Rom Moav

Magnification through competition of genetic differences in yield capacity in carp.

SummaryTen experiments were carried out during the period 1961–69. In each experiment a pair of genetically different groups of carp was tested simultaneously for differences in growth rate in mixed ponds as well as in separate ponds. The aim of the experiments was to estimate the genetic correlation of relative growth rate under inter-group competition in mixed ponds and in the absence of inter-group competition in separate ponds. The estimate of the genetic correlation coefficient was found to be 1·0, and that of the regression coefficient of growth rate in mixed ponds on growth rate in separate ponds was 2·0. The inter-group genetic variance in mixed ponds was four times higher than that of the variance in separate ponds. The higher variance in mixed ponds was partitioned into a component dependent on growth rate in separate ponds and a second independent component. The high genetic correlation means that the dependent component could account for all the amplification of the variance in the mixed ponds and that, apparently, in carp there are no specific genetic factors affecting growth rate under competition. The practical implications of this result for carp breeding is that selection for the improvement of yield capacity can be performed more effectively in mixed ponds than in separate ponds. A theoretical model for analysis of competition is presented and discussed.

Intensive polyculture of fish in freshwater ponds. I. Substitution of expensive feeds by liquid cow manure

Abstract In 1974 and 1975 nine experimental treatments of fish polyculture in stagnant water ponds without aeration were conducted at Dor. The polyculture was composed of common carp, silver carp, white amur (grass carp) and Tilapia . The treatments differed in stocking densities, feeding and manuring levels. The most productive treatment of the experiment, in which the fish were fed with protein-rich pellets, produced 50 kg/ha per day, probably a record for unaerated ponds of stagnant water. Two treatments (low and high stocking densities) fed exclusively with liquid cow manure produced an average yield of around 32 kg/ha per day. The yields of the treatments receiving high-protein pellets exceeded those of the treatments receiving grain pellets by 20 and 9.6 kg/day per ha, at high and low stocking densities, respectively, and in both cases the yield increments justified the extra cost of high-protein feed. The responses of the four fish species to the different levels of feeding and stocking densities were widely different. The common carp and white amur showed the greatest responses to increased feeding inputs while the silver carp and Tilapia , even at high densities, have done equally well at low feeding levels. Total body fat contents of the common carp were 20%, 15% and 6.2% when fed with high-protein pellets, grains pellets and liquid cow manure, respectively. Intermittent harvesting did not result in increased yields.

All-male broods of Tilapia nilotica × T. aurea hybrids

Abstract The proportion of males in single pair crosses between Tilapia nilotica females and T. aurea males was found to vary between 50 and 100%. There was no apparent influence of the T. aurea males on these proportions. In a similar test nine T. vulcani females were paired with T. aurea males, and the proportion of males in their hybrid offspring ranged between 93 and 98%. Two T. nilotica mothers of all-male hybrid broods mated with unselected T. nilotica males, and all their daughters also reproduced all-male hybrid broods when crossed with T. aurea males. The reciprocal cross of T. aurea females with T. nilotica males reproduced three males to each female offspring. Growth rate tests of the all-male T. nilotica × T. aurea hybrids, and the T. vulcani × T. aurea hybrids did not reveal heterosis.

Specialised sire and dam lines. I. Economic evaluation of crossbreds

When commercial livestock are crossbreds, profit for the total operation including cost of production of the breeding stocks, is a function of the performance of both the crossbred offspring and their parents.Since the performance level of the offspring is determined by its parents, it means that the parents contribute to profit determination in two ways. Reproduction cost is determined directly by the parents, that is through their own phenotypes, while productive efficiency (food conversion, growth rate, etc.) and quality are determined by the parents indirectly through the genetic determination of their offspring.In most classes of livestock the number of males in the breeding herds, relative to that of the females, is very small. Consequently, variation in reproductive capacity of the male line contributes only little to the determination of reproductive costs, and this item can be ignored. As a result, the contributions of the parental lines to profit are unequal and of different kinds. Exploitation of this difference may produce ‘profit heterosis’ even when the component traits are genetically additive.When profit is a non-linear function of one or more component traits another deviation of profit from the arithmetic mean of the parents is created. Unlike the previous one, this heterosis deviation is scale dependent.Profit was presented graphically, as profit contours, on the two dimensional plane created by the variables productivity and reproductivity. This was found to be a helpful aid to an understanding of the underlying relationships.

The regression of weight gain on initial weight in carp: I. Methods and results☆

Abstract The dependence of weight gain on initial weight in carp was investigated in a series of eight experiments. The phenotypic (total) regression of weight gain on initial weight was partitioned into a temporary environment component and a residual component. The latter includes genetically caused regression. The partition was done through application of the multiple-nursing method which was devised specifically for this purpose. In all the experiments the phenotypic and the residual (genetic + developmental) regressions of weight gains on initial weights were positive. The ‘temporary environmental’ regression was positive during the warm summer season, but nil during the cool late fall and winter. In one experiment the presence of ‘genotype-season’ interaction was demonstrated.

Profit in a broiler enterprise as a function of egg production of parent stocks and growth rate of their progeny

Synopsis The object of this paper was to determine the dependence of broiler profits on the reproductive performance of parent stocks, and the efficiency of meat production by progeny. This information is essential to assess the economic merits of breeding stocks and to evaluate the relative efficiency of alternative breeding programmes. It was shown that for any particular market the number of hens in the hatchery supply flocks is determined by the ratio of demand (weight of broiler meat absorbed by the market) to reproductivity (weight of broiler meat produced by a single dam). Increased fecundity improves profitability through its effect on chick cost. An analysis of results of several random tests showed that food conversion has a high positive correlation with market age at a fixed market weight. It was also found that for a constant age there is a small negative correlation between food conversion and body weight. Various methods of profit evaluation were discussed and it was shown that evaluations ...

Applications of electrophoretic genetic markers to fish breeding. I. Advantages and methods

Abstract The advantages and methods of application of electrophoretic genetic markers for advanced breeding schemes of fish are described. In particular, four breeding aspects where electrophoretic markers can make special contributions are discussed in detail. These are: (i) breed identification; (ii) efficient experimental designs that may lower drastically the numbers of ponds needed for genetic tests; (iii) construction of complex familial structures, such as dialleles, for genetic analysis of production traits; (iv) family selection programs. It is concluded that the potential contributions of electrophoresis to fish breeding justifies higher priority and investments.

Genetic differences in susceptibility to two diseases among strains of the common carp

Abstract In a test involving 5 inbred strains, and 9 strain crossbreds of the common carp, one inbred strain was found to be infected by Epidermal epithelioma disease and a second inbred strain was infected by a swim bladder inflammation. Crossbreds between these 2 strains, as well as between them and other strains did not show a single fish infected by either disease. It was concluded that susceptibility to both of these diseases is controlled by recessive genetic factors. It appears that the decreased incidence of Epidermal epithelioma in Israeli fish ponds in recent years has been due to the increased use of selected crossbred carp fry. The incidence of Epidermal epithelioma was twice as high in experimental ponds with a high stocking rate than in those with a lower stocking rate. The swim bladder inflammation was apparently due to a blockage of the pneumatic duct, with secondary infection by Aeromonas liquefaciens .

Genetic aspects of the transition from traditional to modern fish farming

SummaryA 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 variation in seine escapability of the common carp

Abstract During the years 1970, 1971 and 1972, 26 genetically diverse groups of common carp were tested in communal ponds, i.e., all the tested groups were co-stocked into the same ponds. These groups included inbred and crossbred domesticated European carp, one representative of the Chinese Big-Belly race, and several hybrids between the two races. The results led to the following conclusions concerning the genetics of seine escapability. (1) The Chinese race is much more adept at escaping seines than the European race. (2) The hybrids between the two races are intermediate with incomplete dominance of the higher escapability of the Chinese race. (3) Genetic variation was found within the European race with a strong dominance, or heterosis, of higher escapability. (4) Body weight as well as growth capacity were not associated with seine escapability. The absence of correlation between growth capacity and seine escapability contradicts earlier results that suggested a strong genetic correlation between the two characters.