Genetic differences between the Chinese and European races of the common carp : 6. Growth of fish in cages.

Relative growth rates of six genetic groups of common carp were compared in small netting cages and in earthen ponds. These groups of carp included an isolate of the Chinese 'Big Belly Carp', its crossbred with a European isolate, and four European progenies, purebreds or crossbreds. Five different environments were produced in the ponds, mainly by varying the stocking rates of carp. Each of the (ten) cages was treated as a different environment. Each cage and each pond were stocked with random samples of each genotype, i.e., 'communal testing' was carried out. The performance of a given genotype in a given environment was estimated from its weight gain in that environment. The mean weight gain of all groups, stocked into a given environment, was taken as an estimate of that environment as it influenced the growth of carp. The characteristics of the regression of growth of a given genotype on the environment in which it grew [i.e., the coefficient of regression (b) and the Y intercept (a)] are taken as measures of its adaptation to that environment. No real differences in adaptation to pond versus cage conditions were isolated for four of the tested groups, the Chinese x European crossbred, the two European crossbreds and one of the European purebreds. The Chinese carp showed a specific adaptation to growth in ponds (or a lack of adaptation to growth in cages), whereas Dor-70 was specifically adapted to cage conditions. These results may be explained by the genetic history of the two lines. The Big Belly Carp was domesticated under conditions of Chinese subsistence aquaculture, which apparently generated an adaptation to gathering and utilizing natural foods. These are prominently absent in cages. Dor-70 was produced in a long-term selection experiment, which apparently generated a response for growth in cages. These results may be of applicative value, if common carp were to be considered as candidates for commercial cage aquaculture. It would then be important to use strains like Dor-70, which are adapted to these conditions, and avoid strains like the Chinese Big Belly carp.

Genetic differences between the Chinese and European races of common carp : 5. Differential adaptation to manure and artificial feeds.

Common carp of the Chinese and European races and their cross were tested in different environments. The test groups were either stocked together into the same pond, or each group was stocked separately. Mean growth, taken as a measure of the quality of the environment, varied widely between treatments. Genotype-environment interactions were estimated by the regression of growth of different genetic groups on this measure of environment. Proportional growth differences between the European and European X Chinese crossbreds, were several times higher in manured ponds than in ponds with artificial feed. The Chinese fish showed the fastest relative growth in poor conditions, with manure as the major nutrient input, while the European fish showed the fastest relative growth under improved conditions and irrespective of its source of food. The Chinese X European crossbred is heterotic over a range of intermediate conditions with manure as the principal nutrient.

Genetic improvement of wild fish populations.

A plan for the genetic improvement of commercially exploited wild animals is presented. It consists of crossing wild with domesticated breeds to produce heterotic hybrids and to upgrade the wild stocks. Empirical evidence is presented from experiments with the carp. Procedures for monitoring the manipulated populations are outlined. The suggested plan is ecologically reasonable and would counteract the negative genetic changes caused by excessive commercial exploitation of many species.

The genetic basis of egg lay response to conditioned medium in the flour beetle, Tribolium castaneum : I. Two-way selection.

The rate of egg laying in Tribolium castaneum is affected by the quality of the environment and can thus serve not only as a component of fitness of the individual, but also as an adaptation to the long-term survival of the population. In an attempt to determine whether it is an independent genetic character, selection for high and low rates of response was carried jut in beetles from three wild populations. When tests were done on virgin females, and responsiveness, corrected for scale effects, was used as the criterion for selection, separation between the lines was achieved in one generation. It is suggested that in natural populations of Tribolium, the responsiveness of the rate of egg laying to the quality of the environment is controlled by a small number of genes.

Two-way selection for growth rate in the common carp (Cyprinus carpio L.)

The domesticated European carp was subjected to a two-way selection for growth rate. Five generations of mall selection for faster growth rate did not yield any response, but subsequent selection between groups (families) resulted in considerable progress while maintaining a large genetic variance. Selection for slow growth rate yielded relatively strong response for the first three generations. Random-bred control lines suffered from strong inbreeding depression and when two lines were crossed, the F1 showed a high degree of heterosis. Selection was performed on pond-raised fish, but growth rate was also tested in cages. A strong pond-cage genetic interaction was found. A theoretical explanation was suggested involving overdominance for fast growth rate and amplification through competition of intra-group but not inter-group variation.

Genetic aspects of the transition from traditional to modern fish farming.

A theoretical model describing the genetic aspect of the transition from traditional to modern animal husbandry is presented. Traditional races are characterized by high tolerance to harsh environments but a low rate of response to increased management inputs. Modern, artificially-selected breeds are efficient convertors of management inputs to higher production but have a low resistance to harsh environments. Thus, under lowinput traditional husbandry, the traditional races are best adapted, while under modern, high-input husbandry, modern breeds are most productive, and in the intermediate zone, hybrids between the two races are capable of closing the 'profit gap' in the shift from traditional to modern husbandry. The domesticated European, and the Chinese Big-belly races of the common carp were tested under many environmental 'treatments' involving variation in density, polyculture, aeration, feeding and fertilization. The Big-belly showed, as expected, high resistance to the poor 'treatments' but low response to environmental improvement. The European breeds performed best in the higher half of the environmental range and their response rates were highest. The F1 hybrids between the two races excelled in the lower third of the range, exhibiting, there, a high heterosis but only an intermediate rate of response. It was concluded that successful changes from one aquaculture system to another, and particularly the change from traditional to modern husbandry, require a simultaneous search for the most efficient genotype × environment combination and, for each level of modernization of traditional fish farming, the most effective genotype must be identified and utilized. The transition from traditional to modern animal husbandry, including fish farming, is best quantified by the levels of invested inputs, other than labour, that induce higher production of the individual animals. The major management inputs of modern fresh water fish farming are expensive feeding, veterinary care, control of predators, organic and chemical fertilizers that enrich the production of natural fish food, water circulation and aeration. Since all these inputs are rather expensive, the fish have to pay for them by increased production, i.e., faster growth rate. Thus, the sina qua non of such a transition is the availability of animal stocks capable of converting increased inputs into economically attractive increased yields. We are all aware of the very great physiological plasticity of farm animals. In the case of the European carp, for example, the same genetic stocks, raised under high stocking density and low feeding level may gain an average weight of 10 to 20 g per fish in a whole year, while under low density and abundant feeding, they may gain over 2 kg in the same period. Such physiological responsiveness may give the wrong impression that all that is needed for the transition to more modern husbandry are improved environmental circumstances. The object of this paper is to point out that the proper choice and changeover of genotypes is equally important for the succesfull implementation of the usually gradual process of fish farming modernization. This demonstration will be based on results of experiments with the European and Chinese races of the common carp, and their F1 hybrids.

Genetic differences between the Chinese and European races of the common carp.I. Analysis of genotype-environment interactions for growth rate.

Growth rate of 12 groups of common carp was measured at five experimental environments. Three of the 12 tested groups were strains of the domesticated European race of the common carp, one group was a representative of the Big-Belly Chinese race, and the remaining eight groups were F1 crossbreds among the European strains and between the European and the Chinese races. The average growth rate over the five environments of the Chinese Big-Belly was considerably poorer than that of the European carp. All the inter-race crossbreds and the crossbreds among the European strains showed heterosis. When the genotype-environment interaction was presented as a linear function of the quality of the environment, the regression coefficient (the overall responsiveness parameter) assumed relatively low values in the Big-Belly and two to two-and-a-half fold higher values in the European carp. The overall responsiveness of crossbreds was, on the average, intermediate between the two parents. When, however, it was partitioned into a scale function of the average genotype and specific independent responsiveness, the two components showed a high degree of heterosis but in opposite directions. An explanation of this genetic system in terms of adaptive evolution to the diverse modes of carp domestication in Europe and China was given.

Genetic differences between the Chinese and European races of the common carp. II. Multi-character variation-a response to the diverse methods of fish cultivation in Europe and China.

The European and Chinese races of the common carp and their F1 crossbreds were tested in five experimental environments. The two races differ widely and conspicuously in many characters. The Chinese carp has poorer growth rate but higher viability and fertility, earlier sexual maturity, higher resistance to crowding, better adaptation to unfavourable pond conditions, higher seine escapability, longer body and larger weight differences between females and males. The crossbreds between the two races are intermediate in some characters (differences in weight between females and males and seine escapability). In other characters (weight gain, specific adaptation to poor conditions and viability), the crossbreds showed dominance or even heterosis. An hypothesis was advanced to explain these genetic differences in terms of selection response to the different fish-farming practices that existed in the two regions. Specific suggestions were made for implementation of the present findings to genetic improvement of carp breeding stocks.

Variability of intermuscular bones, vertebrae, ribs, dorsal fin rays and skeletal disorders in the common carp.

The number of intermuscular bones, vertebrae, ribs, dorsal fin rays and an index of bone disorders were determined from x-ray photographs of over 1000 common carp. These carp represented a broad genetic range, including five distinct lines of the domesticated European carp, one group of the Chinese race Big-Belly and 12 crossbreds. The genetic, and even the phenotypic, variation in intermuscular bones were much smaller than those found in earlier experiments. Variation of other bone characters was also analyzed and the relationship of intermuscular bones and ribs to vertebrae was determined.