Many aspects of common carp (Cyprinus carpio) culture have already been discussed elsewhere in this manual, or in other FAO publications (e.g., Horváth, Tamás and Coche, 1985; Woynarovich and Horváth, 1984). Therefore only topics omitted or insufficiently explained in those papers are covered here.
Modern hatchery methods for carp propagation are very well described in the publications cited above. However, in some circumstances simpler techniques can still be useful.
Carp spawning in large ponds
This is a widespread, simple, carp-propagation method applicable in newly constructed or previously dried ponds covered with grass. These grass-covered areas provide ideal spawning places after filling. Fish ponds in which thin macrovegetation develops by the time of carp spawning can also be used.
When water starts warming up, ponds are filled. Selected breeders are stocked at the rate of 3–4 fish/ha. Generally 2–3 males are stocked with each female. Under favourable conditions, good results can be achieved. It is, however, very hard to check the number of eggs laid and the fertilization ratio. In temperate climates it will be mid-summer before the success of spawning can be assessed by which time it is too late for spawning to be repeated.
This way of spawning should generally be avoided, since it will not provide the quantity of seeds necessary for large-scale fish farming. But it may be useful either as a reserve production under simple circumstances or to provide cheap seed materials.
Spawning in small “Dubisch” ponds
The essence of this technique is that all the natural factors necessary to induce carp spawning are provided under pond conditions: the fast-warming of shallow water (18°–20°C), the macrovegetation on the bottom for spawning, sufficient dissolved oxygen, and the presence of both sexes.
Small shallow ponds (100–1 000 m2) are necessary. The best are small ponds with 30–50 cm water, located in a protected area of the farm. These small ponds are kept dry and under grass when not in use.
In spring, when water temperature stabilizes at 18°–20°C, the ponds are prepared. They are cleaned and the grass is mowed down. Then they are filled with filtered, oxygen-rich water up to 25–30 cm. Spawners are stocked (2–3 females and 4–5 males) and the water level is increased slowly up to 50 cm. One or two days after stocking, spawning should normally occur.
Parent fish are removed after spawning, so as to cause the least possible harm to the eggs laid. The water level is rapidly decreased, which drives the fish to the deeper parts of the pond, from where they can be carefully netted. The water level is then re-adjusted rapidly so as to keep the eggs under water. These eggs are firmly attached to grass and, depending on the temperature, they hatch within 4–8 days. The number of hatched larvae can be estimated using a white plate [from] 10–12 days after hatching. When the larvae are about 12–15 mm long, they should be harvested and stocked into another, larger pond for nursing.
With this method, which is rather time-consuming and labour-intensive, seeds can be produced with fair success. However, the results are greatly influenced by the weather. The number of larvae produced by this method is much higher than under natural conditions, but still many eggs and larvae are lost by predation.
Development of the hypophysation technique has facilitated the further improvement of the Dubisch method. If hypophysis-treated spawners are stocked into the well-prepared Dubisch ponds, spawning almost always occurs. By this method, however, only spawning is ensured, while eggs and larvae still remain without any protection.
Controlled hatching
The stickiness of carp eggs has been a great obstacle to further technological improvement, since carp eggs could not be incubated and hatched in flow-through jars. Several techniques have been tested to overcome this difficulty, but none of them has met the requirements for large-scale seed production. One of these techniques is described below.
Spawners are stocked into Dubisch ponds after hormone treatment, then just before spawning, they are taken out, stripped and the eggs fertilized. Fertilized eggs sticking to baskets, linen or any other suitable material are hatched in tanks or small ponds. This method is an improvement compared to the original Dubisch method in that the development of attached eggs can be better observed and the fertilization ratio easily determined. With daily malachite green treatment, moulding of eggs can be avoided.
Methods applied in tropical regions are based on a similar principle. Carp are spawned in boxes of fine net-cloth (hapas) or in small ponds where eggs are laid on an artificial substrata such as natural fibrous material (kakabans).
Controlled incubation and hatchery
The elimination of the stickiness of carp eggs with a chemical compound has permitted hatching technologies to develop quickly. Carp eggs can now be incubated in vertical jars in the same way as the eggs of pike or trout, increasing at the same time the efficiency of propagation.
Several methods using enzymes, talc, milk, urea, etc., have been elaborated for the elimination of the egg stickiness. In the sixties, a urea salt treatment has been worked out by Prof. E. Woynarovich. It has become the most widely used method due to its efficiency and simplicity. The price and amount of chemical used are very small, and the method gives fairly good results. The hatchery technology based on this technique is described in detail by Horváth, Tamás and Coche (1985).
Improvement of cultured carp varieties has played a significant role in the increase of yield from fish farms. The most important quantitative characteristics of progenies, i.e., growth, viability, food conversion, flesh quality and resistance to diseases, are closely linked to economical carp production. Great efforts have been made in the past decades, both in research and practice, to increase productivity of cultured carp varieties using production-genetic methods based on the results of basic research. In Hungary, pronounced differences have been found in the most important features of different strains. The aim of species improvement work is determined by the common requirements of producers, consumers and the processing industry.
Growth rate and growing capacity are complex, polyfactorial features, which are essentially influenced by the natural food supply of the pond and the conversion efficiency of supplementary feed. Conversion of food is one of the most important factors in intensive carp farming. Survival rate, measured from the percentage of carp stocked and harvested, is also an important parameter determined by both genotype and the effect of various environmental factors. The proportion of edible parts to total live-weight is important as well, together with the quality of flesh (with special emphasis on fat content and number of intermuscular bones). Qualitative properties such as colour and scale pattern are important only if a given species-characteristic is preferred. There can be specific aims in breeding, i.e., resistance to diseases, higher tolerance to oxygen deficiency, delayed sexual maturation in tropical climates, easier artificial propagation of Indian carps, increase of stress tolerance in silver carp, etc.
The classic method of mass selection has not brought the expected results of increased productivity, though in the improvement of other characteristics, e.g., resistance to diseases, it can be successful.
Intraspecific hybridization methods, which have been applied since the 1960s, have given good results in increasing productivity of common carp in Hungary. Under the influence of dominancy from the accumulation of desirable dominant genes of crossed parents, or of overdominancy based on the pronounced heterozygocity expressed in the F1 generation, several useful characteristics will appear in the first generation, at levels higher than those in the parental lines.
Carp hybridization research in Hungary started in 1962, and was organized as follows:
Collection and maintenance of Hungarian and foreign common carp strains, as a live gene bank.
Comparison of the characteristics of different strains.
Selection and inbreeding of the best strains.
Crossing of different genotypes.
Testing of hybrids.
Propagation, rearing and introduction of best-proved hybrids into production, i.e., in commercial hatcheries and carp farms.
As a result of genetic and hybridization research, the common carp hybrids “Szarvasi 215” mirror carp and “Szarvasi P 31” scaly carp, were developed. They have 20–25% higher productivity than that of pure lines.
This programme was complemented in 1974 with the introduction of artificial gynogenesis and sex-reversal.
This facilitated the high-level inbreeding of common carp strains of good combining capacity and their utilization in commercial hybridization.
Inbreeding, the coupling of closely-related specimens or sib-mating, evokes effects contrary to those of crossing. A proportion of the genes will be homozygotic in nature and certain characteristics, especially viability, will be expressed in inbred progenies at a lower level.
Testing and comparison of productivity in carp farming uses methods different from those applied with other livestock. An important advantage of carp is that several thousand progenies can be obtained from parents simultaneously, and different groups can be artificially propagated and reared under identical conditions.
Tests should be made under conditions identical with those in commercial fish farms. Market fish can be compared by stocking individually marked fish (50–300 specimens stocked in wire net pens, 40–50 carp of identical strain in each), so as to test food conversion on the basis of food consumed and weight gained.
With this method, the competition of carp groups of identical and mixed strains, respectively, can also be compared. Survival rate and growth are measured by individual counting and weighing. The proportion of edible parts and fat content can be determined in the laboratory.
An efficient and rapid method of carp inbreeding is induced gynogenesis. By its application, higher inbreeding coefficients can be achieved in the first generation than would be possible through 12 generations of sib-mating.
Since paternal chromosomes do not participate in developing diploid gynogenetic progenies, these will all be females. Gynogenetic female carps produced from paternal lines of good combining capacity will develop into phenotypic males in 40–60 days if fed on methyltestosterone hormone at an early age. When sexually mature, these will produce fertile sperm cells. Their utilization might ensure significant progress in commercial crossing of carps with highly inbred maternal or paternal lines.
Interspecific hybridization of cyprinids and the widespread application of artificial propagation has led to great progress. Several authors have reported the results of studies on hybrids of common carp with Chinese carps, those between different species of Chinese carp, and hybrids of Indian major carps. Hybrids generally showed intermediate inheritance and pronounced maternal effects. Several of them have become economically important, either in polyculture farming (common carp × silver carp; silver carp × bighead carp, catla × rohu), or in biological weed control (grass carp × bighead carp).
References
Horváth, L., G. Tamás and A.G. Coche. 1985 Common Carp 1: Mass production of eggs and early fry. FAO Training Series, (8): 87 p.
Horváth, L., G. Tamás and A.G. Coche. 1985 Common Carp 2: Mass production of advanced fry and fingerlings in ponds. FAO Training Series, (9): 85 p.
Woynarovich, E. and L. Horváth. 1984 The artificial propagation of warmwater finfishes. A manual for extension. FAO Fish.Tech.Pap., (201): 183 p.
