usually at autumn fishing, individual weighing and measuring of fish is not done, unless required for some programme of special work. It is most desirable to weight spawners before and after spawning. This allows one to estimate approximately the actual fecundity of females and to register precisely the results of summer fattening.

4 CONCLUSION

The pedigree carp breeding programme, described above, is applicable in general to other objects of warm-water and cold-water pond culture. Probably, for other objects it will not be necessary to have two separate categories of selection - breeding farms, but separation of purely commercial farms is absolutely essential. This is especially so because polyculture has been used more and more intensively. It is impossible to imagine an economy having equal levels of arrangement in selective breeding of several objects, which very often differ in reproduction biology, requirements of incubation conditions and other characteristics. The selection - breeding farms must produce pedigree material: fish eggs or larvae, for example. This is the practice in fish nurseries, where spawners of Ctenopharyngodon idella, Hypophthalmichthys molitrix and Aristichthys nobilis are kept. These are highly fecund fishes for which norms of selection recommended for carp nurseries are applicable, and for special purposes, more strict selection can easily be used. For fishes of low fecundity, for example trout, such strict norms are not suitable, and the general rate of selection strictness may be about 5 percent, the main burden of selection being on the age group of commodity raising. With early maturing fishes it is necessary that selection should be in conjunction with sex separation.

Adoption of artificial fertilization would allow the purely commercial farms to obtain larvae from the nurseries, and raise the reserve necessary for production of their own stocks, which consequently could be increased. Specialized hatchery methods developed to prevent eggs from sticking to substrata and to incubate eggs under controlled conditions, have helped simplify carp breeding techniques. This method has definite advantages in special selection work (polyallelic crossing, selection for fecundity and fish egg quality, etc.). It is also of importance in preventing fish diseases: fry do not come into contact with spawners, thus avoiding infestation. Besides, numerous labour - consuming operations connected with transportation of spawners are eliminated.

In conclusion, it may be pointed out that purely commercial farms are not excluded from the general selection - breeding activities, the appraisal of selection - breeding farm work is eventually done in purely commercial farms. It is possible and desirable to develop reverse liaison, when spawners, record holders of the results of active rearing are planted into stocks for specialized production for the purpose of establishment of new breed-groups and strains.

5 REFERENCES

Golovinskaya, K.A., 1962 Breeding in pond fish culture. Rybovod.i.Rybolov., (3):7–10

Kirpichnikov, V.S., 1960 Pedigree carp breeding arrangement. Nauch.-tekh.Biull.vsesoiuz. nauch.-issled.Inst.ozer.-rech. ryb.Khoz., (11):38–40

Kirpichnikov, V.S., 1966 First results and tasks in breeding arrangement in North-West of RSFSR. Izv.gosud.nauchno-issled.Inst.ozer.rech.ryb.Khoz., 61:143–53

Schäperclaus, W., 1955 Die Bewertung des Karpfens bei der Zuchtauslese. Z.Fisch., 4(N.F.) (7–8): 483–520

Schäperclaus, W., 1961 Lehrbuch der Teichwirtschaft. Berlin, P. Parey: 582 p.

Shaskolsky, D.V., 1954 On close breeding of carp at commercial fish farms. Trud.vseross. nauch.-issled.Inst.prudov.ryb.Khoz., 7:22–33

Vavilov, N.I., 1935 Theoretical foundations of plant selection. M.-L., Selkhozgis, 1:1–17